Man on Earth [antikvár]

IntroductionKnow then thyself, presume not God to scan,The proper study of mankind is Man. Alexander PopePictures of the earth taken from space have now been available for more than twenty years. They began in 1960 with the first black and white images produced by the TIROS-1 weather satellite and were soon followed by colour photographs taken by the hand-held cameras of the Gemini and Apollo astronauts. To most observers the fascination of these pictures was the opportunity they provided to see the world "in the round' for the first time, as a majestic blue-grey sphere, floating cloud-cloaked against a backdrop of stars. Detail of the surface, comparable with that provided by high-flying aircraft, appeared less interesting, something that would be useful only for purposes of military surveillance.It was not until the late 1960s that other unique advantages of space images became apparent as a means for monitoring the condition of the earth's surface. The first satellite designed specifically for such purposes was launched by N.A.S.A. on 23 July 1972. Known originally as ERTS-1, and later as Landsat-1, that spacecraft is shown opposite. Its objectives: to monitor the resources of the whole earth, and man's activities on the earth, on a regular, widespread basis, and under uniform observing conditions.Landsat-1 was designed to produce images allowing us to assess the relationship between man and the planet he lives on. It would show the effects of man on the environment, monitor the activities of mankind, and serve the needs of man by measuring the earth's natural resources. This book provides graphic proof that Landsat and its successor spacecraft have satisfied the wishes of its designers, probably beyond their expectations; and although aesthetic appeal of the spacecraft image products was never any part of the design criteria, the pictures provided by Landsat often have elements of beauty and mystery.Since that first launch there has been continuous imaging of the earth's surface by a series of Landsat spacecraft. Landsat-2 was launched in January 1975, Landsat-3 in March 1978, and the most recent and most advanced spacecraft, Landsat-4, in July 1982. Together, these satellites have returned hundreds of thousands of images that blanket the earth from latitude 81 degrees north to 81 degrees south. Flying at a height of 917 kilometres (570 miles), each spacecraft returns more than a million separate items of information to the earth each second, every day of the year. In the time that it takes to read this sentence, 10,000 square kilometres (4,000 square miles) of new data have been recorded.It would be quite impractical to record this great mass of data on film on board the spacecraft and then return it to earth in that form. Instead, the operation is wholly electronic. Powered by solar panels, the spacecraft's electronic imaging system converts observed light intensities to numbers, in the form of discrete electric impulses. These numbers are transmitted to a network of receiving stations as a continuous digital radio signal, to be recorded there on magnetic tape, and to provide an archive of information unique to a particular time and ground location. From the tapes, computers convert the stored numerical values to an image format, from which film products are finally created. This is the first point at which the Landsat data are seen as a "picture' in the conventional sense of the word. A single Landsat scene covers a ground area of more than 33,000 square kilometres (13,000 square miles), and more than 30 million numbers must be processed before the image can be created.