Ala Khazendar

Tropospheric delays can be the leading source of error in spaceborne interferometric synthetic aperture radar (InSAR) measurements. Here, we find that the non-uniform troposphere delay features are dependent on the squint angles used for repeat-pass InSAR data acquisitions. Large squint angles cause large along-track shifts in these non-uniform troposphere delay features. By processing the airborne L-band uninhabited aerial vehicle SAR (UAVSAR) data with three different squint angles, we were able to see various non-uniform delay structures of different sizes with varying delays of up to a few centimeters across the observed interferograms. We were also able to estimate the altitude of the effective troposphere delay layers. The understanding of the squint-dependent troposphere delay can help us separate the surface deformation component from the atmosphere delay component in the InSAR phase measurements. A number of methods are proposed for this separation. We used the UAVSAR data and simulated surface deformations to verify these methods. This technique can also be used for spaceborne cases.

Seasonal phytoplankton blooms in Greenland’s coastal waters form the base of marine food webs and contribute to oceanic carbon uptake. In Qeqertarsuup Tunua, West Greenland, a secondary summertime bloom follows the Arctic spring bloom, enhancing annual primary productivity. Emerging evidence links this summer bloom to subglacial discharge from Sermeq Kujalleq, the most active glacier on the Greenland Ice Sheet. This discharge drives localized upwelling that may alleviate nutrient limitation in surface waters, yet this mechanism remains poorly quantified. Here, we employ a high-resolution biogeochemical model nested within a global state estimate to assess how discharge-driven upwelling influences primary productivity and carbon fluxes. We find that upwelling increases summer productivity by 15–40% in Qeqertarsuup Tunua, yet annual carbon dioxide uptake rises by only ~3% due to reduced solubility in plume-upwelled waters. These findings suggest that intensifying ice sheet melt may alter Greenland’s coastal productivity and carbon cycling under future climate scenarios.

In recent decades, the Greenland ice sheet has been losing ice and contributing substantially to global sea level rise. Approximately half of this recent loss is due to glacier acceleration, increasing the calving of icebergs into the ocean. This process has been linked with increased ocean heat content on the continental shelf, yet the pathways delivering this heat into Greenland's fjords and its interactions with fjord‐scale processes modulating glacier ice loss are still unclear. In this study, we use a series of numerical ocean model configurations to examine feedbacks between ocean circulation, subglacial discharge, submarine glacier melt, and ice mélange in Kangerlussuaq Fjord—a major fjord system where Greenland's third‐largest glacier terminates. We find that subglacial discharge is a major control on ocean properties, increasing the up‐fjord advection of deep warm water more than 10‐fold over fjords without discharge and modulating ocean temperature on the continental shelf near the fjord mouth. Further, discharge‐driven upwelling increases ice mélange melt 3‐fold, revealing that subglacial discharge is an important control on mélange melt, particularly in the summer when submarine glacier melt and subsequent glacier retreat is highest. These results suggest that subglacial plume activity contributes to the strong correlation between mélange thickness and retreat noted in previous studies and may contribute to extensive future retreat at Kangerlussuaq Glacier.

In response to the 2017 Decadal Survey, NASA conducted a five‐year study on the Surface Deformation and Change (SDC) designated observable to study potential mission concepts. As part of the SDC mission study, the Commercial Synthetic Aperture Radar (ComSAR) subgroup was tasked with evaluating the current landscape of the SAR and interferometric SAR (InSAR) industry to assess whether NASA could leverage commercial smallsat products to meet the needs of the SDC science mission. The assessment found that although the commercial SAR industry is growing rapidly, off‐the‐shelf products can currently only make a small—albeit distinct—contribution to SDC mission goals. This gap is due to different design goals between current commercial systems (which prioritize targeted high‐resolution, non‐interferometric observations at short wavelengths with a daily or faster revisit) and a future SDC architecture (which focuses on broad, moderate‐resolution, and interferometric observations at long wavelengths). Even by 2030, planned commercial constellations are expected to only cover 65% of the area needed to match NISAR coverage. Still, high‐resolution and rapid‐repeat capabilities can augment scientific findings from a future SDC mission, as demonstrated by recent contributions from commercial data to applied sciences, cryosphere, and volcanology. Future innovations on smallsat constellation concepts could further contribute to SDC science and applications. Although current constellation designs are not fully able to satisfy desired SDC science capabilities, initial positive feedback to a request for information indicates a potential future path for a customized SDC commercial architecture; more studies will be needed to determine the feasibility of these approaches.

