This drawing shows the basic internals of a simple passive pyrgeometer.
Heat flows from roughly earth ground temperature into the body, finds it’s way through the body to the underside of the thermoelectric generator, then through that and for a clear sky then radiates from the top side to space, unless there are heavy clouds or it is raining.
I repeat, heat flow is from the ground upwards. (under very rare meteorological conditions a minor reverse flow happens, the former is overwhelmingly dominant)
This is far from the whole convoluted story, which I will now try and explain. In reality it is very simple.
Some of you will have seen pyrgeometer data with values in the 200 to 400 Watts sqm range perhaps with mention of “downwelling Infra Red”. This has caused a great deal of confusion and contention.
These devices do not measure “downwelling Infra Red” and the figure is a computed number based on the actual outgoing IR and the temperature of the instrument body.
Put in another way, such a figure is a backwards reading with human added offset.
There is a basis for doing this but no excuse for obfuscation, or a failure to explain to lay readers there is a silent jump of context to theoretic.
I will explain more after the next graphics section of the article.
With the following graphics I have tried to take care of this confusion (labelled net_IR_out) so just concentrate on trying to understand what the variation of outbound is saying, how if varies with weather.
This is real data from a similar instrument in southern England during one day this winter when heavy cloud passed over laden the snow, then in the middle of the afternoon the sky cleared to hazy sun. Late on another bank of cloud started to arrive.
Sky photo of near blue sky does actually show thin high cloud, not fully clear.
Cloud, very little heat radiates from the ground. Clear sky, heat radiates from the ground.
The following overlay plots do not have matched zero, I’ve offset for clarity, we are dealing with shape here.
Overlay plot of IR outbound on 35GHz cloud radar graphic.
Overlay plot IR outbound on Lidar graphic. Notice lidar is less able to see the incoming higher cloud. The dense low cloud during the first half of the day shows as a red line with very little seen above that, a laser has less penetration than radar.
You will notice significant undulation in the trace around 15 hours. This will be small cloud not being shown by radar or lidar.
The thorny problem of computed offset
There are two kinds of these pyrgeometer according to the fundamental configuration
- single ended
- double ended, which is two single ended, on pointing up the other down at the ground
- full differential which like double ended sees both ways but without an intermediate
The commercial “full” instruments comprise four single instruments (or two full differential), where the additional two are measuring short wavelength light, sunshine.
This is necessary to try and measure both shorter wavelength radiation incoming and reflected, plus longer wavelength IR incoming / outgoing and reflected. Only from this data can a reasonable estimate be made on the total radiation energy flow into and out of the surface of the earth and only for that precise location.
For example the Kipp & Zonen CRN1 instrument[1] is a net radiometer comprising four units, two pyranometers and two pyrgeometers.
Spectral response of CNR1, overlay to show as one. Strictly solar irradiance should always be shown using log-log plot axis. This would not only show that irradiance follows a log law but in this case would show the filters as somewhat less than ideal. It is possible to produce astoundingly good filters, is done by hand for aerospace and space application, at a very high cost, needing a 100 or more separate layers spluttered onto a substrate.
The difference in height of the two responses above doesn’t matter, calibration of the instrument adjusts that out.
Typical singled ended instruments additionally contain a body temperature sensor feeding a second output cable. An external computer digitises both the thermopile and temperature signals.
The temperature reading is then used as a second input to the formula computing the theoretic offset radiation value as the equivalent downward infra red radiation. There is no direct measurement, no such entity exists and this is the much talked about “downwelling” radiation or heat. (there is a jump of context)
This is literally the Stephan Boltzmann equation applied to an approximation of the temperature of the ground, or more precisely whatever is radiating. It is neither the body temperature of the pyrgoemeter nor the air temperature, but there is usually little difference. Also, no compensation is done for ground emissivity.
A full double ended instrument is more able to measure the up and down flow because it takes the very local ground and ground cover into the measurement.
This is the formula shown in the Kipp & Zonen manual for the CGR4 instrument.
Uemf is thermopile voltage, S is constant calibration factor for that particular instrument.
If it is raining the sensor output is zero the Uemf/S term in the equation equals zero which leaves the Stephan Boltzmann term 5.67E-8 . T4, where T is the body temperature of the instrument, or could be some other thermometer.
This data from 17th March 2013 is a reasonable demonstration of raining and zero output.
Top row second from left is the output of the formula for a CGR4 instrument showing about 325 Watts sqm downwelling IR during the rain storm but there can be no output from the thermopile. I have no data for the CGR4 body temperature but there is an air temperature reading. Since it is raining it is reasonable to whole lot is close to the same temperature, therefore it is fairly safe to back-calculate the air temperature via Stephan Boltzmann to Watts sqm for that air temperature and subtract this figure from the pyrgeometer reading.
This is the bottom right plot labelled net_IR_out where we find as near as makes no difference a value of zero during the rain storm.
And that is what the fuss is about.
Internally within a theoretic set of mathematics, figures can be split into what is going on, we hope, but it is not directly measured by these instruments. Actually measuring needs vastly more expensive equipment but that is an issue I am not covering here.
Those who think there is no “back radiation” are both right and wrong, two different situations. One way showing that internally within a system there must be a heat interchange is by considering time, any alternative would need knowledge of the future, the speed of light says no. (and this would be trivially easy to measure)
I hope it is obvious that water and water vapour dominate what is going on, clouds are dominant.
Independent confirmation, a table from the manual for Kipp & Zonen net radiometer (duplex device, four sensors)
Any effect from eg. CO2 is negligible in this data and would only be detectable under very clear sky with very low humidity, such as in some deserts or using very selective instrumentation.
None of this deals with phase change or gas movement as heat transport. The entire world thing is incredibly complex, as if we know much at all.
Links
The Talkshop has several discussions to do with pyrgeometers, such as here, which has links to the Chilbolton data used.
Article by Tim Channon, co-moderator
Tallbloke's Talkshop 
The filter removes the short waves. Where does the energy from the short wave radiation go? Is it absorbed by the body of the instrument?
Tim Channon, thanks for a comprehensive guide to the operational details of the pyrgeometer.
The Kipp & Zonen user manual would be improved if your article was included as an introduction.
Roger,
there are known problems with sunshine heating of the filter/instrument.
Various workarounds have been used but in the case of CGR4 this is claimed to be negligible. Going on the Chilbolton data on a sunny day this seems to be confirmed. How exactly they achieved this I know not. Guessing, is about detail design of the dome/lens.
The older instrument (obsolete I think) where I have linked a manual it does discuss errors of this nature. Some is supposed to be handled by management software, problem is passed to the user.
One of of the workarounds is the use of a motorised sunshade which tracks the sun.
At Davos, evidence, look at Figure 1 on this web page
http://www.pmodwrc.ch/pmod.php?topic=irc
Many more pictures can be dug out.
Tim
Why do you say there is NO (i.e. zero) radiation from the sky. I thought this had been cleared up in the 1st article?
Clouds radiate downwards as black(ish) bodies. GHGs radiate in all directions including downwards but in discrete bands – not black-body. The mean free path of GHG radiation is very small at 1 atmosphere air pressure. So the radiation will be from just above the lens. This IR may have originated far above or at ground level. It is just that it got re-radiated the last time just above the window.
This is good info:
http://rabett.blogspot.co.uk/2013/04/this-is-where-eli-came-in.html
The type of sensor element resistive/thermoelectric/ is immaterial. it just simply reaches equilibrium with its surrounding emitting as much energy/second as it receives from all around it including the sky through the window.
