Launching in early 2024, the NASA-ISRO SAR (NISAR) mission will provide global data freely accessible enabling large scale surface deformation monitoring with synthetic aperture radar (SAR) acquired at L-band and S-band radar wavelengths. In preparation for calibration and validation of the NISAR L-band data, the NISAR Solid earth science team is systematically processing over 450 Japan Aerospace Exploration Agency (JAXA) ALOS-2 PalSAR-2 wide-swath (ScanSAR) L-band acquisitions covering the West Coast of the United States for measuring co-seismic, secular and transient displacements. The area spans California, Washington and Oregon.

We document one of several methodologies used to validate the NASA-ISRO Synthetic Aperture Radar (NISAR) mission requirements for solid earth deformation. NISAR’s deformation requirements cover steady-state, coseismic, and transient deformation processes and were designed to confirm that the mission is able to meet its solid earth science goals. We use independent observations of earth surface deformation from continuous Global Navigation Satellite System (GNSS) stations as ground truth for NISAR-observed deformation, and we provide a statistical framework to assess the quality of the associated NISAR data products. Our validation workflows have been developed as Jupyter Notebooks and are publicly available via GitHub/GitLab.

National Aeronautics and Space Administration (NASA) Damage Proxy Maps (DPMs) are products that were developed by NASA’s Jet Propulsion Lab (NASA-JPL) to map damage after major natural and anthropogenic disasters. The maps utilize pairs of synthetic aperture radar (SAR) images to detect areas that have experienced significant coherence loss following a disaster event. Areas with significant coherence loss as identified by DPMs are expected to have surface change, which may be related to damage phenomena, such as structural damage. Limited prior research that quantitatively associates a DPM index related to coherence change to structural damage assessed in person is extended here to investigate associations with the probability of exceeding various structural damage states. The damage state considered here is partial or full collapse, using a newly evaluated data set from Amatrice, Italy from the M6.1 Central Italy earthquake (the first major seismic event of the 2016 Central Italy earthquake sequence). Taking a DPM-conditioned probability ≥ 0.5 as a prediction of partial or full collapse, we find that the DPM has a recall of 80.9%, a precision of 60.8%, and an accuracy of 65.8% in regards to identifying partial or full collapse of structures.

We establish a workflow for validating NISAR Solid Earth Science (SES) products based on UAVSAR measurements of secular velocities and coseismic displacements across earthquake faults. UAVSAR is an L-band synthetic aperture radar capable of measuring solid Earth deformations through repeat pass interferometry. High spatial resolution makes UAVSAR especially sensitive to surface deformation at short spatial wavelengths (e.g., near a crustal fault). Furthermore, UAVSAR acquisition schemes can provide a 3D picture of deformation. For NISAR validation, secular (interseismic) deformation will be measured across the creeping section of the San Andreas fault, where fault creep presents a well-defined tectonic signal and a rich UAVSAR data archive exists. The UAVSAR measurements will be quantitatively compared to measurements based on satellite InSAR data. The workflow developed herein is similar to that in the SES algorithm theoretical basis document (ATBD) for validating NISAR products, with changes made to account for the peculiarities of UAVSAR data.

We study the distribution of slip on faults during earthquakes with integrated analysis of geodetic imaging and seismic data to learn about parameters that control how faults slip and potentially how damaging future earthquakes may be. We mapped complex fault ruptures for a number of large earthquakes in 2015–2020 using analysis of synthetic aperture radar (SAR) data from the Copernicus Sentinel-1A and Sentinel-1B satellites operated by the European Space Agency and the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by the Japan Aerospace Exploration Agency (JAXA). We used regular SAR interferometry, along-track or multiple-aperture interferometry, and pixel offset tracking to measure surface displacements and combined this with other geodetic and seismic data to infer slip on faults at depth.

Slow-moving landslides are destabilized by precipitation. The continuous soil moisture monitoring aid the understanding of landslide processes. Here we study time-series soil moisture using NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) at 6-m resolution for a seasonally active grassland landslide in the northern California Coast Ranges, USA. A physically based radar scattering model is used to retrieve the near-surface (5-cm depth) soil moisture. The forward model is developed for polarization HH and VV. The soil moisture retrieval using HH&VV shows unbiased RMSE (ubRMSE) of 0.058 m3/m3. From the Freeman-Durden decomposition for UAVSAR's time-series data, the surface scattering and double bounce dominate the landslide area which suggests the strong correlation with soil moisture for the data. The physical-model based algorithm can be applied to other grassland covered landslides in California to retrieve soil moisture.

