Single-Photon LiDAR Return Time Determination via Dual Edge Detection
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Solution Overview
Problem
Single Photon LiDAR scanners face challenges in accurately determining return times due to amplitude-dependent timing errors, known as 'range walk' effects, especially when dealing with weak return pulse signals, as they lack amplitude information necessary for correcting nonlinearities and noise effects.
Innovation Solution
The method involves identifying a group of detected photons potentially representing a return pulse event and creating a return pulse signal based on a temporal probability distribution, determining the return time using both the rising and falling edges of the signal, which reduces amplitude-dependent biases and jitter noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low energy pulse is used in Single Photon LiDAR mode, then the system can detect weak return pulse signals, but amplitude information is lost and amplitude-dependent timing errors occur
Solution Approach 1:
The patent transitions from analyzing only the temporal dimension (single rising edge timing) to utilizing both temporal dimensions (rising edge and falling edge timings) to extract amplitude information. By measuring the time difference between rising and falling edges, the system recovers amplitude data that would otherwise be lost in binary single-photon detection, thereby resolving the information loss while maintaining measurement precision.
2Difficulty of detecting and measuring
If the threshold for detecting the signal is set to correspond to only one or a few photons, then single photon detection is enabled, but amplitude-dependent timing bias (range walk effect) occurs
Solution Approach 1:
The patent exploits the asymmetric temporal characteristics of the return pulse by separately analyzing the rising edge and falling edge. The rising edge provides timing information while the falling edge provides amplitude information through time difference measurement. This asymmetric utilization of pulse characteristics enables both single photon detection and accurate timing without the range walk effect that plagues conventional threshold-based methods.
3Loss of time
If very short pulses are used, then timing resolution is improved, but the lack of amplitude information prevents correction of nonlinearity and noise effects
Solution Approach 1:
The patent implements a feedback mechanism where the time difference between rising and falling edges is used to infer amplitude information, which then feeds back into the timing correction process. This inferred amplitude data is used to correct nonlinearity and noise effects in the return time measurement, enabling accurate measurements even with very short pulses where traditional amplitude information would be unavailable.
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 stabilizes the determination of return times, reduces amplitude-dependent errors, and improves noise filtering, resulting in a cleaner 3D point cloud dataset with enhanced accuracy for Single Photon LiDAR scanners.
Implementation Method 1
a pulsed electromagnetic radiation, e.g. a pulsed laser beam, is emitted towards the target
Implementation Method 2
a low photon count detector for detecting a returning light pulse, adapted for converting low amounts of photons or single photons to electrical signals
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 2c~2d
AI summary
The invention relates to a method and a device for determining a return time of a returning light pulse by a Single Photon LiDAR scanner, in the following called SPL scanner, in particular in an aerial LiDAR surface scan, a terrestrial monitoring scan, a mobile mapping scan, or a construction or surveying scan, in particular for measuring the time between an outgoing pulse event and a return pulse event, the SPL scanner comprising of a low photon count detector for converting low amounts of photons or single photons to electrical signals, and a control and processing unit for processing the data and for determining the return time of the returning light pulse. The method is characterized in that the control and processing unit • identifying a group of detected photons potentially representing a return pulse event and creating a return pulse signal based on a criterion involving a temporal probability distribution for the detected photons, in particular a defined minimum of consecutively detected low amounts of photons or single photons, • identifying a rising edge and a falling edge of the return pulse signal based on the identified group of detected photons potentially representing a return pulse event, and • determining the return time for each return pulse event based on the rising edge and the falling edge of the return pulse signal.