RDR - 6 Flashcards
Describe Radar Clutter and the effect it has on Radar
Performance.
- Radar Clutter is defined as any unwanted echoes on a
radar screen. - Radar systems are primarily designed to detect the
presence of targets. - Radar energy is scattered by the sea, clouds, rain, the
ground and man-made objects.
Describe SEA Clutter
- Sea clutter is caused when radar energy is reflected
from the sea back to the radar receiver. - Sea clutter is caused by the breaking waves.
- Consideration must be given to the affect on the radar of
a search upwind, downwind or crosswind. - Grazing angle is the most important consideration.
- Rule of thumb: Higher sea states increase the sea clutter, therefore; reduce grazing angle by lowering the search altitude.
Describe Land Clutter
- Land clutter appears as a solid, well-defined mass with features that are usually identifiable on a map.
- Land features are normally easily recognisable from a map and built up areas, such as cities, are usually definable within the land returns because of their higher radar cross-section.
Describe weather Clutter
- Radar systems can display weather in different ways
- Some modes of tactical radars weather clutter is almost eliminated by the use of extremely narrow pulse widths and/or digital anti-clutter process
list the Radar Anti-Clutter Techniques
- Fast Time Constant (FTC)
- Sensitivity Time Control (STC)
- Automatic Gain Control (AGC)
- Pulse Compression
- Constant False Alarm Rate (CFAR)
Describe Fast Time Constant (FTC)
Fast Time Constant (FTC) is a receiver anti-clutter technique that
reduces clutter using a circuit that passes the leading edge of a
return pulse and attenuates the trailing edge.
Describe anti-clutter effects: Fast Time Constant (FTC)
Avoids extended clutter by presenting only the leading edge and chopping all signals longer then the radar pulse width.
Describe anti-clutter effects: Sensitivity Time Control (STC)
- Sensitivity Time Control (STC) is a control circuit that
reduces receiver gain at shorter ranges in order to avoid
severe saturation caused by close in clutter.
Describe anti-clutter effects: AUTOMATIC GAIN CONTROL (AGC)
Changes gain of a receiver
Automatic Gain Control (AGC) is a control circuit (feed back loop) that automatically changes the gain (amplification) of a receiver so that the desired output signal remains essentially constant despite variations in the input signal strength.
Describe anti-clutter effects: PULSE COMPRESSION
- Noise within a received pulse increases as Pulse Width
increases. - Pulse compression is achieved using a frequency dependent delay line or tapped delay line (matched filter).
** The compressed pulse contains less noise than the long transmitted pulse.
Describe anti-clutter effects: CONSTANT FALSE ALARM RATE
- Automatic detection systems apply the output of the receiver filters to a separate detector.
- The integrated signal plus the accompanying noise (clutter), must exceed a certain threshold for the detector to conclude that a valid target should be displayed.
- Occasionally, random noise alone exceeds the threshold and the
detector indicates a false target. This is called a False Alarm.
Explain the term Radar Cross Section.
5 points
- Radar Cross Section refers to how much energy
an object will reflect. - Generally, if a material is a good conductor of
electricity, it is also a good radar reflector.
What contribute to the RCS of an object.
* Target Composition
* Target Size
* Target Shape
* Target Aspect
* Angles (superstructure + masts)
Explain the effect Pulse Width Distortion have on radar performance.
- Pulse Width distortion will misrepresent the targets size due to the physical length of the pulse and may capture multiple targets within a pulse.
- The target will appear larger in range than it actually is.
Explain the effect Beam Width Distortion have on radar performance.
- The further the target is from the origin, the wider the
paint. Remember beam-width is an angle. - The leading edge of the beam strikes the target and
continues painting until the trailing edge of the beam
passes the target - Can hide smaller contacts either side (to left or right)
of large contacts.
Explain the effect Display Resolution Distortion have on radar performance.
- In digital radars, the spot size is the same as the pixel size making up the display and is referred to as display resolution.
- Display resolution distortion can be reduced, and display resolution increased, by decreasing range scales as soon as possible.
