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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Calibration of Two-dimensional Floodplain Modeling in the Atchafalaya River Basin Using SAR Interferometry

Two-dimensional (2D) satellite imagery has been increasingly employed to improve prediction of floodplain inundation models. However, most focus has been on validation of inundation extent, with little attention on the 2D spatial variations of water elevation and slope. The availability of high resolution Interferometric Synthetic Aperture Radar (InSAR) imagery offers unprecedented opportunity for quantitative validation of surface water heights and slopes derived from 2D hydrodynamic models. In this study, the LISFLOOD-ACC hydrodynamic model is applied to the central Atchafalaya River Basin, Louisiana, during high flows typical of spring floods in the Mississippi Delta region, for the purpose of demonstrating the utility of InSAR in coupled 1D/2D model calibration. Two calibration schemes focusing on Manning s roughness are compared. First, the model is calibrated in terms of water elevations at a single in situ gage during a 62 day simulation period from 1 April 2008 to 1 June 2008. Second, the model is calibrated in terms of water elevation changes calculated from ALOS PALSAR interferometry during 46 days of the image acquisition interval from 16 April 2008 to 1 June 2009. The best-fit models show that the mean absolute errors are 3.8 cm for a single in situ gage calibration and 5.7 cm/46 days for InSAR water level calibration. The optimum values of Manning's roughness coefficients are 0.024/0.10 for the channel/floodplain, respectively, using a single in situ gage, and 0.028/0.10 for channel/floodplain the using SAR. Based on the calibrated water elevation changes, daily storage changes within the size of approx 230 sq km of the model area are also calculated to be of the order of 107 cubic m/day during high water of the modeled period. This study demonstrates the feasibility of SAR interferometry to support 2D hydrodynamic model calibration and as a tool for improved understanding of complex floodplain hydrodynamics

Hahn Chul Jung↗
NASA NTRS2008

Deformation, Ecosystem Structure, and Dynamics of Ice (DESDynI)

The National Research Council Earth Science Decadal Survey, Earth Science Applications from Space, recommends that DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice), an integrated L-band InSAR and multibeam Lidar mission, launch in the 2010- 2013 timeframe. The mission will measure surface deformation for solid Earth and cryosphere objectives and vegetation structure for understanding the carbon cycle. InSAR has been used to study surface deformation of the solid Earth and cryosphere and more recently vegetation structure for estimates of biomass and ecosystem function. Lidar directly measures topography and vegetation structure and is used to estimate biomass and detect changes in surface elevation. The goal of DESDynI is to take advantage of the spatial continuity of InSAR and the precision and directness of Lidar. There are several issues related to the design of the DESDynI mission, including combining the two instruments into a single platform, optimizing the coverage and orbit for the two techniques, and carrying out the science modeling to define and maximize the scientific output of the mission.

Donnellan, Andrea↗
NASA NTRS2022

Using Sentinel-1 and GRACE Satellite Data to Monitor the Hydrological Variations Within the Tulare Basin, California

Subsidence induced by groundwater depletion is a grave problem in many regions around the world, leading to a permanent loss of groundwater storage within an aquifer and even producing structural damage at the Earth’s surface. California’s Tulare Basin is no exception, experiencing about a meter of subsidence between 2015 and 2020. However, understanding the relationship between changes in groundwater volumes and ground deformation has proven difficult. We employ surface displacement measurements from Interferometric Synthetic Aperture Radar (InSAR) and gravimetric estimates of terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE) satellite pair to characterize the hydrological dynamics within the Tulare basin. The removal of the long-term aquifer compaction from the InSAR time series reveals coherent short-term variations that correlate with hydrological features. For example, in the winter of 2018–2019 uplift is observed at the confluence of several rivers and streams that drain into the southeastern edge of the basin. These observations, combined with estimates of mass changes obtained from the orbiting GRACE satellites, form the basis for imaging the monthly spatial variations in water volumes. This approach facilitates the quick and effective synthesis of InSAR and gravimetric datasets and will aid efforts to improve our understanding and management of groundwater resources around the world.

