The first two models of the Sea and Land Surface Temperature Radiometers (SLSTR) for the European Copernicus Sentinel-3 missions were tested prior to launch at the Rutherford Appleton Laboratory space instrument calibration facility. The pre-launch tests provide an essential reference that ensures that the flight data of SLSTR are calibrated to the same standards needed for surface temperature measurements and to those used by shipborne radiometers for Fiducial Reference Measurement (FRM). The radiometric calibrations of the thermal infrared channels were validated against accurate and traceable reference BB sources under flight representative thermal vacuum environment. Measurements were performed in both earth views for source temperatures covering the main operating range, for different instrument configurations and for the full field-of-view of the instruments. The data were used to derive non-linearity curves to be used in the level-1 processing. All results showed that the measured brightness temperatures and radiometric noise agreed within the requirements for the mission. An inconsistency that particularly affected SLSTR-A was observed which has been attributed to an internal stray light error. A correction for the stray light has been proposed to reduce the error. The internal stray light error was reduced for SLSTR-B by replacing the coating on the main aperture stop. We present a description of the test methodology and the key results.
Leonardo has been involved in the realization of several infrared payloads for Earth observation since 1990. Among the currently in-orbit operative instruments are the two Sea and Land Surface Temperature Radiometers (SLSTRs) and PRISMA (PRecursore IperSpettrale della Missione Applicativa, meaning Hyperspectral Italian Pre-cursor of Operational mission). The SLSTRs are high-accuracy radiometers that provide sea surface temperature data continuity with respect to previous (A)ATSRs in order to serve climatology over the next 20 years, and exist within the framework of the European Space Agency Sentinel-3 mission, which is part of the Copernicus program. The PRISMA program is the first Agenzia Spaziale Italiana optical hyperspectral mission for Earth observation. It is based on a high spectral resolution spectrometer operating in the visible-short wave infrared channels optically integrated with a panchromatic camera.
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