Minimizing the residual topography effect on interferograms to improve DInSAR results: estimating land subsidence in Port-Said City, Egypt

The accurate detection of land subsidence rates in urban areas is important to identify damage-prone areas and provide decision-makers with useful information. Meanwhile, no precise measurements of land subsidence have been undertaken within the coastal Port-Said City in Egypt to evaluate its hazard in relationship to sea-level rise. In order to address this shortcoming, this work introduces and evaluates a methodology that substantially improves small subsidence rate estimations in an urban setting. Eight ALOS/PALSAR-1 scenes were used to estimate the land subsidence rates in Port-Said City, using the Small BAse line Subset (SBAS) DInSAR technique. A stereo pair of ALOS/PRISM was used to generate an accurate DEM to minimize the residual topography effect on the generated interferograms. A total of 347 well distributed ground control points (GCP) were collected in Port-Said City using the leveling instrument to calibrate the generated DEM. Moreover, the eight PALSAR scenes were co-registered using 50 well-distributed GCPs and used to generate 22 interferogram pairs. These PALSAR interferograms were subsequently filtered and used together with the coherence data to calculate the phase unwrapping. The phase-unwrapped interferogram-pairs were then evaluated to discard four interferograms that were affected by phase jumps and phase ramps. Results confirmed that using an accurate DEM (ALOS/PRISM) was essential for accurately detecting small deformations. The vertical displacement rate during the investigated period (2007–2010) was estimated to be −28 mm. The results further indicate that the northern area of Port-Said City has been subjected to higher land subsidence rates compared to the southern area. Such land subsidence rates might induce significant environmental changes with respect to sea-level rise

Indoor experiments on polarimetric SAR interferometry

A coherence optimization method, which makes use of polarimetry to enhance the quality of SAR interferograms, has been experimentally tested under laboratory conditions in an anechoic chamber. By carefully selecting the polarization in both images, the resulting interferogram exhibits an improved coherence above the standard HH or VV channel. This higher coherence produces a lower phase variance, thus estimating the underlying topography more accurately. The potential improvement that this technique provides in the generation of digital elevation models (DEM) of non-vegetated natural surfaces has been observed for the first time on some artificial surfaces created with gravel. An experiment on a true outdoor DEM has not been accomplished yet, but the first laboratory results show that the height error for an almost planar surface can be drastically reduced within a wide range of baselines by using the optimization algorithm. This algorithm leads to three possible interferograms associated with statistically independent scattering mechanisms. The phase difference between those interferograms has been employed for extracting the height of vegetation samples. This retrieval technique has been tested on three different samples: maize, rice, and young fir trees. The inverted heights are compared with ground truth for different frequency bands. The estimates are quite variable with frequency, but their complete physical justification is still in progress. Finally, an alternative simplified scheme for the optimization is proposed. The new approach (called polarization subspace method) yields suboptimum results but is more intuitive and has been used for illustrating the working principle of the original optimization algorithm.Peer Reviewe