The joint NASA/ISRO SAR (NISAR) satellite mission is anticipated to provide routine L-band coverage of most of the Earth's land surface every 12-days for both ascending and descending orbits. In terms of impact on solid earth science (SES), the primary measurement will be Interferometric SAR (InSAR) observations of ground deformation in two satellite line-of-sight (LOS) directions. Key observation characteristics include acquisitions with small interferometric baselines to maximize interferometric coherence and decrease sensitivity to topography, wide bandwidth allowing for split-band processing to model out the impacts of the ionosphere, and joint L- and S-band observations in selected regions. We describe here the key measurement requirements for solid earth science, as well as our approach to validating these requirements once the mission is underway.

The Copernicus Sentinel-1A/B satellites operating at C-band in terrain observation by progressive scans (TOPS) mode bring unprecedented opportunities for measuring large-scale tectonic motions using interferometric synthetic aperture radar (InSAR). Although the ionospheric effects are only about one-sixteenth of those at L-band, the measurement accuracy might still be degraded by long-wavelength signals due to the ionosphere. We implement the range split-spectrum method for correcting ionospheric effects in InSAR with C-band Sentinel-1 TOPS data. We perform InSAR time series analysis and evaluate these ionospheric effects using data acquired on both ascending (dusk-side of the Sentinel-1 dawn-dusk orbit) and descending (dawn-side) tracks over representative midlatitude and low-latitude (geomagnetic latitude) areas. We find that the ionospheric effects are very strong for data acquired at low latitudes on ascending tracks. For other cases, ionospheric effects are not strong or even negligible. The application of the range split-spectrum method, despite some implementation challenges, largely removes ionospheric effects, and thus improves the InSAR time series analysis results.

Operating at L-band (~24 cm wavelength) in wide-swath modes is one of the characteristics of the new and next generation satellite synthetic aperture radar (SAR) missions. After 3 years of operation, the Japan Aerospace Exploration Agency Advanced Land Observing Satellite-2 (ALOS-2) satellite has acquired a wealth of L-band wide-swath SAR data over many areas using its ScanSAR mode. We present interferometry SAR (InSAR) time series analysis results from ALOS-2 ScanSAR data. We analyze the possible error sources in the InSAR and correct them if possible. We present different time series analysis results including azimuth frequency modulation rate error, line of sight (LOS) ionospheric phase, azimuth shift caused by the ionosphere, and LOS displacement processed using both full-aperture and burst-by -burst workflows. The final InSAR LOS displacement time series result reveals both large-scale tectonic and small-scale anthropogenic deformation components. The results demonstrate the potential for measuring continental or even global-scale tectonic deformation and illustrate the promise of upcoming L-band wide-swath SAR missions, such as the NASA-ISRO SAR mission.

We present a detailed survey on the ongoing destabilization process of the Mosul dam. The dam is located on the Tigris river and is the biggest hydraulic structure in Iraq. From a geological point of view the dam foundation is unstable due to the underlying geology that is formed by alternate and variable strata of highly soluble materials such as gypsum, anhydrite, marl and limestone. Here we present the first comprehensive multi-sensor cumulative deformation map for the dam generated from space-based synthetic aperture radar (SAR) measurements from the Italian constellation COSMO-SkyMed and the European Sentinel-1a satellite. We compared 2014-2016 data to an historic dataset spanning 2004-2010 acquired with the Envisat ASAR sensor. We found that deformation was rapid during 2004-2010, slowed down in 2012-2014, and restarted in August 2014 when grouting operations stopped due to the temporary capture of the dam by the self proclaimed Islamic State in Iraq and Syria (ISIS). We took advantage of the availability of data from multiple SAR satellites to infer the deformation at the dam in great spatial and temporal detail and shed new light on the processes of the ongoing destabilization. This study highlights how new constellations of SAR sensors together with the availability of historical datasets are leading to important advances in deformation monitoring of small scale geologic and manmade features.

