The influence of the spectral response of satellite sensors on estimates of broadband albedo

Abstract

AbstractThe radiative impact of cloudiness variations on climate depends on the relative magnitudes of changes in the planetary albedo and the outgoing longwave radiation. R. D. Cess and co‐workers showed in 1982 that the calculated direction of the cloud‐climate feedback (i.e. whether the earth‐atmosphere system warms or cools with changing cloud amount) depended on the satellite data sets used in their analysis. It was suggested that the different spectral resolutions of the satellite sensors might be responsible. This note examines that suggestion. It is shown that the change in planetary albedo measured by the narrow band scanning radiometers on board NOAAs 2 to 5 as a result of cloudiness variation can be an overestimate of the actual change by a factor of up to 1.38 at low latitudes. The overestimate is not sufficient to explain completely the differences amongst the satellite data. Nevertheless, the results indicate that satellite spectral response must be carefully considered if the strength (and possibly even the sign) of the cloud‐climate feedback is to be correctly assessed from narrow band satellite data. Over snow‐covered surfaces it is shown that the NOAA data may underestimate the effect of cloud cover changes by over 70%, and overestimate the planetary albedo by over 0.2.