Semi-Active Laser Pulse Stacking for Low Reflectivity Targets
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Solution Overview
Problem
Semi-active laser systems face challenges in detecting and tracking low reflectivity targets due to limited sensor sensitivity, which is constrained by payload size and aperture limitations.
Innovation Solution
The method involves pulse stacking and temporal offsetting of laser pulses to increase the signal-to-noise ratio (SNR), allowing for improved target acquisition range and sensitivity independent of aperture size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the aperture size of the SAL sensor is increased to improve signal strength, then the sensitivity to low reflectivity targets improves, but the payload size increases which is not feasible given volume constraints
Solution Approach 1:
The patent combines multiple laser pulses that arrive at different times into a single stacked pulse signal. By temporally aligning and summing N individual pulses, the system achieves signal-to-noise ratio improvement equivalent to having a larger aperture, without physically increasing the sensor size. This merging of temporal information compensates for the limited aperture area.
Solution Approach 2:
Instead of increasing sensitivity in the spatial dimension (larger aperture), the patent transitions to the temporal dimension by processing sequences of pulses over time. The pulse stacking technique exploits the time dimension to accumulate signal energy, achieving enhanced sensitivity without requiring a larger physical aperture.
2Measurement precision
If the pulse repetition frequency is increased to improve target acquisition range, then the signal-to-noise ratio improves, but the processing complexity increases
Solution Approach 1:
The system performs preliminary temporal alignment of pulses before summation. By pre-calculating and applying time offsets to align pulse peaks, the system prepares the signal in advance for optimal stacking. This preliminary action simplifies the subsequent summation process and ensures maximum signal-to-noise ratio improvement.
Solution Approach 2:
The patent replaces complex hardware solutions (larger apertures, more sensitive detectors) with digital signal processing techniques. The pulse stacking algorithm performs temporal alignment and summation computationally, substituting mechanical/optical complexity with algorithmic processing that can be implemented in existing digital systems.
3Volume of moving object
If the sensor aperture is reduced to decrease payload size, then the volume constraints are satisfied, but the signal strength from low reflectivity targets decreases
Solution Approach 1:
The system uses periodic laser illumination of the target, receiving reflected pulses at regular intervals. By accumulating these periodic pulse sequences over time through stacking, the system compensates for the weak signal strength caused by the small aperture. The periodic nature of laser illumination enables systematic accumulation of signal energy without requiring large aperture area.
Data Source
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AI summary
A Semi-Active Laser sensor for determining a line-of-site to a target includes: a receiver for receiving a plurality of target pulses; a processor for starting a target track for pulses that cross a noise threshold opening a pulse gate within the target track; and for every laser pulse received within the pulse gate crossing the noise threshold, determining a time index relative to the pulse gate center; and a memory for storing the pulses that cross the noise threshold and their respective time index, wherein the processor further temporally offsets the stored pulses based on their corresponding time indexes, sums the offset pulses together to generate a summed pulse signal, and determines the line-of-sight error to the target from the summed pulse signal.