SAR Phase Unwrapping Using Offset Tracking Surface Displacement Model
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current Synthetic Aperture Radar (SAR) interferometry techniques face challenges in accurately observing large-scale, high-speed surface displacements due to unwrapping errors, particularly in areas with complex surface scattering characteristics and high decorrelation between SAR image pairs, limiting their effectiveness in 3D analysis of seismicity, volcanic eruptions, and other rapid displacement events.
Innovation Solution
A method and apparatus that utilize the SAR offset tracking method to generate a surface displacement model, which includes acquiring SAR images, producing single look complex images, generating an SAR interferogram, and creating an unwrapped residual interferogram by subtracting the offset tracking surface displacement model from the SAR interferogram, thereby reducing unwrapping errors and enhancing observation precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phase unwrapping processing algorithm is applied, then surface displacement can be observed in areas with small displacement, but unwrapping error occurs in areas with large or complex surface displacement
Solution Approach 1:
The patent applies preliminary action by first generating a surface displacement model using SAR offset tracking method before performing phase unwrapping. This preliminary model estimates the surface displacement component, which is then subtracted from the original interferogram to create a residual interferogram with reduced phase variations. This preliminary estimation prevents unwrapping errors in areas with large displacements by pre-compensating for the dominant displacement signal.
Solution Approach 2:
The patent introduces an intermediary element - the surface displacement model generated by SAR offset tracking - that acts as a mediator between the raw interferogram and the final unwrapped phase. This intermediary model captures the large-scale surface displacement component, allowing the residual interferogram to be unwrapped more accurately. The intermediary effectively bridges the gap between the limitations of conventional unwrapping and the need for accurate large displacement measurement.
2Measurement precision
If SAR interferometry is used to observe surface displacement, then observation precision of several centimeters is achieved, but phase unwrapping error degrades accuracy in areas with large displacement
Solution Approach 1:
The patent applies segmentation by dividing the surface displacement observation into two components: a large-scale component captured by SAR offset tracking and a residual component captured by SAR interferometry. The surface displacement model from offset tracking separates the dominant displacement signal, allowing the interferometric phase unwrapping to focus only on the residual variations. This segmentation enables both methods to operate in their optimal ranges without mutual interference.
Solution Approach 2:
The patent changes the parameter of the interferogram by subtracting the surface displacement model, thereby transforming the original interferogram with large phase variations into a residual interferogram with reduced phase variations. This parameter change (from raw phase to residual phase) makes the phase unwrapping process more reliable by reducing the magnitude of phase discontinuities that cause unwrapping errors.
3Reliability
If SAR offset tracking method is used, then unwrapping error is avoided, but observation precision is lower than SAR interferometry
Solution Approach 1:
The patent merges the advantages of both SAR offset tracking and SAR interferometry into a hybrid approach. The surface displacement model from offset tracking (which is reliable and unwrapping-error-free) is combined with the high-precision interferometric observation. Specifically, the offset tracking model is used to pre-process the interferogram, and the resulting residual interferogram is then unwrapped with high precision. This merging allows the final product to achieve both reliability (no unwrapping errors) and high measurement precision.
Data Source
AI summary
The present disclosure relates to a method and apparatus for phase unwrapping of an SAR interferogram based on an SAR offset tracking surface displacement model, in which the apparatus according to the present disclosure includes a Synthetic Aperture Radar (SAR) image acquisition unit that acquires two SAR images of a same object acquired at different times, a single look complex (SLC) image production unit that produces two SLC images corresponding to each of the two SAR images, an interferogram production unit that generates an SAR interferogram using SAR interferometry for the two SLC images, a surface displacement model production unit that produces an offset tracking surface displacement model using SAR offset tracking method for the two SLC images, an unwrapped residual interferogram generation unit that generates a residual interferogram by subtracting the SAR interferogram and the offset tracking surface displacement model, and generates an unwrapped residual interferogram by unwrapping the generated residual interferogram, and an unwrapped interferogram generation unit that generates an unwrapped SAR interferogram by adding the unwrapped residual interferogram to the offset tracking surface displacement model.