SCARAB
SCAnner for RAdiation BudgetSCARAB is a scientific instrument on-board the French-Indian satellite Megha-Tropiques dedicated to the study of the Earth’s radiative budget. It is a CNES/CNRS instrument, heritage of the first 2 SCARAB instruments on board the Russian satellites Meteor-3-7 (1994) and Resurs-O1-4 (1998).
The SCARAB instrument is a cross track passive multi-spectral scanning radiometer featuring 4 channels from visible range up to far infrared. Its spatial resolution is 40 km at nadir and its swath width is 3300 km.
The following table gives the characteristics of the different channels:
| Channel | Bandwith (µm) | Name | Objective | Filter |
| C1 | 0.55- 0.65 | Visible | Scene identification | Interference filter |
| C2 | 0.2 – 4.0 | Short Wave | Reflected solar radiation | Silica filter |
| C3 | 0.2 – 100 | Long Wave | Total radiation | No filter |
| C4 | 10.5 – 12.5 | Thermal | Scene identification | Interference filter |
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.
Acquisition principle:
The SCARAB instrument features four parallel telescopes, one telescope per channel, they are identical except for their filters. It uses pyroelectric detectors for all bands.
SCARAB points to nadir and scans the full field of view within six seconds. 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. Gray lamps and blackbodies are used for onboard gain calibration and at every scan period, a deep space measurement is performed for offset calibration of the thermal channels.
Products:
The AERIS ICARE Data and Service Center archives and distributes SCARAB Level 1 and Level 2 products.
The Level 1 are processed by ISRO while the Level 2 scientific processing is performed by ICARE.
Level 1 products are available segment wise or orbit wise.
Level-2 are ‘water vapour’ products, obtained for clear and cloudy but non-precipitating scenes, over land and ocean. They include the relative humidity profiles and the upper tropospheric humidity.
SAPHIR products available at ICARE:
- Level 1A – Filtered radiance in the instrument geometry
- Level 1A2 – Filtered radiance resampled in a fix grid
- Level 2 – ‘Radiative Budget’ product in the instrument geometry (40-km Nadir resolution)
- Level 2B – ‘Radiative Budget’ product at 1°
The products available in the catalog start from November 3, 2011.
At the end of 2018, the satellite suffered a degradation of the data management subsystem. Data availability is significantly reduced for the last quarter of 2018 and no product is available between December 2018 and April 2019. From April 2019, to overcome the problems of thermal sensitivity of the memory, it was decided to switch off data management (cycle 90 min ON/300 min OFF) reducing data availability to less than 25%.
Data access:
https://www.icare.univ-lille.fr/data-access/distribution-catalogue/
The data available in AERIS are up to 14 of March 2022.
Contact:
Rémy Roca (Laboratoire d’Etudes en Géophysique et Océanographie Spatiales) – Project scientist
remy.roca@legos.obs-mip.fr
Michel Dejus – CNES project manager
michel.dejus@cnes.fr