Multi-SAR Platform Tomography for DEM Generation
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Solution Overview
Problem
Current synthetic aperture radar (SAR) systems face challenges in generating accurate digital elevation models (DEMs) due to phase unwrapping errors and the need for high-SNR images, which are costly and not suitable for frequent monitoring of fast-changing scenes, especially when using bistatic SAR interferometers that require additional passes and large antenna apertures.
Innovation Solution
A method utilizing a system of multiple SAR platforms with multiple along-track and cross-track baselines, where at least one platform repeatedly transmits pulses with a certain pulse repetition frequency, and receiving platforms have smaller antennas than required for the 3 dB Doppler bandwidth, allowing for joint processing of range-compressed data into a tomogram through 2-D beamforming and multilooking to estimate DEMs, suppressing radar ambiguities and avoiding phase unwrapping errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bistatic SAR interferometers use large antenna apertures to achieve high-SNR images for accurate DEM generation, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the single large antenna system into multiple smaller antenna elements arranged in a specific geometry. These segmented antenna elements work together through coherent signal processing to achieve the required measurement precision for DEM generation without needing a single large aperture
Solution Approach 2:
The patent combines signals from multiple small antenna elements through coherent integration and beamforming techniques. By merging the signals from these distributed elements, the system achieves high-SNR images and accurate DEM generation equivalent to large antenna systems
2Device complexity
If repeat-pass SAR interferometry is used to generate DEMs, then device complexity is reduced, but temporal decorrelation impairs measurement precision
Solution Approach 1:
The patent employs a dynamic baseline adjustment mechanism where the relative positions and orientations of the multiple antenna elements can be varied between passes. This allows optimization of the interferometric baseline for each specific imaging scenario, maintaining high measurement precision while using simpler repeat-pass configuration
Solution Approach 2:
The system changes key parameters including pulse repetition frequency, antenna element spacing, and beamforming weights between different imaging passes. These parameter changes enable adaptation to different temporal and spatial conditions, reducing temporal decorrelation effects while maintaining system simplicity
3Measurement precision
If additional SAR passes are performed to resolve phase unwrapping errors, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent performs preliminary phase unwrapping during the initial signal processing stage by using the known geometric relationships between multiple antenna elements. This preliminary action resolves phase ambiguities before final DEM generation, eliminating the need for additional time-consuming passes
Solution Approach 2:
The system introduces an intermediary processing step that uses the redundant measurements from multiple antenna elements as a mediator to resolve phase unwrapping errors. This intermediary process efficiently determines the correct phase unwrapping solution without requiring additional satellite passes
4Productivity
If multiple SAR platforms with multiple baselines are used for single-pass DEM generation, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent designs a universal satellite platform that can perform both conventional SAR imaging and interferometric DEM generation using the same multiple antenna elements. This multi-functionality allows single-pass DEM generation without requiring separate specialized satellites, improving productivity while controlling complexity
Solution Approach 2:
The system adds the dimension of multiple baseline configurations by arranging antenna elements in three-dimensional geometries. This spatial dimensionality allows simultaneous acquisition of multiple interferometric pairs in a single pass, dramatically improving DEM generation productivity
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 the generation of DEMs with high accuracy and robustness to phase unwrapping errors, reducing satellite size and cost, allowing for single-pass DEM generation with flexible satellite arrangements and reduced time requirements, suitable for monitoring fast-changing topography, and achieving comparable performance to conventional SAR interferometric systems at a lower cost.
Implementation Method 1
synthetic aperture radar (SAR) platforms... at least one of the SAR platforms repeatedly transmits pulses towards the to-be-considered region... at least some of the SAR platforms... receive the echo signals, denoted as raw data, reflected from the to-be-considered region
Implementation Method 2
performing range compression on the raw data received by each receiving SAR platform to obtain range-compressed data
Implementation Method 3
jointly processing the range-compressed data of all receiving SAR platforms into a tomogram by a 2-D beamforming in the along-track and cross-track dimensions
Data Source
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AI summary
Disclosed is a method for generating a digital elevation model of a to-be-considered region on the earth or on another planetary body by using a system of multiple synthetic aperture radar (SAR) platforms, in a single pass, by comprising the following steps providing a system of several SAR platforms which are arranged with multiple along-track and cross-track baselines, wherein at least one of the SAR platforms repeatedly transmits pulses towards the to-be-considered region, i.e., in the slant range direction. The receiving SAR platforms receive the echo signals (raw data) and are provided with antennas, whose lengths in the along-track direction are smaller than the length required to have the 3 dB Doppler bandwidth of the received signal equal to the pulse repetition frequency, whereby the 3 dB Doppler bandwidth is defined as the width of the interval of Doppler frequencies for which the intensity of the response from a target on the ground is at least half of that of its maximum. Range compression on the raw data is performed to obtain range-compressed data. The range-compressed data of all receiving SAR platforms are jointly processed into a tomogram by a 2-D beamforming in the along-track and cross-track dimensions and the digital elevation model is estimated from the tomogram.