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In March and April 2021, buoys were deployed in the Beaufort Sea, Arctic Ocean, to measure sea-ice horizontal deformation over spatial scales that had not been previously achieved. Geodetic-quality position measurements allowed measurements of strain-rate over lengths from about 200 m to 2 km. Conventional ice-drifters extended spatial coverage up to about 100 km. Past studies find there is multi-fractal behavior for horizontal sea-ice deformation from 10 to 1,000 km. Our results demonstrate that such behavior does not hold when including spatial scales below 10 km. We find that sea-ice deformation is not scale invariant between the scale of individual sea-ice floes and aggregates of floes. Therefore, we cannot expect the same physical laws or forcing to describe sea-ice kinematics over these regimes, nor can we assume log-log linear behavior for mean deformation. Using this scaling behavior as a metric to validate models that resolve sea ice floes and their interactions is hence not recommended

An array of twelve high-precision satellite positioning buoys (a,k,a, SATICE buoys) were deployed forming a small-scale network during the Sea Ice Dynamics Experiment (SIDEx) 2021 campaign on the Beaufort Sea, Arctic Ocean, to study sea ice drift, deformation, and fracture. A SATICE buoy is an autonomous, continuously operating, ice-anchored, geodetic-quality, global navigation satellite system (GNSS; i.e., GPS, GLONASS, and Galileo) receiving unit with near-real-time data download capabilities via Iridium satellite constellation. The buoys are also equipped with miscellaneous meteorological and geophysical sensors such as three-dimensional (3D) accelerometer and gyroscope. In this presentation, the engineering designs, mechanical, electrical, and software that went behind the successful deployment and operations of the SATICE-buoy network, along with the lessons learned, will be presented

GNSS-Interferometric Reflectometry (GNSS-IR) utilizes the pattern in GNSS signal-to-noise ratio (SNR) observables resulting from interference between direct and reflected GNSS signals to probe the GNSS antenna’s surrounding physical environment. The technique is used as a sensor for sea level variations, soil moisture changes, snow depth accumulation, in addition to other geophysical applications. Traditionally, GNSS-IR has been applied with static GNSS stations. Here, we use it on a sea-ice floe in the Arctic Ocean drifting up to 25 km daily. A small-scale (~5 km) ice-strain network is formed with the 12 identical GNSS instruments deployed on the floe. This study describes the technique and this network, while also exploring how the redundancy afforded by the spatially-dense network can best be used to determine the estimation precision of snow accumulation changes

The Seismo-Geodetic Ice Penetrator (SGIP) is a platform for delivering a seismometer and GNSS sensor to the Ross Ice Shelf to measure dynamic events and resonant forcings caused by atmospheric and ocean gravity waves. SGIP is composed of two pieces: a lower “body” portion with the seismometer, and a top “flare” portion to increase aerodynamic stability and constrain the terminal velocity. The two portions will be joined when falling through the air; then, when the spike penetrates into the ice, the flange will be left at the surface, attached by cabling to the “body” to transmit data back to operators. We present a modeling workflow which links together a small drop testing model, finite element explicit dynamics model, and a sensitivity analysis of snow conditions using core sample data to provide context for an upcoming full-size field test. Implications of snow, ice, and firn composition on component shock loads are also discussed. Effects of snow conditions on thermal systems, potential snow brake architectures, and shock absorption materials are also analyzed

The International Terrestrial Reference Frame (ITRF) provides a framework for all ground- and space-based measurements that help determine locations on the Earth's surface with high precision. ITRF is realized every few years using the four space geodetic techniques, VLBI, GNSS, SLR, and DORIS. The most recent release, ITRF2020, is expected to be more precise than its predecessor, ITRF2014, which was released in 2016. For the first time, this realization of ITRF includes geodetic products from VLBI Global Observing Systems (VGOS), the next-generation broadband VLBI observing system equipped with fast antennas and wide observing bandwidths. By design, the uncertainties of VGOS observations are significantly smaller than those of its predecessor, the S/X Legacy system. With the inclusion of VGOS observations in ITRF2020, the VGOS network should be compatible and aligned with the S/X Legacy network and other space geodetic techniques. Therefore, one would expect the Earth Orientation Parameters (EOP) estimated from VGOS and S/X Legacy networks to be in good agreement. In this presentation, we will investigate the level of agreement of EOPs estimates from both networks in the ITRF2020, and also in relation to prior realizations such as ITRF2014

