INSAT-3DR will carry a 6-channel Imager and 18-channel infrared Sounder (plus a visible channel for cloud filtering during daytime) similar to INSAT-3D.
2.a. Imager: The Imager instrument characteristics are summarised in table-1 and 2.
Table-1: INSAT-3DR Imager instrument characteristics
|Number of Channels||6 (Vis, SWIR, MIR, WV, TIR 1 & TIR 2)|
|Instantaneous Field of View||Vis & SWIR: 28 μrad; MIR, TIR-1 & TIR-2: 112μrad;
WV: 224 μrad
|Field Of Regard (FOR)||24° E-W x 19° N-S|
|Active Scan Coverage||Normal Mode: 18° E-W x 18° N-S,
Program Mode: 18° E-W x programmable no. of lines
|Scan Offset capability||E-W: ±3° in steps of ±0.016° N-S: Normal: 1st scan line selectable from –9.5° to –8.5° in steps of 0.013° Program: Selectable from -9.5° to + 9.5° in steps of 0.013°|
|Space Look||Every line|
|Scanning||E-W: Bi directional, N-S: Stepping|
|In-flight Calibration||Full Aperture Blackbody and Space view for IR, space view for Vis & SWIR|
|Signal Quantization||10 Bits/Sample|
|System Power||<100 Watts|
|System Weight||<140 Kg|
TABLE-2: INSAT-3D Imager Radiometric Specifications
|Channel Name||Wavelength (μm)||SNR or NEDT (K)||Scene Condition||Saturation radiance / Temperature|
|VIS||0.55 to 0.75||>150:1||100% Albedo||52.4 mW/cm2/sr/μm|
|SWIR||1.55 to 1.70||>150:1||100% Albedo||6.7 mW/cm2/sr/μm|
|MIR||3.80 to 4.00||<1.4K||300K||340K|
|WVP||6.5 to 7.10||<1K||230K||320K|
|TIR1||10.3 to 11.3||<0.35K||300K||340K|
|TIR2||11.5 to 12.5||<0.35K||300K||340K|
The spatial resolution for the Imager channels corresponding to their IFOV at nadir are 1 km for Vis/SWIR, 4 km for MIR/TIR1/TIR2 and 8 km for the WVR channel. This corresponds to the scanning from 8 elements in Vis/SWIR, 2 elements in MIR/TIR1/TIR2 and 1 element in WVR channel in the north-south direction. The Imager can view anywhere within the Field of Regard (FOR), i.e. 24° EW x 19° NS, with two modes of operation:
- full frame mode scans 18° EW x 18° NS covering the entire earth disk and some space around in 26 minutes,
- Programme mode covering 18° in EW direction, NS coverage can be defined in terms of number of lines to be scanned. The signal quantization is 10 bits/sample.
The Sounder instrument characteristics are summarised in table-3 and 4. The Sounder will make observations in 18 infrared channels and an additional visible channel to assist cloud detection during daytime. The spatial resolution of Sounder observation is 10 km at nadir. It can scan a maximum of 640 x 640 pixels, i.e., 6400 km x 6400 km in about 3 hours and a minimum of 64 x 64 pixels (640 km x 640 km). This way the Sounder can make selectable observations in the block sizes of 64 x 64 pixels, anywhere within the FOR. For in-flight blackbody calibration the Sounder looks at space every 2 minutes and at the blackbody every 30 minutes. The entire Indian landmass scanning will take about 50 minutes and can be programmed in synergy with the INSAT-3D in such way that repeated observations (better than 30 minutes) are available for nowcasting applications.
Table-4 provides the details of the Sounder channel characteristics with details about the central wavelength/wavenumber, sensor noise, principal absorbing gas within the channel bandwidth, and the main purpose of the channel.
Table-3: INSAT-3DR Sounder instrument characteristics
|Number of Channels||19 (18 Infrared + 1 Visible)|
|Channel Definition||Interference filters (Table-4)|
|Instantaneous Field of View||≤280 rad (EW) x 280 rad (NS) (10 km x 10 km at nadir)|
|Channel to channel registration||±280 R (1 VIS/ IR element) among all channels|
|Simultaneous sounding per Channel||4 (aligned NS)|
|Field Of Regard (FOR) (optical)||24° EW x 21° NS|
|Step size||EW 280 μR (optical)/100msec, NS 1120 μR/scan line|
|Active Scan Coverage||EW: Selectable from 0.513° (64 steps, 640 km) to 5.13° (640 steps, 6400 km) in steps of 0.513° (640 km).
NS: Selectable from 1.026° (16 lines, 640 km) to 10.2° (160 lines, 6400 km) in steps of 640 km.
|Space Look||Every ~2 minutes (1216 FW revolutions)|
|Scanning||EW: Bi directional, NS: Stepping|
|In-flight Calibration||Full Aperture Blackbody and Space view|
|Signal Quantization||14 bits/sample for LWIR, MWIR & SWIR and
12 bits/sample for Visible
|System Power||< 100 watts|
|System Weight||< 155 kg|
|Table 4: INSAT-3D Sounder Channels Characteristics|
|Detector||Ch. No.||l c
|Principal absorbing gas||Purpose|
|Long wave||1||14.67||682||0.17||CO2||Stratosphere temperature|
|6||12.59||794||0.07||water vapor||Total precipitable water|
|7||11.98||834||0.05||water vapor||Surface temp., moisture|
|Mid wave||8||10.99||910||0.05||window||Surface temperature|
|10||7.43||1346||0.05||water vapor||Low-level moisture|
|11||7.04||1421||0.05||water vapor||Mid-level moisture|
|12||6.52||1534||0.10||water vapor||Upper-level moisture|
|Short wave||13||4.61||2168||0.05||N2O||Low-level temperature|
|18||3.79||2642||0.05||window||Surface temp., moisture|