On the Usefulness of Satellite Infrared Measurements in the Determination of Cloud Top Heights and Areal Coverage

Harry R. Glahn Air Weather Service, Washington, D.C.

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Abstract

The assumptions inherent in the determination of cloud top heights and areal coverage of clouds from infrared measurements made by satellites are discussed. The problems of interpretation caused by radiometer spatial resolution being of the same order of size as individual cloud elements are studied through mathematical simulation of the viewing process. An analysis of the simulated measurements from simple, specified cloud conditions produces quantitative estimates of the errors of interpretation.

It is found that individual cloud elements of a diameter slightly less than the viewed spot can be very misleading and the height of cloud tops might be judged to be several thousand feet below their true height; tops of larger clouds can be determined more accurately. If the actual height of the tops can be determined, either by the infrared measurements from large cloud masses or by other means, the areal coverage can be estimated rather well.

Abstract

The assumptions inherent in the determination of cloud top heights and areal coverage of clouds from infrared measurements made by satellites are discussed. The problems of interpretation caused by radiometer spatial resolution being of the same order of size as individual cloud elements are studied through mathematical simulation of the viewing process. An analysis of the simulated measurements from simple, specified cloud conditions produces quantitative estimates of the errors of interpretation.

It is found that individual cloud elements of a diameter slightly less than the viewed spot can be very misleading and the height of cloud tops might be judged to be several thousand feet below their true height; tops of larger clouds can be determined more accurately. If the actual height of the tops can be determined, either by the infrared measurements from large cloud masses or by other means, the areal coverage can be estimated rather well.

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