Ice shelves play a pivotal role in controlling the evolution of Antarctic glaciology by restraining, buttressing, and modulating the flow of grounded ice into the Southern Ocean. The stability of the Antarctic Ice Sheet thus depends critically on the stability of the ice shelves that fringe the continent. It is therefore important to understand how these shelves respond to environmental stresses, especially those as common as gravity wave forcings. This study focuses on applying machine learning to automatically detect, classify, and catalog low-frequency (0-70 mHz) gravity wave events impacting the Ross Ice Shelf (RIS) by panoptically segmenting seismic spectrograms. The data used to supervise training was collected by a broadband seismic array deployed on the RIS from November 2014 to November 2016 and was used to generate spectrograms of up to 70 mHz that were examined for infragravity waves and swell events. Our modified U-Net architecture achieved a Dice similarity coefficient (DSC) of over 0.73 during event detection, and its corresponding post processing pipeline recorded an accuracy of 94.4% during classification, outperforming alternative rule based techniques. This work serves as a proof-of-concept for using deep-learning algorithms to detect and catalog gravity wave events, a development that would allow for an improved understanding of the long-term stability of Antarctic ice shelves

The next-generation VLBI system called VGOS (VLBI Global Observing System) has been designed and built as a significant improvement over the legacy geodetic VLBI system to meet the accuracy and stability goals set by the Global Geodetic Observing System (GGOS). Improved geodetic products are expected as the VGOS technique transitions from demonstration to operational status, which is underway. Since 2019, a network of nine VGOS stations has been observing bi-weekly under the auspices of the International VLBI Service for Geodesy and Astrometry (IVS) to generate standard geodetic products. These products, together with the mixed-mode VLBI observations that tie the VGOS and legacy networks together will be contributions to the next realization of the International Terrestrial Reference Frame (ITRF2020). Moreover, since 2020 a subset of 2 to 4 VGOS stations has also been observing in a VLBI Intensive-like mode to assess the feasibility of Earth rotation (UT1) estimation using VGOS. Intensives are daily legacy VLBI observations that are run on a daily basis using a single baseline between Kokee Park Geophysical Observatory, Hawaii, and Wettzell Observatory, Germany, made with the goal of near-real-time monitoring of UT1. In this presentation, we will describe the VGOS observations, correlation, post-processing, and preliminary geodetic results, including UT1. We will also compare the VGOS estimates to estimates from legacy VLBI, including estimates from mixed-mode observations, to explore the precision and accuracy of the VGOS products

We measured the components of the 31-m-long vector between the two very-long-baseline interferometry (VLBI) antennas at the Kokee Park Geophysical Observatory (KPGO), Hawaii, with approximately 1 mm precision using phase delay observables from dedicated VLBI observations in 2016 and 2018. The two KPGO antennas are the 20 m legacy VLBI antenna and the 12 m VLBI Global Observing System (VGOS) antenna. Independent estimates of the vector between the two antennas were obtained by the National Geodetic Survey (NGS) using standard optical surveys in 2015 and 2018. The uncertainties of the latter survey were 0.3 and 0.7 mm in the horizontal and vertical components of the baseline, respectively. We applied corrections to the measured positions for the varying thermal deformation of the antennas on the different days of the VLBI and survey measurements, which can amount to 1 mm, bringing all results to a common reference temperature. The difference between the VLBI and survey results are 0.2 ± 0.4 mm, −1.3 ± 0.4 mm, and 0.8 ± 0.8 mm in the East, North, and Up topocentric components, respectively. We also estimate that the Up component of the baseline may suffer from systematic errors due to gravitational deformation and uncalibrated instrumental delay variations at the 20 m antenna that may reach ± 10 and −2 mm, respectively, resulting in an accuracy uncertainty on the order of 10 mm for the relative heights of the antennas. Furthermore, possible tilting of the 12 m antenna increases the uncertainties in the differences in the horizontal components to 1.0 mm. These results bring into focus the importance of (1) correcting to a common reference temperature the measurements of the reference points of all geodetic instruments within a site, (2) obtaining measurements of the gravitational deformation of all antennas, and (3) monitoring local motions of the geodetic instruments. These results have significant implications for the accuracy of global reference frames that require a

