Describe Synthetic Aperture Radar.
- SAR is an airborne or space-borne radar mapping technique
for generating high resolution maps of surface target areas and
terrain. - The purpose of SAR is Ground Mapping.
Explain the following Synthetic Aperture Radar Terminology: Focusing
- SAR focusing is the computational process that transforms raw radar data into detailed images
- SAR images are formed by processing Doppler and
Phase information from the return signal. - A line of sight from a point on the ground to each
individual array elements diverges slightly. - Even if the point is on the bore-sight line, the range to
the elements will not be the same. - Because of the wavelengths used, small differences in
range can result in large difference in phase. - The phase differences limit the useful length of the array
Explain the following Synthetic Aperture Radar Terminology: Motion Compensation
- SAR detects slight differences in signal phase received over relatively long periods of time, typically 1 - 10 seconds.
- For SAR images not to be blurred motion compensation using phase correction is applied to the received returns based on the measured accelerations away from straight line / constant
speed flight.
Explain the following Synthetic Aperture Radar Terminology: Squinting
- It is sometimes desirable to image an area before the
platform arrives, or sometimes, after it departs. - This cannot be achieved when the antenna is fixed
perpendicular (90°) to the platform track.
** Squinting trains the beam of the actual antenna
forward or backwards.
** This allows for the imaging of terrain far ahead or
behind the platform.
Explain the following Synthetic Aperture Radar Terminology: Spotlight SAR
- Spotlight SAR removes the array length limitation.
- The ‘look angle’ of the actual antenna is gradually
changed as the platform advances. - Therefore the antenna is continuously pointed toward
the region being imaged.
* SSAR enables continuous surveillance of an area
and may produce superior quality maps.
Explain the following Synthetic Aperture Radar Terminology: Doppler Beam Sharpening
- DBS is a low resolution version of SAR.
- The length of the array is not increased in
proportion to the range of the area being
mapped. - Images produced are the equivalent of an actual
antenna of extremely narrow beamwidth.
Describe the operation of Inverse Synthetic Aperture Radar.
- ISAR uses the motion of the target to generate an image.
- The radar spotlights the selected target with a beam
wide enough to encompass the entire target. - Various scatterers on the target will exhibit varying
amounts of Doppler shift caused by rotational motion
(pitch, roll and yaw). - The amount of Doppler Shift is directly proportional to
the distance of the moving scatterer to the centre of
rotation.
Describe the operation of High Resolution Range Profiling Radar.
- Data presented on an A Scope type display:
Range vs Amplitude. - After processing, a Range Profile is generated.
- Can be interleaved with other radar functions
such as search and tracking. - HRRP / RS can be used to gain a quick overview of the selected target
to gain the following information:
– Confirmation of target presence.
– Target length.
– Target upright sequence.
Describe the operation and application of Moving Target Indicator
Radar.
- Uses Doppler Effect to distinguish between stationary object and moving
objects. - MTI samples two successive pulses
- If the target is stationary then the two samples will cancel each other, and a small signal will remain. This can now be ignored by the system.
**GMTI – Ground moving target indication
**MMTI – Maritime moving target indication
**DMTI – Dsimount moving target indication
