LADAR Vibrometry Using Phase-Based Phasograms for Low CNR
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Solution Overview
Problem
Existing LADAR systems face challenges in accurately detecting small target vibrations, especially when the optical carrier-to-noise ratio (CNR) is low, as they require large CNR for precise vibration spectrum measurement and are prone to noise interference.
Innovation Solution
The LADAR system employs a method of generating a phasogram by determining the relative phase between the return signal and a reference signal, which allows for the creation of a vibration spectrum that is more sensitive and effective in low CNR conditions, improving the detection of small target vibrations by tracking phase changes over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional spectrogram methods are used for vibration detection, then the system can operate with simple processing, but the measurement precision deteriorates significantly in low CNR conditions
Solution Approach 1:
The patent changes the fundamental parameter used for vibration analysis from amplitude-based spectrograms to phase-based phasograms. By tracking phase changes of the laser return signal over time, the system achieves superior vibration detection precision in low CNR conditions. The phase information remains stable even when signal amplitude is weak, resolving the contradiction between measurement precision and processing complexity.
Solution Approach 2:
The patent replaces traditional amplitude-based spectral analysis with phase-based measurement. Instead of analyzing frequency content through complex spectrogram generation, the system directly measures phase changes which provide a more robust and sensitive indicator of vibration, simplifying the processing while improving precision.
2Use of energy by moving object
If the LADAR system operates at low optical carrier-to-noise ratio (CNR), then energy efficiency improves, but measurement precision of vibration spectrum deteriorates
Solution Approach 1:
The patent fundamentally changes the measurement parameter from amplitude (which degrades with low CNR) to phase (which maintains stability at low CNR). Phase measurements are inherently more robust to noise and signal strength variations, allowing the system to operate efficiently at low energy levels while maintaining high measurement precision for vibration detection.
3Reliability
If traditional amplitude-based vibration analysis is used, then the system is less sensitive to noise, but it cannot detect small target vibrations effectively
Solution Approach 1:
The patent substitutes amplitude-based analysis with phase-based analysis. Phase changes provide a linear response to small vibrations and are less susceptible to noise interference compared to amplitude measurements. This substitution enables the system to detect small target vibrations reliably while maintaining noise resistance, as phase information remains stable even in noisy environments.
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 significantly enhances the sensitivity of vibration measurement, achieving noise equivalent velocity (NEVV) that is up to 100 times better than traditional spectrogram methods, even at low CNR levels, enabling reliable detection of vibration signatures.
Implementation Method 1
A laser detection and ranging (LADAR) sensor, sometimes referred to as laser radar, uses laser beams to measure distances (or ranges) and instantaneous velocities
Implementation Method 2
receives a return signal based on the transmitted laser signal that is reflected from a target
Implementation Method 3
The phasogram is generated by determining a relative phase between the return signal and a reference signal
Implementation Method 4
The LADAR system generates a vibration spectrum of the return signal based upon the generated phasogram
Implementation Method 5
LADAR sensors may be employed to determine the presence and movement of vibrating objects
Data Source
AI summary
Described embodiments provide a laser detection and ranging (LADAR) system. The LADAR system transmits a laser signal including a train of coherent pulses and receives a return signal based on the transmitted laser signal that is reflected from a target. The LADAR system forms one or more range bins of the return signal. Each range bin includes a train of coherent pulses formed based upon the transmitted laser signal. For each range bin, the LADAR system generates a phasogram associated with the train of coherent pulses. The phasogram is generated by determining a relative phase between the return signal and a reference signal. The LADAR system generates a vibration spectrum of the return signal based upon the generated phasogram.