High Resolution Infra Red Radiation Sounder/2 (HIRS/2)
The High Resolution Infra Red Radiation Sounder (HIRS/2) flies on the NOAA/TIROS-N type satellites and provides the basic 20 channel IR temperature and humidity soundings of the TOVS system. All HIRS/2 channels are used to provide information on temperature and humidity profiles, surface temperature, cloud parameters and total ozone. Calibration of HIRS/2 is performed every 40 scan lines, there is a gap of three scan lines in data coverage.. 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 have a diameter of 20 km at nadir. The swath covers ± 1080 km.
HIRS/2 sounder channel characteristics
| Channel | Centre Wave number (cm-1) |
Centre Frequency (mm) |
Half Bandwidth (cm-1) |
Anticipated Max. Scene Temperature (K) | Specified NEDN (mW/m2/ sterad/cm-1) |
| 1 | 669 | 14.95 | 3 | 280 | 3.00 |
| 2 | 680 | 14.71 | 10 | 265 | 0.67 |
| 3 | 690 | 14.49 | 12 | 240 | 0.50 |
| 4 | 703 | 14.22 | 16 | 250 | 0.31 |
| 5 | 716 | 13.97 | 16 | 265 | 0.21 |
| 6 | 733 | 13.64 | 16 | 280 | 0.24 |
| 7 | 749 | 13.35 | 16 | 290 | 0.20 |
| 8 | 900 | 11.11 | 35 | 330 | 0.10 |
| 9 | 1030 | 9.71 | 25 | 270 | 0.15 |
| 10 | 797 | 12.55 | 16 | 290 | 0.20 |
| 11 | 1365 | 7.33 | 40 | 275 | 0.20 |
| 12 | 1488 | 6.72 | 80 | 260 | 0.19 |
| 13 | 2190 | 4.57 | 23 | 300 | 0.006 |
| 14 | 2210 | 4.52 | 23 | 290 | 0.003 |
| 15 | 2240 | 4.46 | 23 | 280 | 0.004 |
| 16 | 2270 | 4.40 | 23 | 260 | 0.002 |
| 17 | 2360 | 4.24 | 23 | 280 | 0.002 |
| 18 | 2240 | 4.13 | 28 | 330 | 0.002 |
| 19 | 2660 | 3.76 | 100 | 340 | 0.001 |
| 20 | 14500 | 0.69 | 1000 | 100 % Alb. | 0.10 % A |