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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

Year 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 2021

The processing of geodetic VLBI experiments involving both S/X and VGOS stations is highly desirable for a multitude of reasons. Beyond the express purpose of obtaining geodetic ties between existing S/X stations and the rapidly expanding network of VGOS stations, a period of overlap and integration between the two systems is beneficial in order to help preserve reference frame continuity during the transition from the S/X to VGOS network, as well as to provide an opportunity to study any systematic differences between the two. Therefore, it is important to correlate and fringe-fit data collected contemporaneously by both S/X and VGOS stations to obtain delay observables on mixed baselines. A brief overview of one possible implementation of this process will be presented, describing correlation (including the use of the DiFX zoom-bands feature) along with the peculiarities of data handling on mixed S/X-VGOS baselines during post-processing with fourfit. Some results from the mixed-mode sessions RD2005 and RD2006 will be presented, and future prospects will be discussed

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

In 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 Intensives

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 next-generation VLBI system called VGOS (VLBI Global Observing System) is now operational. A network of 8 VGOS stations has been observing bi-weekly since 2019 under the auspices of the International VLBI Service for Geodesy and Astrometry (IVS) for the creation of standard geodetic products. Moreover, a subset of 2-4 of those VGOS stations has also been observing, starting in 2020, in a VLBI Intensives-like mode to assess the feasibility of earth¿s rotation (UT1) estimation using VGOS. Intensives are VLBI observations that are run on a daily basis using a single baseline, for instance, between Kokee Park Geophysical Observatory, Hawaii, and Wettzell Observatory, Germany, with the goal of near-real time monitoring of UT1. We will describe the VGOS observations, correlation, post-processing, and preliminary geodetic results, including UT1. We will compare the VGOS estimates to estimates from legacy VLBI and other geodetic techniques such as GNSS, when and where possible, to draw some conclusions on the precision and accuracy of the VGOS estimates

The International VLBI Service for Geodesy and Astrometry (IVS) currently employs a two-band VLBI system (legacy S/X system) as its operational system for product creation. Over the past decade a new VLBI system called VGOS (VLBI Global Observing System) has been under development and in recent years strides have been made to implement the new broadband system globally. A modernized station infrastructure has been (and will continue to be) established worldwide and in 2020 a fledgling network of 8-10 VGOS stations started observing in operational IVS sessions. It is anticipated that the global VGOS network will grow to 25 stations and more in the next couple of years. As part of the modernization process also other infrastructure components of the VLBI processing chain have been further developed, including the VGOS correlation and post-processing capabilities as well as VGOS data analysis. We will provide a status overview of the infrastructure realization efforts of the VGOS station network, the correlation centers and analysis, and we will present some initial results from the limited network VGOS sessions

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

Monitoring sea ice concentration is required for operational and climate studies in the Arctic Sea. Technologies used so far for estimating sea ice concentration have some limitations, for instance the impact of the atmosphere, the physical temperature of ice, and the presence of snow and melting. In the last years, L-band radiometry has been successfully used to study some properties of sea ice, remarkably sea ice thickness. However, the potential of satellite L-band observations for obtaining sea ice concentration had not yet been explored. In this paper, we present preliminary evidence showing that data from the Soil Moisture Ocean Salinity (SMOS) mission can be used to estimate sea ice concentration. Our method, based on a maximum-likelihood estimator (MLE), exploits the marked difference in the radiative properties of sea ice and seawater. In addition, the brightness temperatures of 100 % sea ice and 100 % seawater, as well as their combined values (polarization and angular difference), have been shown to be very stable during winter and spring, so they are robust to variations in physical temperature and other geophysical parameters. Therefore, we can use just two sets of tie points, one for summer and another for winter, for calculating sea ice concentration, leading to a more robust estimate. After analysing the full year 2014 in the entire Arctic, we have found that the sea ice concentration obtained with our method is well determined as compared to the Ocean and Sea Ice Satellite Application Facility (OSI SAF) dataset. However, when thin sea ice is present (ice thickness ≲ 0.6 m), the method underestimates the actual sea ice concentration. Our results open the way for a systematic exploitation of SMOS data for monitoring sea ice concentration, at least for specific seasons. Additionally, SMOS data can be synergistically combined with data from other sensors to monitor pan-Arctic sea ice conditions

