The SCARAB instrument, designed to study the Earth Radiation Budget, is a cross track passive multi-spectral scanning radiometer sensing the Earth/atmosphere when the spacecraft is moving ahead. It is composed of two units:
- The electronic module (EM) manages the interfaces with the platform (power, telemetry, commands) and drives the optical unit for the science data acquisition.
- The optical sensor module (OSM) provides the optics, mechanisms and close electronic.
The SCARAB instrument has already flown on RESURS and METEOR missions and will be redesigned to be adapted to the Megha-Tropiques mission.
The optical radiometer is featuring four parallel and independent telescopes focusing the reflected solar and emitted thermal radiation of the Eearth and atmosphere on four detection channels.
|Channel 1||0.5 to 0.7 µm||Interference filter||Visible channel|
|Channel 2||0.2 to 4 µm||Silica filter||Solar or SW|
|Channel 3||0.2 to 200 µm||No filter||Total channel|
|Channel 4||10.5 to 12.5 µm||Interference filter||Thermal channel|
Channel 2 and channel 3 are considered the main channels; channel 2 directly provides the solar energy reflected by the Earth-atmosphere, whereas channel 3 measures the total energy (solar and thermal). Channel 1 and channel 4 are narrow band channels used for scene identification in the visible (channel 1) and in the Infrared (channel 4) domains. The scanning is obtained by the rotation of the telescopes and associated detectors in the Nadir plane, which is perpendicular to the satellite speed vector. At every scan period, a space view measurement is performed for calibration except for the visible channel.
The pixel geometry is driven by the orbit, the cross track scanning and the square aperture of the telescopes.