CALIBRATION OF THE IMPROVED STRATOSPHERIC AND MESOSPHERIC SOUNDER .1.INTRODUCTION, SPECTRAL, AND RADIOMETRIC CALIBRATION

The Improved Stratospheric and Mesospheric Sounder (ISAMS) is an infra red spectroradiometer that formed part of the science instrument paylo ad of the Upper Atmosphere Research Satellite. An essential part of th e success of ISAMS in orbit was a program of prelaunch calibration and characterization of many aspects of the instrument's performance. A b rief description of ISAMS is followed by a detailed discussion of the calibration and characterization methodology, the facilities used in t his program, and the results from the spectral and radiometric measure ments. The results are discussed in terms of factors affecting the in- flight performance of ISAMS, particularly the spectral response of the measurement channels, the radiometric linearity, stray radiations and their dependence on the line of sight view, signal-to-noise ratios, a nd the sensitivity of the in-flight radiometric calibration to anticip ated changes to the thermal environment within ISAMS. Some of the ''le ssons learned'' are discussed with reference to the ISAMS design and t he design of future instruments and test facilities.