<title>Numerical simulation of ground calibration of the CERES thermistor bolometer radiometers</title>

Abstract

NASA's clouds and the Earth's radiative energy system (CERES) program is a key component of the Earth Observing System (EOS). Under CERES an array of radiometric instruments will be placed in Earth orbit to monitor the longwave and visible components of the Earth's radiative energy budget. High-level dynamic electrothermal models of these instruments have been formulated under NASA sponsorship. Accurate optical and thermal-radiative characterization of the instruments is assured by a Monte-Carlo-based ray-trace in which tens of millions of rays are traced, and a transient finite-difference formulation involving hundreds of nodes is used to describe thermal and electrical diffusion within the thermistor bolometer sensing elements. The external electronic circuit is also correctly included in the instrument model. The actual CERES instruments will undergo pre-launch calibration in a unique thermal-vacuum radiometric calibration facility equipped with blackbodies, a cryogenically cooled active-cavity radiometer, and shortwave sources. This ground calibration can also be simulated using the high-level, dynamic electrothermal models of the CERES instruments. This offers a quick and inexpensive means of verifying the calibration procedure and anticipating any problems that may arise. The results obtained from these simulations may then be used to predict the regression coefficients in the count-conversion equation used to convert instrument readings into radiance, and to determine which parameters should be included in the count-conversion equation to maximize its sensitivity. The paper presents results of the simulated ground calibrations of the CERES total channel instrument, including predicted values for instrument accuracy during the ground calibrations.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.