Warm its box and the box will radiate more energy into the sensor
Get more IR through the window and it will warm
Use a second temperature sensor to determine the radiation from the box.
Some use a 3rd to measure the window temperature (this will radiate because it is warm i.e. above -273degC).
This conforms with the analysis I have presenter on my in posts like How to Fool Yourself with a Pyrgeometer.
PS ..on my blog claesjohnson.blogspot.se I mean DS
I am a little confused: Your first picture has several inbound red arrows labeled “Ground/air heat into body”. The body seems to be a metal, not a thermal insulator. How can the instrument separate a thermal input from the air from a thermal input from the ground radiation? For example, a wind may make a lot of difference. Or a snow cover.
CG, it can’t separate and must not.
The metal body, which is the thermopile cold side, ought to be at the same temperature as the actual ground. That is the reference temperature; there has to be a reference. That is what is being radiated from to the sky.
Can’t be that crude? It is. So simple.
If the body was say in a dewar, highly insulated from it’s surroundings, the whole thing would get colder than a deep freeze when the sky is clear. Literally you can make ice like this.
Second point, ground frost?
A web trawl might turn up some gems about ice making at night.
Tchannon, thank you. I accept that for an inexpensive instrument we must accept a combination of a ground temperature and an air temperature for a reference. I still think that a design with a black metallic bottom and insulated sides could approximate a ground temperature better, but then of course I am free to make my own polystyrene insulation.
Just nitpicking, you probably meant to say that the metal body is a termopile WARM side, when you measure an outgoing radiation.
“Just nitpicking, you probably meant to say that the metal body is a termopile WARM side,”
Oi! Grin.
It’s so darn easy to get things wrong way up. Arguably I should use a negative sign a few places too.
So it ought to have a black bottom. Trendy eh?
Real point is making it clear these devices operate backwards from how I think it is assumed. Hopefully it then makes intuitive sense.
I forgot to link in this, does the same thing
None of this is helped by some poor usage of language by well known names, a matter where I am having trouble biting my lip and not quoting their words from some time ago back at them… so quit trying to blame the lay person for what you did. Or are we seeing a slow change of tune?
Tim, from your diagram it is clear that radiation flux is not measured. This is often overlooked and should be emphasised What is measured is a voltage difference at the thermocouple. This needs to be calibrated by comparisons with other instruments to standard defined points on the temperature scale (eg the boiling point of water at 1 atm pressure). The measurement then is related to a temperature. Two questions immediately arise. Firstly, the thermocouple only gives a voltage difference. Thus, it can not give an absolute temperature. The base temperature needs to be separately measured and the zero adjusted. Next is the question what does the measurement actually mean, and how does it relate to a particular source of heat and other interfering sources.
The makers of the radiation meters then apply a mathematical formula ( a corrected or mangled Stefan-Boltzman equation) to give a calculated radiation flux in some units such as w/m2. This is a construct not a physical measurement. Unless one understands heat transfer and applies the appropriate correction factors the output result is meaningless.
The original S-B equation was based on measured data of surfaces (note surfaces) in a vacuum (note vacuum) Fourier himself stated that when there is an atmosphere over a surface heat transfer becomes complex. Engineers later pointed out that it is necessary for the determination of of heat transfer by radiation to take in account the emissivity of the surfaces and the temperature of the receiver of heat. It should be clear that the atmosphere and clouds are not surfaces and need to be treated differently Prof Hoyt Hottel (who seems to be only known by engineers with some actual experience with heat transfer) developed the concept of path length and partial pressures for gases in furnaces (eg flames) and heat exchangers to give an indication of bulk heat transfer by radiation to aid engineering design. It should be noted that in a furnace that temperature differences are very large (and radiation assuming a T to the power of 4 very significant) but unlike the assumptions of so-called scientist who do not understand heat transfer, heat transfer by convection still takes place and can not be ignore.
When surface temperatures are low (ie below 50C) and temperature differences small forced convection (from winds in the atmosphere) is a greater loss of heat from a surface than radiation.
The ideas that a surface radiates heat at all times and that heat transfer occurs first by radiation and then to a lesser extent by other mechanisms is not based on facts. Radiation is just one of the mechanisms of heat transfer and depending on the surrounding conditions it may or may not be important.
I have my doubts about the UAH so-called measurements (a better term is calculated estimates of some temperature) and the calculated estimates of radiation from the sun( the visible project of the sun is not a surface- no one knows the actual surface area or its temperature, then the earth’s distance from the sun continuously varies so there can be no single figure which is correct without a large error margin)
tchannon,
huge thanks. I have read a number of explanations and yours is the first one that made sense!!!
The fellows who have been trying to tell us that pyrgeometers are directly sensing DLR aren’t gonna be happy. Got some body guards lined up??
Surely the best way to determine the direction of heat flow is to measure the temperature of the top of the thermopile and its bottom. Heat flows from high temp towards low temp.
OK, please educate me here. (And I may need some correction as well, because I’m not picking up the subtleties from the table above.)
The theory is very clear: Any object above 0 degrees K will radiate energy, if it is a real-world grey body, how much energy is proportional to that body’s emissivity value and its temperature. Ignore for a minute the convection and the evaporation loss and the conduction losses that are also going on, and give me the real world values for the following four circumstances:
First case. Cloudy day, surface of ice temperature = -5 deg C, 1 meter air temperature = -5 deg C, cloud temperature (?) at 15,000 ft = -50 deg C, space temperature doesn’t matter, right?
Inbound radiation will be scattered and diffuse because of the clouds, but will it be independent of air temperature? Obviously, inbound radiation will be proportional to what’s theoretically available from the sun, but what is the equation describing the outbound radiation heat loss from the ice surface?
Second case. OK, same temperatures as above, but at night. Outbound radiation heat losses should be the same, but now, what is the inbound radiation equation now that there is no sunlight at all?
Third case. Ocean water, clear night, same air temperature. Now, the ocean surface will be hotter than the surface of the ice was (assume 4 degrees C) but emissivity of water is about the same as emissivity of ice, so radiation heat losses should be greater (water temp = (273 + 4)^4 degrees K compared to ice surface of (273 -5)^4 deg K). Further, it is now a clear night, but what “temperature” and emissivity is the water radiating into?
“Space” would be near 0 K, but is that realistic? Upper atmosphere is still at -40 deg C at 40,000 feet, but is that the correct value?
We would think that these are simple questions, available right from elementary “climate science” … But across the web, all I can find are endless approximations of the “pure black body” S-B equations, or gray-body equal area equal emissivity approximations of (T1^4 – T2^4) that are equally useless.
Here is my analysis of the pyrgeometer illusion:
http://claesjohnson.blogspot.se/search/label/pyrgeometer
I’m struggling trying to work out what to say on various loose ends. Don’t like ignoring people but whittering is too easy to do.
RACookPE1978,
It might be better to deal in flux, any domain conversions are risky. (flux interchange temperature)
SB is a theoretic construct, is useless in the physical world. An extended version needs additional information which is at best approximated, if known at all. Missing variable problem is close.
Flux is a counter-intuitive entity, an energy packet in time which has no temperature yet seems to have a limit on achievable temperature.
Entropy is more the matter (sic) which depends on physical properties. We measure this by proxy, temperature.
I used pure SB as part of the lunar surface simulation, it was free to do whatever it does but it was in contact with an approximation to physical matter yet had no knowledge of eg. acceptance or emissivity in a radiative sense. The concept was surface conductance and thermal capacity, a thermal delay line. Works well.
The earth is not so homogeneous or simple.
