XCH4 and XCO2 proxies from MethaneAIR observations
Abstract
The area-mapping MethaneSAT satellite will aim to estimate CH4 oil & gas emissions from over 80% of emitters. It will use one spectrometer to retrieve CH4 from a window centered at 1.66 µm, and CO2 from a window centered at 1.61 µm, and a second spectrometer to retrieve O2 and surface pressure in a window centered at 1.27 µm. MethaneAIR is the airborne simulator for the MethaneSAT satellite, its observations are used to test the retrieval algorithms that will be used to process MethaneSAT data. We will present MethaneAIR Level 2 results (trace gas concentrations derived from observed spectra) obtained with the "proxy" method.
A "proxy" retrieval does not include the effect of aerosols on the light path in the forward model, it instead uses the column of another gas retrieved from a band spectrally close to the target gas as proxy for the aerosol-induced light path changes, assuming that they are similar in the two neighboring spectral regions. Typically, CO2 has been used as the proxy species for XCH4, but the variability in the modelled XCO2 can introduce biases, especially over targets with sources of both CH4 and CO2.. XO2 (~0.2095) is much less variable than XCO2. However, the O2 window is more spectrally distant from the CH4 window than the CO2 window, making the O2 proxy more sensitive to aerosols. For MethaneSAT, the O2 window will also be affected by airglow. We present XCH4 results using the CO2 or O2 columns as proxies, and XCO2 using O2 as a proxy.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.A15L1403R