시계열 InSAR 기법을 사용하여 비정상적 해수면 상승 기록을 보인 조위관측소의 수직지반변위 평가

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 지구환경과학부, 2021.8. 김덕진.Global sea level rise has been a serious threat to the low-lying coasts and islands around the world. It is important to understand the global and regional sea level changes for preventing the coastal zones. Tide gauges are installed around the world, which directly measures the change in sea level relative to the local datum. Sea level in the past three decades has risen to 1.8 mm/year compared to the sea level rise in the 20th century (3.35 mm/year), estimated by the Intergovernmental Panel on Climate Change (IPCC). However, along with the contributors of sea level rise, vertical land motion (VLM) is indeed an essential component for understanding the regional sea level change; however, its contribution remains still unclear. The VLM is referred to as change in elevation of land at tide gauge due to the regional and local processes by both natural and anthropogenic activities can deteriorate the sea level records and lead to spurious sea level acceleration. Assessing the vertical land motion at tide gauges with the accuracy of sub-millimeters is essential to reconstruct the global and regional sea level rise. Previous studies attempt to observe the vertical land movements at sparse locations through Global Positioning System (GPS). However, the VLM observed from the sparse GPS network makes the estimation uncertain. In this study, an alternative approach is proposed in this study to directly measure the relative vertical land motion including spatial and temporal variations through Synthetic Aperture Radar (SAR) data by using time-series SAR interferometric (InSAR) techniques. This work presents a contribution enhancing the estimation of VLM rates with high spatial resolution over large area using time-series InSAR analysis. First, the C-band Interferometric Wide-swath (IW) mode SAR data from the Sentinel-1 A/B satellite was used in this study to estimate the VLM rates of tide gauges. The Sentinel-1 A/B SAR data were obtained during the period between 2014/10 and 2020/12 (~ 6 years). Stanford Method for Persistent Scatterers – Persistent Scatterer Interferometry (StaMPS-PSI) time-series InSAR algorithm was initially applied to the case study: Pohang tide gauge in the Korean peninsula for monitoring the stability of tide gauge station and its VLM rates during 2014 ~ 2017. For the Pohang tide gauge site, SAR data acquired in both ascending and descending passes and derived the ground movement rates at tide gauge along the line-of-sight direction. The vertical movements from the collocated POHA GPS station were compared with the InSAR derived VLM rates for determining the correlation between the two methods. The VLM rates at the Pohang tide gauge site were -25.5 mm/year during 2014 ~ 2017. This VLM rate at Pohang tide gauge derived by StaMPS-PSI estimates were from the strong dominant scatterers along the coastal regions. Second, for the terrains, with few dominant