Sticking with a single domain, temperature or flux is much safer. This does though crash into reality, leading to we don’t have that figure or can’t locate the actual body. Yep.
I’m probably making no sense.
Well, seems like we’d have to begin with temperatures, since those are fundamentally measurable.
As mentioned above, when a furnace is designed or specified, the wall temperatures and surface conditions (distance from the burner, gas flow rate, temperature of the burning gases, etc.) establish the radiation heat flux. In a furnace (a boiler) radiation heat flux dominates, but all three must be included.
When a typical power plant heat exchanger is designed, the desired inlet and outlet fluid temperatures, length of the heat exchanger, flow rates, size of the coils and length of the coils and diameter of the tubes establish area, flows and heat rates. Radiation heat flux is near meaningless because water-to-oil (fluid/fluid) heat exchange dominates.
Here, in the real world of an open ocean environment (the Arctic near the floating sea ice) CAGW pretends that it will be catastrophic if any given area of sea ice melts and an equal area of open ocean is exposed. If so, you would think they (the CAGW theists) would have exact knowledge of exactly how much added heat is available at the surface for each hour of each day of the year at each degree latitude, reflected from each surface for each incident angle, absorbed into each surface for each incident angle for direct and diffuse radiation under each predicted cloud and clear sky condition. Their heat losses must include what is evaporated away (from the water), conducted away (from the ice into water), radiated away (from each surface, at each different surface temperature, into each “receiver” of again clear sky, cloudy sky and night skies), and how much is convectively lost into the polar air at each hour’s temperatures for each day’s typical wind speeds.
Sure, you can estimate heat fluxes, but you need to start those estimates (calculations for each heat gain and loss) from the temperature of the material. The only other variable affecting heat loss is weather: wind speed and degree of cloudiness between the ocean and the sky. The only variable affecting received radiation is cloudiness. Everything is strictly a function of day-of-year, time-of-day, and latitude of the sea ice edge.
When I run those numbers, at the latitude where the sea ice actually is, I see that open ocean loses more heat than ice-covered ocean.
Phrased differently, the more the Arctic sea ice melts in September (from today’s record sea ice minimums), the colder the planet gets. On the other hemisphere, the more the Antarctic sea ice expands (from today’s record high extents), the more the planet cools.
Thank you for your posting. it’s about time more people joined in the fight against bad science! Climate Alchemy’s ‘back radiation’ claim is junk science because in addition to it being an artefact of the [single] pyrgeometer, the instrument does not measure as is claimed and you get real gems like the claim that clouds radiate energy to the surface!
One of the problems is Houghton who made three mistakes in the theory, including claiming the atmosphere is a grey body emitter. Clouds are to some degree but a clear sky is semi-transparent.
In reality the net energy flux for just radiation to a clear sky is an operational emissivity of ~0.4 and of that IR, a third is in non self-absorbed water vapour side-bands and trace gases, the rest being to space via the ‘atmospheric window’. This causes dew and ground frost. the argument that humid air provides more ‘back radiation’ is mostly wrong [there will be a bit of extra thermal impedance but most of the effect is condensation latent heat which does not necessarily exist as dew].
Thus a pyrgeometer sensor viewing clear atmosphere has to cool well below the air emission temperature.before the IR it loses to space equals IR to it from the main GHG bands in the air. This bidirectional radiative heat transfer has been missed by Climate Alchemists. Theoretically you need a -13.5 °C sensor to equilibrate with 15 °C air.
Therefore, for a clear sky, the heat transfer in the instrument to the AW is from convection. hence thermistors are used in newer equations. You can’t calibrate such a device against a black body.
My views on this are based on lots of experience in practical heat transfer and temperature measurement. Climate Alchemy is just starting to realise that the Energy Budget most of whose data are reliable, has in it 100s of wasted man years from failure to understand their main instrument does not work as claimed.
Claes, we recognise you were out in front in raising this issue.
AlecM: (quoting from above)
I agree with you – in theory. In practice, as well. I’ve had many nightshifts outside on clear nights and cloudy nights, the difference is (literally) breathtaking as you try to stay warm while working outside in the moutains. Now, back to the question: How much colder is it? How much more radiation heat loss am I feeling?
Now, back out of all nice comfortable approximations and give me a specific credible calculation or a calibrated measurement: How much radiation heat loss is there on a cloudy night into an air temperature of -5 degrees C from a water-covered surface at 5 degrees C, and from a ice-covered surface at -5 degrees C?
How much radiation heat loss is there from a ice-covered surface at -15 degrees C into a clear night sky?
But recognize that the actual question needs to be:
What is the total heat loss from:
1) One square meter of ice-covered salt water at 4 degrees C into -15 degree C air moving at 2 meters/sec under cloudy conditions?
2) One square meter of open salt water at 4 degrees C into -15 degree C air moving at 2 meters/sec under cloudy conditions?
3) One square meter of ice-covered salt water at 4 degrees C into -15 degree C air moving at 2 meters/sec under clear conditions?
4) One square meter of open salt water at 4 degrees C into -15 degree C air moving at 2 meters/sec under clear conditions?
Expressed that way, all four methods (gain of energy from the hotter water below the surface, loss by radiation, loss by evaporation, loss by conduction, and loss by convection are all included.
RACookPE1978
The answer has to be derived by subtracting the air Planck Irradiation Function convolved with the wave-number dependent emissivity from that for the surface. This is effectively taking the IR spectrum form the air away from that of the surface.
MODTRAN does this and you can access it on line here: http://forecast.uchicago.edu/Projects/modtran.html
You need to save the data and import them into a spreadsheet. it’s quite simple but it takes time so I won’t do it for you.
What you will get is the net IR emission to air and space and then you integrate it numerically.
The climate models assume S-B with an average emissivity. This is plain wrong.
PS The above assumes just radiation. It will be a good approximation for zero wind speed. Any wind and you must incorporate convective heat loss. This is a function of the true temperature distribution in the convective boundary layer so must be modelled, and it ain’t easy.
For each hour of an given assumed day’s weather (I’m reading daily weather info as data for 80 north at sea level for example) I’ve got a commercial program that uses air temperature and wind speed as inputs to its convective heat transfer outputs.
So I’m covered for the other losses. Not for radiation. Yet.
But, upon testing Modtran, I found no way to input emissivity for the different surfaces.
(Now, admittedly, there is very, very little difference between ice and water, but …..)
To vary emissivity of the surface, you need the stand alone version of the programme – it is set at 0.98 for the surface [bottom of output file]. This is a basic assumption of all such modelling.
Your comments, your corrections, are a large part of how I learn.
AlecM, Claes Johnson has found a problem with Modtran (eg http://claesjohnson.blogspot.com.au/2013/02/inflated-modtran-effect-of-atmospheric.html) He has put up a series of posts that show very low CO2 (1ppm) gives very high sensitivity which is unrealistic. There is a problem in the computer code or in formulae used for calculations. As is common with the models put out by the alarmists they do not publish the basis of their calculations or the computer code so that it can be verified. No (registered) professional engineer should use computer models, calculation methods, data etc unless they can understand the concepts, verify to the information is appropriate, and justify their selections (in court) when they sign off. I have often found problems with package programs due different assumptions, wrong use of dimension conversion factors etc. I always like to go to basics for a quick check to see if a program gives the correct answer. The AGW crowd (including lukewarmers) do not understand the basics. They are quick to grasp something which fits their thinking. For them, it does not matter if it is the output of a model which is derived from unrealistic assumptions. There are still papers, trying to be published, which attempt to justify Michael Mann’s nonsense “Hockeystick”
Ah, but remember my original question: Specifically, I was trying NOT to ask “What is the theorectical average flux for an average flat half-disk earth (under so-and-so stated conditions)?” but rather “What is the correct sky temperature and night air temperatures that corresponds to the real world (for so-and-so stated conditions)?
