Understanding Plot Extraction
Plot extraction is a critical aspect of radar signal processing, enabling the identification and analysis of relevant targets from radar data.
Plot Generation and Threshold Crossings:
The plot extraction process begins with the output of the signal processor, which generates hits across the radar's beamwidth, typically where the returned signal crosses a dynamic threshold. These hits represent potential targets detected by the radar system and may only be present in certain Doppler filter outputs depending on the speed of the target.
During the antenna scan, threshold crossings may span multiple inter pulse periods, Coherent Processing Intervals (CPIs), and adjacent range resolution cells. The plot extractor's primary function is to correlate these threshold crossings, identifying and grouping them into plots that likely originate from the same target.
The hit processor plays a crucial role in generating target reports with comprehensive information on validated targets. These reports typically include range, azimuth and amplitude details, as well as radial velocity if Doppler information is available too. The process of correlating hits to form a plot report is historically accomplished using a sliding window process. However, modern plot processing often employs more advanced correlation techniques, such as the Center of Mass Correlation method, which offers improved accuracy and reliability.
Plot Energy Assessment and Discrimination
The plot extractor can assess the energy in a plot based on the distribution of amplitudes across the radar's beamwidth. This plot energy information serves as a valuable discriminator, aiding in the differentiation between real targets and unwanted artefacts. By analysing the plot energy, radar engineers can identify and remove false echoes caused by environmental factors or non-target objects, enhancing the accuracy and reliability of the plot extraction process.
Advanced Plot Extraction Functions
In addition to the core functions mentioned above, plot extractors can perform various advanced processing functions, including:
- Declare Detection: Based on a predefined false alarm rate, the plot extractor declares the presence or absence of a target detection. This function helps filter out spurious plots and noise, focusing on genuine target signals.
- Declare Centroid Position: The plot extractor calculates the centroid position of the target plot, representing the centre point of the target's spatial distribution. This information provides a more precise location estimate that can be used for tracking the target.
- Declare Radial Speed: If information on the Doppler shifts of the plots are available, the plot extractor determines the radial speed or velocity of the target. This value is useful for tracking moving targets and predicting their future positions accurately, as well as filtering out unwanted reports.
- Declare Energy/Amplitude: The plot extractor evaluates the energy or amplitude distribution of the plots, allowing for the discrimination of target signals from clutter or unwanted returns. This information helps refine the plot extraction process, ensuring that only valid targets are considered.
Further Reading on Plot Extraction
Radar Terminology
How to Track and Detect Small Targets with Radar