The SLSTR measures Sea and Land Surface Temperature, with performance equivalent to or exceeding that of the ENVISAT AATSR. The SLSTR design and development are based on the re-use of AATSR concept. Its detectors cover the visible and the infrared spectrum, including thermal (TIR) and short wave (SWIR) infrared. The SLSTR uses rotary scan mirror mechanism(s) to produce a wide swath. It features ~1 km spatial resolution at nadir for TIR channels and 500 m spatial resolution for visible and SWIR channels. As in AATSR, it has dual-view capability—inclined forward and near-vertical nadir—to provide robust atmospheric correction over a 750 km swath. The nadir and forward views are generated using separate scanners to allow for a wider swath than possible with the single conical scan ATSR design. The channels selection (1.6, 3.7, 10.8 and 12 ^m in the IR and 0.55, 0.66 and 0.85 ^m in the visible) include the AATSR and ATSR-2 channels for continuity. Additional channels at 1.378 and 2.25 ^m enhance cloud detection, besides being used for new products. SLSTR instrument is dedicated to the measurement of Sea and Land Surface Temperature, with equivalent ENVISAT A/ATSR baseline performance. Consequently, wherever possible, the SLSTR proposed design and development are based on the reuse of ATSR concepts, supported by existing and qualified technologies. The proposed sensor design is based on the following main concepts:

• Photo Conductive detectors with two elements for TIR channels and on small multi-element arrays of Photo Voltaic detectors for the other channels. Infrared detectors are operated at 80 K.

• A dual view capability (inclined backward and near-nadir) to provide ATSR-style robust atmospheric correction over a 750 km swath.

• Both Backward and near nadir views share common focal plane optics and detectors in such a way as to ensure spectral and radiometric probity of the design and the resulting data.

• Rotary scan mirror mechanisms to produce a wide swath running at constant angular velocity. A flip mirror mechanism is foreseen to manage the swapping between the two views

• Ground Sampling Distance at nadir for the TIR channels is ~1 km, while it is 500 m for Visible and SWIR channels.

• The complete suite of AATSR and ATSR-2 spectral channels in order to maintain continuity with the previous sensors.

• Accurate and stable in-flight calibration performed by means of suitable onboard radiometric sources.

The instrument (see Fig. 14) includes on-board radiometric sources for accurate and stable in-flight calibration. The infrared detectors are cooled to 80 K using active cooling.

Fig. 14 SLSTR external configuration

The instrument is integrated on a single plate with its control electronics and cooling radiators. The SLSTR mass is approximately 90 kg.

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