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NASA's clouds and the Earth's radiant energy system (CERES) program is a key component of the Earth observing system (EOS). The CERES proto-flight model (PFM) instrument is to be launched on NASA's tropical rainfall measuring mission (TRMM) platform on 1 November 1997. Each CERES instrument contains three scanning thermistor bolometer radiometers to monitor the longwave and visible components of the Earth's radiative energy budget. An integral part of analyzing these measurements will be the use of high-resolution cloud imager data in conjunction with data from the CERES instruments. The use of high-resolution cloud imager data requires that the point spread function (PSF), or the dynamic response of the radiometric channels as they scan across a far-field point source, be well characterized. The PSF is determined by the field-of-view of the radiometric channel, its optical geometry, and the time response of the thermistor bolometer and its associated signal conditioning electronics. The PSF of the CERES instruments is measured in the laboratory using a state of the art radiometric calibration facility (RCF) developed by TRW. Intrinsic difficulties in making this measurement suggest that a better understanding of the data could be obtained by the use of an independent instrument model. High-level first-principle dynamic electrothermal models of the CERES radiometric channels have been completed under NASA sponsorship. These first-principle models consist of optical, thermal and electrical modules. Accurate optical characterization of the channels is assured by Monte-Carlo- based ray-traces in which tens of millions of rays are traced. Accurate thermal and electrical characterization is assured by transient finite-difference formulations involving thousands of nodes to describe thermal and electrical diffusion within the thermistor bolometer sensing elements and the instrument mechanical structure. The signal conditioning electronics are also included in the models. Numerical simulations of the PSF's of the CERES proto-flight model (PFM) radiometric channels have been completed. This paper presents a comparison between the measured PSF and the independent numerically predicted PSF for the CERES proto-flight model total channel. Agreement between the measured and predicted PSF's is excellent. The result of this agreement is a high confidence in the model to predict other aspects of instrument performance. For example, the model may now be used to predict channel PSF's for elevation scan rates different from the nominal Earth scan rate.
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