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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How long has the erroneous data been collected with the type of instrument in question? What is the date it was first commissioned?
OT,slightly. Phys-Org.com has noted Schwartz/Charlson paper on the mysterious failure of the earth to warm as predicted.
http://www.physorg.com/news183142998.html
Probably not worth going there, it ends like all the rest of them; we still need to do something even if we don’t know what’s wrong.
REPLY: Thanks for the tip – Anthony
Looks like these guys have developed a better system…
http://www.springerlink.com/content/9522350713363×85/fulltext.pdf?page=1
I wonder what kind of windows they are using… NaCl, KBr.. LOL
I would not even use windows but just a shutter that could be programmed not to open when water is splashing everywhere…
Ray, that’s like suggesting that drones could do a better job than the Caitlin Arctic Ice survey did of measuring Arctic ice thickness! I mean, LOL! LITERALLY!!!
Or not.
Ray, not enough opportunities for adjustment.
Maybe they could use self-cleaning windows
http://www.ehow.com/how_110278_self-cleaning-windows.html
… as long as the TiO2 layer does not interfere with the CO2 infrared band.
Murray Duffin (13:25:25) :
“There’s that word “robust” again. Why does that give me doubt?”
Everytime I hear robust I think “thou protesteth too much.”
Murray Duffin (13:25:25) :
“There’s that word “robust” again. Why does that give me doubt?”
Everytime I read “robust” I think “thou protesteth too much.”
Jimbo (15:39:47) :
Murray Duffin (13:25:25) :
“There’s that word “robust” again. Why does that give me doubt?”
“Everytime I read “robust” I think “thou protesteth too much.” ”
Every time I read “robust” I think that what they are really trying to say is “rob us”.
Derek (13:16:28) :
” 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.
Derek, the Mauna Loa data don’t need to be corrected, as (near) all water is freezed out at -70 C before CO2 measurements are done… That is a little more difficult on a buoy with limited power supply.
K (13:52:46) :
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.
Sometimes the difference in thinking between scientists and engineers (and other people with common knowledge) is glaring.
My favorite example comes from a nature show just a few years back. They were wondering if dinosaurs in the past could have crossed the land bridge at the Bering Straits and migrated to the Americas. After all, dinosaurs were cold blooded and needed external heat (like from the Sun) to keep moving. Thus at sunset they would chill off and fall over, and possibly die.
Then after studying large sea tortoises, they realized dinosaurs were basically largely water, and water retains heat, so after nightfall the dinosaurs could keep moving. Given their size and all the retained heat, they could keep going all through the night.
These scientists discovered, within about a decade ago, that water retains heat, creatures are largely water, therefore creatures retain heat. Isn’t science amazing?
George E. Smith (14:38:10) :
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.
I don’t think that the researchers are interested in one way CO2 transfer between air and oceans. Both are of interest, as the equatorial oceans acts as permanent sources and polar waters as permanent sinks, while the mid-latitude oceans work in both directions, depending of the seasons.
See Feely e.a.: http://www.pmel.noaa.gov/pubs/outstand/feel2331/maps.shtm
And as the detailed description gives, both seawater pCO2 and CO2 in the atmosphere are measured, thus the flux in both directions is measured, depending which is the highest:
http://www.noc.soton.ac.uk/ooc/CRUISES/HiWASE/DOCS/Fluxes-English-web.pdf
And I fear that your proposed system will not work when waves are 1 or more meters high… The “Pacific” is not always that peaceful…
R. Craigen (14:06:06) :
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
As far as I have read, they measure both humidity and CO2, at different spectral lines. The pure water line then is used to substract the water part of the mixed CO2/water spectral line via a fixed algorithm. And some calculation is done to compensate for the influence of temperature. That is what is done in many hand-held CO2 measurement devices. In this case there seems to be an additional problem not directly caused by water vapor, but by water adhered to salt particles on the lens.
Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.