We analyze the methods for measuring azimuth deformation with the L-band Advanced Land Observing Satellite-2 (ALOS-2) scanning synthetic aperture radar (ScanSAR) interferometry. To implement the methods, we extract focused bursts from the ALOS-2 full-aperture product, which is the only product available for ScanSAR interferometry at present. The extracted bursts are properly processed to measure azimuth deformation using interferometric phase. We apply the range split-spectrum method to ScanSAR to estimate the differential ionospheric phase of the interferogram, and take the azimuth derivative of the differential ionospheric phase to mitigate the relative azimuth shift caused by ionosphere. For the first time, azimuth deformation of a large earthquake (April 25, 2015 Nepal earthquake) is nearly completely measured by the L-band ScanSAR interferometry with moderate precision. The result is validated by the azimuth deformation measured by incoherent cross correlation using a pair of high-resolution RADARSAT-2 images. In addition to the final azimuth deformation, we show the possibility of processing full-aperture ScanSAR product using a burst-by-burst approach to form regular interferograms. We also show the recent strong large-scale ionospheric effects on the L-band ALOS-2 ScanSAR interferograms. Other possible applications of this paper include measuring the movement of glaciers.

Advanced Land Observing Satellite-2 (ALOS-2) is designed to routinely acquire both scanning synthetic aperture radar (ScanSAR) and stripmap data. In this paper, we present a special multiband bandpass filter (MBF) to remove azimuth nonoverlap spectra for the interferometric processing of ALOS-2 full-aperture ScanSAR product. As required by the MBF, we estimate the important ScanSAR system parameters and the start times of raw bursts using ALOS-2 full-aperture ScanSAR image. The resulting MBF can remove the nonoverlap spectra caused by both Doppler centroid frequency difference and burst misalignment. It can be used in ScanSAR-ScanSAR interferometry, as well as ScanSAR-stripmap interferometry. Based on the MBF, we propose a single processing workflow that is able to implement both ScanSAR-ScanSAR interferometry and ScanSAR-stripmap interferometry. Finally, we present example interferograms of the 2015 Gorkha earthquake in Nepal processed using the proposed processing workflow. The interferograms are greatly improved after applying the MBF to remove the significant amount of nonoverlap spectra in the data.

Estimating azimuth offset with double-difference interferometric (DDI) phase, which is called multiple-aperture interferometric synthetic aperture radar (InSAR) or spectral diversity, is increasingly used in recent years to measure azimuth deformation or to accurately coregister a pair of InSAR images. We analyze the effect of frequency modulation (FM) rate error in focusing on the DDI phase with an emphasis on the azimuth direction. We first comprehensively analyze the errors in various focusing results caused by the FM rate error. We then derive the DDI phase error considering different acquisition modes including stripmap, ScanSAR, and TOPS modes. For stripmap mode, typical DDI phase error is a range ramp, while for burst modes including ScanSAR and TOPS modes it is an azimuth ramp within a burst. The correction methods for the DDI phase error are suggested for different acquisition modes.

The April 25, 2015 M7.8 Gorkha earthquake caused more than 8,000 fatalities and widespread building damage in central Nepal. Four days after the earthquake, the Italian Space Agency's (ASI's) COSMO-SkyMed Synthetic Aperture Radar (SAR) satellite acquired data over Kathmandu area. Nine days after the earthquake, the Japan Aerospace Exploration Agency's (JAXA's) ALOS-2 SAR satellite covered larger area. Using these radar observations, we rapidly produced damage proxy maps derived from temporal changes in Interferometric SAR (InSAR) coherence. These maps were qualitatively validated through comparison with independent damage analyses by National Geospatial-Intelligence Agency (NGA) and the UNITAR's (United Nations Institute for Training and Research's) Operational Satellite Applications Programme (UNOSAT), and based on our own visual inspection of DigitalGlobe's WorldView optical pre- vs. post-event imagery. Our maps were quickly released to responding agencies and the public, and used for damage assessment, determining inspection/imaging priorities, and reconnaissance fieldwork.