scatterers and more distributed scatters, a short temporal InSAR pair selection approach was introduced, referred as Sequential StaMPS-Small baselines subset (StaMPS-SBAS) was proposed in this study. Sequential StaMPS-SBAS forms the interferograms of short temporal sequential order (n = 5) to increase the initial pixel candidates on the natural terrains in the vicinity of tide gauges. Sentinel-1 A/B SAR data over ten tide gauges in the Korean peninsula having different terrain conditions were acquired during 2014 ~ 2020; and employed with sequential StaMPS-SBAS to estimate the VLM rates and time-series displacements. The initial pixel density has been doubled and ~ 1.25 times the final coherent pixels identified over the conventional StaMPS-SBAS analysis. Third, the potential for the fully automatic estimation of time-series VLM rates by sequential StaMPS-SBAS analysis was investigated. A fully automatic processing module referred to as ‘Seq-TInSAR’, was developed which has three modules 1) automatically downloads Sentinel-1 Single look complex (SLC) data, precise orbit files, and Digital Elevation Model (DEM); 2) SLC pre-processor: extract bursts, fine Coregistration and stacking and, 3) Sequential StaMPS-SBAS processor: estimates the VLM rates and VLM time-series. Finally, the Seq-TInSAR module is applied to the 100 tide gauges that exhibit abnormal sea level trend with par global mean sea level average. For each tide gauge site, 60 ~ 70 Sentinel-1 A/B SLC scenes were acquired and 300 ~ 350 sequential interferograms were processed to estimate the VLM at tide gauge stations. The final quantitative VLM rates and time-series VLM are estimated for the selected tide gauges stations. Based on the VLM rates, the tide gauges investigated in this study are categorized into different VLM ranges. The in-situ GPS observations available at 12 tide gauge stations were compared with InSAR VLM rates and found strong agreement, which suggests the proposed approach more reliable in measuring the spatial and temporal variations of VLM at tide gauges.전 세계적으로 발생하는 해수면 상승은 저지대 해안과 도서 지역에 심각한 위협으로 작용한다. 해안 지역을 보호하기 위해 전 지구 및 해당 지역의 해수면 변화를 이해하는 것은 대단히 중요하다. 조위 관측소는 전 세계에 설치되어 해당 지역 기준에 따른 해수면 변화를 직접 측정한다. 지난 30 년간 해수면은 IPCC (정부 간 기후 변화 패널)가 추정한 20 세기의 해수면 상승 (3.35mm / 년)대비 1.8mm / 년 가까이 상승하였다. 그러나 해수면 상승의 원인과 함께 연직 지반 운동 (VLM)은 지역 해수면 변화를 이해하는 데 필수적인 요소이지만 그 기여도는 여전히 불분명하다. VLM은 자연 활동과 인간 활동 모두에 의한 지역적 변화로 인해 조위 관측소에서 지반의 고도 변화로 정의되며 해수면 변화 정확도을 악화시키고 유사 해수면 변화의 가속을 초래할 수 있다. 전 세계 및 지역 해수면 상승을 재구성하려면 1 밀리미터 미만의 정확도로 조위 관측소에서 VLM을 평가하는 것이 필수적이다. 이전 연구는 GPS (Global Positioning System)를 통해 제한된 위치에서 VLM 을 관측하려고 시도하였으나 국소적인 GPS 신호들로부터 관측된 VLM으로는 그 추정이 불확실하다. 본 연구에서는 시계열 SAR 간섭계 (InSAR) 기법을 이용하여 SAR (Synthetic Aperture Radar) 데이터를 통해 공간적, 시간적 변화를 포함한 상대적 VLM을 직접 측정하기 위한 대안적 접근 방식을 제안한다. 이 작업은 시계열 InSAR 분석을 사용하여 광대역에 걸쳐 높은 공간 해상도로 VLM 속도의 추정을 향상시키는 데 기여한다. 첫째로, Sentinel-1 A / B 위성의 C-band Interferometric Wide-swath (IW) 모드 SAR 영상이 본 연구에서 조위 관측소의 VLM 속도를 추정하는 데 사용되었다. Sentinel-1 A / B SAR 영상은 2014 년 10 월부터 2020 년 12 월까지 (~ 6 년) 기간 동안 수집되었다. 