I want to discuss a project I found interesting from both a geophysics and instrumentation development points of view … everyone’s favourite: measuring carbon dioxide. I’ll be up front – I’m not a “Believer”, I tend to think “climate change” is a natural phenomena that has much more to do with variations in solar radiation and geotechnical processes than too many Moms driving SUVs. The land of my birth was quite recently (in geological terms) under a mile and half of ice – and they still dig up mastodon carcasses there every once in a while. Of course things are warming. Then they’ll get cold again.
Roman villages are found underwater; ancient seaports are now miles inland – the earth changes.
Is sea level rising? Coastal cities soon to be inundated with no chance to escape?
Plymouth Rock is still at the edge of the ocean where it’s been for 400 years.
Are we going to die because the sun expands in its death throes and burns up up, or because the sun will shrivel away and we freeze to death while the earth becomes a cold lifeless rock drifting through the universe?
Neither. We’ll be eons gone before either can occur.
But yes, the climate is changing … back when I was a boy and had to walk through snow all the way to the end of the driveway to catch the school bus, we actually had winter. A northern climate winter. 80 proof vodka will freeze at about -15°F or so – it was not uncommon for the stuff to freeze when we stored it outside on the dorm window sills (college daze!). You didn’t blindly walk through the door at the end of a hall on the 2nd floor; the door was possibly the “escape hatch” with no balcony so that you could get out when the snow got deep.
Needed such a door that last winter before I made my move to a different part of the country. Seems they haven’t had winters like that since I left … but it also seems they’ve been headed back that way the past few years.
Back then it was global cooling (and CO2) that was going to do us in. But this is now and everybody’s still freeking out because of CO2 (water is a far more significant green house gas and we don’t live in a positive-feedback system).
I would argue the Believers possibly have cause and effect reversed; CO2 is quite likely increasing due to warming. Why is it increasing? Many may recall the concern in the 80s and 90s of the vast clearing of what used to be called jungles in South America and elsewhere. Plants “eat” CO2. Less plants, more CO2?
Maybe magnetic pole shifts. Let’s check from where I received my first engineering degree – University of Nevada-Reno. The magnetic declination in early 2018 is 13.43° W. But 50 years ago – 1968 – it was 17.32° W. 4° in 50 years? Hm-m-m … Why would a magnetic pole shift affect things? Perhaps it changes the interaction characteristics of solar radiation with the ionosphere of the earth.
Or possibly – airplanes
? Exhaust gases and thermal disturbances at the top of the troposphere.
Maybe.
But meanwhile …
Perhaps my “gut” feeling about CO2 cause and effect is wrong. The first step to prove or disprove myself is to make accurate measurements. So this isn’t (too many) tales of me or my feelings on the general topic; this is a discussion on the engineering aspects of measuring atmospheric CO2.
Regardless of other factors, the measurement of an atmospheric gas over large distances represents an interesting challenge. I first became interested in the topic when I was assigned to a project involving a 3D atmospheric measurement system intended to study the distribution characteristics of liquid natural gas (methane) as it evaporates after a possible spill. That was long enough ago that I was a certified by DEC (who?) on PDP-11s (what?) as a computer geek.
Some mumble-mumble years later, I had gained enough education and experience to understand that much of the sensing technology hadn’t changed much … but my “expertise” with PDP-11s had limited – some might suggest “none” – applicability. And I was always more interested in collecting the data than interpreting it. That involves the study of sensors, sensor interfaces, and an understanding of what was being measured. Gee whiz, geofizz! (so that’s what I later studied)
So. How we gonna do this?
I want to cover a fairly large area fairly quickly. The most accurate means of making such a measurement would be to place a grid of mass spectrometers over the region desired. Muy moola. I’d need to consider the defining the desired grid spacing. Altitude comes to mind – ground or near-ground based instruments would be easy to maintain. How about the height of wind towers? Those things are about 250 ft high? Should I put instruments up every 50 ft? Maybe 1 at ground level, one at the top, and two somewhere in between?
Is $25k each or more a factor? Isn’t 50 ft spacing rather close?
Maybe some guys in a pickup truck wandering around the countryside? Wouldn’t need so many instruments. Hard to obtain synchronized measurements though. Hard on lab-grade instruments as well. But 1 km or so grid spacing might be feasible.
If I want to cover a large area, what grid spacing is appropriate? 1 m is probably meaningless … likely 10 m is as well. How about 100m? 1 km? 10 km? 100 km?
Maybe I want to measure concentrations where there are no wind towers or pickups can’t go. Maybe I want to make measurements where others don’t want me to go.
I’ve worked in the space industry. Maybe a satellite or two? Gets great coverage. Bit of a problem with concentration gradients through the somewhat undefined “top-of-atmosphere” if I’m mostly interested in the concentration within the troposphere where most of us reside. Hard to segment vertical gradients by altitude from above. Especially difficult if I’d like to detect localized “hot spots”.
Perhaps an airplane? There are umpty-gazillion
aircraft buzzing all around the planet at any given time; perhaps aircraft-based measurements?
Aircraft seems to be a good compromise. Covers a fair amount of ground fairly quickly, can fly at the top of the troposphere, and given the right circumstances, can fly when and where desired.
Lots of instrumentation aircraft around. I think the old Convair 580s have been retired; perhaps someone has a spare 737 laying around … Early on in my career, this was the first instrumentation aircraft I was involved with … and since I flew North Central/Republic Airlines on these planes quite a bit once upon a time, I may have flown in this airplane.
NASA flies a Douglas DC-8 as an instrumentation aircraft.
Consider a flight level of 33,000 ft, a cruising speed of about 450 mph on an aircraft with a range of 3400 miles. Maybe a better platform exists, but these numbers are suitable for this back-of-envelope analysis (a BIG envelope).
I’m by no means qualified to select an appropriate aircraft for such purposes other than specifying “it shall fly when it’s supposed to and not fly when it’s not supposed to … and shall remain under the pilot’s control at all times”. But I’m selecting something for feasible instrument platform movement parameters.
So I’ve decided on a transportation platform and measurement methodology: aircraft-based optical molecular absorption.
Among other issues, I need to consider:
- Platform characteristics: speed, altitude, positional errors
- Atmospheric characteristics: nominal characteristics, temperature, pressure, concentration gradients, interfering materials
- Energizing source: absorption wavelength, transmit energy, transmission characteristics
- Surface characteristics: absorption, reflection, region of coverage, scattering
- Detection: optical sensitivity, optical filtering (assume linear optics and ideal FOV)
- Interface networks to ADC: SNR, gain, filtering, other processing
Lots of topics for future articles.
Let’s see just how precise such a measurement may be …
That’s good for now.
According to the Air Transport Action Group, air flights worldwide produced 705 million tons of CO2 in 2013. Yet Al Gore buzzes around on a private jet so he can fly at his convenience to tell the rest of us to quit polluting. Volcanic gases emit roughly ½ this amount yearly.
“umpty-gazillion” is a scientific term meaning somewhere well over 100,000 flights per day (just shy of that in the US alone – I just checked ” FlightTracker” and at that instant, there were over 12,000 planes in the air world-wide).