Donald W. Vasco↗
NASA NTRSDate not supplied

Terrestrial Analogue Studies from ISRO’s Venus Mission Perspective: Polarimetric Radar Properties of Hawaiian Lava Flows

Detection of present and past volcanism on Venus is one of the major goals of the proposed ISRO’s Venus orbiter mission. The S-band, high-resolution (40 m/pixel) fully Polarimetric Synthetic Aperture Radar (PolSAR) instrument on this mission [1] may have the capabilities to detect volcanism within the mission lifetime using repeated PolSAR imagery, and possibly SAR Interferometry (InSAR, experimental mode). The global mapping efforts of Venus by Magellan mission has enabled comprehensive mapping of lava flows and indicated that Venus has an extensive history of volcanism, the ages of which are largely unknown (e.g. [2]). While Magellan radar emissivity data (e.g. [3, 4]) and Near Infrared emissivity data from VIRTIS [5] suggested the occurrence of recent episodes of volcanic activity (e.g. Maat Mons and Ganis Chasma), as well as the presence of stratigraphically young lava flows (e.g. Idunn Mons), measuring changes in radar backscatter amplitude alone to identify lava flows has many challenges. Although very large changes in the shape of the terrain can be observed in radar backscatter amplitude changes (e.g. [6]), smaller, or relatively flat lava flows are difficult to detect. Previous terrestrial studies suggest that PolSAR and InSAR techniques are very effective for mapping lava flows (e.g. [7-9]), and can be used when changes cannot be distinguished in radar backscatter images. We use the unvegetated lava flows on Hawaiʻi island as a terrestrial analogue to study Venus lava flows for the following reasons: (a) It is extensively studied at several wavelengths commonly used in remote sensing studies (including PolSAR and InSAR methods); and (b) it is a volcanically active area with new lava flows frequently covering older emplaced flows. To investigate the surface roughness, texture, and fine-grained mantling associated with Mauna Loa and Kilauea lava flows, we utilize C- and L-band PolSAR datasets obtained from RISAT-1A (EOS-4) and ALOS PALSAR missions respectively. In particular, we will use the quad-polarized backscatter and polarimetric parameters to characterize the texture of the terrestrial lava flows to understand whether the Venus crust is continuously disrupted during flow emplacement. While some previous studies (e.g. [10, 11]) suggested that surface roughness of most of the Venus flows is comparable to that of terrestrial pāhoehoe flows, other studies indicated that fractal dimensions of some large lava flows on Venus imply high eruption rates which favour the formation of a’a flows (e.g. [12]). We will also analyse the terrestrial flows for the presence/absence of pyroclastic mantling as radar-bright diffuse deposits near the summit regions of some coronae on Venus have been proposed to be young pyroclastics, and possible evidence of a renewed epoch of mantle volcanism that taps into deeper volatiles [13]. A recent study using EOS-4 RISAT-1 data of a part of fresh Mauna Loa lava flows (2022 eruption) emphasizes the ability of fully polarimetric SAR data to understand the diversity of physical properties (e.g. texture and morphology) associated with them (Sreejith et al. 2024); and we will apply similar methods to the PolSAR data obtained from ISRO’s Venus mission for our proposed objectives.

Sriram S Bhiravarasu↗
NASA NTRS1992

Theory and design of interferometric synthetic aperture radars

A derivation of the signal statistics, an optimal estimator of the interferometric phase, and the expression necessary to calculate the height-error budget are presented. These expressions are used to derive methods of optimizing the parameters of the interferometric synthetic aperture radar system (InSAR), and are then employed in a specific design example for a system to perform high-resolution global topographic mapping with a one-year mission lifetime, subject to current technological constraints. A Monte Carlo simulation of this InSAR system is performed to evaluate its performance for realistic topography. The results indicate that this system has the potential to satisfy the stringent accuracy and resolution requirements for geophysical use of global topographic data.

