Encyclopedia Astronautica
1998.07.10 - Fasat-Bravo

Customer: Chilean Air Force (FACH). Chile's second satellite carrying store and forward and Earth observation payloads, replacing those lost on FASat-Alpha. Still operational as of 2000.

FASat-Bravo Cameras

Wide Angle Camera (WAC) & Narrow Angle Camera (NAC): The FASat-Bravo WAC and NAC use CCD sensors made by EEV Ltd. with 568 x 560 active imaging pixels. The WAC was fitted with an ultra wide angle lens (focal length 4.8 mm) to give a coverage area of 1500 x 1050 km at a mean resolution of 2 km per pixel (from FASat's 816 km orbit). The TMSat mission carried an identical WAC. The NAC was fitted with a 75 mm focal length to give a coverage area of 93 x 62 km at a mean resolution of 120 metres

The cameras were fitted with a near-IR optical filter (810-890 nm) to provide strong contrast between land, sea and clouds (NB. Although invisible to the human eye, these wavelengths were very close to the visible range, and behave in the same way. Thus the camera was recording light from the Sun, reflected off the Earth's surface and atmosphere. This should not be confused with thermal infra-red imaging, where the Sun's energy was absorbed by the Earth and then reradiated.

Ozone UV Backscatter Instruments (Oubi): In addition to the two visible cameras, FASat-Bravo carried two UV-enhanced cameras (OUBI0 & OUBI1) employing specially-coated CCD sensors. The sensors were made by EEV Ltd. with 384 x 280 active imaging pixels. The optics used by the OUBIs were identical (except for the optical filters as already discussed) with a 12.5 mm focal length to give a coverage area of 560 x 400 km at a mean resolution of 1.4 km per pixel.

OUBI1 imaged a narrow band centred around 380 nm. The role for OUBI1 was to record the Earth's albedo in a UV band which was not subject to significant ozone absorption. OUBI0, on the other hand, imaged at 313 nm which was a peak ozone absorption band. Thus by comparing the differences in the OUBI images it should be possible (after extensive modeling and calculation) to retrieve the ozone concentration in the area imaged.

The resolution of these cameras was slightly lower than for the visible cameras, but offer significantly greater sensitivity (the Sun produced approximately 1000 times less light in the UV spectrum compared to the visible). OUBI1's sensitivity was virtually in the visible, and the images produced would resemble those from the visible cameras. The images from OUBI0, on the other hand, should contain virtually no land features but show atmospheric features.

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