VLBI Digital-Backend Intercomparison Test Report

Issues related to digital-backend (DBE) systems can be difficult to evaluate in either local tests or actual VLBI experiments. The 2nd DBE intercomparison workshop at Haystack Observatory on 25-26 October 2012 provided a forum to explicitly address validation and interoperability issues among independent global developers of DBE equipment. This special report discusses the workshop. It identifies DBE systems that were tested at the workshop, describes the test objectives and procedures, and reports and discusses the results of the testing

Automatic Gravity Wave Detection on the Ross Ice Shelf Using Supervised Panoptic Spectrogram Segmentation

American Geophysical Union Fall Meeting, 12-16 December 2022, ChicagoIce 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 shelvesPeer reviewe

GNSS Reflectometry on Arctic Sea Ice using a small-scale network of GNSS sensors

American Geophysical Union Fall Meeting, 12-16 December 2022, ChicagoGNSS-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 changesPeer reviewe

Experience from S/X-VGOS mixed-mode observations

25th European VLBI Group for Geodesy and Astronomy Working Meeting, 14-18 March 2021Year 2020 was the culmination of a few earlier years of meticulous preparatory work for obtaining observations simultaneously with the legacy S/X and the VGOS networks as if they were a single, seamless network. The main goal of these so-called mixed-mode sessions is to determine the positions of the new VGOS stations in the terrestrial reference frame defined by the long-lived, stable legacy stations, thus effectively tying both networks together. Three mixed-mode sessions had been executed prior to 2020, each session adding one new small-step to the previous session to ensure technology development and advancement. Indeed, the first session involved a single VGOS station, Westford, participating in a standard R&D S/X observing network in tag-along mode in 2016. The second and third sessions involved the participation of two (add GGAO) and three (add KPGO) VGOS stations, respectively, in 2018, hence expanding from a station to a VGOS baseline and then a triangle, or closure. An important component of this progressive approach has been to identify, and where possible, solve software challenges and limitations, to then move forward with knowledge transfer to the IVS community. An ambitious plan was then launched in 2020 when, building on the success of the earlier sessions, a series of three mixed-mode sessions were run whereby the existing entire VGOS network of 8 stations joined in R&D-type 8-station S/X sessions, thus synthesizing a 16-station mixed-mode network. The main goal of these augmented sessions was to strengthen the network ties for the upcoming ITRF2020 realization. This presentation will focus on the goals of the original vision for the sessions, how the goals morphed to what became the reality, and the impact on the processing and software of these modifications; a lessons-learned perspective. We will conclude with what may a best way forward for 202

Autonomous Sea-Ice Drifting GNSS Buoys for Advanced Arctic Science

American Geophysical Union Fall Meeting, 12-16 December 2022, ChicagoAn 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 presentedPeer reviewe

Review of Operational VGOS Sessions in 2020

25th European VLBI Group for Geodesy and Astronomy Working Meeting, 14-18 March 2021In 2020, the IVS observed for a second year an operational 24-hr VGOS session series (VGOS-O) at a bi-weekly cadence. The total number of sessions amounts to 24 for the full year; the network size was between 8 and 9 stations. In February 2020, we began an Intensive-type VGOS session series (VGOS-V2) of one-hour observing designed to measure UT1. There were a total of 21 VGOS-V2 sessions that were scheduled in the weeks when there was no 24-hr VGOS session and ran concurrently with the legacy S/X INT1 sessions. The VGOS-V2 sessions generally included the KOKEE12M¿WETTZ13S baseline with GGAO12M, MACGO12M, and WESTFORD being tagged along or scheduled in depending on their availability. There were a total of 21 VGOS-V2 sessions. For both VGOS-O and VGOS-V2 sessions we discuss the scheduling, correlation, and analysis.We contrast the 24-hr VGOS sessions with 24-h S/X sessions of similar size. For the VGOS-V2 sessions we compare UT1 estimates with those obtained from the corresponding S/X Intensive

A preliminary assessment of the accuracy of the VGOS geodetic products: implications for the terrestrial reference frame and Earth orientation parameters

European Geosciences Union (EGU) General Assembly, 19-30 Apr 2021.-- 1 pageThe 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 product

Effects of Snow Conditions on Antarctic Air-Dropped Penetrator

American Geophysical Union Fall Meeting, 12-16 December 2022, ChicagoThe 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 analyzedPeer reviewe