Howard A. Zebker's research while affiliated with Stanford University and other places
What is this page?
This page lists the scientific contributions of an author, who either does not have a ResearchGate profile, or has not yet added these contributions to their profile.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
Publications (360)
Permafrost-affected ecosystems of the Arctic-boreal zone in northwestern North America are undergoing profound transformation as a result of rapid climate change. NASA’s Arctic Boreal Vulnerability Experiment (ABoVE) is investigating characteristics that make these ecosystems vulnerable or resilient to this change. ABoVE employs airborne synthetic...
p>Soil moisture can vary spatially at the scale of agricultural fields (~10 -100 m), which is generally too fine to resolve using passive radiometric methods. Active radar provides an opportunity for finer resolution measurements; in particular, the interferometric synthetic aperture radar (InSAR) closure phase parameter is sensitive to changing so...
p>Soil moisture can vary spatially at the scale of agricultural fields (~10 -100 m), which is generally too fine to resolve using passive radiometric methods. Active radar provides an opportunity for finer resolution measurements; in particular, the interferometric synthetic aperture radar (InSAR) closure phase parameter is sensitive to changing so...
Linear frequency-modulated (chirp) transmits have been used successfully in the past to increase penetration depth of ultrasound signals in tissue and to improve the signal-to-noise ratio (SNR) in the resulting ultrasound images. However, beamforming chirp signals using delay-and-sum (DAS) can be slow on systems without a GPU. We propose using the...
Seasonal subsidence induced by ground ice melt can be measured by interferometric synthetic aperture radar (InSAR) techniques to infer active layer thickness (ALT) in permafrost regions. The magnitude of subsidence depends on both how deep the soil thawed and how much ice/water content existed in the active layer soil. To provide the later, P‐band...
Algorithmic changes that increase beamforming speed have become increasingly relevant to processing synthetic aperture (SA) ultrasound data. In particular, beamforming SA data in a spatio-temporal frequency domain using F-k (Stolt) migration has been shown to reduce beamforming time by up to two orders of magnitude compared to conventional delay-an...
The study of volcano deformation has grown significantly through they year 2020 since the development of interferometric synthetic aperture radar (InSAR) in the 1990s. This relatively new data source, which provides evidence of changes in subsurface magma storage and pressure without the need for ground-based equipment, has matured during the past...
The Delaware Basin, Texas is currently a hot‐spot of induced seismicity and ground deformation due to fluid extraction and injection associated with horizontal drilling techniques; however, the driving mechanism behind the seismicity and deformation remains under debate. Using vertical and east‐west horizontal surface deformation measurements deriv...
Persistent scatterer interferometric synthetic aperture radar (PS-InSAR) is a remote sensing technique that maps patterns of crustal deformation with large spatial coverage and fine resolution. By identifying a network of reliable points called persistent scatterers (PS) that are used to improve estimates of decorrelation and atmospheric noise, PS-...
Abstract Interferometric synthetic aperture radar (InSAR) has been used to quantify a range of surface and near surface physical properties in permafrost landscapes. Most previous InSAR studies have utilized spaceborne InSAR platforms, but InSAR datasets over permafrost landscapes collected from airborne platforms have been steadily growing in rece...
In permafrost regions, active layer thickness (ALT) observations measure the effects of climate change and predict hydrologic and elemental cycling. Often, ALT is measured through direct ground-based measurements. Recently, synthetic aperture radar (SAR) measurements from airborne platforms have emerged as a method for observing seasonal thaw subsi...
Active layer thickness (ALT) is a critical metric for monitoring permafrost. How soil moisture influences ALT depends on two competing hypotheses: (a) increased soil moisture increases the latent heat of fusion for thaw, resulting in shallower active layers, and (b) increased soil moisture increases soil thermal conductivity, resulting in deeper ac...
Geodynamics, like Earth’s plate tectonics (PT), governs long-term planetary evolution and habitability. Beyond Earth, only Venus may have key elements of PT: subduction (the 1st step in PT) and continents. Revealing Venus’ geodynamics is key to understanding how PT began on Earth, and how to predict the geodynamic evolution of other rocky bodies.
Atmospheric propagational phase variations are the dominant source of error for InSAR (interferometric synthetic aperture radar) time series analysis, generally exceeding uncertainties from poor signal to noise ratio or signal correlation. The spatial properties of these errors have been well studied, but, to date, their temporal dependence and cor...
The accuracy of geophysical parameter estimation made with interferometric synthetic aperture radar (InSAR) time-series techniques can be improved with rapidly increasing available data volumes and with the development of noise covariance matrices applicable to joint analysis of networks of interferograms. In this article, we present a new decorrel...
Here we present a physics-based decorrelation phase covariance model and discuss its role in effective decorrelation noise reduction in interferogram stacks. We test our model in both Cascadia - a rapidly decorrelating region, and Death Valley - a slowly decorrelating region, with observations collected by Sentinel-1. We find that in Cascadia, incl...
