From a National Oceanography Centre, Southampton (NOCS) press release
Measuring carbon dioxide over the ocean
Reliable measurements of the air-sea flux of carbon dioxide – an important greenhouse gas – are needed for a better understanding of the impact of ocean-atmosphere interactions on climate. A new method developed by researchers at the National Oceanography Centre, Southampton (NOCS) working in collaboration with colleagues at the Bjerknes Center for Climate Research (Bergen, Norway) promises to make this task considerably easier.
Infrared gas sensors measure carbon dioxide based on its characteristic absorption spectra and are used to evaluate the air-sea flux of the gas¬¬. So-called closed-path sensors precondition air before measurements are made, while open-path sensors can be used to measure the air in situ.
One advantage of using open-path sensors at sea is that wind measurements can be taken contemporaneously in the same place. Moreover, because they are small and don’t use much power they can be used on buoys.
“Open-path sensors have the potential greatly to increase our understanding of the variability of air-sea carbon dioxide fluxes,” said John Prytherch of NOCS.
However, a long-standing concern has been that the values from open-path sensors do not tally with those from closed-path sensors, or with measurements made using other techniques.
“Other scientists have been sceptical about the reliability of carbon dioxide flux measurements taken at sea using open-path sensors,” says Prytherch: “However, we now believe that we understand the reason for the discrepancy and that we can correct for it.”
The problem turns out to be that the sensors are sensitive to humidity, meaning that fluctuations in the amount of water vapour in the sample air skew the carbon dioxide measurements. This is probably caused by salt particles on the sensor lens that absorb water.
Having identified the problem, Prytherch and his colleagues developed and rigorously tested a novel method for correcting the data for the cross-sensitivity to humidity.
Data were collected aboard the Norwegian weather ship Polarfront, equipped with a battery of instruments to measure wind speed, humidity and carbon dioxide. Even the motion of the ship was monitored.
The researchers noted that carbon dioxide fluxes calculated from open-path sensor data were clearly too high and affected by humidity. They were also very variable, suggesting that the effect is caused by salt on the optics, which accumulate before being washed off by rain. Indeed, the researchers were able to mimic this effect in the laboratory.
However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.
“This robust method opens the way for widespread use of open-path sensors for air-sea carbon dioxide flux estimation,” said Dr Margaret Yelland of NOCS: “This will greatly increase the information available on the transfer of carbon dioxide between the air and sea – information crucial for understanding how the interaction between the oceans and the atmosphere impacts climate.”
The work was supported by the United Kingdom’s Natural Environment Research Council and is part of the UK SOLAS project HiWASE (High Wind Air-Sea Exchanges).
The researchers are John Prytherch, Margaret Yelland, Robin Pascal and Bengamin Moat (NOCS), and Ingunn Skjelvan and Craig Neill (Bjerknes Center for Climate Research, Bergen, Norway).
Prytherch, J., et al. Direct Measurements of the CO2 flux over the ocean: development of a novel method. Geophys. Res. Lett. (published on-line, 2010) doi:10.1029/2009GL041482.
www.agu.org/journals/pip/gl/2009GL041482-pip.pdf
www.noc.soton.ac.uk/ooc/CRUISES/HiWASE/
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Am I wrong to think that mathematical adjustment of known bad data is not what the AGW debate needs more of?
“suggesting that the effect is caused by salt on the optics, which accumulate before being washed off by rain.”
Could they not install a fresh water washing device? You know, as fitted to cars.
LOL.
However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.
There are a great deal of corrections involved in climate science. Has anyone considered the possibility that observation has refuted the proposition of AGW, but the data was erroneously corrected?
Ah, good. I feel better. All that’s needed is for the data to be adjusted a little. What could possibly go wrong with that?
At last, something I know about!
Measurement of CO2 in gases by infra-red absorption is a very old technique. As a retired anaesthetist (anesthesiologist for N American readers) we used these all the time. The technique has always been very sensitive to temperature, water vapour, vapour condensation so no surprises here. Several other gases interfere with the measurement as they have some absorption at the relevant wavelengths, including oxygen. I wonder how they check the calibration; premixed standardised gases, mass spectrometer? At the concentrations they are measuring small errors in calibration could result in big errors in measurement.
I don’t have access to the paper. Can anyone summerize the method used to correct the data. Is it a numerical adjustment? Is it calebrated against some standard reference? Is it a mechanical “cleaning” of the lens?
Tim
Instrumental based correction where they sense the amount of humidity would be a fine. If they calibrate correctly during the manufacturing process, it should be correct. Perhaps there would need to recalibration of these instruments at time, but then it should be reliable. If they do the adjustments back at the data center, then it would be more prone to manipulation.
