Satellite radar altimetry signals from glaciers and ice sheets represent a combination of scattering from ice-surface topography and the snow and firn volume. Changes in surface topography through time, even at sub-footprint scales, will change the interaction between the wavefront and surface, impacting the shape of the return waveform. Here, we describe a new facet-scattering model that uses arbitrary topographic inputs and can be used for testing hypotheses about ice-sheet surface change in the historical, three-decade-long pulse-limited radar altimetry record. We demonstrate the scattering model on both synthetic and real topographies, showing how off-nadir features and a deforming surface impact the returned waveform. We anticipate this simulator can be used to quantify sub-footprint surface change and the evolution of dynamic ice-sheet processes on rugged, high velocity ice streams and outlet glaciers in the decades before our modern, continuous laser altimetry and high-resolution stereophotogrammetric records capable of observing such changes began.

This investigation quantifies the dynamic geometries of Antarctic active subglacial lakes by leveraging satellite altimetry data and an image processing algorithm. Using high-resolution altimetry satellite data from 2010 to 2023 and a computer-vision-based contour finding algorithm to delineate contours of ice-surface, height-change anomalies indicative of lake activity, we generated evolving outlines of 131 previously identified Antarctic active subglacial lakes. Evolving outlines provided a novel time series of wetted area to quantify changes in the bed substrate available for geochemical and microbial processes. Evolving outlines revealed previously unseen transitory lake lobes that refine preexisting time series of height change and ice-volume displacement, from which we can infer subglacial water flux. The findings underscore the value of employing evolving subglacial lake outlines to record active subglacial lake geometric changes across Antarctica and suggest broader glaciological applications, such as the identification of new active subglacial lake candidates.

We describe a novel algorithm to accurately characterize burned area and generate a time series of active burned areal extent during an actively burning wildfire based upon changes in the second-order statistics of interferometric synthetic aperture radar (InSAR) phase measurements. We present this algorithm and demonstrate its use with Sentinel-1 InSAR data collected during the 2020 Cameron Peak Fire, which burned along the Front Range in Colorado, USA. We show that this algorithm can successfully discriminate recently burned and actively burning areas within a fire zone from unburned areas at high spatial resolution (~10s of m). We further introduce a method for estimating a time series of burned areal extent from interferometric observations of burned area-change via a singular value decomposition (SVD) inversion. We compare the results of our algorithm with fire progression maps from the National Interagency Fire Center (NIFC) and find good agreement on total burned area (IoU=0.65) and excellent agreement on burned area extent (mIoU=0.91).

Rising air temperatures in the Arctic threaten the stability of permafrost and will result in an increase in the severity and frequency of tundra wildfires. Wildfires can dramatically alter local hydrology, vegetation, topography, and permafrost physical properties and processes, including emission of greenhouse gases. Despite this, permafrost-wildfire interactions remain a poorly understood component of the global carbon cycle. Here, we use interferometric synthetic aperture radar (InSAR) observations to quantify the annual subsidence and deformation rates of seasonally thawing/freezing permafrost across a study region characterized by unburned tundra and tundra recently burned from a series of wildfires in 2015. We propose a method to estimate and remove the component of the interferometric phase measurement due to time-varying soil moisture. We resolve elevated seasonal deformation rates over recently burned tundra in comparison to unburned tundra. Although burned deformation rates tend to revert to unburned values within a decade post-fire, surface soil moisture values within fire scars remain elevated. Lastly, we comment on the unique opportunities that the upcoming NISAR mission will enable to better study permafrost-wildfire interactions.

Antarctica’s ice shelves play a critical role in modulating ice loss to the ocean by buttressing grounded ice upstream. With the potential to impact ice-shelf stability, persistent polynyas (open-water areas surrounded by sea ice that occur across multiple years at the same location) at the edge of many ice-shelf fronts are maintained by winds and/or ocean heat and are locations of strong ice–ocean–atmosphere interactions. However, in situ observations of polynyas are sparse due to the logistical constraints of collecting Antarctic field measurements. Here, we used wintertime (May–August) temperature and salinity observations derived from seal-borne instruments deployed in 2014, 2019, and 2020, in conjunction with thermal imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Landsat 8 Thermal Infrared Sensor (TIRS) to investigate spatial, temporal, and thermal structural variability of polynyas near Pine Island Glacier (PIG). Across the three winters considered, there were 176 anomalously warm ($3\sigma $from background) seal dives near the PIG ice front, including 26 dives that coincided with MODIS images with minimal cloud cover that also showed a warm surface temperature anomaly. These warm surface temperatures correlated with ocean temperatures down to 150 m depth or deeper, depending on the year, suggesting that MODIS-derived surface thermal anomalies can be used for monitoring polynya presence and structure during polar night. The finer spatial resolution (100 m) of TIRS wintertime thermal imagery captures more detailed thermal structural variability within these polynyas, which may provide year-round insight into subice-shelf processes if this dataset is collected operationally.

