The MADRAS instrument is a nince-channel self-calibrating microwave imager. It is the main instrument of the MEGHA-TROPIQUES mission, jointly managed by the CNES and ISRO agencies.
MADRAS is a conical scanning radiometer, it is a total power type. The rotation speed is around 25 rpm.
MP4 Format ~29.3 Mb (or WMV format ~13.5 Mb)
MADRAS has operating frequencies in the range 18.7GHz-157GHz. The table below gives the main mission objective for each channel.
|Frequencies||Main mission objective|
|18.7 GHz||Rain above oceans|
|23.8 GHz||Integrated water vapour|
|36.5 GHz||Liquid water in clouds, rain above sea|
|89 GHz||Convective rain areas over land and sea|
|157 GHz||Ice detection in clouds|
The microwave radiation from the scene is collected by the antenna reflector and focused to the respective horns. The scene is scanned by rotation of the complete antenna i.e. the reflector and the horns. During every rotation, the angular sector where the antenna beam faces at the platform is used to calibrate the receivers. A calibration mirror is used to collect the energy coming from the cold sky. An on board hot target provides another calibration point. The radiometric sensitivity requirements imply that the receivers must be close to the horns so they are implemented in the mobile part. The purpose of the receivers is to deliver signals, the magnitude of which is proportional to the brightness temperature of the scene. A rotating joint allows the transfer of the electrical signals (video, TM/TC, power supplies, heater lines) between the fixed part and the mobile part.
Channel definition for each channel
|Channel nb.||Frequencies||Polarization||Spatial resolution (km)|
|M1||18.7 GHz||H + V||40|
|M3||36.5 GHz||H + V||40|
|M4||89 GHz||H + V||10|
|M5||157 GHz||H + V||6|
The MADRAS instrument is made up of the following equipment:
- MARFEQ A: MADRAS RF EQuipment A.
- MARFEQ B: MADRAS RF EQuipment B.
- MSM: MADRAS Scan Mechanism.
- MBE: MADRAS Back-end Electronic divided in 2 units (rotating and static).
- MCW: Momentum Compensating Wheel.
- MSM/MCW Electronic.
- MADRAS power supply unit: DC-DC Converter.
MADRAS Instrument Architecture
MP4 Format ~22.3 Mb (or WMV format ~17 Mb)