| DMSP OLS - Operational Linescan System |
| Visible and infrared imagery from DMSP Operational Linescan System (OLS) instruments
are used to monitor the global distribution of clouds and cloud top temperatures twice
each day. The archive data set consists of low resolution global and high resolution
regional, imagery recorded along a 3,000 km scan, satellite ephemeris and solar and
lunar information. Infrared pixel values correspond to a temperature range of 190
to 310 Kelvins in 256 equally spaced steps. Onboard calibration is performed during
each scan. Visible pixels are relative values ranging from 0 to 63 rather than absolute
values in Watts per m^2. Instrumental gain levels are adjusted to maintain constant
cloud reference values under varying conditions of solar and lunar illumination. Telescope
pixel values are replaced by Photo Multiplier Tube (PMT) values at night. A telescope
pixel is 0.55 km at high resolution (fine mode) and 2.7 km at low resolution(smooth
mode). Low resolution values are the mean of the appropriate 25 high resolution values. |
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