Processing scanning synthetic aperture radar (ScanSAR) data using a stripmap processor, which is called full-aperture processing, has been the choice of many researchers. ScanSAR data are known to require very high azimuth coregistration precision which is usually achieved by a geometrical coregistration followed by a spectral diversity coregistration on the ScanSAR burst. However, for full-aperture processing, since individual bursts are no longer available for spectral diversity coregistration, the cross-correlation method in practice is still used to coregister ScanSAR data as stripmap data. We analyze the azimuth coregistration precision requirement of full-aperture processing and find that its requirement can be significantly relaxed. This is confirmed by a number of experiments, including simulations and real data experiments whose results are in good agreement with each other. An additional experiment on the cross-correlation method supports its use in full-aperture processing. Concluding from the experimental results, we further propose a simple method to evaluate the azimuth coregistration precision requirement for practical use. Finally, we present examples with ALOS-2 ScanSAR data.

In order to measure the response of the Slumgullion landslide to hydraulic forcing, we utilize the unique capabilities of the NASA/JPL's UAVSAR airborne repeat-pass SAR interferometry system to provide surface geodetic measurements with “landslide-wide” spatial coverage. Unlike traditional space-based INSAR we are not restricted to fixed flight tracks or fixed repeat times, allowing for optimal imaging geometries and timing. We combine four look directions chosen based on the landslide geometry and invert for the full 3-D landslide-wide surface deformation. These observations complement ongoing GPS measurements and in-situ observations of pore-pressure and atmospheric parameters acquired by the U.S. Geological Survey.

This paper addresses the November 2013 Balochistan Earthquake. A co-seismic TerraSAR-X pair acquired in wide-swath ScanSAR mode has been used to derive two-dimensional deformation measurements (radar line-of-sight and azimuth direction) of the eastern part of the main M7.7 earthquake and the large M6.8 aftershock by correlating SAR amplitude images. Atmospheric and solid Earth tide corrections have been considered to achieve accuracy in the order of several centimeters. Correlation measurements from Landsat-8 images have been additionally estimated. The intention is to isolate vertical and horizontal components in order to obtain three-dimensional deformation measurements. Interferometric processing issues of ScanSAR data for non-stationary scenarios, specifically co-registration, are additionally discussed.

We evaluate early postseismic deformation after the 2010 Darfield, New Zealand, earthquake documented by radar satellite interferometry observations. Applying interferometric techniques to TerraSAR-X, COSMO-SkyMed, and ALOS data, we derive evidence for a variety of coupled solid-fluid postseismic processes after the Darfield event. The contractional jog of the Greendale Fault shows a time-dependent subsidence signal during the first ~6 months after the event. We detect a dominant subsidence signal in the epicentral area of the Charing Cross fault and also observe a narrow zone (<; 15km) of right-lateral shear along the eastern end of the Greendale Fault, a likely indication of postseismic afterslip process that is operative there after the event.

A tropospheric correction method for Interferometric Synthetic Aperture Radar (InSAR) was developed using profiles from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Zenith Total Delay (ZTD) from the Global Positioning System (GPS). The ECMWF data were interpolated into a finer grid with the Stretched Boundary Layer Model (SBLM) using a Digital Elevation Model (DEM) with a horizontal resolution of 1 arcsecond. The output were converted into ZTD and combined with the GPS ZTD in order to achieve tropospheric correction maps utilizing both the high spatial resolution of the SBLM and the high accuracy of the GPS. These maps were evaluated for three InSAR images, with short temporal baselines (implying no surface deformation), from Envisat during 2006 on an area stretching northeast from the Los Angeles basin towards Death Valley. The RMS in the InSAR images was greatly reduced, up to 32%, when using the tropospheric corrections. Two of the residuals showed a constant gradient over the area, suggesting a remaining orbit error. This error was reduced by reprocessing the troposphere corrected InSAR images with the result of an overall RMS reduction of 15-68%.

