Matched Filter for SAL Seeker Angle Measurement
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Solution Overview
Problem
Laser-guided projectiles face ambiguity in angle measurement over a wide field-of-view, particularly in extended fields of view, due to rollover in the spatial transfer function, which limits precise guidance at close ranges and large angles.
Innovation Solution
A matched filter with weights corresponding to the normalized response of the SAL detector is used to disambiguate angle measurements, effectively extending the central monotonic region of the spatial transfer function and providing unambiguous angle measurements across a wide field-of-view, including the extended region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If optical techniques are used to increase spot size to widen the linear region of the STF and FOV, then the FOV is widened, but rollover in the STF occurs creating ambiguity in the extended FOV
Solution Approach 1:
A processor acts as an intermediary between the detector and guidance system, implementing a matched filter algorithm that compares detected signal patterns against pre-stored templates to disambiguate angle measurements in the extended FOV region where traditional centroid calculation fails
Solution Approach 2:
The system changes the parameter of spot size through optical techniques to widen the FOV, then compensates for the resulting STF rollover ambiguity by changing the measurement parameter from simple centroid calculation to matched filter pattern recognition
2Reliability
If thresholding is applied to preserve a wide linear region, then measurement ambiguity is reduced, but precise angle measurement is lost in the extended FOV
Solution Approach 1:
The system dynamically adapts its measurement approach by using the matched filter algorithm that can handle both linear and extended FOV regions, transitioning from simple thresholding to pattern-matched disambiguation based on the detected signal characteristics
3Measurement precision
If the matched filter is used to disambiguate angle measurements in the extended FOV, then unambiguous angle measurement is achieved, but device complexity increases
Solution Approach 1:
The system performs preliminary action by pre-calculating and storing template patterns of detector responses for various angle positions in the extended FOV before operation, allowing the matched filter to simply compare incoming signals against these pre-prepared templates rather than performing complex real-time calculations
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 matched filter approach enhances the resolution and accuracy of angle measurements, allowing for precise guidance at close ranges and large angles, reducing false alarms and improving the overall guidance system performance.
Implementation Method 1
A non-imaging optical system captures and focuses the scattered laser EMR into a spot onto a segmented non-imaging detector
Implementation Method 2
The detector compares the integrated EMR incident on each cell (segment) to calculate a spatial displacement of the centroid of the spot
Data Source
AI summary
A SAL seeker focuses laser energy reflected off a target into a spot on the surface of a multi-segment non-imaging detector. A matched filter is responsive to the normalized detector response to estimate an angle measurement to the target. The matched filter is particularly well-suited for use in wide FOV systems as it unambiguously selects the angle measurement over the extended FOV whereas the conventional centroid calculation introduces ambiguity. The centroid calculation and angle selection may be used to improve the search and selection of the matched filter. Alternately, the matched filter may be used to disambiguate the angle selection based on the centroid calculation.