Observing the distribution of atmospheric methane from space

Fig 2: Transmission of the SCIAMACHY detector and absorption cross-sections of CO2 and CH4. Ideally CO2 and CH4 would be retrieved from ch.7 & 8 however due to a build up of ice, channel 6 is used instead (PhD thesis: C. Frankenberg, 2005, pg 7). The periodic build up of an ice layer on the SCIAMACHY detector adversely affects the quality of data that can be gained from channels 7 and 8, which cover the most prominent spectral bands of CH4. Retrievals of CH4 therefore have to be performed using absorption features between 1630-1670 nm in channel 6 (see Fig 2). The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) is a passive imaging spectrometer, launched in 2002 onboard ENVISAT, and has eight spectral channels covering the wavelength range 214-2386 nm non-continuously. Using the near infra-red (NIR) channels 6, 7 & 8 allows the detection of CO2 and CH4 down to the planetary boundary layer (unlike thermal IR detectors) and hence the retrieval of total atmospheric columns.