LADAR Waveform Design for Range-Resolved Vibration Imaging
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Solution Overview
Problem
Current LADAR systems face challenges in isolating the vibration signature of targets from clutter, such as tree leaves, and in achieving high-resolution range and vibration measurements simultaneously, due to limitations in range resolution and coherent integration time.
Innovation Solution
The method employs large time-bandwidth waveforms, specifically trains of coherent pulses or linear frequency modulation chirps, combined with spectrograms to separate vibration signatures from clutter and achieve high-fidelity Doppler information, allowing for range-resolved vibration imaging by using matched filters and Fourier transforms to process the return signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional LADAR waveforms are used, then the system can operate with simple waveform structures, but the range resolution and vibration measurement precision are limited
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional simple waveforms to large time-bandwidth product waveforms (TBWP > 100). This involves changing the waveform parameters (time duration and bandwidth) to achieve superior range resolution and vibration measurement precision. The matched filter processing and spectrogram analysis further exploit parameter optimization to resolve the contradiction between measurement precision and waveform complexity.
2Measurement precision
If long observation time is used for vibration measurement, then vibration measurement precision improves, but range resolution capability deteriorates
Solution Approach 1:
The patent resolves this contradiction by transitioning to a two-dimensional time-frequency analysis using spectrograms. Instead of choosing between long observation time or good range resolution, the large TBWP waveform enables simultaneous optimization in both time and frequency domains. The spectrogram provides a time-frequency representation that captures both the range information (through frequency content) and vibration information (through time evolution), effectively adding a dimensional perspective that resolves the trade-off.
3Measurement precision
If large time-bandwidth product waveforms are used, then range resolution and vibration precision are improved, but the waveform processing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-designing the large time-bandwidth product waveforms with specific structures (such as chirp waveforms or phase-coded waveforms) that facilitate subsequent processing. The waveforms are engineered in advance to have properties that enable efficient matched filter correlation and spectrogram computation. This preliminary waveform design reduces the computational burden during real-time processing compared to analyzing arbitrary complex waveforms.
4Measurement precision
If coherent integration is performed over long periods, then vibration signature detection improves, but the system becomes more susceptible to target motion and clutter
Solution Approach 1:
The patent applies segmentation by dividing the long observation period into multiple coherent integration segments, each processed separately through matched filter and spectrogram analysis. This segmentation allows the system to maintain high vibration detection precision through cumulative integration while reducing susceptibility to target motion and clutter by processing shorter, more stable intervals. The segmented approach enables selective combination of results while rejecting components affected by motion or clutter interference.
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
This approach enables the creation of three-dimensional images with high angle-angle-range resolution, effectively isolating target vibrations while ignoring surrounding noise, and can distinguish different vibration characteristics across an extended body like an airframe.
Implementation Method 1
The LADAR sensor transmits a signal having a coherent train of subsignals... high-fidelity Doppler information
Implementation Method 2
LADARs may be mounted on stationary objects and on vehicles such as airplanes, for example. Laser vibration sensing is known from KACHELMYER
Data Source
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AI summary
In one aspect, a method includes forming range bins from range compressed data, the range compressed data comprising a train of coherent pulses formed based on a transmitted signal from a laser detection and ranging (LADAR) sensor and having a large time-bandwidth product and for each range bin, compensating for motion of the LADAR sensor, performing a Fourier transform on the compressed range data, determining a centroid of individual velocity measurements and performing Fourier transform of the centroid to determine a vibration.