camera, mounted in an environmentally controlled enclosure, will occupy
approximately 1/4 of a European Space Agency pallet located in the pay-
load bay of the Shuttle Orbiter.
Microwave Sensors
The role of microwave remote sensors in the Earth Resources Program has
a rich heritage from instrumentation developed for lunar and planetary
programs. For example, the first active microwave signature acquisition
device in the Earth Resources Program was a modification of a lunar landing
microwave system developed for the Apollo program in the 1960's. The term
scatterometer was devised as a descriptor of this sensor which operated
at 13.3 GHz. Also during the 1960's, the first passive microwave radio-
meters used for Earth resources studies were radiometers designed for a
Mars spacecraft.
In the 1970's, most of the development work in microwave sensors for
Earth resources activities has been with instruments tested on NASA
research aircraft. The current complement of microwave sensors is shown
in figure 2 and includes active and passive sensors roughly bounded in
the low frequency end by a 400 GHz scatterometer radar, and on the high
frequency end by a 37 GHz radiometer. These frequencies are those of
principal interest to Earth resources scientists. Figure 2 also shows
the general uses of microwave data at various frequencies.
The current Seasat program, while principally intended for support of
oceanographic studies, has a range of microwave instruments, including:
an imaging L-band radar, an altimeter, a scatterometer, and an imaging
multi-channel radiometer. A limited number of Earth resources studies
are to be conducted using Seasat data - primarily data from the imaging
L-band radar.
The first use of microwave sensors using the Shuttle as the orbital
vehicle will be on an Earth-viewing mission carrying a version of the
Seasat radar, now planned for 1980. This system is referred to as
Shuttle Imaging Radar-A (SIR-A), and is designed to provide a larger
incidence angle than the Seasat radar, to better perform geologic
studies.
NASA is also considering a number of future microwave sensors - both active
and passive. Of particular interest is a Shuttle Imaging Radar
research facility capable of addressing a broad range of data needs in a
number of Earth resources discipline areas, Figure 3 depicts current and
future space sensors and missions for Earth resources activities.
Applications
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Applications of satellite remote sensing have been developing in many
disciplines. The major applications and current activities are discussed
by discipline below.