NSSDCA ID: 1970-025A-10
Mission Name: Nimbus 4The Nimbus 4 Selective Chopper Radiometer (SCR) observed the emitted infrared radiation in the 15-micrometer absorption band of carbon dioxide. From these measurements the temperatures of six successive 10-km layers of the atmosphere were determined from earth or cloudtop level to 60-km height. Height resolution was obtained by a combination of optical multi-layer filters and selective absorption of radiation using carbon-dioxide-filled cells within the experiment. The SCR had six channels, which were arranged in three units of two. The four lower channels were called single-cell channels. The optics of each channel consisted of a cantilever-mounted blade shutter that oscillated at 10 Hz and successively chopped the field of view (FOV) between earth and space. The chopped radiation was then passed through a 10-cm path length of carbon dioxide, the pressure being set for each channel to define the viewing depth of the atmosphere. Behind the carbon dioxide path was a narrow-band filter, the centers of which were different for each channel, and a light pipe which focused the radiation on a thermistor-bolometer detector. To obtain adequate height resolution in the upper layers of the atmosphere, the upper two channels operated on a slightly different principle and were known as double-cell channels. The technique consisted of switching the radiation between two half-cells, which were semicircular in shape and of 1-cm path length, and which contained different pressures of carbon dioxide. A movable 45-deg mirror replaced the oscillating shutter used in the lower four channels. During one half-period, earth radiation passed through one half-cell and space radiation through the other. The situation was reversed during the other half-period. The radiation then passed through a light pipe onto a thermistor-bolometer detector. Inflight calibration was carried out by viewing of an internal reference blackbody of known temperature prior to the view of space. The output of each channel was sampled once every second. The upper two channels had a circular FOV approximately 160 km in diameter, and the lower four had a rectangular FOV about 112 km square. For a complete description, see Section 9 in "The Nimbus IV User's Guide" (TRF B06861), available from NSSDC. The channel 1 temperature monitoring system failed on June 15, 1970, thereby reducing the accuracy of the SCR data. Channels 3 and 4 became noisy and unusable on April 18, 1972. The remaining channels were usable until June 15, 1973.
Mass: 15.3 kg
Power (avg): 5 W
Bit rate (avg): 0.05 kbps
Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. S. D. Smith | Other Investigator | Reading University | |
Prof. John T. Houghton | Principal Investigator | Oxford University | john-houghton@seh.ox.ac.uk |