Synthetic Aperture Lidar Target Detection and Imaging
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Solution Overview
Problem
Conventional synthetic aperture lidar (SAL) systems face challenges in adjusting the optical path length of the local oscillator (LO) signal to match the round-trip optical path length of transmission/return signals, especially in applications like spaceborne systems where the target locations are unknown or not precisely known, leading to limitations in detection and imaging of space objects.
Innovation Solution
A method and system for detecting and imaging targets using a platform in relative movement, which involves illuminating a scene with a search signal, estimating the target's range and angular location, generating an SA transmission signal with a time delay based on the estimated range, and adjusting the imaging direction of the SA transmission signal to refine the angular location, allowing for accurate SA imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical delay line is used to adjust the LO signal path length, then the optical path length matching is improved, but the system complexity increases and prior knowledge of target range is required
Solution Approach 1:
The system performs preliminary target detection and ranging using the search signal before conducting SA imaging. The estimated target range from the search phase is then used to set the LO signal path length, eliminating the need for complex optical delay lines and prior knowledge of target range.
Solution Approach 2:
The system uses feedback from the search signal return to estimate target range and adjust the LO signal path length accordingly. This feedback mechanism allows the system to adapt to unknown target ranges dynamically, reducing system complexity while maintaining path length matching precision.
2Measurement precision
If the field of view is narrowed to improve resolution, then the imaging precision is improved, but the detection capability for unknown target locations deteriorates
Solution Approach 1:
The system segments the detection process into two distinct phases: a search phase using a wide beam to detect and locate targets, and an imaging phase using a narrow beam to provide high-resolution SA imaging. This segmentation allows the system to maintain both wide field of view for detection and narrow field of view for imaging without compromise.
Solution Approach 2:
The system dynamically switches between wide beam and narrow beam modes based on the operational phase. During the search phase, a wide beam is used to scan the scene and locate targets. Once a target is identified, the system transitions to narrow beam mode for high-resolution imaging of that specific target, thereby adapting the field of view to the current operational needs.
3Device complexity
If the LO signal path length is fixed, then the device complexity is reduced, but the adaptability to unknown target locations deteriorates
Solution Approach 1:
The LO signal path length is made dynamically adjustable based on the estimated target range from the search phase. The system can adapt the path length to match different target distances without requiring complex optical delay lines, thereby maintaining simplicity while improving adaptability to unknown target locations.
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 improved target detection and localization capabilities, allowing for high-resolution SA imaging of space objects with enhanced accuracy and adaptability, even in scenarios where precise target locations are unknown.
Implementation Method 1
receiving, on the platform, a search return signal produced by reflection of the search signal from a target present in the scene
Implementation Method 2
Typical implementations of SAL are based on coherent detection with chirped signals. In coherent detection, the return signal reflected from the target is mixed with a local oscillator (LO) reference signal.
Implementation Method 3
The mixing of the return signal with the LO signal results in the generation of a beat signal having a frequency, the beat frequency, representative of the difference between the frequencies of the two mixed signals.
Data Source
AI summary
A method and a system for detection and synthetic aperture (SA) imaging of a target are disclosed. The method may include illuminating a scene with a search signal transmitted from a moving platform, receiving a search return signal from a target present in the scene, and estimating, from the search return signal, the range and the angular location of the target. The method may also include generating an SA transmission signal and a local oscillator (LO) signal with a time delay therebetween based on the estimated range, and illuminating the scene with the SA transmission signal pointed along an imaging direction based on the estimated angular location of the target. The method may further include receiving an SA return signal from the target, mixing the SA return signal with the LO signal to generate SA signal data, and generating an SA image of the target from the SA signal data.