고정 산란체를 위한 스탠포드 기법 – 고정 산란 간섭계 (StaMPS-PSI) 시계열 InSAR 알고리즘이 한반도 포항 조위 관측소의 2014 ~ 2017 년 동안의 조위 관측소의 안정성과 VLM 속도를 모니터링하기 위해 적용되었다. 포항 조위 관측소 부지의 경우, 위성궤도의 상승 및 하강 경로로 획득한 SAR 영상을 통해 시선 방향을 따라 조위 관측소에서의 지면 이동 속도를 도출하였다. 포항 GPS 관측소의 연직 이동은 두 기법 간의 상관성를 판단하기 위해 InSAR기법으로부터 추정된 VLM 속도와 비교되었다. 포항 조위 관측소의 VLM 속도는 2014 ~ 2017 년의 기간 동안 -25.5mm / 년으로 관측되었다. StaMPS-PSI 추정에 의해 도출 된 포항 조위 관측소의 VLM 속도은 해안 지역의 강한 산란 체에서 기인한다. 둘째로, 강한 산란체가 수가 적고 분산된 산란체가 더 많은 지형의 경우, 본 연구에서 Sequential StaMPS-Small baselines (StaMPS-SBAS)이라는 하는 단기 InSAR 쌍의 선택에 의한 접근 방식이 제안되었다. Sequential StaMPS-SBAS는 짧은 시간 범위(n = 5)의 간섭계 영상을 형성하여 조위 관측소 부근의 자연 지형에서 변화가 적은 화소 선택을 증가시킨다. Sentinel-1 A / B SAR 영상은 2014 년 ~ 2020 년 사이에 서로 다른 지형 조건을 가진 한반도의 10 개 조위 관측소에서 수집되었으며, VLM 속도 및 시계열 변위를 추정하기 위해 Sequential StaMPS-SBAS와 함께 사용되었다. 초기 화소 밀도는 기존 StaMPS-SBAS 분석을 통해 확인 된 최종적인 불변화소 밀도의 약 1.25 배와 두 배로 도출되었다. 셋째로, Sequential StaMPS-SBAS 분석에 의한 시계열 VLM 비율의 완전한 자동 추정 가능성을 조사하였다. Seq-TInSAR라고하는 완전한 자동 처리 모듈이 개발되었으며, 3 개의 하위 모듈로 구성되어있다. 1) Sentinel-1 SLC (Single Look Complex) 영상, 정밀한 궤도 정보 및 DEM (Digital Elevation Model)의 자동 다운로드 2) SLC 전 처리기 : 영상 별 Burst 추출, 정밀한 통합 및 Stacking, 3) Sequential StaMPS-SBAS 프로세서 : VLM 속도 및 VLM 시계열 변위의 추정 마지막으로, Seq-TInSAR 모듈은 동위 평균 해수면 평균으로 비정상적인 해수면 추세를 보이는 100 개의 조위 관측소에 적용된다. 조위 관측소 지점별로 60 ~ 70 개의 Sentinel-1 A / B SLC 영상을 획득하고 300 ~ 350 개의 시계열 간섭계 영상을 처리하여 조위 관측소에서 VLM을 추정하였다. 정량적인 VLM 속도와 시계열 VLM은 선정한 조위 관측소에 대해 추정하였다. VLM 속도을 기반으로 본 연구에서 도출한 조위 관측소는 다양한 VLM 범위로 분류된다. 12 개의 조위 관측소에서 취득한 현장 GPS 관측 자료를 InSAR로부터 추정한 VLM 비율과 비교하여 강력한 상관성을 찾았고, 이는 본 연구에서 제안한 접근 방식이 조위 관측소에서 VLM의 공간적 및 시간적 변화를 측정하는데 신뢰할 수 있는 자료로 사용될 수 있음을 시사한다.Chapter 1. Introduction 1 1.1. Brief overview of sea-level rise 1 1.2. Motivations 4 1.3. Purpose of Research 9 1.4. Outline 12 Chapter 2. Sea Level variations and Estimation of Vertical land motion 14 2.1. Sea level variations 14 2.2. Sea level observations 14 2.3. Long term sea level estimation 19 2.4. Factors contributing tide gauge records: Vertical Land Motion 19 2.5. Brief overview of InSAR and Time-series SAR Interferometry 24 Chapter 3. Vertical Land Motion estimation at Tide gauge using Time-series PS-InSAR technique: A case study for Pohang tide gauge 36 3.1. Background 36 3.2. VLM estimation at Pohang tide gauge using StaMPS-PSI analysis 38 3.3. Development of StaMPS-SBAS InSAR using Sequential InSAR pair selection suitable for coastal environments 55 3.4. Discussion 80 Chapter 4. Application of time-series Sequential-SBAS InSAR for Vertical Land Motion estimation at selected tide gauges around the world using Sentinel-1 SAR data 85 4.1. Description of PSMSL tide gauge data 87 4.2. Sentinel-1 A/B SAR data acquisitions 92 4.3. Automatic Time-series InSAR processing module ”Seq-TInSAR” 93 4.4. Results: Estimation of vertical land motions at selected tide gauges 97 4.5. Comparison of InSAR results with GNSS observations 112 4.6. Discussion 125 Chapter 5. Conclusions and Future Perspectives 128 Abstract in Korean 133 Appendix – A 136 Appendix – B 146 Bibliography 151박

