Flash LADAR Sensor Range Gating for Landing Clutter
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Solution Overview
Problem
Existing laser radar systems face challenges in achieving true 3-D imaging for controlled approach, docking, and landing applications due to issues with high reflectance near-field objects, airborne particulates, foliage, and other visual clutter, which affect range accuracy and image quality.
Innovation Solution
A flash LADAR sensor utilizing range gating techniques and a multiple pixel laser radar system to capture three-dimensional images with a single laser pulse, enhancing range accuracy and image quality by penetrating through optical clutter and enabling underwater docking and bathometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single laser pulse is used for 3-D imaging, then the imaging speed is improved, but the range accuracy deteriorates due to optical clutter from airborne particulates and foliage
Solution Approach 1:
The patent divides the return signal detection into multiple time-gated intervals, separating early returns (from near-field objects and clutter) from late returns (from distant targets). This temporal segmentation allows the system to capture the entire scene in a single pulse while selectively processing different depth ranges, thereby maintaining both high imaging speed and accurate range measurement.
Solution Approach 2:
The patent applies preliminary range gating to define the detection window before signal processing. By pre-establishing time gates that correspond to specific depth ranges, the system prepares to selectively accept or reject signals based on their arrival time, thus eliminating clutter from airborne particulates and foliage before they interfere with range accuracy.
2Measurement precision
If multiple pulses are used to improve range accuracy, then the measurement precision is improved, but the imaging speed deteriorates due to the need to scan over time
Solution Approach 1:
The patent employs periodic pulsed laser illumination with each pulse equipped with time-gated detection. Instead of using multiple sequential pulses to build up a complete image, the system uses repeated periodic pulses where each pulse captures the entire scene simultaneously at different time gates, achieving both high precision and high speed through parallel temporal sampling.
Solution Approach 2:
The patent adds the time dimension to the spatial detection by implementing time-gated range gating. This transforms the detection process from purely spatial scanning to four-dimensional detection (x, y, z, t), allowing the system to capture complete 3-D information in a single pulse while using the time dimension to separate and eliminate optical clutter.
3Loss of information
If the laser and optical receiver are scanned over the field of view, then the complete picture of the scene is captured, but the positional relationship of objects in motion shifts
Solution Approach 1:
The patent merges the functions of multiple detectors into a single detector array that simultaneously captures the entire field of view. By combining spatial detection across all pixels with temporal detection through range gating, the system achieves complete scene coverage without mechanical scanning, thereby eliminating positional shifts of moving objects.
Solution Approach 2:
The patent replaces the mechanical scanning system with a stationary detector array that uses electronic time-gating for spatial selection. This substitution eliminates the need for physical movement of the laser or receiver, thereby preventing positional relationship changes while maintaining complete scene coverage through parallel detection across all pixels.
4Measurement precision
If range gating is applied to penetrate optical clutter, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent changes the temporal parameter of signal detection by implementing time-gated range gating. Instead of adding complex spatial filtering or multiple physical components, the system simply varies the detection time window to selectively accept signals from specific depth ranges, thereby penetrating optical clutter with minimal additional hardware complexity.
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
The solution provides improved range accuracy and better image quality for automatic and pilot-assisted landing, approach, and docking systems in terrestrial, ocean surface, underwater, and space environments, effectively overcoming visual clutter and enhancing control capabilities.
Implementation Method 1
a pulsed laser transmitter that produces a high power, short duration laser pulse for illuminating the scene
Implementation Method 2
a rectangular array of avalanche photodiode detectors positioned at the focal plane of the receive optics
Implementation Method 3
timing circuits associated with each pixel of the imaging optical receiver for measuring a time of flight of the laser pulse
Data Source
AI summary
A system for landing or docking a mobile platform is enabled by a flash LADAR sensor having an adaptive controller with Automatic Gain Control (AGC). Range gating in the LADAR sensor penetrates through diffuse reflectors. The LADAR sensor adapted for landing/approach comprises a system controller, pulsed laser transmitter, transmit optics, receive optics, a focal plane array of detectors, a readout integrated circuit, camera support electronics and image processor, an image analysis and bias calculation processor, and a detector array bias control circuit. The system is capable of developing a complete 3-D scene from a single point of view.