Wide-swath radar imaging requires that the time interval to collect each radar pulse echo is large and can often exceed the interpulse period. As it is difficult to both transmit and receive from the same antenna simultaneously, there will be "blind ranges" when the receive and transmit times overlap. This leads to gaps in the radar echo and thus d...
Persistent scatterer (PS) techniques are a set of important time-series tools for interferometric synthetic aperture radar (InSAR) that enable deformation analysis in highly decorrelated terrain. Detailed knowledge of the statistics of persistent scatterers in InSAR images is critical for the design of better techniques that will enable both the ex...
No PDF available
ABSTRACT
Frequency domain beamforming methods, such as Stolt migration, yield efficient and fast processing of ultrasound data. Stolt migration, by migrating the individual element data in a 2-D frequency domain, improves processing speed by up to two orders of magnitude compared to conventional delay-and-sum (DAS) beamforming. How...
We propose a novel method for quantifying and correcting phase errors in interferometric synthetic aperture radar (InSAR) data associated with signal decorrelation. This proposed method relates the observed phase nonclosure (referred to as the closure phase) of triplet combinations of any three individual SAR scenes to the decorrelative phase signa...
Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the p...
![A schematic of fire response in permafrost [15]. (1) Fire removes...](publication/329765976/figure/fig3/AS:1132450797359108@1647008718253/A-schematic-of-fire-response-in-permafrost-15-1-Fire-removes-vegetation-and-part-of_Q320.jpg)
The Yukon–Kuskokwim (YK) Delta is a region of discontinuous permafrost in the subarctic of southwestern Alaska. Many wildfires have occurred in the YK Delta between 1971–2015, impacting vegetation cover, surface soil moisture, and the active layer. Herein, we demonstrate that the remotely sensed active layer thickness (ReSALT) algorithm can resolve...
Persistent scatterer interferometry is a powerful time-series technique which uses the most temporally stable pixels (denoted persistent scatterers, or PS), to enable measurement of deformation in decorrelation-prone data sets. System performance depends heavily on the density of identified PS, which is influenced by two factors: image resolution a...
Interferometric Synthetic Aperture Radar (InSAR) data from multiple satellite missions were combined to study the temporal and spatial variability of head and storage properties in a confined aquifer system on a decadal time scale. The area of study was a 4,500 km2 agricultural basin in the San Luis Valley (SLV), Colorado. We had available previous...
Interferometric synthetic aperture radar (InSAR) methods provide high-resolution maps of surface deformation applicable to many scientific, engineering, and management studies. Despite its utility, the specialized skills and computer resources required for InSAR analysis remain as barriers for truly widespread use of the technique. Reduction of rad...
We present a new interferometric synthetic aperture radar processing approach that removes topography–dependent phase from single-look complex (SLC) radar images, making interferogram formation more efficient. We first adopt motion compensation techniques to resample SLC images with respect to an ideal reference orbit and then separate the residual...
River systems reveal planetary tectonics
Earth, Mars, and Titan have all hosted rivers at some point in their histories. Rivers erode the landscape, leaving behind signatures that depend on whether the surface topography was in place before, during, or after the period of liquid flow. Black et al. developed two metrics to measure how well river cha...
In the San Joaquin Valley, California, recent droughts starting in 2007 have increased the pumping of groundwater, leading to widespread subsidence. In the southern portion of the San Joaquin Valley, vertical subsidence as high as 85 cm has been observed between June 2007 and December 2010 using Interferometric Synthetic Aperture Radar (InSAR). Thi...
Acquisition of a series of spaceborne interferometric synthetic aperture radar (InSAR) scenes permits imaging of a surface in four dimensions, that is the several mm-level temporal evolution of the three dimensional structure of the ground surface. The spatio-temporal variations of a surface measured at mm accuracies not only reveals activity on th...
Interferometric Synthetic Aperture Radar (InSAR), a remote sensing technique for measuring centimeter-level surface deformation, is used to estimate hydraulic head in the confined aquifer of the San Luis Valley (SLV), Colorado. Reconstructing head measurements from InSAR in agricultural regions can be difficult, as InSAR phase data are often decorr...
Active-layer thickness (ALT) is an important parameter for studying surface energy balance, ecosystems, and hydrologic processes in cold regions. We measured ALT along 10 routes with lengths ranging from 0.7 to 6.9 km located on the Alaska North Slope near Toolik Lake and the Happy Valley airstrip (between 68.475° and 69.150°N, and -149.512° and -1...
The region of Titan’s hydrocarbon sea, Ligeia Mare, where transient bright features were previously discovered, was anomalously bright in the first of two more recent Cassini RADAR observations but not the second. Another transient bright feature in a different region of Ligeia Mare was also discovered in the first of the new observations. Here we...
Interferometric synthetic aperture radar (InSAR) is a radar remote sensing technique for measuring surface deformation to millimeter-level accuracy at meter-scale resolution. Obtaining accurate deformation measurements in agricultural regions is difficult because the signal is often decorrelated due to vegetation growth. We present here a new algor...