Atmospheric water-vapor effects represent a major limitation of interferometric synthetic aperture radar (InSAR) techniques, including InSAR time-series (TS) approaches (e.g., persistent or permanent scatterers and small-baseline subset). For the first time, this paper demonstrates the use of InSAR TS with precipitable water-vapor (InSAR TS$+$PWV) correction model for deformation mapping. We use MEdium Resolution Imaging Spectrometer (MERIS) near-infrafred (NIR) water-vapor data for InSAR atmospheric correction when they are available. For the dates when the NIR data are blocked by clouds, an atmospheric phase screen (APS) model has been developed to estimate atmospheric effects using partially water-vapor-corrected interferograms. Cross validation reveals that the estimated APS agreed with MERIS-derived line-of-sight path delays with a small standard deviation (0.3–0.5 cm) and a high correlation coefficient (0.84–0.98). This paper shows that a better TS of postseismic motion after the 2003 Bam (Iran) earthquake is achievable after reduction of water-vapor effects using the InSAR TS$+$PWV technique with coincident MERIS NIR water-vapor data.

The National Research Council's Decadal Survey for Earth Science identified InSAR (Interferometric Synthetic Aperture Radar) observations among the highest priorities for new NASA Earth missions. A system making observations required by the solid Earth, vegetation, and ice/climate science communities is recommended. In response, analyses are underway to evaluate efficient combinations of science objectives and mission/instrument scenarios. The InSAR component can be satisfied by a new radar instrument concept capitalizing on existing technology and hardware, including a large commercial mesh reflector antenna and transmit/receive modules developed for the UAVSAR airborne radar. This InSAR system satisfies key science objectives and addresses several shortcomings of existing InSAR capable satellites. To reduce temporal decorrelation, L-Band (23 cm) wavelength is used. A 300 km wide-swath scanSAR mode with 8 day repeat enhances study of ice dynamics, pre/post earthquake deformation, volcano monitoring, and other dynamic phenomena. With a minor orbit change, global biomass surveys are possible using multipolarization. Key challenges are involve scheduling to optimize conflicting observational requirements of various science communities served.

The study of the Earth as a system is being adopted widely by geoscientists. Numerical models and simulations are providing the capability to rapidly test hypotheses and make forecasts of complex geophysical behavior. International efforts are seeking to integrate existing and emerging Earth observation systems into a global network, with enhanced data distribution, models, and decision support tools. Remote sensing is poised to fulfil the increasing need for a synoptic framework. However, the desire to improve the connection between scientific research and societal benefits has not been matched with resources and tools required to bridge the gap between research and applications. Natural hazards research and disaster management are a prime example. Here, we present a conceptual case for how interferometric synthetic aperture radar (InSAR) data could make a definitive contribution to understanding earthquake processes while simultaneously supporting policy- and decision-making. InSAR measurements derived from time series of radar observations from Earth orbit uniquely can provide geographically comprehensive maps of surface deformation. Observing system simulations are suggested to evaluate the potential contributions of a future system. Simulations would adopt an open seismic hazard analysis (SHA) framework, OpenSHA, recognizing the need for more physics-based modeling and computational infrastructure. SHA is employed by the HAZUS-MH earthquake module to estimate losses. InSAR measurements of strain accumulation would provide event magnitude recurrence bounds for probabilistic SHA, while coseismic InSAR measurements would add constraints on fault rupture models for deterministic approaches. Moreover, interferograms would be incorporated graphically as proxy seismic risk maps for planning and mitigation

Interferometric synthetic aperture radar (InSAR) techniques are used to calculate the volume of extrusion at Okmok volcano, Alaska by constructing precise digital elevation models (DEMs) that represent volcano topography before and after the 1997 eruption. The posteruption DEM is generated using airborne topographic synthetic aperture radar (TOPSAR) data where a three-dimensional affine transformation is used to account for the misalignments between different DEM patches. The preeruption DEM is produced using repeat-pass European Remote Sensing satellite data; multiple interferograms are combined to reduce errors due to atmospheric variations, and deformation rates are estimated independently and removed from the interferograms used for DEM generation. The extrusive flow volume associated with the 1997 eruption of Okmok volcano is 0.154/spl plusmn/0.025 km/sup 3/. The thickest portion is approximately 50 m, although field measurements of the flow margin's height do not exceed 20 m. The in situ measurements at lava edges are not representative of the total thickness, and precise DEM data are absolutely essential to calculate eruption volume based on lava thickness estimations. This study is an example that demonstrates how InSAR will play a significant role in studying volcanoes in remote areas.