Modeling of Temperature Rises at Focal-Plane-Array and Their Impact on the Performance of a CCD-Based Spaceborne Earth-Observing Imaging System

Abstract

Space optical imaging systems are subject during their in-orbit lifetime to many damaging effects caused by aging and harsh conditions (temperature and radiation) in the low Earth orbit environment threatening consequently instruments’ performance and durability. In particular, the time-dependent increase of the detector’s thermally-induced dark current due to temperature rises at the Focal-Plane-Array (FPA) may well lead to an unacceptable degradation in the radiometric performance of the optical imager. The aim of this work is to establish measures for the mitigation of FPA thermal effects on the radiometric performance and calibration of a space-borne optical imaging payload through FPA design optimization and in-orbit operation of the optical imaging payload. The temperature rises at FPA during long strip acquisition are first modeled, and results are used to assess the consequent effect on radiometric performance by predicting time-variable changes in detector offset due to thermal leakage current. Then, based on the outcomes of the thermal model and offset signals calculation, recommendations regarding FPA design and the operation of the optical imaging payload are made to mitigate the effect of FPA temperature rises on the imager’s radiometric performance. Finally, in-flight FPA temperature measurements taken during on-orbit operation are compared with the FPA thermal model results. The modeling results exhibit a strong correspondence with the measurements acquired during the flight. The dark current derived from in-flight data demonstrates that the time-dependent increase in the detector offset signals induced by temperature rises at FPA during image acquisition is negligible, validating the proposed thermal mitigation strategy.