This section describes the TOVS system, which includes three separate sensors: HIRS/2, MSU, and SSU. A fourth sensor, a Solar Backscattered ultraviolet system (SBUV/2) for ozone measurement, was added to the instrument complement starting with the NOAA-9 spacecraft. SSB began archiving SBUV data in 1985. Separate documentation entitled: Solar Backscattered Ultraviolet Radiometer Version 2 (SBUV/2) User's Guide (November 15, 1990), is available from SSB upon request. Although SBUV/2 data is available from SSB, there exists no selection software. Therefore, when ordering SBUV/2 data, the only option is tape-to-tape copies.

Table 4.0-1 lists the instrument parameters for the HIRS/2, MSU, and SSU sensors on the TIROS-N series. The spectral response of every channel for each TOVS sensor can be found in Section 1.4 (in each satellite's corresponding subsection).

Section 4.1 describes the HIRS/2 instrument, data characteristics, and the tape formats available (full copy, unpacked format, and selective extract subsets). Similarly, Sections 4.2 and 4.3 contain specific information about SSU and MSU data, respectively. Section 4.4 contains general information pertaining to the SBUV/2 data, although specific tape formats are not included. Section 4.5 describes the procedures for calibrating TOVS data (both visible and thermal).

Table 4.0-1. Instrument Parameters for TOVS Sensors.
TOVS Instrument Parameters HIRS/2 SSU MSU
Calibration Stable blackbodies (2) and space background Stable blackbody and space Hot reference body and space background each scan cycle
Cross-track scan angle (degrees from nadir) ± 49.5 ± 40.0 ± 47.35
Scan time (seconds) 6.4 32.0 25.6
Number of steps 56 8 11
Angular FOV (degrees) 1.25 10.0 7.5
Step angle (degrees) 1.8 10 9.47
Step time (seconds) 0.1 4.0 1.84
Ground IFOV at nadir
(km diameter)
17.4 147.3 109.3
Ground IFOV at end of scan 58.5 km cross-track x 29.9 km along-track 244 km cross-track x 186.1 km along-track 323.1 km cross-track x 178.8 km along-track
Distance between IFOV centers (km along-track) 42.0 62.3 168.1
Swath width ± 1120 km ± 737 km ± 1174 km
Data rate (bits per second) 2880 480 320
Data precision (bits) 13 12 12
Time between start of each scan line 6.4 sec 32 sec 25.6 sec
Step and dwell time 0.1 sec 4.0 sec 1.81 sec
Time (see Note 1) 0.5 sec 2.0 sec 0.9 sec

1. Time - The difference between the start of each scan and the center of the first dwell period.