Asteroid Models from Multiple Data Sources

In the past decade, hundreds of asteroid shape models have been derived using the lightcurve inversion method. At the same time, a new framework of 3-D shape modeling based on the combined analysis of widely different data sources such as optical lightcurves, disk-resolved images, stellar occultation timings, mid-infrared thermal radiometry, optical interferometry, and radar delay-Doppler data, has been developed. This multi-data approach allows the determination of most of the physical and surface properties of asteroids in a single, coherent inversion, with spectacular results. We review the main results of asteroid lightcurve inversion and also recent advances in multi-data modeling. We show that models based on remote sensing data were confirmed by spacecraft encounters with asteroids, and we discuss how the multiplication of highly detailed 3-D models will help to refine our general knowledge of the asteroid population. The physical and surface properties of asteroids, i.e., their spin, 3-D shape, density, thermal inertia, surface roughness, are among the least known of all asteroid properties. Apart for the albedo and diameter, we have access to the whole picture for only a few hundreds of asteroids. These quantities are nevertheless very important to understand as they affect the non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth, or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I

Integration of high-resolution, Active and Passive Remote Sensing in support to Tsunami Preparedness and Contingency Planning

In the aftermath of the Sri Lanka tsunami disaster, a stack of synoptic procedures and remote sensing techniques was chosen for satisfying the urgent mapping needs of the Government. This choice presented the undebated advantage of (a) allowing to start the work immediately (b) without relying upon ground logistics until the onset of the air campaign, (c) minimizing the duration of the work on spot, while (d) covering fast - and at an otherwise unreacheable resolution - large portions of a difficult-to-penetrate territory, (e) keeping the work sustainable and, overall, (f) allowing to carry out the work. This combination of airborne and spaceborne techniques is ready-to-use worldwide, and the techniques for flooding simulation and scenario building can be chosen at whatever level of complexity - choosing preferably robustness. It is also worth noting further that the new generation of metric resolution, X-band Radar satellite constellations (as TerraSAR-X and Cosmo-SkyMED), may allow creating LiDAR-like products avoiding airborne missions. The products of the space-and-air campaign were handed over by the Ambassador of Italy to the Minister for Disaster Management and Humanitarian Affairs on 7th December 2006, Colombo, Sri Lanka

Spacecraft applications of advanced global positioning system technology

The purpose of this study was to evaluate potential uses of Global Positioning System (GPS) in spacecraft applications in the following areas: attitude control and tracking; structural control; traffic control; and time base definition (synchronization). Each of these functions are addressed. Also addressed are the hardware related issues concerning the application of GPS technology and comparisons are provided with alternative instrumentation methods for specific functions required for an advanced low earth orbit spacecraft

Exploiting satellite SAR for archaeological prospection and heritage site protection

Optical and Synthetic Aperture Radar (SAR) remote sensing has a long history of use and reached a good level of maturity in archaeological and cultural heritage applications, yet further advances are viable through the exploitation of novel sensor data and imaging modes, big data and high-performance computing, advanced and automated analysis methods. This paper showcases the main research avenues in this field, with a focus on archaeological prospection and heritage site protection. Six demonstration use-cases with a wealth of heritage asset types (e.g. excavated and still buried archaeological features, standing monuments, natural reserves, burial mounds, paleo-channels) and respective scientific research objectives are presented: the Ostia-Portus area and the wider Province of Rome (Italy), the city of Wuhan and the Jiuzhaigou National Park (China), and the Siberian “Valley of the Kings” (Russia). Input data encompass both archive and newly tasked medium to very high-resolution imagery acquired over the last decade from satellite (e.g. Copernicus Sentinels and ESA Third Party Missions) and aerial (e.g. Unmanned Aerial Vehicles, UAV) platforms, as well as field-based evidence and ground truth, auxiliary topographic data, Digital Elevation Models (DEM), and monitoring data from geodetic campaigns and networks. The novel results achieved for the use-cases contribute to the discussion on the advantages and limitations of optical and SAR-based archaeological and heritage applications aimed to detect buried and sub-surface archaeological assets across rural and semi-vegetated landscapes, identify threats to cultural heritage assets due to ground instability and urban development in large metropolises, and monitor post-disaster impacts in natural reserves