Radar Surveillance System Interleaved Dwell Sea Clutter
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Solution Overview
Problem
Conventional maritime surveillance radars face challenges in distinguishing real targets from false alarms due to high correlation between target and sea clutter returns, leading to either false targets being displayed or real targets being suppressed, especially in adverse sea conditions where fleeting targets are often missed.
Innovation Solution
The use of an electronically scanned radar antenna with an interleaved dwell strategy, allowing for short re-visits of the same area and exploiting natural temporal de-correlation of sea clutter, combined with pulse-to-pulse frequency agility and coherent processing, enhances target discrimination and reduces false alarms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional maritime surveillance radar uses fixed beam scanning with non-coherent azimuth integration, then the system can achieve complete 360° coverage, but it cannot effectively distinguish real targets from false alarms caused by sea clutter correlation
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed beam scanning pattern to a dynamic beam pattern that adapts between two modes: a search pattern for wide coverage and a dwell pattern for focused observation of specific areas. This dynamic adaptation allows the system to maintain both broad surveillance capability and enhanced target discrimination through prolonged observation of suspicious areas.
Solution Approach 2:
The patent segments the scanning process into distinct phases: a search phase that covers the entire surveillance area, and a dwell phase that focuses on specific regions of interest. This segmentation allows the system to separate the functions of wide-area surveillance from detailed target analysis, improving both coverage and detection accuracy.
2Speed
If the radar uses fast scan mode with high angular rotation rate, then re-visit time is reduced to 1 second or less, but the number of radar pulses per dwell becomes as low as one, requiring many scans for target integration
Solution Approach 1:
The patent employs periodic action by implementing repeated dwell observations on specific areas of interest. Instead of relying on a single fast scan, the system periodically returns to dwell on suspicious areas multiple times, accumulating target energy through coherent integration across these periodic observations. This approach enables effective target integration without requiring excessively high scan rates.
3Reliability
If the radar uses slow scan mode with slow antenna azimuth angular rate, then temporal de-correlation of sea clutter is achieved within dwell time, but the time to cover the 360° scene becomes long
Solution Approach 1:
The system dynamically adjusts the scan rate based on operational requirements. During search phases, a faster scan rate is used to cover the surveillance area efficiently. When targets or suspicious areas are detected, the system transitions to a dwell mode with slower effective scan rate on those specific areas, allowing sufficient integration time and clutter de-correlation without sacrificing overall search speed.
Solution Approach 2:
The surveillance process is segmented into search operations covering the full 360° area and dwell operations focused on specific regions. This segmentation allows the system to achieve clutter de-correlation during dwell phases on areas of interest without requiring the entire scan to be slow, thus maintaining overall search efficiency while achieving reliable target discrimination.
4Measurement precision
If scan to scan integration is used for clutter de-correlation, then large stationary targets can be detected, but fleeting small targets such as periscopes and small boats are missed
Solution Approach 1:
The system uses periodic dwell observations on areas of interest to detect fleeting targets. By repeatedly observing the same area over multiple radar scans and integrating the returns coherently, the system can detect small targets like periscopes and small boats that may be present only briefly. The periodic nature of the dwell allows accumulation of target energy even when the target is fleeting.
Solution Approach 2:
The radar system dynamically switches between search and dwell modes based on detected targets or suspicious areas. When a potential target is identified during search, the system transitions to dwell mode on that specific area, increasing the observation time and integration opportunities. This dynamic response enables the system to adapt to both stationary and fleeting targets effectively.
Data Source
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AI summary
A radar surveillance system is described in which the radar beam re-visits each area of interest after a short period of time, by electronically reconfiguring a scanned beam to an offset position for an interleaved sub-dwell, within a scan period. This 'look-back' capability, where the area under test is re-visited after approximately 1 second, allows the natural de- correlation of sea clutter to take place between the initial and look-back samples of the surveillance area. The re-visit time can be adjusted to best exploit the de-correlation characteristics of the sea clutter return.