Your comment is WHY I’m trying to focus my attention on the basic equations and basic temperatures of the latitudes of interest in the Arctic and Antarctic – NOT looking endlessly at esoteric theoretical questions about radiating spheres of perfect metal surrounded by radiating spheres of perfect metal in a perfect vacuum of space?
RACooke, I was not making any suggestions about your questions. I was trying to point it seems not successfully, that one should have doubts about the Modtran model which appears to be one of the so-called scientific facts called on by the IPCC and other alarmist to back their claims about the importance of CO2. Maybe this page (http://claesjohnson.blogspot.se/search/label/emissivity) from Claes Johnson elaborates a bit more of his findings. I can not at present find the post where he actually makes calculations at different CO2 concentrations from zero to 650pmm.
It does seem strange to advise the use of a computer program (model) to produce basic data, when the jury is very much ‘out’, on most climate data, methods and outcomes.
Interesting “test” of the Modtran program. I will reserve judgement whether the results are conclusive, or merely conclusive of my need for further training and edication. 8<)
In Modtran, I entered SubArctic Winter, leaving the remainder of input data at default values for "No Clouds" as case 1, "Stratus Clouds" as case 2.
For case 1, I entered T_surface values (the Offset temperature) from =15C to -15C, then recorded the resultant Heat flux (watts). I then compared the flux at each temperature with the theorectical flux from a "0.98 emissivity gray body" S-B at the temperature range +15C to -15 C.
Well those two tests failed:
At =15 C offset , Modtran matched S-B if T_sky = -48 degrees C.
None of the rest matched, the difference getting larger as temperature decreased..
S-B No clouds Status
T_Surf T_sky Watts Modtran Modtran
15 -48 240 240.1 243.6
10 -48 214 224.8 228.1
5 -48 189 210.4 213.4
0 -48 166 196.6 199.4
-5 -48 144 183.7 186.2
-10 -48 123 171.2 173.6
-15 -48 104 159.5 161.6
Clearly Modtran, using defaults, is not calculating heat loss based on surface temperature changes.
Tim C,
Paraphrasing, it seems you are saying…
“Downwelling IR is not directly measured, but is inferred from Conservation of Energy and estimates of the other energy flows in/out of the detector.”
Some people seem to be making a big deal out of this, but it seems pretty obvious and a pretty reasonable approach.
The net power into the sensor is (pretty much by definition)
(net power) = (IR in) + (other power in) – (IR out) – (other power out)
The left side will be (net power) = 0 (since we are assuming conservation of energy and that the instrument has reached as steady-state condition where none of the temperatures are changing rapidly). (other power out) is the heat flow through the thermopile. (other power in) is zero.
[NOTE: Whether you call the heat flow from the body “in” or “out” is simply a sign convection. ]
[NOTE 2: (other power out) would also include IR from the dome and similar effects. Hopefully these are either 1) too small to be important or 2) accounted for by eg measuring the temperature of the dome.]
Rearranging this gives “Formula 2”:
(IR in) = (other power out) + (IR out)
L_d = (U_emf / S) + εσT(b)^4
The (other power out) = (heat flow out from the sensor to the body) is estimated from the thermopile voltage –> – U/S. [NOTE: (other power out) will usually be negative, since power usually is heading in during normal operations.] S is an experimentally determined “conversion factor” between voltage and power.
There are definitely a couple engineering challenges
1) determining “S” to calibrate the instrument
2) eliminating/reducing/accounting for other sources of “(other power in)” besides heat flow through the thermopile.
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“There is a basis for doing this but no excuse for obfuscation, or a failure to explain to lay readers there is a silent jump of context to theoretic.”
But you are referring to a technical document for a technical device intended for a technical audience. They have no obligation to explain things on a level that a “lay reader” (eg someone with only a high school science background) would comprehend.
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“Those who think there is no “back radiation” are both right and wrong, two different situations. One way showing that internally within a system there must be a heat interchange is by considering time, any alternative would need knowledge of the future, the speed of light says no. (and this would be trivially easy to measure)”
Could you explain what you mean here? Who is right and wrong about “no back radiation” and in what circumstances? In what way are you “considering time”?
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“… water and water vapour dominate …Any effect from eg. CO2 is negligible
Sort of …
When it is 20 C, the IR up from the sensor is ~419 W/m^2. When it is cloudy or rainy, then the sky is covered with a “black body” @ ~ 20 C radiating ~ 419 W/m^2 downward. Hence the net IR is zero. When is it NOT cloudy, the sensor is STILL radiating ~419 W/m^2 up and the net is ~ 100 W/m^2, so the sky is STILL radiating ~ 319 W/m^2. This is not coming from liquid water, so it must be coming from other sources = aerosols and GHGs.
Until you quantify how much of the ~319 W/m^2 is coming from aerosols vs H2O vapor vs CO2 vs O3 vs CH4 vs … , there is now way to conclude whether or not CO2 is “negligible”.
Certainly the single biggest, most obvious factor in the incoming IR is the presence/absence of a blackbody radiator covering the whole sky –> liquid water “dominates”. But that does not remove the effects of OTHER radiators when the clouds are absent!
Can anyone provide a use for the pyrgeometer other than to mislead the public into thinking that it directly measures atmospheric backradiation?
Bryan, the same could be asked about just about any instrument. The speedometer on your car does not “directly measure” your speed — it measures how long it takes the axle to spin and uses this to estimate the speed. If your tires are under-inflated, or if your tires are spinning on an icy road, the estimate can be quite far off.
Does a speedometer have any use other than to mislead the public into thinking that it directly measures the speed of a car?
The speedometer has a direct input of a distance measurement and a time measurement.
If these are accurately determined then a highly accurate speed measurement is obtained.
Since there is a very accurate determination of the metre and the second a speed can be determined to a very high degree of accuracy.
How accurate does it need to be is then a question of economics.
The pyrgeometer is more like the American police use of a lie detector where several ‘iffy’ assumptions are made to draw a even more ‘iffy’ conclusion.
Another instrument that seeks to give some sort of ‘sci-ency’ credibility to a religion is the e-meter used by scientologists.
Sure a pointer moves and a reading is obtained but does it correspond to reality?
Bryan,
I’m often slow to respond because I am busy.
Briefly, TJF is hard decoding work. I think the point he was trying to make is correctly that almost all instrumentation is a proxy, in many cases a multiple proxy, some very dodgy. He is also imputing the missing variable(s).
I’ll probably reply to TJF later.
tchannon, I said above
“The speedometer has a direct input of a distance measurement and a time measurement.
If these are accurately determined then a highly accurate speed measurement is obtained.
Since there is a very accurate determination of the metre and the second a speed can be determined to a very high degree of accuracy.”
What could be more direct than that!
A direct feed from the gearbox gives the number of engine revolutions per second or minute modified by gear ratio.
Gearbox is coupled to wheels.
Gear circumference size known to high precision.
Wheels are assumed to be circular or if even more accuracy is desired the slight deformation of a correctly pressured tyre can be factored in.
Length travelled per engine revolution known to a high degree of accuracy.
Time taken to travel this length known to a high degree of accuracy from engine frequency.
=> Speed = length travelled/time taken is known to a high level of accuracy .
In practice many manufacturers set the speedometer slightly higher than reality for safely reasons I suppose.
