Coherent Lidar Imaging Method for High-Rate 3D Distance and Speed Measurement
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Solution Overview
Problem
Current coherent frequency-modulated lidar systems are limited by slow image refresh rates and range limitations, making them unsuitable for high-rate 3D imaging at long distances, such as several kilometers, which is essential for applications like autonomous vehicles and non-destructive testing.
Innovation Solution
The method involves generating a local oscillator signal with periodic frequency slopes, emitting multiple signals with synchronized frequency slopes in different directions to cover a field, collecting backscattered signals, and performing complex demodulations to determine distance and speed information for each pixel, allowing simultaneous measurement of multiple pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single local oscillator signal with periodic frequency slopes is used to illuminate multiple pixels simultaneously, then the image refresh rate is improved, but the system complexity increases due to the need for complex demodulation processing
Solution Approach 1:
The local oscillator signal is segmented into multiple frequency slope segments within each period, where each segment corresponds to a specific pixel. This segmentation allows parallel measurement of multiple pixels by assigning unique frequency slope combinations to each pixel, thereby improving the image refresh rate while maintaining manageable processing complexity through structured demodulation.
Solution Approach 2:
The local oscillator frequency is modulated periodically with P linear segments per period, creating a time-varying frequency pattern that cycles through different pixel assignments. This periodic modulation enables systematic multiplexing of multiple pixels over time, allowing high-speed imaging by measuring multiple pixels within each period while using predictable, repeatable signal patterns that simplify demodulation.
2Speed
If multiple emission signals with different frequency slopes are generated for simultaneous pixel measurement, then the measurement speed is improved, but the difficulty of detecting and measuring increases due to signal separation requirements
Solution Approach 1:
Each emission signal is assigned a unique local frequency slope characteristic that differs from other signals. This local differentiation in frequency domain allows the receiver to distinguish and separate signals from different pixels through demodulation, enabling simultaneous measurement of multiple pixels while maintaining detectability through unique spectral signatures for each signal.
Solution Approach 2:
The frequency slopes of the emission signals are predetermined and synchronized with the local oscillator frequency slopes before transmission. This preliminary assignment of unique frequency characteristics to each signal enables the receiver to prepare appropriate demodulation parameters in advance, simplifying the separation and detection process while achieving high-speed simultaneous measurement of multiple pixels.
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 high-rate 3D imaging capable of operating at long distances, overcoming the limitations of existing systems by allowing simultaneous measurement and processing of multiple pixels, thereby enhancing image refresh rates and range capabilities.
Implementation Method 1
The interference of these two waves is detected by a photodetector D, and the electrical signal at the detector's output exhibits an oscillating term called the beat signal Sb
Implementation Method 2
The Doppler frequency shift ν Dop of the backscattered wave is a function of the radial velocity v of the target T
Implementation Method 3
A coherent lidar comprises a coherent source L, typically a laser that emits a coherent light wave
Implementation Method 4
The coherent source is frequency modulated so that the local oscillator frequency is modulated according to a predetermined function called a waveform
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~4g
AI summary
The invention relates to a coherent LIDAR imaging method (10) comprising the steps of: - A generating a signal called the local oscillator, - B generating, from the local oscillator, N transmission signals Si, - C transmitting each transmission signal Si in an associated direction, - D collecting N back-scattered signals, - E detecting an impact signal Sb generated from the interference between the local oscillator and the N back-scattered signals, - F complexly modulating the impact signal Sb by the modulation frequency of the local oscillator fmodOL, - G carrying out NxP complex demodulations of the modulated impact signal, - H determining NxP power spectral densities SPi,j , - I determining characteristic frequencies (vij), - J determining for each pixel Aj at least one speed information item (vi) and at least one distance information item (di) from the characteristic frequencies (vij).