Rodriguez, E.↗
NASA NTRS1999

Radar Interferometry Studies of the Mass Balance of Polar Ice Sheets

The objectives of this work are to determine the current state of mass balance of the Greenland and Antarctic Ice Sheets. Our approach combines different techniques, which include satellite synthetic-aperture radar interferometry (InSAR), radar and laser altimetry, radar ice sounding, and finite-element modeling. In Greenland, we found that 3.5 times more ice flows out of the northern part of the Greenland Ice Sheet than previously accounted for. The discrepancy between current and past estimates is explained by extensive basal melting of the glacier floating sections in the proximity of the grounding line where the glacier detaches from its bed and becomes afloat in the ocean. The inferred basal melt rates are very large, which means that the glaciers are very sensitive to changes in ocean conditions. Currently, it appears that the northern Greenland glaciers discharge more ice than is being accumulated in the deep interior, and hence are thinning. Studies of temporal changes in grounding line position using InSAR confirm the state of retreat of northern glaciers and suggest that thinning is concentrated at the lower elevations. Ongoing work along the coast of East Greenland reveals an even larger mass deficit for eastern Greenland glaciers, with thinning affecting the deep interior of the ice sheet. In Antarctica, we found that glaciers flowing into a large ice shelf system, such as the Ronne Ice Shelf in the Weddell Sea, exhibit an ice discharge in remarkable agreement with mass accumulation in the interior, and the glacier grounding line positions do not migrate with time. Glaciers flowing rapidly into the Amudsen Sea, unrestrained by a major ice shelf, are in contrast discharging more ice than required to maintain a state of mass balance and are thinning quite rapidly near the coast. The grounding line of Pine Island glacier (see diagram) retreated 5 km in 4 years, which corresponds to a glacier thinning rate of 3.5 m/yr. Mass imbalance is even more negative on Thwaites Glacier. This sector of West Antarctica probably initiated its collapse decades or centuries ago, once the embaying ice shelves in front of them started to melt because of enhanced basal melting from warmer ocean waters. Additional information is contained in the original.

Rignot, Eric↗
NASA NTRS2002

Airborne Microwave Imaging of River Velocities

The objective of this project was to determine whether airborne microwave remote sensing systems can measure river surface currents with sufficient accuracy to make them prospective instruments with which to monitor river flow from space. The approach was to fly a coherent airborne microwave Doppler radar, developed by APL/UW, on a light airplane along several rivers in western Washington state over an extended period of time. The fundamental quantity obtained by this system to measure river currents is the mean offset of the Doppler spectrum. Since this scatter can be obtained from interferometric synthetic aperture radars (INSARs), which can be flown in space, this project provided a cost effective means for determining the suitability of spaceborne INSAR for measuring river flow.

Plant, William J.↗
NASA NTRS2003

Application of Satellite SAR Imagery in Mapping the Active Layer of Arctic Permafrost

A method of mapping the active layer of Arctic permafrost using a combination of conventional synthetic aperture radar (SAR) backscatter and more sophisticated interferometric SAR (INSAR) techniques is proposed. The proposed research is based on the sensitivity of radar backscatter to the freeze and thaw status of the surface soil, and the sensitivity of INSAR techniques to centimeter- to sub-centimeter-level surface differential deformation. The former capability of SAR is investigated for deriving the timing and duration of the thaw period for surface soil of the active layer over permafrost. The latter is investigated for the feasibility of quantitative measurement of frost heaving and thaw settlement of the active layer during the freezing and thawing processes. The resulting knowledge contributes to remote sensing mapping of the active layer dynamics and Arctic land surface hydrology.