On the other hand the output from a pyrgeometer is ………….?
Doesn’t sound QUITE so simple now. 🙂
And it is clearly inaccurate when the wheels are spinning (like the pyrgeometer is inaccurate when covered with frost). It is inaccurate as the tread wears from the tires. It is in accurate when the tires are under-inflated.
The main point, as Tim C basically reiterated, was that pretty much ALL measurements are
1) indirect
2) dependent on several assumptions about conditions.
Neither of these invalidates the overall results — they are simply facts that need to be acknowledged. Pyrgeometers are relatively simple instruments that make a few relatively reasonable assumptions and give relatively good estimates of downward IR.
tjfolkerts, only a person who has a deep AGW religious conviction would try to maintain that measuring speed is as indirect as measuring backradiation.
It is indeed a measure of the blindness to reality induced in a person by accepting global warming hysteria.
This condition too might be measurable.
On a ten point scale where belief in Micheal Mann’s ‘hockeystick ‘ being ten your conjecture that measuring speed is as indirect as measuring backradiation would be about nine.
Speed can be measured by several methods.
So the cheapest one with enough accuracy for legal road requirements will often be
chosen.
https://www.ncjrs.gov/App/Publications/abstract.aspx?ID=16062
On the other hand if a very accurate determination of speed is required it can be attained
For instance the speed of light in vacuum to be c = 299,792,456.2±1.1 m/s.
All attempts at measuring backradiation seem to involve the ridiculous pyrgeometer.
After 50 years of pathetic results (often discussed here) users still cannot agree on the calibration formula.
However if the instrument brings some comfort to the faithful believers in AGW, why should rational people intrude.
Very well said, Bryan!
Any attempt at conveying sensible or rational lines of reasoning on any issue regarding the magical case of the radiative GHE to this person ends up being like the proverbial talking to a wall.
I must say, this thread constitutes a most interesting development to the whole DLR argument. ‘Told you so’ does come to mind. I wonder when David ‘Back Radiation is measured and anyone claiming otherwise is a fool’ Socrates is joining in …
Why don’t we suggest a ‘proper’ calibration method for a pyrgeometer.
My first pass would be to produce a source, perhaps a flat plate, parsons black with 100 resistors glued to the upper surface.
Connect the resistors in series/parallel as necessary, to a power supply to give 1344 Watts (or whatever figure is deemed necessary.
Mount plate in polystyrene cube with an open bottom.
Suspend box/plate above pyrgeometer, the pyrgeometer will ‘see’ 1344 Watts or what is transmitted.
Note the pyrgeometer output, compare with sky/ground readings.
Obviously this method would need refining: distance of plate to pyrgeometer; what the ‘lens of the pyrgeometer ‘sees’; amount of insulation.
Isn’t this ‘just a regular measurement issue’?
TJF
Most of what you reflected is subtly not what I intended. I think this is an ethos problem. I’ve come across something like this many times in real life.
The manual? That is a user manual not a technical manual. It’s only a small company.
You asked about my mention of speed of light. That is about a reason why those who have trouble comprehending theoretic interchange ought to consider some more. Nothing can know the future and react in advance. If this was not so there would be easy to find manifestations, it would be a strange world.
Effect of CO2 negligible? So far as I know yes and as far as these particular instruments are concerned is irrelevant because of the considerable error, some of which you have already dismissed. I reject your opinion. (said nothing at the time)
The instrument does not measure back radiation, close to fraudulent where my ire is aimed not at the instrument makers but at the clients.
Try this: –
Back radiation does not exist as an entity no more than E or M in isolation of EM radiation can travel or X or Y (or Z) of a complex vector are valid in isolation.
I have not touched clear sky or what passes for it.
Bryan,
This is a discussion of scientific instrumentation. It has nothing to do with my religious views or Mann’s hockey stick or even AGW — about which I have said nothing here. Why are you sidetracking the discussion with such irrelevancies? I am afraid your post reveals YOUR preconceptions and , not mine.
Bryan says: “All attempts at measuring backradiation seem to involve the ridiculous pyrgeometer.”
Ah .. the old “proof by bold assertion”. What SPECIFICALLY is “ridiculous” about this instrument? Do you doubt it estimates IR radiation within ~ 10%? Or perhaps you you doubt it estimates IR radiation at all? Do you think that all IR thermometers (and that are ALSO used by engineers and doctors and electronics techs around the world) are also “ridiculous”, or perhaps only ones owned by “a person who has a deep AGW religious conviction”?
PS Interestingly, speedometers in the US are only required to be within +/- 10% @ 50 mph. European requirements are even laxer: +/- 10% +/- 4 kmph. This is no better than the accuracy of pyrgeometers.
PPS The speed of light is EXACTLY 299 792 458 m/s. It is the “length of 1 meter” that is uncertain.
Tim C:
I am curious … do you object because you think it “indirectly estimates back-radiation” rather than “measures back radiation”? Or do you object to its ability to even estimate incoming IR? Or something else?
Do you similarly think that pyranaometers don’t measure incoming UV/visible/near IR radiation?
Local heat flow.
Object to what? There is a surface where SB plays out against reality.
“Do you similarly think that pyranaometers don’t measure incoming UV/visible/near IR radiation?”
They approximate on a real flux. This is incomplete.
Actually there is a loose end with me on flux from an intense source, is an oddity, perhaps the wave/particle duality.
Bryan 4:15pm: “All attempts at measuring backradiation seem to involve the ridiculous pyrgeometer.”
Kristian 7:45pm: “Very well said, Bryan!”
Hey guys, no, Bryan has not said it very well since DWIR (aka downwelling longwave flux aka broadband longwave flux aka backradiation) is also being measured by a ridiculous spectrometer based interferometer instrument cited and explained in March 2000 right here:
“Two instruments are being used to obtain the downwelling flux measurements: the
pyrgeometer, which measures the flux for the full hemispherical solid angle and the entire longwave spectrum, and the AERI interferometer, which measures the zenith spectral radiance from 550 cm-1 to 3000 cm-1.”
“The good agreement between the observation- and (radiative transfer) calculation-based determinations of broadband longwave flux leads to increased confidence in the measurements, (radiative transfer) model calculations, and the specification of the atmospheric state in the radiating column.”
Even the Moderate Resolution Transmittance model (MODTRAN) gets mentioned. Go for it, read up on this science (it is not my interest but I’d like to learn more); now you have another body of instruments to disbelieve and/or for Tim C. to untangle.
Like Tim F. asked, an additional challenge to say it well and provide an answer: “What SPECIFICALLY is “ridiculous” about (these) instrument(s)?”
Especially note the discussion of DWIR measurement complications from ridiculous aerosols.
Click to access clough_sa.pdf
More & later details of the AERI interferometer instrument:
Click to access aeri_handbook-1.pdf
tjfolkerts says
“PS Interestingly, speedometers in the US are only required to be within +/- 10% @ 50 mph. European requirements are even laxer: +/- 10% +/- 4 kmph. This is no better than the accuracy of pyrgeometers.”
So you think that backradiation as measured by a pyrgeometer is as accurately measured and as directly measured as the measurement of speed.
Its sad to see such nonsense proposed.
I was going to point out that the pyrgeometer is claimed to be a ‘state of the art’ scientific instrument producing the most accurate results possible.
Speed can be measured by several methods with typical ultimate accuracy > 99.99% if required
Rational explanations involving technology and science are wasted on you.
You are entrenched in the dogma of AGW.
All I read from you is trivia not worth replying to.
Trick asks
‘What SPECIFICALLY is “ridiculous” about (these) instrument(s)?’