Increasing freshwater input to the subpolar North Atlantic through iceberg melting can influence fjord‐scale to basin‐scale ocean circulation. However, the magnitude, timing, and distribution of this freshwater have been challenging to quantify due to minimal direct observations of subsurface iceberg geometry and melt rates. Here we present novel in situ methods capturing iceberg change at high‐temporal and ‐spatial resolution using four high‐precision GPS units deployed on two large icebergs (>500 m length). In combination with measurements of surface and subsurface geometry, we calculate iceberg melt rates between 0.10–0.27 m/d over the 9‐day survey. These melt rates are lower than those proposed in previous studies, likely due to using individual subsurface iceberg geometries in calculations. In combining these new measurements of iceberg geometry and melt rate with the broad spatial coverage of remote sensing, we can better predict the impact of increasing freshwater injection from the Greenland Ice Sheet

Linear elastic fracture mechanics suggests that short-lived flow accelerations, such as the one initiated by a flooding event beneath Byrd Glacier in 2006, can form abnormally large basal crevasses at the grounding line. Airborne radar measurements acquired in 2011 reveal hundreds of basal crevasses ranging in height from urn:x-wiley:00948276:media:grl62752-math-000140–335 m. Particle tracking results show that formation of the largest basal crevasse occurred at the grounding line during the 2006 flooding event. Very large basal crevasses form distinctive surface depressions directly overhead, which are observed along the Byrd Glacier flowline to the terminus of the Ross Ice Shelf. By using these surface depressions as proxies for abnormally large basal crevasses, we create a timeline of past subglacial flooding events on Byrd Glacier. Understanding the frequency of flooding events and their effect on glacier dynamics will help inform models of ice sheet stability and subglacial hydrology

The International VLBI Service for Geodesy and Astrometry (IVS) is a globally operating service that coordinates and performs Very Long Baseline Interferometry (VLBI) activities through its constituent components. The VLBI activities are associated with the creation, provision, dissemination, and archiving of relevant VLBI data and products. The operational station network of the IVS currently consists of about 40 radio telescopes worldwide, subsets of which participate in regular 24-hour and 1-hour observing sessions. This legacy S/X observing network dates back in large part to the 1970s and 1980s. Because of highly demanding new scientific requirements such as sea-level change but also due to the aging infrastructure, the larger IVS community planned and started to implement a new VLBI system called VGOS (VLBI Global Observing System) at existing and new sites over the past several years. In 2020, a fledgling network of 8 VGOS stations started to observe in operational IVS sessions. We anticipate that the VGOS network will grow over the next couple of years to a global network of 25 stations and will eventually replace the legacy S/X system as the IVS production system. We will provide an overview of the recent developments and anticipated evolution of the geodetic VLBI station infrastructure

The Helheim glacier, located in southeast Greenland, has more than ten campaign-type Global Positioning System (GPS) sites; data processing led to the observation of a very rapid change in the ionospheric delay. To identify the cause of these sporadic disturbances, we analyzed the slant total electron content (STEC), single-differenced STEC (SD-STEC) and scintillation proxy index called the delta phase rate (DPR). From this analysis, the abrupt change of those ionospheric indicators was attributed to the line-of-sight direction to the satellite and the temporal sequence of the event was found to be highly correlated with the geometry of the GPS sites. In addition, the disturbance based on the result of SD-STEC occurred mostly during the night, from 17 UTC through 7 UTC, and across a band spanning the east-west direction. Based on the DPR indices obtained from GPS stations distributed across all of Greenland, Iceland, and northeastern Canada, the rapid ionospheric variation was found to be correlated with the time of the day and the geomagnetic latitude of the station. The disturbance was larger at the relatively low geomagnetic latitudes at night but was more significant at higher latitudes in the daytime. These rapid ionospheric variations tended to appear in band shapes parallel to the geomagnetic field. These results allow us to attribute such disturbance observed at the Helheim glacier to aurora-related phenomena

NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA¿s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the

A prototype broadband geodetic very long baseline interferometry system has been implemented, and measurements of the baseline length over approximately two years, between December 2014 and January 2017, have been made in the process of exercising the system, developing operational procedures, and assessing geodetic precision for the new broadband observing concept. In addition to developing a broadband signal chain and installing the instrumentation on both a new 12-m antenna at the Goddard Geophysical and Astrophysical Observatory and the 18-m Westford antenna at the Massachusetts Institute of Technology Haystack Observatory, it was necessary to develop new correlation and analysis procedures to process the four-band, dual-linear-polarization data. A geodetic analysis of the data from 19 sessions that were observed during this period yielded a weighted root-mean-square deviation of the baseline length residuals about the weighted mean of 1.6 mm. These results validate several of the expectations set forth for the vision of the next-generation geodetic very long baseline interferometry system