Radar tomography of glaciers promises to improve imaging and estimates of subsurface ice-sheet structures and properties, including temperature distributions, basal materials, ice fabric, and englacial water content. However, bistatic radar data with long (i.e., larger than the ice thickness) walk-away surveys are required to constrain high-fidelity tomographic inversions. These long-offset data have proven difficult to collect due to the hardware complexity of existing synchronization techniques. Therefore, we remove the hardware complexity required for real-time synchronization by synchronizing in postprocessing. Our technique transforms an Autonomous phase-sensitive Radio Echo Sounder (ApRES) system and a software-defined radio receiver into a coherent bistatic radar capable of recovering basal echoes at long offsets. We validated our system at Whillans Ice Stream, West Antarctica, with a walk-away survey up to 1300 m (797 m thick) and at Store Glacier, Greenland, up to 1450 m (1028 m thick). At both field sites, we measured the basal echo at angles beyond the point of total internal reflection (TIR), whose previous literature had set as a hard physical limit. We support our experimental results with high-frequency structure simulation, which shows that ground-based radar systems capture evanescent waves and are not hindered by TIR. Our analysis and experiments demonstrate a system capable of executing wide-angle bistatic radar surveys for improved geometric and radiometric resolution of inversions for englacial and subglacial properties.

The full velocity structure of glacial ice is critical to understanding glacier dynamics, but such measurements are rare. We propose a novel data processing method to resolve the horizontal and vertical velocity profile of an ice column using existing autonomous phase-sensitive radio echo sounder (ApRES) systems. The availability and relatively low cost of these systems can enable more widespread measurement of the 3D velocity structure of ice, with important implications for observational constraints on ice dynamics and basal drag.

We develop and test a bistatic radar system and processing chain that recovers weak echoes at large antenna separations, which is a necessary step towards high precision temperature inversions. Traditional ice penetrating radars have limited capacity to infer temperature distributions because monostatic measurements do not provide sufficient information to resolve the depth-dependent ice temperature profile. Bistatic radar introduces quasi-independent measurements that can address this challenge, but existing systems are unable to attain the large antenna separations necessary to resolve the small temperature gradients important to glaciological processes. Existing bistatic systems are either limited in antenna separation by losses in synchronization cables or by poor signal-to-noise-ratio (SNR) for unsynchronized systems. We address this challenge through coherent summation of phase re-aligned signals to recover the basal and internal layer reflections at large antenna separations without requiring hardware synchronization. The system consists of an Autonomous Phase-sensitive Radio Echo Sounder (ApRES) as the transmitter and a Software Defined Radio (SDR) as the receiver. We assess the system's capacity to achieve high SNRs and large offsets at Whillans Ice Stream, West Antarctica, with up to a 1.3 km antenna separation. This experiment charts a course for even larger antenna separations to resolve small temperature signals with high fidelity.

The Geoscience Laser Altimeter System (GLAS) aboard the National Aeronautics and Space Administration's Ice, Cloud, and land Elevation Satellite (ICESat) collected data from early 2003 to late 2009 with the specific goal of measuring ice-surface elevation changes. While the precision of GLAS instrumentation has been studied over its intended target (ice), its accuracy has only been robustly estimated using independent (terrestrial nonlaser) methods over salt flats. Here, we perform repeat high-precision Global Positioning System (GPS) surveys under four passes of ICESat track 0412 (campaigns L3I, L3J, L2D, and L2E) to compare directly GLAS elevation data footprints to a coincident GPS ground truth near Summit, Greenland. Analysis and comparison of GLAS data with GPS data show a campaign-dependent elevation bias ranging from -0.112 ±0.030 m (L3J) to 0.121 ± 0.071 m (L2E). Although uncorrected reflectance values and field observations both indicate that forward scattering of the laser signal through the atmosphere accounts for the anomalously negative L3J bias, the biases of all campaigns studied are within the instrument's goal accuracy of ±0.15 m. However, our analysis shows a campaign dependence in the bias, which may propagate through estimates of mass balance. The error introduced from intercampaign biases illustrates the importance of long-term independent validation experiments of satellite altimetry data over ice sheets.