Well as the article above points out what is measured is a voltage across a thermopile caused by a heat flow from pyrgeometer to atmosphere.
This is then computed on the basis of calculations to use what users think they know leaving behind what they think they don’t know which they hope must be the LWIR.
Can you spot the flaw in the logic?
If you have time google – history – problems – pyrgeometer.
You will find almost 60 years of hopes and false dawns.
Even now there is disagreement as to the calibration formula.
Trick says
“Two instruments are being used to obtain the downwelling flux measurements: the
pyrgeometer, which measures the flux for the full hemispherical solid angle and the entire longwave spectrum, and the AERI interferometer, which measures the zenith spectral radiance from 550 cm-1 to 3000 cm-1.”
Have a look a page 4239 of the link below
The pyrgeometer is consistantly giving about double the readings of the interferometer.
I would have much more confidence in the interferometer and perhaps a post on this instrument might be interesting.
Click to access TownEtAl_2005.pdf
Bryan 9:18am – Thanks for that piece. The difference in Table 4 does not seem to concern the authors on first read. One instrument being wide field view and one being narrow field view. More Watts do get into the pyrgeometer per m^2 measuring more of the DWIR bath than the interferometer.
This is not my interest to dig into but a couple more readings of the paper and ref.s might enable how the authors use both readings.
Place the pyrgeometer on a stove top. What does it read then?
Been a lovely sunny day but quite cool. The cherry is now in blossom but the photos are rubbish, grrr… do I hate digital cameras, refuse to do what you try and insist, try again tomorrow, maybe with the larger step ladder if I don’t hurt too much.
I think the Chilbolton data from today is going to be useful, fairly clean. Looks as though I might be able to tackle the phase data. What this means, well, that’s why I am looking. Damn shame so much other data is missing (ground conditions).
Rare case they have both 35GHz and 94GHz radar operating.
There is high cloud/haze, doesn’t show.
If you are quick (or try yesterday)
http://www.stfc.ac.uk/Chilbolton/weather/cloud+radars/24989.aspx
and
http://www.stfc.ac.uk/Chilbolton/weather/Visible+and+IR+radiation+sensors/26697.aspx
“The pyrgeometer is consistantly giving about double the readings of the interferometer.”
The pyrgeometer also has a wider bandwidth of radiation that it measures (4-50 um vs 5.6-22 um). This would lead to a 50% higher measurement for the pyrgeometer for a blackbody @ -50 C (a typical Antarctic temperature). The paper says the pyrgeometer extends its effective band width to much longer wavelengths, so that would be a BIGGER difference between the two instruments. Throw in the fact that the sky is not at all a blackbody, and a 2x difference between the two instruments is about what might be expected.
As TC says, most (all?) measurement technology uses changes in materials to ‘capture’ the variable you are trying to measure.
The worlds most popular industrial temperature sensor is the PT100 which give 100 ohms at 0 degrees C.
The second most popular industrial sensor is the thermocouple which generates a small voltage for each degree K.
To measure pressure we have a number of means available but the most popular (currently) is metal or ceramic diaphragms with strain gauges which vary in resistance to flexing, due to pressure change.
To measure flow the most popular industrial technology is to measure the pressure drop across an orifice plate (blimey, were using pressure to measure plow….)
In each case the engineer needs to know the environmental sensitivity of his sensor. Does the pressure reading change if the ambient temperature changes?
If it does, your sensor needs to be redesigned to remove unwanted sensitivities.
Luckily, in control engineering, the sensing of process variable has been understood and improved year on year over many year.
Moving to the instrument in question, it seems a reasonable task to design an instrument to measure ‘some radiation’ from the sky towards the ground (i’m not worried about direction).
This instrument is measuring ‘some’ radiation, which direction, I do not know, I suspect a quick test by rotating the instrument through 180 degrees would be quite informative
Why they do not use a PT100 to measure the temperature of the plate I do not know, I would find that more informative in calculating the amount of ‘power’ the device is receiving.
In the industrial world, the only reason to use a thermocouple is if you want to measure a high temperature.
PT100 measures from -200 to 850 degrees C with an accuracy of approx 0.5 to 1 degree C
Thermocouples measure (depending upon type) from -270 to 1800 degrees C with an accuracy of 2 to 3 degrees C (can be up to 9 degrees C).
If you have a thermopile (many thermocouples) with each couple doing its own thing, the accuracy of the complete pile will vary substantially from sample to sample and temperature to temperature.
As I suggested earlier, a method needs to be developed to adequately calibrate these instruments to a known source.
steverichards1984 says:
“As I suggested earlier, a method needs to be developed to adequately calibrate these instruments to a known source”
Agreed, they are gauged against themselves.
When Climate ‘Science’ say a particular pyrgeometer error is plus or minus10% say,
how do they get an actual reading is to fix the error bars around?
It might as well be 50% (or any figure) because the acknowledged problem of circular reasoning remains.
If the wrong calibration equation is used the pyrgeometer will faithfully report the faulty reading.
For instance speed can be measured in several different ways and the various method used to cross check against each other
For this reason it is doubtful the interferometer and a pyrgeometer will give exactly the same reading when pointed to a radiation source.
Filtering and masking could be used to ensure the same incident energy with exactly the same wavelength spread.
You would think that such a comparison would be used in a preliminary calibration.
Yet there are no reports of such a comparison.
A few quick comments to Richard & Bryan:
The temperature of the body is usually measured with a thermistor, which has a much larger change in resistance as temperature changes, so it is generally more precise.
For the sensor itself, the temperature difference is important. A small temperature difference would be tough to measure with a pair of Pt thermometers. On the other hand, a thermopile is specifically designed to provide a large signal directly proportional to that temperature difference.
Unfortunately your proposed method is a bit inadequate.
1) Your 1344 W heater would need to direct its heat only in one general direction, so other sides would need to be insulated.
2) The rest of the surroundings would need to be near absolute zero so as not to add any thermal IR of their own.
A much simpler solution would be to put a constant temperature source around the instrument. This would provide a known power (via Stefan-Boltzmann Law). In fact, that sounds sort of like what they do.
Disagreed. 🙂
They are calibrated by comparison to another calibrated pyrgeometer. But that is a typical method of calibration. You measure something with a trusted instrument, then see if the other instrument agrees.
But the original “trusted instrument” would not be calibrated by some sort of guessing. Instead of assuming their engineers are incompetent, why not contact them if it is of such interest to you?
Again, why not just contact the manufactures?
tjfolkerts says:
“The temperature of the body is usually measured with a thermistor, which has a much larger change in resistance as temperature changes, so it is generally more precise”
This is nonsense!
It should be noted that we are talking about two entirely different physical processes here.
The thermopile works due to the Seebeck effect not resistance change.
The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage.
Hence a passive pyrgeometer does not require a battery
A thermistor works due to a resistance change .
This is typically coupled to an out of balance Wheatstone bridge to amplify the signal from the resistance change.
This set up requires a battery.
……………………………………………………
tjfolkerts says on pyrgeometers
“They are calibrated by comparison to another calibrated pyrgeometer. But that is a typical method of calibration. You measure something with a trusted instrument”
Round and round in circular logic.
There is no trusted pyrgeometer.
A PT100 is the temperature sensor of choice in industry, not the thermistor.
To calibrate a thermistor, a PT100 or ‘Hotwell’ is used.
To calibrate ‘hotwell’ temperature sources in industry/science, a Standard PT100 (SPT100)
is used. To calibrate those, a PT25.5 (SPT) is used.
All can be calibrated by a triple point water cell which is the final judge of temperature.
