July 8, 2016

MADRAS instrument

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.

Principe de fonctionnement de l'instrument MADRAS
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.

FrequenciesMain mission objective
18.7 GHzRain above oceans
23.8 GHzIntegrated water vapour
36.5 GHzLiquid water in clouds, rain above sea
89 GHzConvective rain areas over land and sea
157 GHzIce 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.FrequenciesPolarizationSpatial resolution (km)
M118.7 GHzH + V40
M223.8 GHzV40
M336.5 GHzH + V40
M489 GHzH + V10
M5157 GHzH + V6

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.

Description de l'instrument MADRAS
MADRAS Instrument Architecture
MP4 Format ~22.3 Mb (or WMV format ~17 Mb)