So a source, possibly laser based at around 3.75 microns could be grabbed by CO2 with not much water effect at all; but it would be not such a big deal to remo=ve any water vapor, through prefreezing or dessication etc, to remove H2O from the sample.
Given a sizeable government Grant, i am sure I could develop an even more definitive method to measure actual CO2 and not H2O.
“”” Ferdinand Engelbeen (16:14:23) :
George E. Smith (14:38:10) :
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.
And I fear that your proposed system will not work when waves are 1 or more meters high… The “Pacific” is not always that peaceful… “””
Well I did not write the story above, which only mentioned air-sea flux; but I don’t mind. I’ll double the computer power to handle all those measurements, and maybe make it the size of two sugar cubes instead (not counting the standpipe and floating buoy.)
As to your last comment, I understand that the Pacific Ocean depth also varies from a few inches to over 36,000 feet. So ok my gizmo won’t likely work for water shallower than maybe two metres. Well I could scale it down to say 20 cm instead of +/- 2 metres. The 36,000 foot depth won’t bother it a bit; after all if that ship can ride up and down on that water depth and those waves you mentioned, so can my gizmo; and mine is just an 8th grade gizmo remember; not a NASA or NOAA unlimited budget gizmo
The sensors that are affected by humidity are being deployed at sea? Is the humidity stable at sea?
NO! NOT MORE CODE! NOOOOOOOOOOO!
(redhead sits wimpering in the corner sucking on her thumb)
Humidity has always been a problem in CO² readings. See Pettenkofer’s apparatus, which has a sulfuric acid drying tube to remove water from the inlet gas sample.
Now, if I read this correctly, they want to use cheap-ass CO² sensors on buoys all over the oceans. Said cheap-ass sensors are affected by humidity and/or (somehow) sea salt crystals on the lenses. They’ve come up with a novel method to get around this. But they don’t tell us in the abstract what the novel method is…do they? Just that it’s “robust!
My hackles are up.
The intent seems to be good, but I guess we’re all cynical after reading the UEA emails. I’d really like to see more about the design, the methodology, and some of the standardization results before commenting further. My suspicion is that the ‘novel’ correction method may not be valid after about 4 months.
OT… Brown beats Coakley
End of Cap and Tax… End of Health Care mess…
Pardon me, I’m only a humble engineer, but I would have thought one would have tested for humidity effects in an ocean deployed sensor. Is this stupidity or naivety?
Before I woulsd have launched such a project dependant on these sensors, I would have characterized them versus humidity, atmospheric pressure, temperature. The buoys would be strapped up to measure these other parameters, and the “CO2 content” and then we would have vaguely reliable data.
er………………..why is it nessesary to measure CO2 on the oceans surface??
was this dreampt up by some with more money then brains? Oh yeh government grants. Just seems to me that the Mauna Loa data and satellite pictures already provide the data needed although George E. Smith’s toy sounds real cool and way to well thought out.
“Robert of Ottawa (19:04:56) :
Pardon me, I’m only a humble engineer, but I would have thought one would have tested for humidity effects in an ocean deployed sensor. Is this stupidity or naivety?”
What good is data if it can’t be adjusted to match the climate models?
George E. Smith (16:30:44) :
Well not surprisingly, the article is about as uninformative as it could be. Not a mention of the operating wavelength range of the CO2 detector..
No real point in using the 15 micron CO2 band, since water vapor overlaps pretty much all of that to some extent, and other issues.
But CO2 also has a strong absorption line at around 3.5-4.0 microns, whcih is right in a water hole.
Not much overlap in the 15μm band really, there are plenty of lines to work with. Check out the spectra below: H2O top, CO2 below.
http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif
Wasn’t it the famous scientist Arroneous who first posited the CO2/Earth temperature connection?
More CO2 than we thought? Disaster is nearer.
Less CO2 than we thought? The model sensitivity to CO2 must be increased.
And no mater what climate science is improved.