Differential absorption in the near-infrared is used to retrieve total column water vapour from MODIS (Gao and Kaufman, 2003), OLCI (Preusker et al., 2021), and others. The idea is that reflected sunlight in one channel is strongly attenuated by water vapour, but not in the nearby window channel, while other properties (aerosol absorption, surface properties) are similar enough such that the difference or ratio between the reflectances can be attributed mostly to total column water vapour. Reading about this principle in the context of OLCI I came across the term ρστ-absorption band. Some examples:

water vapour absorption within the 940 nm ρστ-absorption band

using the ratio of measurements in the ρστ-absorption band and a nearby window band

like the oxygen A band at 0.76 μm or the ρστ absorption band of water vapor around 0.9 μm

studied using the ρστ-water vapor absorption band

Why is it called the ρστ absorption band?



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