Satellite Spotlight Steering for Extended SAR Dwell Time
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Solution Overview
Problem
Existing Synthetic Aperture Radar (SAR) systems face limitations in achieving extended dwell times and improved azimuth resolution, which affect the accuracy and range of information provided by satellite imagery.
Innovation Solution
The use of mechanical steering in satellites, particularly micro satellites, to prolong dwell times and enhance viewing angles, combined with processing techniques like multilooking, back projection SAR processing, and chronocolour imaging, to improve image resolution and dynamic observation capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If electronic beam steering is used to maintain target visibility, then the system can maintain a target area within the radar aperture, but the dwell time is limited and cannot be extended sufficiently for ultra-high resolution imaging
Solution Approach 1:
The patent replaces electronic beam steering with mechanical satellite steering. The satellite physically repositions itself to maintain the target area within the radar aperture, enabling extended dwell times of 10-60 seconds compared to the limited dwell time of electronic steering. This mechanical substitution allows the satellite to achieve ultra-high azimuth resolution while maintaining target visibility throughout the extended observation period.
2Duration of action of moving object
If the satellite maintains a fixed orbit without mechanical steering, then the system structure is simpler, but the dwell time over a target is too short to achieve extended duration imaging
Solution Approach 1:
The patent employs mechanical satellite steering using reaction wheels or control moment gyroscopes to rotate the satellite body and maintain target illumination. This approach, while introducing additional control mechanisms, enables dwell times of 10-60 seconds by physically tracking the target area, thereby achieving extended duration imaging capability that outweighs the added system complexity.
3Measurement precision
If conventional SAR processing is used, then the processing is straightforward, but the signal-to-clutter ratio and speckle noise performance are insufficient for detailed target detection
Solution Approach 1:
The patent applies multilook processing by dividing the extended dwell time into multiple sub-apertures or looks. Each sub-aperture processes a portion of the collected data, and the results are combined to produce the final image. This preliminary segmentation of the imaging process improves signal-to-clutter ratio and reduces speckle noise through coherent or incoherent combination of multiple looks, enabling detailed target detection despite increased processing complexity.
Solution Approach 2:
The patent employs dynamic focusing techniques where the processing adapts to the specific characteristics of each sub-aperture or time segment within the extended dwell period. This dynamic approach optimizes the signal-to-clutter ratio by adjusting processing parameters for different portions of the extended observation, thereby improving detection capability while managing processing complexity through adaptive algorithms.
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
Enhances azimuth resolution and enables extended dwell times, allowing for ultra-high resolution imaging and dynamic observation of Earth's surface, with improved signal-to-clutter ratio and reduced speckle noise, facilitating detailed imaging and detection of moving targets.
Implementation Method 1
the ADCS is configured for mechanically steering the satellite in the azimuth direction to prolong a dwell time, during which a selected target is visible from the satellite
Implementation Method 2
raw data comprising pulse recordings resulting from the reflection of radio energy pulses transmitted from the satellite, from a target on Earth
Data Source
AI summary
A satellite (140) for operation in orbit around the earth comprises an ADCS (131, FIG. 1) configured for mechanically steering the satellite in the azimuth direction to prolong a dwell time (1105), during which a selected target is visible from the satellite, as the satellite orbits over the target. A processor at the ground station may be configured to process raw SAR data from any of the satellites described here. The raw SAR data may be processed in a number of ways to provide image information including but not limited to forming multilook images, compiling video sequences and colour coding images.