Evidence of atmospheric contamination on the measurement of the spectral response of the GMS-5 water vapor channel

The GMS-5 geostationary satellite carries a channel centered at 6.7 mu m fo r the measurement of upper-tropospheric humidity. This channel's spectral r esponse shows structures that are similar to those shown by the atmospheric transmission. This note shows that these structures probably result from w ater vapor absorption between the calibration source and the instrument whi le making the response measurement, A corrected filter is proposed after no rmalization by the inferred atmospheric transmission. The brightness temper atures computed by a radiative transfer model using the spurious response e xhibit a warm bias of about 1 K.