This data set includes estimates of permafrost Active Layer Thickness (ALT; cm), and calculated uncertainties, derived using a ground-penetrating radar (GPR) system in the field in August 2014 near Toolik Lake and Happy Valley on the North Slope of Alaska. GPR measurements were taken along 10 transects of varying length (approx. 1 to 7 km). Traditi...
Thawing of ice-rich permafrost followed by surface subsidence results in irregular, depressed landforms known as thermokarst. Many remote sensing studies have identified thermokarst landforms and mapped their changes. However, the intrinsic dynamic thermokarst process of surface subsidence remains a challenge to quantify and is seldom examined usin...
Active layer thickness (ALT) is a critical parameter for monitoring the status of permafrost that is typically measured at specific locations using probing, in situ temperature sensors, or other ground-based observations. Here we evaluated the Remotely Sensed Active Layer Thickness (ReSALT) product that uses the Interferometric Synthetic Aperture R...
We present here an Small BAseline Subset (SBAS) algorithm to extract both transient and secular ground deformations on the order of millimeters in the presence of tropospheric noise on the order of centimeters, when the transient is of short duration and known time, and the background deformation is smooth in time. We applied this algorithm to stud...
Groundwater exploitation is a major cause of land subsidence, which in coastal areas poses a flood inundation hazard that is compounded by the threat of sea-level rise (SLR). In the lower Mekong Delta, most of which lies <2 m above sea level, over-exploitation is inducing widespread hydraulic head (i.e., groundwater level) declines. The average rat...
Interferometric synthetic aperture radar (InSAR) is a remote sensing method that maps relative ground surface deformation. In previous work, we investigated the relationship between deformation and hydraulic head change in the San Luis Valley, CO, USA, and determined that we must quantify the spatially variable uncertainty in the InSAR deformation...
Wildfire is a major disturbance in the Arctic tundra and boreal forests, having a significant impact on soil hydrology, carbon cycling, and permafrost dynamics. This study explores the use of the microwave Interferometric Synthetic Aperture Radar (InSAR) technique to map and quantify ground surface subsidence caused by the Anaktuvuk River fire on t...
The sustainability of the confined aquifer system in the San Luis Valley, Colorado is of utmost importance to the valley's agricultural economy. There is a dearth of hydraulic head measurements in the confined aquifer to which the current groundwater flow model can be calibrated. Here we investigate the extent to which spatially and temporally dens...
Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on Arctic
tundra lowland. Their dynamic states are seldom
investigated, despite their importance for landscape stability,
hydrology, nutrient fluxes, and carbon cycling.
Here we report results based on high-resolution
Interferometric Synthetic Aperture Radar (InSAR) measurements using...
[1] We construct the depth profile—the bathymetry—of Titan's large sea Ligeia Mare, from Cassini RADAR data collected during the 23 May 2013 (T91) nadir-looking altimetry fly-by. We find the greatest depth to be about 160 m and a seabed slope that is gentler towards the northern shore, consistent with previously imaged shoreline morphologies. Low r...
radar observations of the surface of Ligeia Mare collected during the 23 May 2013 (T91) Cassini flyby show that it is extremely smooth, likely to be mostly methane in composition, and exhibits no surface wave activity. The radar parameters were tuned for nadir-looking geometry of liquid surfaces, using experience from Cassini's only comparable obse...
Interferometric synthetic aperture radar (InSAR) is a valuable tool for the study of geophysical phenomena such as crustal deformation, ice motion and structure, and vegetation canopy depths, but it is adversely affected by uncharacterized inhomogeneities in ionospheric propagation delay. Ionospheric disturbances distort both InSAR phase and correl...
Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on
arctic tundra lowlands, but their present-day dynamic states are seldom
investigated. Here we report results based on high-resolution
Interferometric Synthetic Aperture Radar (InSAR) measurements using
space-borne data for a study area located near Prudhoe Bay, Alaska where
we focu...
Phased arrays can be formed by separating elements in time as well as space. In this configuration, surface or target velocities may be observed, rather than the radar backscatter at each position in an image or area. We have used time series data acquisitions using imaging radars to map and measure mm-scale velocities at m-scale resolutions over a...
Deep aquifers in South and Southeast Asia are increasingly exploited as presumed sources of pathogen- and arsenic-free water, although little is known of the processes that may compromise their long-term viability. We analyze a large area (>1,000 km(2)) of the Mekong Delta, Vietnam, in which arsenic is found pervasively in deep, Pliocene-Miocene-ag...
Despite the abundance of rock glaciers in the Sierra Nevada of California, USA, few efforts have been made to measure their surface flow. Here we use the interferometric synthetic aperture radar (InSAR) technique to compile a benchmark inventory describing the kinematic state of 59 active rock glaciers in this region. In the late summer of 2007, th...
Interferometric synthetic aperture radar (InSAR) is an effective tool for measuring temporal changes in the Earth's surface and producing high accuracy, wide coverage images of crustal deformation fields. Decorrelation due to spatial and temporal baseline is a major limiting factor in estimating the deformation signal, but may be ameliorated by usi...