Ladar Range Rate Estimation via Iterative Sinusoidal Fitting
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Solution Overview
Problem
Ladar systems face challenges in accurately characterizing moving targets due to blurring caused by accumulating photon counts over long periods, which affects signal-to-noise ratio and results in imprecise range and range rate estimates.
Innovation Solution
A method and system for ladar signal processing that involves transmitting a sequence of laser pulses, detecting return photons with a camera, and forming a one-dimensional time series array, which is then fitted with a superposition of sine and cosine functions to iteratively adjust the frequency until a completion criterion is met, allowing for precise range rate estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photon counts are accumulated over a relatively long period of time to improve the signal to noise ratio, then the signal to noise ratio is improved, but blurring occurs resulting in reduced measurement precision
Solution Approach 1:
The patent applies periodic action by using a pulse repetition frequency (PRF) to periodically transmit laser pulses and sample the target at discrete time intervals. This periodic sampling creates a time series of range measurements that can be analyzed using frequency domain methods, allowing the system to achieve both adequate signal accumulation and motion resolution by selecting an appropriate PRF that matches the target's velocity characteristics.
Solution Approach 2:
The patent implements dynamics by using iterative frequency adjustment methods to adapt to the target's motion characteristics. The system dynamically adjusts the tentative frequency parameter during processing to optimize the fit between the expected Doppler shift and the observed time series data, enabling accurate range rate estimation even when target velocity changes during the measurement period.
2Reliability
If photon counts are accumulated over a relatively long period of time, then the signal to noise ratio is improved, but blurring occurs resulting in imprecise range and range rate estimates
Solution Approach 1:
The patent transitions from spatial domain analysis to frequency domain analysis by applying a sinusoidal fit to the time series of range measurements. This dimensional transformation allows the system to separate target motion effects from measurement noise, as the Doppler-induced frequency modulation appears as a distinct spectral component that can be identified and measured independently of the spatial blurring that occurs in the time domain.
3Measurement precision
If a high pulse repetition frequency is used to improve range rate measurement capability, then range rate measurement precision is improved, but the system may miss photons from slower moving targets
Solution Approach 1:
The patent employs parameter changes by iteratively adjusting the tentative frequency parameter to match the actual Doppler shift of the target. This allows the system to optimize the pulse repetition frequency and time bin allocation based on the specific target's velocity characteristics, ensuring that both fast-moving and slow-moving targets can be effectively measured by adapting the sampling parameters to each target's motion regime.
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 enhances the accuracy of target characterization by reducing blurring and improving the signal-to-noise ratio, enabling more precise range and range rate estimates of moving targets.
Implementation Method 1
a camera including a photodiode array, which generates electrical pulses when it absorbs photons
Implementation Method 2
transmitting a plurality of laser pulses at a pulse repetition frequency; forming a one dimensional time series array corresponding to a time record of ladar return photons detected with the array detector
Data Source
AI summary
A system and method for forming a range rate estimate for a target with a laser detection and ranging system including a laser transmitter and an array detector. The method includes: transmitting a plurality of laser pulses at a pulse repetition frequency; forming a one dimensional time series array corresponding to a time record of ladar return photons detected with the array detector; fitting the time series array with a superposition of a sine and a cosine of an initial value of a tentative frequency; iteratively fitting the time series array with a superposition of a sine and a cosine of the tentative frequency, and adjusting the tentative frequency until a completion criterion is satisfied at a final value of the tentative frequency.