Li, Shu-Sun↗
NASA NTRS2006

Impact of the Ionosphere on an L-band Space Based Radar

We have quantified the impact that the ionosphere would have on a L-band interferometric Synthetic Aperture Radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data. We conclude that, except for high latitude scintillation related effects, the ionosphere will not significantly impact the performance of an L-band InSAR mission in an appropriate orbit. We evaluated the strength of the ionospheric irregularities using GPS scintillation data collected at Fairbanks, Alaska and modeled the impact of these irregularities on azimuth resolution, azimuth displacement, peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR). Although we predict that less than 5% of auroral zone data would show scintillation related artifacts, certain sites imaged near the equinoxes could be effected up to 25% of the time because the frequency of occurrence of scintillation is a strong function of season and local time of day. Our examination of ionospheric artifacts observed in InSAR data has revealed that the artifacts occur primarily in the polar cap data, not auroral zone data as was previously thought.

Synthetic Aperture Radar (SAR) ionospheres↗
NASA NTRS2006

Rapid, Repeat-sample Monitoring of Crustal Deformations and Environmental Phenomena with the Uninhabited Aerial Vehicle Synthetic Aperture Radar

The Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) is a precision repeat-pass Interferometric Synthetic Aperture Radar (InSAR) mission being developed by the Jet Propulsion Laboratory and the Dryden Flight Research Center in support of NASA s Science Mission Directorate. UAVSAR's unique ability to fly a repeatable flight path, along with an electronically steerable array, allows interferometric data to be obtained with accuracies measured in millimeters. Deploying the radar on an airborne platform will also allow for radar images to be collected and compared with images from the same area taken hours or even years later - providing for long-term trending and near real-time notification of changes and deformations. UAVSAR s data processing algorithms will provide for near-real time data reduction providing disaster planning and response teams with highly accurate data to aid in the prediction of, and response to, natural phenomena. UAVSAR data can be applied to increasing our understanding of the processes behind solid earth, cryosphere, carbon cycle and other areas of interest in earth science. Technologies developed for UAVSAR may also be applicable to a future earth-orbiting InSAR mission and possibly for missions to the Moon or Mars. The UAVSAR is expected to fly on a Gulfstream III aircraft this winter, followed by a flight test program lasting until the second half of 2007. Following radar calibration and data reduction activities, the platform will be ready for science users in the summer of 2008.

Smith, Robert C.↗
NASA NTRS2008

L-Band Transmit/Receive Module for Phase-Stable Array Antennas

Interferometric synthetic aperture radar (InSAR) has been shown to provide very sensitive measurements of surface deformation and displacement on the order of 1 cm. Future systematic measurements of surface deformation will require this capability over very large areas (300 km) from space. To achieve these required accuracies, these spaceborne sensors must exhibit low temporal decorrelation and be temporally stable systems. An L-band (24-cmwavelength) InSAR instrument using an electronically steerable radar antenna is suited to meet these needs. In order to achieve the 1-cm displacement accuracy, the phased array antenna requires phase-stable transmit/receive (T/R) modules. The T/R module operates at L-band (1.24 GHz) and has less than 1- deg absolute phase stability and less than 0.1-dB absolute amplitude stability over temperature. The T/R module is also high power (30 W) and power efficient (60-percent overall efficiency). The design is currently implemented using discrete components and surface mount technology. The basic T/R module architecture is augmented with a calibration loop to compensate for temperature variations, component variations, and path loss variations as a function of beam settings. The calibration circuit consists of an amplitude and phase detector, and other control circuitry, to compare the measured gain and phase to a reference signal and uses this signal to control a precision analog phase shifter and analog attenuator. An architecture was developed to allow for the module to be bidirectional, to operate in both transmit and receive mode. The architecture also includes a power detector used to maintain a transmitter power output constant within 0.1 dB. The use of a simple, stable, low-cost, and high-accuracy gain and phase detector made by Analog Devices (AD8302), combined with a very-high efficiency T/R module, is novel. While a self-calibrating T/R module capability has been sought for years, a practical and cost-effective solution has never been demonstrated. By adding the calibration loop to an existing high-efficiency T/R module, there is a demonstrated order-of-magnitude improvement in the amplitude and phase stability.

