EM 1110-2-2907
1 October 2003
tem. This system is used for text data. You may need to be aware of the type of data used
in an image, particularly when determining the digital number in a pixel.
c. Transferring the Data from the Satellite to the Ground. The transfer of data stored
in the sensor from the satellite to the user is similar to the transmission of more familiar
signals, such as radio and television broadcasts and cellular phone conversations. Every-
thing we see and hear, whether it is a TV program with audio or a satellite image, origi-
nates as a form of electromagnetic radiation. To transfer satellite data from the sensor to a
location on the ground, the radiation is coded (described in Paragraph 2-7a) and attached
to a signal. The signal is generally a high frequency electromagnetic wave that travels at
the speed of light. The data are instantaneously transferred and detected with the use of
an appropriate antenna and receiver.
d. Satellite Receiving Stations.
(1) Satellite receiving stations are positioned throughout the world. Each satellite
program has its own fleet of receiving stations with a limited range from which it can
pick up the satellite signal. For an example of locations and coverage of SPOT receiving
stations go to
(2) Satellites can only transmit data when in range of a receiving station. When
outside of a receiving range, satellites will store data until they fly within range of the
next receiving station. Some satellite receiving stations are mobile and can be placed on
airplanes for swift deployment. A mobile receiving station is extremely valuable for the
immediate acquisition of data relating to an emergency situation (flooding, forest fire,
military strikes).
e. Data is Prepared for User. Once transmitted the carrier signal is filtered from the
data, which are decoded and recorded onto a high-density digital tape (HDDT) or a CD-
ROM, and in some cases transferred via file transfer protocol (FTP). The data can then
undergo geometric and radiometric preprocessing, generally by the vendor. The data are
subsequently recorded onto tape or CD compatible for a computer.
f. Hardware and Software Requirements. The hardware and software needed for sat-
ellite image analysis will depend on the type of data to be processed. A number of free
image processing software programs are available and can be downloaded from the inter-
net. Some vendors provide a free trial or free tutorials. Highly sophisticated and powerful
software packages are also available for purchase. These packages require robust hard-
ware systems to sustain extended use. Software and hardware must be capable of man-
aging the requirements of a variety of data formats and file sizes. A single satellite image
file can be 300 MB prior to enhancement processing. Once processed and enhanced, the
resulting data files will be large and will require storage for continued analysis. Because
of the size of these files, software and hardware can be pushed to its limits. Regularly
save and back up your data files as software and hardware pushed to its limits can crash,
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