Dual Wedge Scanner for 3D LIDAR Imaging
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Solution Overview
Problem
Conventional spaceborne laser altimeters face challenges in achieving high along-track resolution and cross-track coverage due to prime power, weight, and instrument longevity constraints, especially in orbits around other planets, with high signal-to-noise ratio approaches inefficiently using laser photons and requiring complex waveform interpretation from volumetric scatterers like tree canopies.
Innovation Solution
A microchip laser-based LIDAR system with a small diameter telescope, emitting high-repetition-rate pulses, and a dual wedge scanner for cross-track interrogation, using photon counting detectors and spectral/spatial filters to reduce solar background noise, enabling sub-centimeter ranging resolution and angularly resolving single photon events for point-to-point measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional high signal-to-noise ratio approach is used with large telescopes and high laser energy, then detection reliability is improved, but instrument mass and prime power usage increase severely
Solution Approach 1:
The patent changes the fundamental parameters of the LIDAR system by using low energy laser pulses (nanosecond to picosecond duration, microjoule to nanosecond energy levels) combined with single photon detection thresholds. This parameter transformation allows the system to achieve reliable detection without requiring large telescopes and high laser energies, thereby reducing instrument mass while maintaining detection reliability
Solution Approach 2:
The patent replaces the conventional mechanical/optical approach (large telescopes, high energy lasers) with a photon counting detection system. By using single photon sensitive detectors and time-correlated single photon counting techniques, the system achieves high detection reliability without the mass penalty of large optical components
2Measurement precision
If laser fire rate is scaled up to achieve higher along-track resolution, then spatial sampling is improved, but prime power and weight constraints are exceeded
Solution Approach 1:
The patent employs high repetition rate pulsed laser operation (kHz to MHz frequencies) where low energy pulses are fired in rapid periodic sequences. This periodic action at high frequency achieves fine along-track spatial sampling without requiring high energy per pulse, thus avoiding excessive prime power consumption while improving measurement precision
Solution Approach 2:
The patent segments the detection process into individual photon counting events rather than detecting multi-photon returns as a single signal. By detecting and time-tagging individual photons from each laser pulse, the system achieves high along-track resolution through rapid sequential measurements without the power requirements of conventional high-energy approaches
3Device complexity
If single element detector is used with high ground speed, then instrument complexity is reduced, but cross-track coverage and along-track resolution cannot be achieved simultaneously
Solution Approach 1:
The patent adds the time dimension to the detection process by using time-correlated single photon counting. Each photon is detected and its arrival time is precisely recorded relative to the laser pulse emission. This temporal dimension allows a single element detector to achieve high spatial resolution and cross-track coverage by resolving photons in the time domain, effectively transforming a one-dimensional detection problem into a four-dimensional solution (x, y, z, t)
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 reduces telescope size, power requirements, and mechanical complexity, achieving higher spatial resolution with lower detection thresholds, enhancing instrument sensitivity and allowing for high-resolution topographic mapping of planetary surfaces and vegetation without severe resource demands.
Implementation Method 1
an optical scanner comprising, a first optical wedge, a second optical wedge, and means for rotating the first and second optical wedges
Implementation Method 2
using photon counting detectors and spectral/spatial filters to reduce solar background noise, enabling sub-centimeter ranging resolution and angularly resolving single photon events
Implementation Method 3
using photon counting detectors and spectral/spatial filters to reduce solar background noise
Implementation Method 4
using photon counting detectors and spectral/spatial filters to reduce solar background noise
Implementation Method 5
enabling sub-centimeter ranging resolution and angularly resolving single photon events for point-to-point measurements
Data Source
AI summary
An optical scanner system for contiguous three-dimensional topographic or volumetric imaging of a surface from an aircraft or spacecraft is disclosed. A servo controller synchronizes the rotation rates of a pair of wedge scanners with high precision to the multi-kilohertz laser fire rate producing an infinite variety of well-controlled scan patterns. This causes the beam pattern to be laid down in precisely the same way on each scan cycle, eliminating the need to record the orientations of the wedges accurately on every laser fire, thereby reducing ancillary data storage or transmission requirements by two to three orders of magnitude and greatly simplifying data preprocessing and analysis. The described system also uses a holographic element to split the laser beam into an array that is then scanned in an arbitrary pattern. This provides more uniform signal strength to the various imaging detector channels and reduces the level of optical crosstalk between channels, resulting in a higher fidelity three-dimensional image.