Andricos, Constantine↗
NASA NTRS2011

UAVSAR Active Electronically Scanned Array

The Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) is a pod-based, L-band (1.26 GHz), repeatpass, interferometric, synthetic aperture radar (InSAR) used for Earth science applications. Repeat-pass interferometric radar measurements from an airborne platform require an antenna that can be steered to maintain the same angle with respect to the flight track over a wide range of aircraft yaw angles. In order to be able to collect repeat-pass InSAR data over a wide range of wind conditions, UAVSAR employs an active electronically scanned array (AESA). During data collection, the UAVSAR flight software continuously reads the aircraft attitude state measured by the Embedded GPS/INS system (EGI) and electronically steers the beam so that it remains perpendicular to the flight track throughout the data collection

Sadowy, Gregory, A.↗
NASA NTRS2010

UAVSAR Active Electronically-Scanned Array

The Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) L-band (1.2-1.3 GHz) repeat pass, interferometric synthetic aperture radar (InSAR) used for Earth science applications. Using complex radar images collected during separate passes on time scales of hours to years, changes in surface topography can be measured. The repeat-pass InSAR technique requires that the radar look angle be approximately the same on successive passes. Due to variations in aircraft attitude between passes, antenna beam steering is required to replicate the radar look angle. This paper describes an active, electronically steered array (AESA) that provides beam steering capability in the antenna azimuth plane. The array contains 24 transmit/receive modules generating 2800 W of radiated power and is capable of pulse-to-pulse beam steering and polarization agility. Designed for high reliability as well as serviceability, all array electronics are contained in single 178cm x 62cm x 12 cm air-cooled panel suitable for operation up 60,000 ft altitude.

Sadowy, Gregory↗
NASA NTRS2010

Measurement and Mitigation of the Ionosphere in L-Band Interferometric SAR Data

Satellite-based repeat-pass Interferometric Synthetic Aperture Radar (InSAR) provides a synoptic high spatial resolution perspective of Earth's changing surface, permitting one to view large areas quickly and efficiently. By measuring relative phase change from one observation to the next on a pixel-by-pixel basis, maps of deformation and change can be derived. Variability of the atmosphere and the ionosphere leads to phase/time delays that are present in the data that can mask many of the subtle deformation signatures of interest, so methods for mitigation of these effects are important. Many of these effects have been observed in existing ALOS PALSAR data, and studies are underway to characterize and mitigate the ionosphere using these data. Since the ionosphere is a dispersive medium, it is possible in principle distinguish the ionospheric signatures from the non-dispersive effects of deformation and the atmosphere. In this paper, we describe a method for mapping the ionosphere in InSAR data based on a multi-frequency split-spectrum processing technique.

Rosen, Paul A.↗
NASA NTRS2018

Vegetation Height Estimate in Rice Fields Using Single Polarization TanDEM-X Science Phase Data

This study presents the retrieval of rice paddy height using single polarization (single-pol) interferometric SAR (InSAR) data by means of model-based height inversion without an external DEM. A total of eight TanDEM-X (TDX) scenes were used and the TDX images were; acquired using a large cross-track baseline configuration during the TDX Science Phase (June–August 2015). A single-pol inversion approach for a flooded rice field is proposed and evaluated over the Buan test site in South Korea. A novel approach is adopted for the estimation of the ground (i.e., water level) interferometric phase within a flooded rice paddy from TDX data acquired during a period of early rice growth. It is consequently possible to apply the model-based inversion algorithm to the single-pol InSAR data. Rice height maps during the rice growth cycle presented and validated by field measurements. The results demonstrated the high performance of the inversion with a correlation coefficient of 0.78 and an RMSE of 0.10 m. The proposed methodology will be useful to monitor rice plants and to predict a gross rice yield, along with dual and fully polarimetric interferometric SAR data.

