MADRAS
Microwave Analysis and Detection of Rain and Atmospheric StructuresMADRAS is a scientific instrument on-board the French-Indian satellite Megha-Tropiques mainly dedicated to the study of precipitation in the intertropical belt. It was developed jointly by the space agencies ISRO and CNES.
MADRAS is a conical scanning microwave radiometer with 9 channels. The rotation speed is about 25 rpm. It operates in the 18.7 GHz – 157 GHz frequency band. Its swath width is 1700 km.
The following table gives the characteristics of the different channels (4 of them have dual Horizontal and Vertical polarization) and the main associated mission objectives:
| Channel | Frequency | Polarization | Spatial Resolution | Key mission objectives |
| M1 | 18.7 GHz | H + V | 40 km | Rain over sea |
| M2 | 23.8 GHz | V | 40 km | Water vapour distribution |
| M3 | 36.5 GHz | H + V | 40 km | Liquid water in clouds, Rain over sea |
| M4 | 89 GHz | H + V | 10 km | Convective rain areas over land and sea |
| M5 | 157 GHz | H + V | 6 km | Ice detection in clouds |
Acquisition principle:
The microwave signal from the scene is collected by a reflector and focused to the different horns. The scanning of the scene is obtained by the rotation of the complete antenna, i.e. the reflector and the horns. During each rotation, the angular area where the antenna beam looks towards the platform is used to calibrate the receivers. A calibration mirror is used to collect energy from the cold sky (space). An on-board hot target provides another calibration point. The requirements of radiometric sensitivity imply to have the receivers close to the horns, which are thus implanted on the mobile part. The objective of the receivers is to deliver a signal whose level is proportional to the brightness temperature of the scene. A rotating joint allows the routing of electrical signals (video signals, telemetry, remote control, power supply, heaters) between the fixed and mobile parts.
Products:
The AERIS ICARE Data and Service Center archives and distributes SAPHIR 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 – Brightness temperature in the scan geometry
- Level 1A2 – Brightness temperature resampled in a fix grid
- Level 2 – ‘Water vapour’ product at 10-km resolution
- Level 2B – ‘Water vapour’ 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%.
SAPHIR level 1 data are also available in NRT via EUMETCast and assimilated for weather forecasting by several Meteorological Agencies.
Data access:
https://www.icare.univ-lille.fr/data-access/distribution-catalogue/
Contact:
Point of 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