The OP touches on the question of "why the focus on plumes and not on tundra or wetlands", and has a quote from Andrew Thorpe hinting at an answer. >> “These t

The OP touches on the question of "why the focus on plumes and not on tundra or wetlands", and has a quote from Andrew Thorpe hinting at an answer. >> “These types of emissions are really, really important and very poorly understood,” [Andrew] said. “So I think there’s a heck of a lot of potential to work towards the sectors that have been really hard to do with current technologies.” I try to keep touch with work in this area. I think it's a combination of SNR and resolution/coverage. The CH4 from a gas leak is very concentrated and so it puts a strong imprint on the spectrum of light passing through it. The natural sources are more diffuse and have less contrast with the surroundings. (For earlier airborne experiments, the JPL team [which included Andrew] was using a simple matched filter aligned with the methane absorption bands - now they may be using something more complex. This was able to run on a computer on the airplane holding the sensor as it flew over regions of interest.) Anyway, for sources with a lower CH4 concentration, there will be a much weaker spectral signature. It will be hard to distinguish from other influencers like water, aerosols/dust, etc., or from instrumental effects that may be correlated with location. (E.g., "sometimes high water concentration has spectral effects that appear as high CH4 concentration, so our CH4 values over moist areas are sometimes too high.") You can improve the effective SNR by accumulating results over a larger area (of space or time). As noted in OP, the ability to get large-area, frequent coverage is quite new. And also, CH4 moves, so to combine measurements taken at different times, you need to account for transport. This is the difference between measuring "concentration" (a quantity we're more-or-less directly measuring) and "flux" (an emission rate over time, which we don't get to measure directly). As noted in OP, the plumes were a low-hanging fruit (or as they say, a fruit lying on the ground. ;-)