The ability to check the self-reported emissions with remote sensing is new, and has led to a recalibration (ahem) of self-reported emissions.
The technology for remote sensing of CH4 is very exciting and it's being pushed forward in a lot of different ways. As you pointed out, you need sensors at various scales (in situ, airborne, space), calibration of retrieved concentrations (it's not a direct measurement), and inversions to find out what the sources are, given that you observe a certain set of concentrations. It's a complex problem!
So now we know that in at least two places in California, power companies didn't report leaks. This most recent one is much smaller, but as you joke about, having independent studies is the only thing we have. There should be a criminal policy with levels that require reporting. There should be financial and criminal penalties for not reporting.
The viewpoint I have heard is that most enterprises want to fix the leaks if they are informed about where they are to a high degree of specificity (e.g., ~20 meters). Then they can send a crew with detection equipment. They're trying the carrot rather than the stick for now. Anecdotally, this has worked.
It's not clear, to me at least, that there should be criminal penalties for medium sized leaks like in TFA. I don't know at all what the regulations are.
I did a really quick skim of the program and didn't really see remote sensing. It looks like the program does collect data reports and map them - which is always nice.
I did pick up this "For reporters subject to the California Cap-and-Trade Program, submitted data are verified by a CARB-accredited independent third-party verifier." Is it the remote sensing satellite that is a third-party verifier?
See at the bottom -- a third-party will fly a plane in circles around the site to measure all concentrations in a surface enclosing the site. The concentrations, plus wind speed, give the site emissions. (I think that's intuitive, but it's also the divergence theorem from vector calculus.)
That's a lot of work to get just one day's emissions. And there are technical issues already because you want to get the whole surface concentrations+windspeed at the same time, but you can't, because the plane has to circle the site over many hours.
Despite those cautionary footnotes, this approach is used in calibration/validation of the concentration/emission relationship. Getting it all quantitatively right, as opposed to just seeing a plume, is a complex problem. People are still exploring how it can all work together (space, airborne, in situ, plus modeling).
https://ww2.arb.ca.gov/our-work/programs/greenhouse-gas-inve...
The ability to check the self-reported emissions with remote sensing is new, and has led to a recalibration (ahem) of self-reported emissions.
The technology for remote sensing of CH4 is very exciting and it's being pushed forward in a lot of different ways. As you pointed out, you need sensors at various scales (in situ, airborne, space), calibration of retrieved concentrations (it's not a direct measurement), and inversions to find out what the sources are, given that you observe a certain set of concentrations. It's a complex problem!