Lee, Seung-Kuk↗
NASA NTRS2017

Large-scale fine-resolution products of forest disturbance using new approaches from spaceborne SAT interferometry

Spaceborne SAR interferometry (InSAR) has the potential ofdetecting forest change on a global scale with fine (meter-level)spatial resolution as well as on a monthly/weekly basis under allweather conditions. This is significant to characterize the land usechange and its impact on climate change. In this paper, bothsingle-pass and repeat-pass SAR interferometry from spacebornesensors are combined in order to detect and quantify (withNormalized RMSE 30%) forest disturbance at a large scale(dozens of kilometers) however with a fine spatial resolution (<1 hectare) based on two newly developed approaches. The singlepassInSAR approach is not only able to detect forest disturbancebut also capable of characterizing meter (or even sub-meter)level change of forest phase-center (mean) height due to forestgrowth and/or degradation. The methodology described in thispaper can be considered as complimentary tools and thus can becombined with the existing PolInSAR technique (that has beenwidely used for retrieving forest height from single-pass SARinterferometry). These methods are extensively validated with thepast and current spaceborne single-pass and repeat-pass InSARmissions (i.e. JAXA’s ALOS-1, ALOS-2 and DLR’s TanDEM-X)over subtropical forests in Australia as well as tropical forestsin Brazil. Such techniques also serve as observing prototypes forthe fusion of the future spaceborne InSAR missions (such asNASA-ISRO’s NISAR and DLR’s TanDEM-L).

Schmidt, Michael↗
NASA NTRS2022

Measurement of Surface Deformation Related to the December 2018 Mt. Etna Eruption Using Time-Series Interferometry and Magma Modeling for Hazard Zone Mapping

Mount Etna has erupted several times since it was first formed. Recently, Mount Etna began erupting again over 24–27 December 2018. Because it erupts frequently, Mount Etna should be observed on a frequent basis. From June 2018 to October 2019, 34 and 56 interferometric synthetic aperture radar (InSAR) images were acquired from the ascending and descending tracks of the Sentinel-1 satellite, respectively. We employed the Stanford Method for Persistent Scatterers (StaMPS) and a refined small baseline subset (SBAS) InSAR method to produce a surface deformation time-series map. In the time-series analysis, the phase signal remained unaltered with time. The Okada model was then applied to the result to generate a modeled interferogram, and the Q-LavHA program was run to generate a lava flow prediction model. A direct comparison of the results showed that Persistent Scatterers Interferometry (PSI)-StaMPS and the refined SBAS technique were comparable in terms of the displacement pattern, with slightly different velocity values obtained for individual points. In particular, a velocity range of −25 to 21 cm/yr was obtained from PSI-StaMPS, whereas a range of −30 to 25 cm/yr was obtained from the refined SBAS method. Upon computation of the vertical and east-west displacement components based on ascending and descending track data using both methods, deformation velocities of 51.5 and 52.5 cm/yr in the westerly direction on the western flank of Mount Etna were obtained from PSI-StaMPS and the refined SBAS method, respectively, whereas on the eastern flank, deformation toward the east was estimated to occur at a velocity of 50.1 or 54.2 cm/yr, respectively. PSIStaMPS estimated a vertical deformation velocity of −5.3 to 18.3 cm/yr, whereas the refined SBAS method produced a velocity range of approximately −7 to 19 cm/yr. The interferogram obtained via Okada modeling showed two fault sources in the 2018 Mount Etna eruption and a total volume change of approximately 12.39 × 10 6 m 3 . From the modeling results, a lava flow prediction model was generated using the Q-LavHA program. The approaches described in this study can be used by government officials, authorities, and other decision-makers to monitor and assess the risk of volcanic activity in the region.

Suci Ramayanti↗
NASA NTRS1994

The Accuracy of Airborne Interferometric SAR's

We extend the analysis of the accuracy of Interferometric SAR (InSAR) for topographic mapping to cover a variety of topics which have not been previously examined in the literature.

SAR interferometry interferometric SAR's InSAR top↗