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 
MACA_C_T7TL_ANDQR 
Applications of satellite remote sensing have been developing in many 
disciplines. The major applications and current activities are discussed 
by discipline below.