The rates of degradation of VISSR (Visible and Infrared Spin Scan Radiometer) visible radiometers on three GMS-series satellites, GMS-3, GMS-4 and GMS-5, were estimated from 1987 to 2000 by a simple method in which the long-term behaviour of the higher end of brightness was used as a calibration target. The sensitivity of GMS-3/VIS was found to have decreased by about 3.5% per year during March 1987 through to December 1989. GMS-4/VIS appeared to have deteriorated steadily at a similar rate as GMS-3/VIS except in the first five months when quicker degradation is thought to have occurred. The degradation rate of GMS-5/VIS was estimated to be about 1.1% per year, which is nearly one-third of the preceding two satellites. The results are compared with the vicarious calibration by ISCCP (International Satellite Cloud Climatology Project). Both results agree in general degrading tendency for GMS-3 and GMS-4 visible channels, but the deterioration was likely more constant than ISCCP shows. The most distinct difference is that GMS-5/VIS seems to have also been degraded in the present investigation though ISCCP shows an increase of sensitivity.
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