In recent decades, the Greenland ice sheet has been losing mass through glacier retreat and ice flow acceleration. This mass loss is linked with variations in submarine melt, yet existing ocean models are either coarse global simulations focused on decadal‐scale variability or fine‐scale simulations for process‐based investigations. Here, we unite these scales with a framework to downscale from a global state estimate (15 km) into a regional model (3 km) that resolves circulation on the continental shelf. We further downscale into a fjord‐scale model (500 m) that resolves circulation inside fjords and quantifies melt. We demonstrate this approach in Scoresby Sund, East Greenland, and find that interannual variations in submarine melt at Daugaard‐Jensen glacier induced by ocean temperature variability are consistent with the decadal changes in glacier ice dynamics. This study provides a framework by which coarse‐resolution models can be refined to quantify glacier submarine melt for future ice sheet projections.

The Surface Deformation and Change (SDC) mission study is investigating a synthetic aperture radar (SAR) mission that is expected to launch in the next decade, building on the foundation established by the NASA ISRO Synthetic Aperture Radar (NISAR) mission. Since 2019, the SDC study team has updated the observation needs identified by the 2017 Earth Science Decadal Survey, developing a Science and Applications Traceability Matrix (SATM) that includes an expanded set of geophysical observables (GOs). These needs were further refined by a team of discipline experts, resulting in 48 GOs. For each GO, imaging characteristics such as revisit, accuracy, resolution, polarisation, data latency, are defined in the SATM. This paper describes the benefit assessment methodology, provides an example to generate current commercial feasibility scores for each GO in the SATM, even though the SDC mission will not be launched until the next decade. This methodology generates a quantitative assessment of commercial SAR data in meeting the measurement needs of a GO defined in SDC's SATM. Our assessment suggests that current commercial SAR data are particularly useful for constraining geophysical processes that benefit from short-repeat acquisition times and high spatial resolution.

For the past 5 years, NASA’s Oceans Melting Greenland (OMG) mission has been motivated by the question: “to what extent are the oceans melting Greenland’s ice from below?” Three out of the mission’s four observational components employed aircraft to collect data on and around the ice sheet: (i) airborne gravity above the continental shelf to infer seafloor geometry, (ii) airborne radar (GLISTIN-A) to measure year-to-year glacier elevation changes, and (iii) airborne-deployed oceanographic instruments (AXCTDs, ALAMO and APEX floats, XBTs, and drifters) to measure year-to-year ocean temperature and salinity changes. After highlighting the mission’s operational parameters and key scientific findings, we will detail our rationale for designing the mission to include extensive aircraft-based measurements. Now that OMG has completed its final observational campaign, we will summarize our experience with using aircraft in polar environments and suggest ways in which aircraft could be used to efficiently extend the ocean climate data record started by OMG and the potential for using aircraft in future missions to make similar oceanographic measurements around Antarctica.

The innovations in high-performance, low-power electronics and low-cost space access are unlocking affordable distributed radar systems and new remote sensing opportunities. The Distributed Element Beamformer Radar for Ice and Subsurface sounding (DEBRIS) is a concept to implement a 2D sparse radar aperture to improve the radar's spatial resolution and sounding investigation depth through the reduction of surface clutter. Here, we introduce this system and highlight its applications, orbital configurations, and the implementation considerations to achieve state-of-the-art performance for spaceborne radar sounders.

The airborne glacier and ice surface topography interferometer (GLISTIN-A) is a single-pass radar interferometer developed for accurate high-resolution swath mapping of dynamic ice surfaces. We present the first validation results of the operational sensor, collected in 2013 over glaciers in Alaska and followed by more exhaustive collections from Greenland in 2016 and 2017. In Alaska, overlapping flight-tracks were mosaicked to mitigate potential residual trends across-track and the resultant maps are validated with lidar. Furthermore, repeat acquisitions of Columbia Glacier collected with a three day separation indicate excellent stability and repeatability. Commencing 2016, GLISTIN-A has circumnavigated Greenland for 4 consecutive years. Due to flight hour limitations, overlapping swaths were not flown. In 2016, comparison with airborne lidar data finds that residual systematic errors exhibit evenly distributed small slopes (all less than 10 millidegrees) and nadir biases were typically less than 1 m. Similarly 2017 data exhibited up to meter-scale nadir biases and evenly distributed residual slopes with a standard deviation of ~10 millidegrees). All satisfied the science accuracy requirements of the Greenland campaigns (3 m accuracy across an 8 km swath).