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High Resolution Infra Red Radiation Sounder (HIRS/3 and HIRS/4)

The High Resolution Infra Red Radiation Sounder (HIRS) will fly on NOAA K to N and provides the basic 20 channel IR temperature and humidity soundings of the ATOVS system. All HIRS channels will be used to provide information on temperature and humidity profiles, surface temperature, cloud parameters and total ozone.

Calibration of HIRS is performed every 40 scan lines, there will be a gap of two scan lines in data coverage. Calibration repeatability is specified to be better than 0.3 K and inter channel accuracy better than 0.2 K.

HIRS scans across track in a ‘stop and stare’ mode at a scan rate of 6.4 sec. There are 56 Earth Views per scan. The circular field-of-views of HIRS/3 have a diameter of 20 km at nadir. In the case of HIRS/4 on NOAA-N and METOP this size will be reduced to 10 km. The swath covers ± 1080 km.

HIRS/3 Sounder Channel Characteristics

Channel Centre Wave number (cm-1) Centre Frequ. (mm) Half Bandwidth (cm-1) Anticipated Max. Scene Temperature (K) Specified NEDN (mW/m2/sterad/cm-1)
1 668.5 ±1.3 14.959 3.0 + 1/-.5 280 3.00
2 680.0 ±1.8 14.706 10.0 + 4/-1 265 0.67
3 690.0 ±1.8 14.493 12.0 +6/-0 240 0.50
4 703.0 ±1.8 14.225 16.0 +4/-2 250 0.31
5 716.0 ±1.8 13.966 16.0 +4/-2 265 0.21
6 733.0 ±1.8 13.643 16.0 +4/-2 280 0.24
7 749.0 ±1.8 13.351 16.0 +4/-2 290 0.20
8 900.0 ±2.7 11.111 35.0 ± 5.0 330 0.10
9 1030.0 ±4.0 9.709 25.0 ± 3.0 270 0.15
10 802.0 ±2.0 12.469 16.0 +4/-2 300 0.15
11 1365.0 ±5.0 7.326 40.0 ±5.0 275 0.20
12 1533.0 +2/-6 6.523 55.0 ±5.0 255 0.20
13 2188.0 ±4.4 4.570 23.0 ±3.0 300 0.006
14 2210.0 ±4.4 4.525 23.0 ±3.0 290 0.003
15 2235.0 ±4.4 4.474 23.0 ±3.0 280 0.004
16 2245.0 ±4.4 4.454 23.0 ±3.0 270 0.004
17 2420.0 ±4.0 4.132 28.0 ±3.0 330 0.002
18 2515.0 ±5.0 3.976 35.0 ±5.0 340 0.002
19 2660.0 ±9.5 3.759 100.0 ±15.0 340 0.001
20 14500 ±220 0.690 1000 ±150.0 100 % Alb. 0.10 % A