Megha-Tropiques carries the following four payloads:
- Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS), an Imaging Radiometer developed jointly by CNES and ISRO
- Sounder for Probing Vertical Profiles of Humidity (SAPHIR), from CNES
- Scanner for Radiation Budget (ScaRaB), from CNES
- Radio Occultation Sensor for Vertical Profiling of Temperature and Humidity (ROSA), procured from Italy
MADRAS (Microwave Analysis and Detection of Rain and Atmospheric Structures)
MADRAS system is a five channel, self calibrating, microwave radiometer system. The radiometer is designed to estimate atmospheric water parameters and wind speed in the equatorial belt. The choice of the channels has been driven by their potential contribution to the measurement of the parameters defined above.
Geophysical Parameters
- Rainfall
- Cloud Ice Content
- Wind Speed
- Total Precipitable Water
- Cloud Liquid Water
| Channel No. | Frequency | Pol | NEΔT | Spatial Resolution |
|---|---|---|---|---|
| M1 | 18.7 GHz | H+V | 0.5 K | 40km |
| M2 | 23.8 GHz | V | 0.5 K | 40km |
| M3 | 36.5 GHz | H+V | 0.5 K | 40km |
| M4 | 89 GHz | H+V | 1.0 K | 10km |
| M5 | 157 GHz | H+V | 1.0 K | 6km |
SAPHIR microwave humidity sounder and radiometer
The mission specifications call for determination of humidity with an accuracy of 10 to 20 percent in 5 to 7 layers of the troposphere, over 10 km pixels. For realizing that performance, it is necessary to choose channels for which the atmospheric contribution to the radiance comes from different levels of the troposphere. This can be obtained by sampling an absorption line of water vapour by channels more or less close to the centre of the line. A candidate line, already chosen for other instruments, is the line at 183.3 GHz. It is possible to get contribution functions peaking from heights of 2 km.up to 10 to 12 km in tropical redundant to use more than 5 channels. A sixth complimentary channel in a window regions has to be used to correct for the surface effects in the lowest channels; the 150 channel of MADRAS can be used for that. This is the principle of SAPHIR instrument, which has been studied in the frame of micro satellites.
Geophysical Parameters
- Humidity Profile
| Channel No. | Centre Frequencies(GHz) | Max. Passband (MHz) | ΔT(K)Sensitivity at 300 K | Absolute Calibration (K) Over 180 - 300K | Pol. |
|---|---|---|---|---|---|
| S1 | 183.31 ± 0.2 | 200 | <2 (TBC) | ± 1 | H |
| S2 | 183.31 ± 1.1 | 350 | <2 (TBC) | ± 1 | H |
| S3 | 183.31 ± 2.8 | 500 | <2 (TBC) | ± 1 | H |
| S4 | 183.31 ± 4.2 | 700 | <2 (TBC) | ± 1 | H |
| S5 | 183.31 ± 6.8 | 1200 | <2 (TBC) | ± 1 | H |
| S6 | 183.31 ± 11.0 | 2000 | <2 (TBC) | ± 1 | H |
ScaRaB- Broadband radiation measurement instrument
SCARAB is a four channel instrument mainly measuring in Visible (Sc1), InfraRed (Sc4) along with Solar Radiation (Sc2) and Total Radiation (Sc3). The long-wave irradiance is deduced from the difference between Sc3 and Sc2 measurements. Channels in Visible and IR window, Sc1 and Sc4 are used for scene identification (surface, clouds, partially covered) and for assuring compatibility and comparisons with the images from operational satellites.
Geophysical Parameters
- Radiation Fluxes
| Channel | Wavelength | Signal Dynamics | Noise (Crest) |
|---|---|---|---|
| Sc1-Visible | 0.5 to 0.7 µm | 120 W.m2.sr.-1 | < 1 W.m2.sr.-1 |
| Sc2-Solar | 0.2 to 4.0 µm | 425 W.m2.sr.-1 | < 0.5 W.m2.sr.-1 |
| Sc3-Total | 0.2 to 100 µm | 500 W.m2.sr.-1 | < 0.5 W.m2.sr.-1 |
| Sc4-IR Window | 10.5 to 12.5 µm | 30 W.m2.sr.-1 | < 0.5 W.m2.sr.-1 |
ROSA Radio Occultation Sensor
GPS Radio Occultation sensor enables measurement of water vapour and temperature profiles in the tropics. GPS ROS payload is there to supplement / complement the mission for the atmospheric studies. A GPS ROS payload, ROSA (GPS-ROS) provided by the Italian Space Agency (ASI), is configured as the fourth payload.
| Parameter | Specification |
|---|---|
| Frequency | L1 1.56 to 1.59 GHz; L2 1.212 to 1.242 GHz |
| GPS code used | C/A and P Code |
| GPS code used | <300 km |
| Hor Res | 0.3 km (Low Troposphere); 1-3 km (High Troposphere) |
| Vert Res | <1 K Temperature; 10% or 0.2g/Kg Humidity |
