RDR - 7

Question 1

Describe Synthetic Aperture Radar.

Answer 1

• 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.

Question 2

Explain the following Synthetic Aperture Radar Terminology: Focusing

Answer 2

• 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

Question 3

Explain the following Synthetic Aperture Radar Terminology: Motion Compensation

Answer 3

• 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.

Question 4

Explain the following Synthetic Aperture Radar Terminology: Squinting

Answer 4

• 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.

Question 5

Explain the following Synthetic Aperture Radar Terminology: Spotlight SAR

Answer 5

• 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.

Question 6

Explain the following Synthetic Aperture Radar Terminology: Doppler Beam Sharpening

Answer 6

• 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.

Question 7

Describe the operation of Inverse Synthetic Aperture Radar.

Answer 7

• 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.

Question 8

Describe the operation of High Resolution Range Profiling Radar.

Answer 8

• 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.

Question 9

Describe the operation and application of Moving Target Indicator
Radar.

Answer 9

• 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