Reconnaissance SatellitesBoth the United States and the former USSR have orbited considerable numbers of reconnaissance
Satellites
for photo surveillance, electronic intelligence, nuclear-explosion detection, and strategic-missile launch detection (see, for example, Cosmos; SAMOS). Other nations have also launched a few such
satellites.Weather SatellitesSince the launch on Apr. 1, 1960, of the first weather satellite, TIROS 1 (see TIROS), the extent of cloud-cover pictures taken from satellites has gradually increased until, beginning in 1966, the entire Earth has been photographed at least once daily on a continuous basis. Satellite data provide information about the ocean, desert, and polar areas of the Earth where conventional weather reports are unavailable or limited. Satellite photos locate weather featuresÑstorm systems, fronts, upper-level troughs and ridges, jet streams, fog, sea ice conditions, snow cover, and, to some extent, upper-level wind direction and speedsÑthat are characterized by certain cloud formations. Coastal and island stations can use such data to locate and track major storms.Both optical and infrared cameras are used, the latter showing sea-surface temperatures more frequently and over a larger area than is possible by any other means. These data are useful for shipping and fishing interests and are important for
meteorological forecasts. The United States has used low-altitude (700 to 1,700 km/435 to 1,050 mi), geostationary, and Sun-synchronous weather satellites (see GOES; Nimbus; Synchronous Meteorological Satellite).