Page 145 - Intro to Space Sciences Spacecraft Applications

CHAPTER 6

Remote Sensing

On August 7, 1959, Explorer 6 sent back the first satellite-produced pic-
ture of the earth taken from an altitude of about 20,000 km in space.
Although grainy and lacking detail, it gave a spectacular view of swirling
cloud formations over the oceans and landmasses of a large portion of the
earth. Perceiving the immense value of observations from space, planners
quickly began to take advantage of the benefits of this perspective view,
and a few months later, on April 1, 1960, TIROS I was launched. TIROS I
ushered in an age of continuous operational meteorological satellites (often
referred to as weather satellites) by returning thousands of pictures of the
earth during its two-and-a-half-month lifetime. These and many other pio-
neering satellites demonstrated the basic advantages of satellite remote
sensing: the relatively large (compared to airborne perspectives) amount of
the earth in view at any time; the rate of coverage possible from a space-
based platform; and the ability to view even the remotest locations on the
earth’s surface. For example, a typical polar orbiting weather satellite at an
altitude of 830 km circles the earth every 102 minutes, moving with an
earth velocity of nearly 6,600 dsec, viewing thousands of square kilome-
ters each second as its sensors scan cross-track from horizon to horizon.
Two of these operational meteorological satellites obtain a global view of
the earth twice a day, providing government and private weather services
with surface and atmospheric data that improve and extend weather pre-
diction. A stark contrast and testimony to the value of satellite weather
observation is the accuracy and timeliness of observations of severe
storms, such as hurricanes, compared to presatellite times when we relied
on data from ships of opportunity or sparse information from weather air-
craft designated to search for hurricanes. Although property damage still
occurs, the advanced warning provided by timely space-based weather
observation mitigates damage and has sharply reduced loss of life.
There are a multitude of remote sensing satellites that enjoy the cover-
age benefits offered by the vantage point of space. In addition to environ-

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