HRV
in scheme: instruments
definition: [Text Source: NSSDC, http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1986-019A-01 ] The SPOT-A High Resolution Visible (HRV) imager provides acquisition of high-resolution data of the earth's surface on a global basis. It consists of two identical high-resolution visible (HRV) imaging instruments and a package comprising two magnetic-tape data recorders and a telemetry transmitter. The HRV experiment is designed to operate in either or both of two modes, in the visible and near infrared spectral regions: (1) a panchromatic (black and white) mode corresponding to observation over a broad spectral band (0.51 0.73 micrometer) and (2) a multispectral (color) mode corresponding to observation in three narrower spectral bands (0.50 - 0.59, 0.61 0.68, and 0.79 - 0.89 micrometer). The instrument's sampling mesh corresponds to a ground element (pixel) that is 10 m x 10 m in the first case and 20 m x 20 m in the second, for nadir viewing. The two detectors are of the CCD (charge-coupled device) type. Each array consists of 6000 detectors without any mechanical scanning. Light from the scene being viewed enters the HRV instrument via a plane mirror that is steerable by ground control. The viewing axis can thus be oriented as required in the plane perpendicular to the orbit. This off-nadir viewing capability covers a range of plus or minus 27 deg relative to the vertical (in 45 steps of 0.6 deg each). This allows the instrument to image any point within a strip extending 475 km to either side of the satellite ground track. The width of the swath actually observed varies between 60 km for nadir viewing and 80 km for extreme off-nadir viewing. With this special feature of off-nadir viewing, the two HRV instruments can be pointed to cover adjacent fields in order to obtain complete earth coverage. Among other possibilities introduced by this feature are increased revisit coverage at intervals ranging from one to several days and the recording of stereoscopic pairs of images…
type: Concept

Imaging Spectrometers/Radiometers
type: Concept