Sensitivity Study and Intercomparison of CO2 Absorption Bands in SWIR Region

The short-wave infra-red (SWIR) region is sensitive to Carbon dioxide (CO
2
) gas and this region is used for detection of CO
2
source and sink. Generally, three channels of CO
2
absorption have been used for this purpose: 1570, 1602 and 2009 nm. Out of all the three bands, 2009 nm band has been widely used by various researchers, followed by 1602 nm band. CO
2
and water vapor (WV) absorption coexist in the same spectral locations, which makes retrieval of atmospheric CO
2
concentration quite challenging. The main objective of the study is to compare the sensitivity of these three CO
2
absorption bands and to understand the effect of WV on it. In order to model and decouple the WV and CO
2
absorptions, we have used MODTRAN (MODerate spectral resolution atmospheric TRANsmittance) 5.3 radiative transfer model simulations by varying WV and CO
2
levels in SWIR channels. Through the statistical analysis, we found band 2009 nm is strongly affected by WV absorption and 1570 nm band is partially affected, while 1602 nm band is quite clear and unambiguous with respect to WV absorption. Moreover, band 1602 nm shows narrow width, sharp absorption and less sensitivity to the WV concentration compare to other bands. Therefore, 1602 nm band is also suitable for differential absorption methods to retrieve CO
2
concentration.