Documentation for the model of instrument in question states that they are calibrated by placing them next to a ‘known good’ instrument and adjusting the subject instrument until it reads the same!!!!!
I always thought you had to use an instrument of higher accuracy to calibrate another instrument!
From: http://www.kippzonen.com/?downloadcategory/661/Pyrgeometers.aspx
“CGR 4 pyrgeometers are calibrated outdoors at Kipp & Zonen under a mainly clear sky during nighttime. The test instruments are installed next to the reference CGR 4. The pyrgeometer detector outputs (Uemf) and housing temperatures (Tb) are measured each second and compressed to one minute averages. Afterwards the downward radiation (Ld) on the reference pyrgeometer is calculated using Formula 2.”
“5.3. Traceability to World Radiometric Reference
Reference radiometers, which are calibrated annually by the World Radiation Centre in Davos, are used for the calibration of radiometers manufactured by Kipp & Zonen. The reference radiometers are fully characterized, i.e. linearity, temperature dependence and directional response are recorded. Kipp & Zonen keeps two reference radiometers for each radiometer model. These reference radiometers are sent alternate years to WRC for calibration, so production and calibration in Delft can carry on without interruption.”
Reading: http://www.patarnott.com/atms749/pdf/LongWaveIrradianceMeas.pdf
“Atmospheric longwave irradiance uncertainty: Pyrgeometers
compared to an absolute sky-scanning radiometer, atmospheric
emitted radiance interferometer, and radiative transfer model calculations, Philipona et al, 2001
shows, surprisingly to me, that black body calibration is now used as a first step only, followed by field calibration against a absolute sky-scanning radiometer (ASR).
Conclusion: calibration of these devices is somewhat unusual and could be improved slightly.
Bryan,
This is a really good guide to temperature measurement.
Click to access 5965-7822E.pdf
Among other things, it says:
Yes, Pt100 thermomenters are very stable, which makes them great choices for reference standards. No, they are not the most sensitive, and hence not the most precise.
A Pt thermometer typically changes ~ 0.4% per degree C. A typical thermistor might change by 4% per degree C. Throw in the fact that the resistance is much higher and hence a 4 lead technique is not needed, and you have thermistors as the much better choice here.
This is the opposite of nonsense.
“This set up requires a battery.
Sigh. Whether you are measuring the resistance of a piece of platinum, or a piece of semiconductor, your DMM needs a battery. The “passive” feature is that you do not need an active heater/cooler, which makes the power demands go WAY down.
Steve, I agree with pretty much everything you just said. Calibration techniques can almost always be improved.
When possible, it is always better to calibrate against instruments of higher quality. But calibrating against similar instruments is not especially unusual. Nor is is especially unusual to only have the first calibration done against the actual primary standard and then to have further calibrations only be “traceable” to the original standards.
Steve Richards did you notice
“and radiative transfer model calculations,”
So the instrument uses radiative transfer calculations for calibration.
So the instrument cannot then be used to verify the radiative calculations.
Circular logic
The drawing at the top shows no temperature sensor.
Ignore temperature sensor details because it is an irrelevant aside.
tchannon: alas, a thermocouple/pile only displays the difference in temperature between the hot and cold junction, we need to know both temperatures or keep the body/reference/cold temperature at a known constant.
We need the PT100 or thermistor to measure the second junction, without it the reading has no value to anyone.
Bryan: I did not notice, well spotted.
Bryan says: “So the instrument uses radiative transfer calculations for calibration.
No, you missed the point. They are comparing the results of various calibrations methods to theoretical predictions. For a speedometer, the equivalent would be to calibrate the speedometer, then test it by eg rolling the car down a hill and using models to predict the car’s speed at the bottom of the hill (based on mass, friction, aerodynamics, etc). If the calibrated instrument agrees with a well-respected model calculation, that is CONFIRMATION that the calibration was good. It is NOT using that model as part of the calibration.
The conclusion of that paper states:
So they conclude that the pyrgeometers agreed quite well with each other, agreed quite well with a SECOND independent measurement, and agreed quite well with theory.
Steve, pull back your thinking to more of an overview.
The point this whole exercise is making is that the device as shown indicates energy flow from the body outbound to space. Split that from any temperature measurement.
Now, externally a temperature, keep away from of what for this moment, can be domain converted without a figure for emissivity to a flux figure. This number can be added to the above figure but it is a notional value, not an actual flux figure. This is bundled and put out as a back radiation figure.
Temperature of what? Well that is one of the problems. TJF has previously denied this exists as a problem.
Just earlier I commented what happens if the instrument is popped on a hot stove. Silence.
An instrument independent of itself would ignore this. I don’t have one to hand so I can only guess at the effect.
If you want to know the outbound flux you need to know from what exactly, over what area. Doing a proxy by converting a thermometer reading of something else and without knowing anything about the surfaces is distinctly iffy.
If the body temperature of one of these devices was taken where this is at say the South Farnborough Met Office synoptic site, how does this relate?
Seems to be in a large short grass area. Anything else radiating?
Bing maps
tchannon, I am happy to expand my view and am always very happy to learn something new.
However, thermocouple devices such as these, measure radiation of such a wavelength that, thermal effects can be measured.
We only have thermal effects, no other.
That said, to get accurate thermal measurements with a TC, we need to measure or ‘know’ the cold junction temperature. There is no other way of doing it.
It does not matter what the body temperature (cold junction) is, because we subtract it from the hot junction temperature.
With reference to your last paragraph, the only relationship is between the top and bottom of the thermopile.
Tim Folkerts says:
“They are comparing the results of various calibrations methods”
What various calibration methods?
I can find only one method!
Compering one pyrgeometer with a super dooper pyrgeometer does not cut it.
The super dooper pyrgeometer will use the same or slightly different formula to guess at a scale.
There is no physical effect to measure.
Circular reasoning
.
Tim C,
* The “outbound flux” is from the surface of the thermopile that serves as the sensor. Presumably this surface is painted/coated to make the emissivity very close to 1.0. This is the “5.67×10^-8 T_b^4” term in the equation. The “outbound conduction” is the “U_emf/S” term. These two power fluxes can be determined from the temperature of the body and the temperature gradient across the thermoplile. Together these two “outbound fluxes” should equal the “inbound flux” = L_d. (NOTE: in most actual cases, the “outbound conduction” will be negative meaning that the conduction is actually INTO a cool sensor, not out of a warm sensor).
* If the pyrgeometer is put on a stove, it will melt 😛
But with smaller changes, it should make no significant difference. Look in the table you posted at the top. Day or night, sunny or cloudy, the “typical” results don’t change for the pyrgeometer (CG) for different body temperatures (+20 C vs -20 C). The calibration takes into account the body temperature and compensates for it. (The “compensation” is certainly not perfect, but it is presumably good enough for the accuracy of this instrument.)
Bryan:
Click to access Infrared%20Radiometer%20Centre.pdf
Page 25 onwards
Note the date of the paper cited above
“radiative transfer model calculations, Philipona et al, 2001”
Yet by the 2006 paper I have cited many times, they find a persistent -17W/m2 error and a further 5% relative error.
Same old false dawn.
Even these figures are uncertain because of the circular reasoning problem.
Bryan asks; “What various calibration methods?”
There is a whole section in the paper labeled “3. Evaluation Formulas and Calibration Factors”.
Bryan says: “Compering one pyrgeometer with a super dooper pyrgeometer does not cut it.”
How do you think calibrations are done? You take a calibrated “super dooper” instrument and measure something. Then you measure the same something with another instrument and see if the uncalibrated instrument gets the same result (and adjust it if it doesn’t agree).