Funny how, every time there is some sort of a mistake or an error in calculation, etc, it always produces more warming, and in this case more CO2.
It must be a coincidence.
This sounds great if there are people where the sensor is to determine when an adjustment is needed based on weather conditions.
But at an automated station how do they know how much salt is on the lens? How do they know when rain has rinsed the lens? Just because it rains other factors such as wind direction may prevent the lens from being cleaned or a short rain may only partially clean the lens.
I am sure there are many other issues that an automated station can’t audequately take account of, which means I don’t believe that an automated stations output can’t be accurately adjusted. Only a manned station, which would allow for fudging of data.
” The researchers noted that carbon dioxide fluxes calculated from open-path sensor data were clearly too high and affected by humidity. They were also very variable, ”
Humidity.
Mauna loa, who’d of believed that. !
also,
After the fact corrections to get the “right” answer.
Mauna Loa, who’d of believed that. !
Can’t they ever use traceable methods to measure things? This is insane to have used methods that were not fully tested in laboratories with simulated environments and so on. The instruments and methods should have been certified before being put in place. They patch up the data from a questionable instrumentation and method and expect people to take their words that all is good… with such convincing phrases as “However, after correction using their newly developed method, the calculated carbon dioxide fluxes WERE IN LINE with previous studies that used different sensors or techniques.”
WERE IN LINE!!!!???? That translates to what in term of error and deviation? Apparently they were not convinced to use the term “exactly comparable” or “right on the button”… no they used “were in line”… yeah, sure… I will take your words for it and give you my tax money for you guys to travel around and publish papers…
From the start the data are questionable and no amount of “correction” will give them credibility. Bandaid data won’t give healthy results.
Quoting from above
So-called closed-path sensors precondition air before measurements are made, while open-path sensors can be used to measure the air in situ.
I think the closed path capture the air and then freeze the humidity out.
In the Greek constitution there is an ending paragraph:
“Faithful adherence to these statements rests on the conscience of the Greeks”.
The scientific system is an honor system. Of course there will be calibrations and corrections to any real measurements.
Unfortunately the honor system has been badly broken in any climate “science” that has to do with AGW, and CO2 is a red flag :(. Is there a link to the article to see what the “other methods” are and how the corrections are made?
There’s that word “robust” again. Why does that give me doubt?
There is another problem here they don’t mention.
Humidity sensors are notoriously difficult to calibrate and keep in calibration. Typically errors are several percent.
Unless they have some super-special set-up rather than your run-of-the-mill temperature and humidity sensors, the correction based on humidity is itself suspect.
The whole thing is a waste of money.
Anna, the physiological “closed-path” sensors keep the chamber heated so that all water is present as vapour and can’t condense on the lens. The only problem is that you have to control the chamber temperature to very tight limits, not easy if the incoming gas is very cold and very humid as it will be over the sea
Like I’m going to trust any data that has been – ahem – “corrected.”
And like I’m going to trust anyone who tells me I should, because the method is “robust.” Those words have me reaching for my tinnitus medicine, such is the noise from those internal alarm bells.
The wording seems somewhat curious. Part of it reads as if they just recently thought of water vapor, yelled “eureka”, and a long-standing puzzle was solved.
Obviously it didn’t happen that way. Apparently they have constructed an adjustment protocol. The words “robust” and “novel” make me uneasy.
IMO this approach to solving a measurement error seems backward. Perhaps I don’t understand the matter.
I would have first approached companies – chemical equipment makers, medical equipment firms, etc. – that make sensors and asked them how to improve the devices.
Until we learn more ….. At the moment the PDF seems to be behind some wall I won’t bother to scale.
Surely they don’t propose (in the case of buoys) regular washing with fresh water. Further, is there not a question of how consistently such washing can be done?
I would suggest something other than washing, like a filtration process that eliminates salt.
Presuming that salt is not present as free ions in the air, place the sensors along a passage designed to settle out all but the finest particles, simply by gravity. Around the sensor place several meshes to filter out first, macro particulate matter, then liquid-spray born particulate matter, then micorfilters to filter out all but purely molecular gaseous particles. The passage could be open on two ends and wind would suffice to refresh the air around the sensor.
The design I have in mind, unfortunately, doesn’t fit into a text box very well, but it would also avoid the problem of physical wash-over, even short-interval submersion of such a buoy.
However, as others have pointed out here, there remains a question of humidity. It appears these guys are dealing with the effects of spray-borne salt, which is not the same thing as humidity, which would not be eliminated out by the procedure I have in mind. If there is a humidity-dependence that is not well-understood, perhaps it could be determined empirically to calibrate the readings.
