MADRAS Instrument on MEGHA-TROPIQUES

The MADRAS instrument is a 9 channels 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.

MADRAS has operating frequencies in the range 18.7GHz-157GHz. The table below gives the main mission objective for each channel.

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. Every rotation, the angular sector where the antenna beam looks 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 allows to have another calibration point. The required radiometric sensitivity needs to have the receivers close to the horns and 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.

MADRAS instrument is made up of the following equipments:

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 Architecture

Latest Update 09/10/2006