Radiometric Characteristics of the Broadband Radiometer (BBR) Instrument for the EarthCARE Mission

Abstract

AbstractThe Broadband Radiometer (BBR) is one of a suite of instruments to be flown on the Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) space mission. Its role is to make broadband measurements of Earth radiance in terms of reflected solar radiation and emitted thermal infrared radiation for use with the other EarthCARE instruments for the study of Earth atmosphere processes. The Broadband Radiometer has its design based on the principles and heritage of previous instruments for studying the earth radiation budget (ERB). The radiometer has common features with those instruments: two measurement bands—shortwave (solar energy of 0.25–4 µm) and total wave (0.25 to >50 µm)—with a longwave band (thermal emission of 4 to >50 µm) being obtained by subtraction of the two measured bands. Multiple simultaneous views of Earth at three different view angles are used to account for angular variations in radiance. The radiometer requires an accuracy of 1% in each band, similar to those of the previous instruments, and detailed calibration measurements on ground and in orbit. This paper describes the instrument calibration algorithms and the corresponding requirements on the ground calibration of the flight instrument prior to launch. It includes a description of the main methods to be used and the error sources to be controlled, based on the design heritage and analysis results of the previous ERB instruments.