The calibration of the “super dooper” instrument was done with reference blackbodies in the lab that put out know IR power (as were the regular instruments as well). I’m not sure what more you want.
This would be like driving 15 cars at the same speed and using a calibrated radar gun (calibrated independently with objects moving at accurately determined speeds) to measure the speeds of the cars — and finding that all 15 speedometers agree not only with each other but with the radar gun at a variety of speeds.
Bryan, we seem to be splitting hairs here. The two main points seem to be:
1) Yes, the calibrations are not perfect, and can be off considerably (~ 10% in some cases).
2) The instruments really are measuring the incoming IR flux — and that IR flux really does exist and really is a few 100 W/m^2.
“2) The instruments really are measuring the incoming IR flux — and that IR flux really does exist and really is a few 100 W/m^2.”
No. They measure outgoing.
Strictly, outgoing from the instrument, not from the ground because it has no knowledge.
Tim C,
I think it is perfectly legit to say it either way. They measure the “outgoing IR” and the “outgoing conduction” from the sensor. When these are steady, then the difference must be the “incoming flux” (assuming that no other heat flows are significant). It is a somewhat indirect measurement, but it is a measurement of the incoming IR from the clouds.
This corresponds to the “333 W/m^2” in the Trenberth diagram — that is what they are measuring. I agree that is it not measuring IR “from the ground” — ie not measuring the “396 W/m^2” upward IR. Well, when they mount a second pyrgeometer pointing downward, then they are. Each instrument measures one direction of IR.
The main point it that there IS a real IR flux from the sky (a point hat many people disagree with) and this instrument gives us a pretty good estimate of that value.
I tend to agree with Bryan on the issue here. What we are primarily told is circular illogic.
Last night I posted the following on standards on the other thread:
Apparently the standards for pyrgeometers and IR is The Infrared Radiometry Section of the World Radiation Centre (WRC-IRS) at WISG:
http://www.pmodwrc.ch/pmod.php?topic=irc
Interesting stuff.
It would appear calibration consists of comparing to the standard instrument at PMOD facility. To find out about the set up and operation of the standard you have to contact:
julian.groebner(at)pmodwrc.ch
http://www.pmodwrc.ch/pmod.php?topic=calibration#BM2__Calibration_of_Longwave_Radiometers
I won’t be doing that. It might ruin my Conspiracy Theory about pyrgeometers!!
It seems in Climate Science there are a number of Priests who are responsible for single secrets that the rest of the Priesthood are not allowed to speak. Kinda like partitioned insurgency cells also!! 8>)
kuhnkat says: May 2, 2013 at 11:12 pm
It would appear calibration consists of comparing to the standard instrument at PMOD facility. To find out about the set up and operation of the standard you have to contact:
julian.groebner(at)pmodwrc.ch
——————–
Very few instruments are calibrated to the national standards.
Most are calibrated to a transfer standard which has a calibration traceable to national physical laboratory standards.
You do not, for example, take watch crystals to the NPL and tell them to compare its frequency against their caesium fountain
from NPL:
—
Two other atomic fountains, one based on caesium and the other on rubidium, are being developed. This research effort is aimed at realisation of the SI second with reduced uncertainty and improved stability. Low phase noise microwave oscillators are also being developed to support this work.
—
So even the standard is not standard!
With pyrgeometers it seems that a BB sphere has been developed as the standard this is heated to different temperatures (where’s the temperature standard?). and units are calibrated against this. If the calibrated units are sufficiently stable then these can be used as transfer standards to calibrate others.
It all depends on what accuracy is acceptable.
tchannon says: May 2, 2013 at 9:40 pm
[quoting TJF]
“2) The instruments really are measuring the incoming IR flux — and that IR flux really does exist and really is a few 100 W/m^2.”
[tchannon writes]
No. They measure outgoing.”
1. The do not measure atmospheric temperature
2. they do not measure ground or sensor body temperature
ALL temperatures have to be nulled else it will be more inaccurate.
3. IR traverses the sensor window in both directions
4. Outgoing IR energy is ONLY set by the body temperature of the detector. It will be BB radiation spectrum.
5. Outgoing radiation will cause a reduction in energy balance of the sensor.
6. Outgoing radiation energy will not be affected by the external environment of the sensor.
7. Incoming IR will be set by stuff in its field of view. Clouds will be near BB radiators. GHGs will emit band spectra. Water on the window will absorb external IR but will then radiate as a near BB with a spectrum depending on its temperature. It will wreck measurements.
8. Incoming IR will cause an increase in energy balance of the sensor.
10!!! the energy balance of the sensor will determine the its final in balance temperature and hence its output to the recorder.
There is nothing magic about these energy balance devices!
thefordprefect,you’ve got a bit garbled on who wrote what.
As a moderator I will add [thus] to you comment. If this is wrong, you have my email, no intent at misleading nor that you intended. Fings appen.
I’ve updated the Chilbolton data, plots and archive, now through 4th May 2013 and will do for now. so I can focus more elsewhere.
TFP,
Are you saying that manufacturers who claim they send their reference instruments to this group for calibration are lying to us??
No-one is lying kuhnkat but there is trouble communicating.
TFP says
“Very few instruments are calibrated to the national standards.
Most are calibrated to a transfer standard which has a calibration traceable to national physical laboratory standards.”
It would be wrong to equate the self styled ‘World Radiation Centre’ with the NPL.
It seems to be largely a users group who formed to try to get their pyrgeometers to read the same value when pointed at the same source.
Their results can be summarised by the paper
“radiative transfer model calculations, Philipona et al, 2001″
Yet the 2006 paper I have cited many times, finds a persistent -17W/m2 error and a further 5% relative error.
Same old false dawn.
Pyrgeometer users face a problem.
If theirs was a truly accurate standard integrated into the International System of Units,
it would then be possible that the other units such as the Watt and the Metre could be cross checked to agree with the pyrgeometer.
How realistic is that when the even the users realise the problem of circular reasoning and the error bars are so high .
Bryan (and Tim C),
To me there are three fundamentally issues to discuss.
1) Whether the instruments “measure” back-radiation or simply “indirectly determine” back-radiation.
2) Whether the instruments determine back-radiation to a desired level of accuracy.
3) Whether back-radiation even exists, or if it is simply a figment of CAGW alarmists’ imaginations.
Issue (1) is simply semantics to me. Pretty much all electronic instruments “indirectly determine” the quantity they purport to measure. The net result of these instruments is a number that is designed to approximate the back-radiation reaching them.
I have no problem saying that (2) is an issue — the instruments could certainly be be made better; the calibrations techniques could be made more robust. They probably not accurate enough to determine that back-radiation back radiation to ± 1 W/m^2 in a given location, let alone 333 ± 1 W/m^2 averaged over the whole earth.
But I will not compromise (3) — the idea that 333 ± 50 (to be safe) W/m^2 of real IR photons are on average coming downward from the sky to get absorbed by the surface.
Tim F: But I will not compromise (3) — the idea that 333 ± 50 (to be safe) W/m^2 of real IR photons are on average coming downward from the sky to get absorbed by the surface.
Always remembering that over 80% of whatever is coming from “the sky” is in fact coming from only a few hundred metres above the ground.
Rog,
Yes, certainly much of the radiation comes from near the surface. This is especially true in the CO2 & H2O absorption/emission bands. Outside of these bands (the “atmospheric window”), the radiation is either a) mostly absent or b) coming from clouds (which means it might be coming from a few 1000 m up).
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