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Surface clutter refers to reflections of a radar signal from land, sea, or the land-sea interface. When trying to detect or track targets moving on or above the surface, you must be able to distinguish between clutter and the targets of interest. For example, a ground moving target indicator (GMTI) radar application should detect targets on the ground while accounting for radar reflections from trees or houses.
If you are simulating a radar system, you might want to incorporate surface clutter into the simulation to ensure the system can overcome the effects of surface clutter. If you are analyzing the statistical performance of a radar system, you might want to incorporate clutter return distributions into the analysis.
Phased Array System Toolbox™ software offers these tools to help you incorporate surface clutter into your simulation or analysis:
When you use phased.ConstantGammaClutter, you must configure the object for the situation you are simulating, and confirm that the assumptions the software makes are valid for your system.
The ConstantGammaClutter object has properties that correspond to physical aspects of the situation you are modeling. These properties include:
Propagation speed, sample rate, and pulse repetition frequency of the signal
Operating frequency of the system
Altitude, speed, and direction of the radar platform
Depression angle of the broadside of the radar antenna array
The object has properties that correspond to the clutter characteristics, location, and modeling fidelity. These properties include:
Gamma parameter that depends on the terrain type and system's operating frequency.
Azimuth coverage and maximum range for the clutter simulation.
Azimuth span of each clutter patch. The software internally divides the clutter ring into a series of adjacent, nonoverlapping clutter patches.
Clutter coherence time. This value indicates how frequently the software changes the set of random numbers in the clutter simulation.
In the simulation, you can use identical random numbers over a time interval or uncorrelated random numbers. Simulation behavior slightly differs from reality, where a moving platform produces clutter returns that are correlated with each other over small time intervals.
The ConstantGammaClutter object has properties that let you obtain results in a convenient format. Using the OutputFormat property, you can choose to have the step method produce a signal that represents:
A fixed number of pulses. You indicate the number of pulses using the NumPulses property of the object.
A fixed number of samples. You indicate the number of samples using the NumSamples property of the object. Typically, you use the number of samples in one pulse. In staggered PRF applications, you might find this option more convenient because the step output always has the same matrix size.
The clutter simulation that ConstantGammaClutter provides is based on these assumptions:
The radar system is monostatic.
The propagation is in free space.
The terrain is homogeneous.
The clutter patch is stationary during the coherence time. Coherence time indicates how frequently the software changes the set of random numbers in the clutter simulation.
The signal is narrowband. Thus, the spatial response can be approximated by a phase shift. Similarly, the Doppler shift can be approximated by a phase shift.
The radar system maintains a constant height during simulation.
The radar system maintains a constant speed during simulation.