Ground-Based Pulse Doppler Radar Clutter Suppression
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Solution Overview
Problem
Ground-based pulse Doppler radar systems face challenges in distinguishing true targets from windmill returns and rain clutter due to low unambiguous Doppler velocity intervals and range blind zones, which impede detectability.
Innovation Solution
Implementing a Medium Pulse Repetition Frequency (MPRF) waveform with a PRF range of 3 to 7 kHz, allowing for the suppression of windmill and rain clutter returns by emitting successive bursts of different PRFs, enabling clear classification of windmill signals and rain clutter regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If LPRF waveform with PRF below 1000Hz is used, then unambiguous range measurement is improved (greater than 150km), but unambiguous Doppler velocity interval deteriorates (low interval of 57m/s)
Solution Approach 1:
The system dynamically switches between multiple PRF values (including LPRF, MPRF, and HPRF) rather than using a fixed PRF. This allows the radar to adapt the PRF selection based on the specific detection scenario, thereby simultaneously achieving large unambiguous range (with LPRF) and large unambiguous Doppler velocity interval (with HPRF/MPRF) as needed.
Solution Approach 2:
The invention changes the PRF parameter from a fixed value to a variable that can be selected from multiple discrete values. By implementing PRF staggering with different PRF values (e.g., 500Hz, 1kHz, 2kHz, 4kHz, 8kHz), the system can optimize the balance between range and velocity measurement capabilities according to different operational requirements.
2Length of stationary object
If LPRF waveform is used, then range measurement capability is improved, but detectability of targets deteriorates due to complete coverage of Doppler velocity region by windmill returns and rain clutter
Solution Approach 1:
The system employs dynamic PRF selection from multiple discrete values to create time-varying range-Doppler maps. By alternating between LPRF, MPRF, and HPRF, the radar can suppress windmill and rain clutter returns that completely cover the Doppler velocity region at LPRF, while maintaining good range measurement capability.
Solution Approach 2:
The invention segments the Doppler velocity region analysis by using multiple PRF values to create multiple range-Doppler maps. Each PRF value provides a different segmentation of the velocity coverage, allowing the system to identify and suppress clutter regions that would otherwise completely mask targets in a single PRF mode.
3Difficulty of detecting and measuring
If MPRF waveform with PRF of 3 to 7kHz is used, then suppression of windmill and rain clutter returns is improved, but unambiguous range measurement deteriorates (reduces to 32.5km)
Solution Approach 1:
The system dynamically alternates between LPRF (for large unambiguous range) and MPRF/HPRF (for clutter suppression) based on the detection scenario. This dynamic switching allows the radar to achieve both large unambiguous range and effective clutter suppression by selecting the appropriate PRF value for each measurement cycle.
Solution Approach 2:
The invention merges the advantages of multiple PRF modes by combining LPRF (large range) with MPRF/HPRF (clutter suppression) in a unified PRF staggering scheme. The system processes returns from multiple PRF values and integrates the information to achieve both large unambiguous range and effective suppression of windmill and rain clutter.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The MPRF waveform effectively isolates windmill and rain clutter signals, allowing for unambiguous detection of targets by expanding the unambiguous range and velocity intervals, thereby improving the radar's ability to detect targets in areas previously obscured by clutter.
Implementation Method 1
ground based pulse doppler radar
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
The invention is concerned with a method for suppressing windmill returns in a ground based pulse Doppler radar comprising the following steps: a) emitting a waveform comprising a train of pulses at an average pulse repetition frequency of 3 to 7 kHz, b) upon reception of the echo pulses, transforming the echo pulses into a range Doppler matrix containing the signal power levels of the radar detections and indicating their respective range gate and Doppler filter, c) determining the detections in any of the second, third, penultimate and last Doppler filters in a range gate where windmills are suspected, d) determining the signal power levels of detections in the first Doppler filter at range gates that are identical or adjacent to the range gate where windmills are suspected, e) determining the maximum of the signal power levels determined in the previous step, f) comparing the corresponding radar cross section of the maximum signal power level determined in the previous step with a predefined threshold value derived from the characteristic radar cross section of a rotor head of a windmill, g) excluding the detections in the range gate where windmills are suspected in the second, third, penultimate and last Doppler filter from further processing if the radar cross section of the maximum signal power level is above the predefined threshold.