I would think one should also determine temperature-dependence as well (I can’t think of other factors, but perhaps mechanical, electrical and magnetic influences could be problematic, say during inclement weather). If this thing is coupled with a good array of instruments to measure these things, proper calibration should give reliable readings, and I think it is possible to design a robust buoy system based on it.
First, I thought, oh no, not another robust method. Then after rereading this: ” However, after correction using their newly developed method, the calculated carbon dioxide fluxes were in line with previous studies that used different sensors or techniques.
This robust method opens the way for widespread use of open-path sensors for air-sea carbon dioxide flux estimation,” said Dr Margaret Yelland of NOCS: “This will greatly increase the information available on the transfer of carbon dioxide between the air and sea – information crucial for understanding how the interaction between the oceans and the atmosphere impacts climate.” my reaction changed to: Whut?(copied from a former president). Are their procedures valid?
How much do these open path sensors cost, and, can a public network be set up on the same buoys to allow analysis of raw data controlled by a second source of info?
Doesn’t inspire confidence.
DaveE.
Why bother? I thought the tipping point has already passed or soon to be passed (depending on which loony you listen to) and we are all doomed. Or are the “climate scientists” having second thoughts?
Well here we go again. I see that term; “CO2 fluxes”, and off go a dozen sirens playing all kinds of tunes. Well I see in the first line of the small print, that it says; “air-sea flux” …”of carbon dioxide – an important (read inconsequential) Greenhouse gas”. Now lookie here “the readings are too high and are affected by humidity”. NO ! the Readings are wrong, and are not measurments of CO2 air-sea flux. They might be even better measures of “humidity” which evidences the presence of a real Greenhouse gas H2O !
So what means “air-sea flux” ? Well put that way, and sans translation for those not indoctrinated into the “climatology theology”, ordinary street lingo; jargon, interprets that to mean the rate of flow of CO2 from air into sea; air > sea; how simple is that ! Of course that is the party line version. To others, the logical assumption might be that the flux is from sea-air as in sea > Air. Well a simple negative sign convention could settle that.
Well a totally dumb 8th grade science idea might be to set up a stable (small diameter) column of air, in contact with the water of not too great a height (I’d vote for 1 metre the SI unit of length; well maybe 2 metres, and then I would have sampling tubes at say 1 metre height (hence the need for two total), and as close to zero height as water surface disturbances would allow. Hey make the tube smaller in diameter to reduce those surface disturbances. Then I would siphon off those zero and one metre air samples, and feed them to a mass spec; to actually count the molecules of any species I might find there that I could ionize. From the difference in the one metere and near zero metre samples, one over time could infer the loss of CO2 at one end or tother and decide the amount and polarity of the CO2 flux.
For good measure, a similar contraption could be maintained below the water line, and samples of the water at two heights be made and MS’d to determine the changes, and prove continuity of the flux across the air-sea interfaced.
Well that’s a hand waving description; you can fill in the finesse points; I did say it was a dumb 8th grade approach.
Process control engineers know too well to measure THAT WHICH THEY WANT TO CONTROL and then control that (via feedback); rather than deriving a supposed relation between THAT WHICH THEY WANT TO CONTROL and their sister’s dandruff itchiness, and then measuring their sister’s dandruff itchiness, to control THAT WHICH THEY WANT TO CONTROL. NOW that is a truly dumb idea.
Hey I said a MASS spectrometer; not a MASSIVE spectrometer. In this day and age, I would think you could build a mass spec about the size of a sugar cube. Well if I can build a complete 3,000 frames per second digital videocamera, along with the illumination sytem to see in total darkness, and the computer and digital image processor, needed to process all those images in real time, and compute some desired output function; and don’t forget all the highly aspheric tilted and decentered custom Optics for that videocamera; and get the whole shebang into the size of one ordinary sugar cube; somebody ought ot be amble to build a mass spec that size. Oh and it helps if you can make them for under a buck ($1) like I can.
Well I do cheat a little, I do feed the necessary power to run the thing in from the outside on a couple of fine wires; not counting the wire that spits out the results. So yes I do have to use up a couple of AA cells to run the thing for six months; but I can’t work real miracles.
Well I do hope this new ship based (sounds humungous) CO2 air-sea fluxometer works and keeps a whole lot of otherwise unemployed “scientists” gainfully occupied. Don’t forget to make the (raw) data available to us tax paying chumps who anted up for your grants.
Why not just put the laser in a small plane or unmanned drone and fly over the water every week or so? That might actually be less costly than doing what they are trying to do. The windows will stay clean at least.