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INSAT-3DR Payloads

The satellite has 3 payloads:

  • Meteorological (MET) - IMAGER and SOUNDER
  • Data Relay Transponder (DRT)
  • Satellite Aided Search and Rescue (SAS&R)

Meteorological Payload

The INSAT-3DR spacecraft incorporates advanced Imager and Sounder instruments.

IMAGER

The INSAT-3DR imager provides imaging capability of the earth disc from geostationary altitude in one visible (0.52 - 0.72 micrometers) and five infrared; 1.55 - 1.70(SWIR), 3.80 - 4.00(MIR), 6.50 - 7.00 (water vapour), 10.2 - 11.2 (TIR-1) and 11.5 - 12.5 (TIR-2) bands. The ground resolution at the sub-satellite point is nominally 1km x 1km for visible and SWIR bands, 4km x 4km for one MIR and both TIR bands and 8km x 8km for WV band.

The Imager is an improved design of VHRR-2 (Very High Resolution Radiometer) heritage instrument flown on the Kalpana-1 resolution in the visible band for the monitoring of meso scale phenomena and severe local storms. The two new SWIR and MWIR bands with a resolution of 1 km and 4 km, respectively, will enable better land-cloud discrimination and detection of surface features like snow. One more significant improvement is the split-band TIR channel with two separate windows in 10.2-11.2 and 11.5-12.5 Micrometer regions with a 4 km resolution.

This new element enables the extraction of sea surface temperature over the Indian region with a far greater accuracy since the dual-window algorithm can be applied to eliminate the atmospheric attenuation effects. The 1 km resolution of the visible channel and 4 km resolution of the thermal IR channels indirectly improve the accuracy of the derived products like outgoing longwave radiation and cloud motion vectors. The INSAT-3DR Imager payload is a replica of INSAT-3D Imager.

Key Parameters of the Imager
Telescope aperture 310 mm diameter
Number of bands (6) 0.52 - 0.72 µm, VIS (Visible) 1.55 - 1.70 µm, SWIR (Short Wave Infrared) 3.80 - 4.00 µm, MWIR (Mid Wave Infrared) 6.50 - 7.00 µm, WV (Water Vapor) 10.2 - 11.2 µm, TIR-1 (Thermal Infrared) 11.5 - 12.5 µm, TIR-2 (Thermal Infrared)
Spatial resolution 1 km for VIS and SWIR 4 km for MWIR 8 km for WV 4 km for TIR-1 and TIR-2
Band separation, band definition Beam splitter, interference filters
IFOV (Instantaneous Field of View) 28 µrad for VIS and SWIR (1 km) 112 µrad for MWIR, TIR-1, & TIR-2 (4 km) 224 µrad for WV (8 km)
Sampling interval 1.75 samples / IFOV for VIS, SWIR,MIR & TIR-1 / -2 3.5 samples / IFOV for WV
Scan step angle Linear in E-W direction (8 µR step size)
Line step 224 µrad in N-S direction
Scan rate Scan linearity Inflight calibration 200º/s +0.2 s turnaround time
56 µR (peak to peak)
Full aperture blackbody and spaceview
Scan modes Full, normal and programmable sector for quick repetivity
Frame time 25 minutes for normal mode
Signal quantization 10 bit/sample
Downlink data rate 4.0 Mbit/s

SOUNDER

The INSAT-3DR sounder has 18 infrared channels distributed over longwave and shortwave bands alongwith one visible band. A visible channel provides synoptic view of the clouds and the earth to aid in generating three dimensional maps of temperature and moisture structure of the atmosphere.

The Sounder is a first time instrument of the geostationary INSAT series designed and developed at ISRO. The overall objective is to measure the temperature and humidity profiles (vertical distributions) to obtain a three-dimensional representation of the atmosphere. The instrument requirements call for soundings at 10 km ground resolution every 3 hours for a full frame scan. This enables the derivation of vertical profiles of temperature and humidity. These vertical profiles can then be used to derive various atmospheric stability indices and other parameters such as atmospheric water vapor content and total column ozone amount. The INSAT-3DR Sounder payload is a replica of INSAT-3D Sounder.

Key Parameters of the sounder
Telescope aperture 310 mm diameter
Number of bands (6) 18 Infrared + 1 Visible
Band definition Filter wheel with interference filters
IFOV (Instantaneous Field of View) 280 µrad x 280 rad, corresponding to 10 km x 10 km on the surface
Sampling interval 280 µrad E-W / N-S
No of simultaneous soundings 4 per band
Scan step angle 10 km E-W, every 0.1 s, and 40 km N-S after completion of E-W scan, 150 µR rms
Step and dwell time 0.1, 0.2 and 0.4 s
Turnaround time 0.1 s per scan
In-flight calibration Full aperture blackbody and space view
Scan modes Options provided to cater to quick dynamic environmental phenomena
Frame time 160 minutes for 6000 km x 6000 km area sounding
Signal quantization 13 bit/sample
Downlink data rate 40 kbit/s
Frame time 90 kg, (without cooler), 100 W

Spectral parameters and sensitivity of the sounder
Band No. Center wavelength µm (cm-1) Bandwidth µm (cm-1) NEDT at 300 K (typical) K
1 14.71 (680) 0.281 (13) 1.5
2 14.37 (696) 0.268 (13) 1
3 14.06 (711) 0.256 (13) 0.5
4 13.96 (733) 0.298 (16) 0.5
5 13.37 (749) 0.286 (16) 0.5
6 12.66 (790) 0.481 (30) 0.3
7 12.02 (832) 0.723 (50) 0.15
8 11.03 (907) 0.608 (50) 0.15
9 9.71 (1030) 0.235 (25) 0.2
10 7.43 (1425) 0.304 (55) 0.2
11 7.02 (1425) 0.394 (80) 0.2
12 6.51 (1535) 0.255 (60) 0.2
13 4.57 (2188) 0.048 (23) 0.2
14 4.52 (2210) 0.047 (23) 0.15
15 4.45 (2245) 0.045 (23) 0.15
16 4.13 (2420) 0.0683 (40) 0.15
17 3.98 (2513) 0.0683 (40) 0.15
18 3.74 (2671) 0.140 (100) 0.15
19 0.695 (14367) 0.05 (1000) (0.67-0.72)   0.1% albedo

 Communication Payload

Communication transponders are required to be configured to provide continuity of some of the INSAT services. A total satellite mass of 2211kg is considered for the launch compatibility, and 70 kg (approximately) of mass apportionment is done for the communication payload components. The communication payload components are - Meteorological Transmitter, Data Relay Transponder, Satellite Aided Search and Rescue (SAS&R) Transponder & S-band Broadcast Satellite Services Transponder.