Laser Scanning Apparatus Blind Zone Reduction
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Solution Overview
Problem
Airborne Laser Terrain Mapping systems face data loss due to blind zones caused by simultaneous detection of outgoing and incoming pulses, as well as backscattered light from the atmosphere, which are difficult to manage especially at high pulse repetition frequencies.
Innovation Solution
The system employs special optical elements and real-time electronic circuits to differentiate and adjust the timing of laser pulses to prevent collisions, reducing blind zones by predicting and avoiding simultaneous detections, and using a secondary scanner mirror to minimize atmospheric backscatter, while maintaining constant swath width and spot density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the laser pulse repetition frequency is increased to improve productivity, then more data points can be collected per unit time, but the blind zone problem worsens causing data loss
Solution Approach 1:
The patent applies dynamics by making the laser pulse repetition frequency variable rather than fixed. The system dynamically adjusts the PRF based on real-time detection of atmospheric backscatter conditions and target range, allowing optimal data collection rates while avoiding blind zones. This is implemented through a control system that monitors detector signals and modulates the laser firing rate accordingly, enabling the system to operate at high productivity when conditions permit and reduce PRF when blind zones would cause data loss.
Solution Approach 2:
The patent changes the temporal parameter of laser pulse emission by introducing variable time intervals between pulses. Instead of uniform spacing, the system modifies the pulse repetition frequency parameter in response to detected atmospheric conditions, target elevation changes, and range variations. This parameter adaptation allows the system to maintain high data collection rates while preventing the overlap of outgoing and incoming pulses that causes blind zones.
2Reliability
If the aircraft altitude is adjusted to minimize blind zone impact, then measurement coverage can be optimized, but the complexity of flight planning increases significantly
Solution Approach 1:
The patent applies self-service by enabling the laser scanning system to automatically adapt to varying flight conditions without requiring complex pre-planned altitude adjustments. The system uses real-time feedback from the detector and range measurements to autonomously modify operational parameters such as pulse repetition frequency and scanner excitation angles. This self-adjusting capability eliminates the need for sophisticated flight planning algorithms while maintaining optimal measurement coverage across diverse terrain.
Solution Approach 2:
The patent implements feedback mechanisms where detector signals regarding atmospheric backscatter and target returns are continuously monitored and fed back to the control system. This feedback loop enables real-time adjustments to laser firing parameters and scanner operation, allowing the system to compensate for changing flight conditions and terrain variations dynamically, thereby simplifying flight planning while maintaining measurement reliability.
3Reliability
If optical elements are added to reduce atmospheric backscatter, then blind zones can be minimized, but the device complexity increases
Solution Approach 1:
The patent applies the extraction principle by selectively removing or filtering out the harmful atmospheric backscatter signals from the detection path. Rather than adding complex optical elements to block backscatter, the system extracts and eliminates the unwanted scattered light components through temporal gating and spectral filtering, allowing only the desired target return signals to reach the detector. This approach minimizes blind zones without significantly increasing optical system complexity.
Solution Approach 2:
The patent uses intermediary elements such as temporal gates and spectral filters that mediate between the incoming light signals and the detector. These intermediaries selectively transmit valid target returns while blocking atmospheric backscatter, effectively reducing blind zones. The temporal gate acts as an intermediary that opens only during the expected arrival window of target returns, excluding earlier backscatter signals, while spectral filters serve as intermediaries that separate desired wavelengths from scattered light components.
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 solution enables continuous data collection at high pulse repetition frequencies without data loss, reducing blind zones and maintaining consistent measurement quality across varying altitudes and terrain elevations.
Implementation Method 1
A short pulse of visible or infra-red light is emitted by a light source such as a laser, and directed towards a target. The light pulse propagates to the target and a fraction is reflected and travels back to the LiDAR system where it is detected
Implementation Method 2
The light pulse propagates to the target and a fraction is reflected and travels back to the LiDAR system where it is detected by a high-sped optical detector such as an avalanche photodiode, which converts the light pulse to an electrical signal
Implementation Method 3
By measuring the time interval from the instant the light pulse was emitted to when the return signal was received, the distance to the target can be calculated using the accurately-known speed of propagation of the light pulse. The TOF can be measured by an electronic subsystem such as a Time Interval Meter
Data Source
AI summary
The disclosed embodiments include an apparatus and method of using a laser to scan the ground or a target from an airborne or ground-based platform. In certain embodiments, the apparatus and method produces a 3-D elevation model of the terrain. In some embodiments, the apparatus includes a pulsed laser, a receiver to detect and amplify the pulse after being reflected by objects on the ground (or the ground itself), and electronics which measures the time of flight of the optical pulse from which the slant range to the target is calculated. Technical advantages of the disclosed embodiments include avoiding blind zones to ensure that no laser shots are wasted. In certain embodiments for airborne applications, the apparatus may also be configured to maintain a constant swath width or constant spot spacing independent of aircraft altitude or ground terrain elevation.