| Synthetic
Aperture Radar System
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Introduction
When
a disaster occurs it is very important to grasp the situation as soon as possible.
But it is very difficult to get the information from the ground because there
are a lot of things which prevent us from getting such important data such as
clouds and volcanic eruptions. While using an optical sensor, large amount of
data is shut out by such barriers. In such cases, Synthetic Aperture Radar or
SAR is a very useful means to collect data even if the observation area is covered
with obstacles or an observation is made at night at night time because SAR uses
microwaves and these are radiated by the sensor itself. The SAR sensor can be
installed in some satellite and the surface of the earth can be observed.
To support the scientific applications utilizing space-borne imaging radar systems,
a set of radar technologies have been developed which can dramatically lower the
weight, volume, power and data rates of the radar systems. These smaller and lighter
SAR systems can be readily accommodated in small spacecraft and launch vehicles
enabling significantly reduced total mission cost.
Specific areas of radar technology development include the antenna, RF electronics,
digital electronics and data processing. A radar technology development plan is
recommended to develop and demonstrate these technologies and integrate them into
the radar missions in a timely manner. It is envisioned that these technology
advances can revolutionize the approach to SAR missions leading to higher performance
systems at significantly reduced mission costs.
The SAR systems are placed on satellites for the imaging process. Microwave satellites
register images in the microwave region of the electromagnetic spectrum. Two mode
of microwave sensors exit- the active and the passive modes. SAR is an active
sensor which carry on -board an instrument that sends a microwave pulse to the
surface of the earth and register the reflections from the surface of the earth.
One way of collecting images from the space
under darkness or closed cover is to install the SAR on a satellite . As the satellite
moves along its orbit, the SAR looks out sideways from the direction of travel,
acquiring and storing the radar echoes which return from a strip of earth's surface
that was under observation. The raw data collected
by SAR are severely unfocussed and considerable processing is required to generate
a focused image. The processing has traditionally been done on ground and a downlink
with a high data rate is required. This is a time consuming process as well. The
high data rate of the downlink can be reduced by using a SAR instrument with on-board
processing.
X-Band SAR Instrument Demonstrator
The X-band SAR instrument demonstrator forms the standardized part or basis for
a future Synthetic Aperture Radar (SAR) instrument with active front- end. SAR
is an active sensor. Active sensors carry on-board an instrument that sends a
microwave pulse to the surface of the earth and register the reflections from
the surface of the earth. Different sensor use different bands in the microwave
regions of the electromagnetic spectrum for collecting data. In the X-band SAR
instrument, the X-band is used for collecting data.
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