An Improvement of the Performance of SAR Offset Tracking Approach to Measure Optimal Surface Displacements

Abstract

For the measurement of abrupt and large surface movements caused by earthquakes, volcanic eruption and melting glacier, Synthetic aperture radar (SAR) offset tracking method would be a feasible solution because it can provide unambiguous ground displacements in both the ground range and azimuth directions when the interferometric phase is not coherent. However, the measurement performance of the method largely depends on the kernel size, which denotes the size of search window to estimate the azimuth and range offsets between reference and target SAR images. Thus, there is a trade-off between sensitivity and measurement density depending on the search kernel size. In this study, an enhanced SAR offset tracking method based on multi-kernel processing has been developed to find an optimized measurement from the trade-off between resolution and measurement accuracy. It can obtain optimal surface displacement measurements by calculating multiple offset measurements and determining a final measurement from the statistical properties of the multiple measurements. The measurement performance of the proposed method was evaluated by using European Remote Sensing 2 (ERS-2) satellite SAR data sets of the Hector Mine earthquake event in 1999 and Advanced Land Observing Satellite-2 Phased Array type L-band Synthetic Aperture Radar-2 (ALOS-2 PALSAR-2) data sets of the 2016 Kumamoto earthquake event. Our results showed that an optimized measurement from the trade-off between the observation accuracy and resolution can be effectively determined by our proposed processing strategy. The results are improved results for measurement density and accuracy over previously published results. It further confirmed that our new method is allowed for the optimal measuring the large-scale fast surface displacements that cannot be sufficiently observed with the phase-based SAR method.INDEX TERMS Synthetic aperture radar (SAR), SAR offset tracking, surface deformation measurements, the 1999 hector mine earthquake, the 2016 Kumamoto earthquake.

Satellite radar observation of large surface collapses induced by the 2017 North Korea nuclear test

“…2, as the kernel size is smaller, the measurement accuracy is much lower but the spatial resolution is much higher while the measurement accuracy is higher, but the spatial resolution is lower, as the kernel size is larger. It means that the measurement accuracy and spatial resolution have a trade-off relation 24,[36][37][38] .…”

“…The main processing steps are composed of the following three parts: (a) Generating initial OT maps 24,41 . (b) Conducting error mitigation 24,[36][37][38]41 . (c) Mapping 3D surface deformation 16,40,42 .…”

“…First, InSAR measurements near the test site was too decorrelated to map the deformation 1,2,8,[35][36][37] . The biggest explosion inevitably caused complex and steep surface deformation which exceeds the phase difference of 2 π between adjacent pixels 1,8,[36][37][38] . Thus, InSAR could not be utilized to describe the deformation nearby the test site 34 .…”

“…Thus, InSAR could not be utilized to describe the deformation nearby the test site 34 . The OT method is an alternative aprpoach to measure the large and complex surface deformation induced by the 2017 North Korea Nuclear test because the method is allowed to measure the complex and steep surface deformation by using intensity cross-correlation approach 26,[36][37][38] .…”

“…In this study, we show the evidence of large collapse induced by the 2017 North Korea Nuclear test. For that, a multi-kernel OT (MKOT) approach was employed to overcome the limitation of the trade-off between measurement precision and spatial resolution [36][37][38] . The two ALOS PALSAR-2 stripmap interferometric pairs were acquired from the ascending (20170829_20170912) and descending (20170831_20170928) orbits, and the pairs were utilized to measure the ascending and descending LOS and AT deformations.…”