The launch of the Soil Moisture and Ocean Salinity (SMOS) mission, in 2009, marked the dawn of a new type of space-based microwave observations. Although the mission was originally conceived for hydrological and oceanographic studies [1,2], SMOS is also making inroads in the cryospheric sciences. SMOS carries an L-band (1.4 GHz, or 21-cm wavelength), passive interferometric radiometer (the so-called MIRAS) that measures the electromagnetic radiation emitted by the Earth’s surface, at about 50 km spatial resolution, full polarization, continuous multi-angle viewing, large wide swath (1200-km), and with a 3-day revisit time at the equator, but more frequently at the poles. A significant difference of the L-band microwave radiometers with respect to higher frequency radiometers, such as SSMI/AMSR-E/AMSR-2, is that the former can also “see through the ice.” That is because ice is more transparent (i.e., optically thinner) at 1.4 GHz than at higher frequencies (19-89 GHz). In radiometric terms, the brightness temperature measured by an L-band antenna radiometer does not correspond to the emissivity of the topmost surface layer but of a larger range of deeper layers within the ice (about 60 cm, depending on ice conditions). Thanks to that increased penetration in the medium, L-band radiometers can provide, for the first time, thin ice thickness from space [3, 4]. A novel radiometric method to determine sea ice concentration (SIC) is presented. The method exploits the distinctive radiative properties of sea ice and seawater when observed at low microwave frequencies and from a range of incidence angles, to discern both media. The Bayesian-based Maximum Likelihood Estimation (MLE) approach is used to retrieve SIC. The advantage of this approach with respect to the classical linear inversion is that the former takes into account the uncertainty of the tie-point measured data in addition to the mean value, while the latter only uses a mean value of the tie-point data. When th, [1] Font, J.; Camps, A.; Borges, A.; Martin-Neira, M.; Boutin, J.; Reul, N.; Kerr, Y.; Hahne, A. & Mecklenburg, S. SMOS: The Challenging Sea Surface Salinity Measurement From Space Proceedings of the IEEE, no. 5, 2010, 98, 649 -665 [2] Kerr, Y.; Waldteufel, P.; Wigneron, J. P..; Delwart, S.; Cabot, F.; Boutin, J.; Escorihuela, M.J..; Font, J.; Reul, N.; Gruhier, C.; Juglea, S.; Drinkwater, M.; Hahne, A.; Martin-Neira, M. & Mecklenburg, S. The SMOS mission: New tool for monitoring key elements of the global water cycle Proc. IGARSS 2010, no. 5, 2010, 98, 666-687 [3] Kaleschke, L., Tian-Kunze, X., Maass, N., Mäkynen, M., and Drusch, M.: Sea ice thickness retrieval from SMOS brightness temperatures during the Arctic freeze-up period, Geophys. Res. Lett., doi:10.1029/ 2012GL050916, 2012. [4] Huntemann, M., Heygster, G., Kaleschke, L., Krumpen, T., Mäkynen, M., and Drusch, M.: Empirical sea ice thickness retrieval during the freeze up period from SMOS high incident angle observations, The Cryosphere Discuss., 7, 4379–4405, 2013

[EN] Since the mid-1980s, physical oceanographers at the Institute of Marine Sciences have been involved in the use of Lagrangian drifters as a complementary technology for their oceanographic research. As Lagrangian observations became more feasible, these researchers continued developing their own drifters in what was to be the seed of current technological activities at the Physical and Technological Oceanography Department. In this paper we overview the work done during the last 30 years with special focus on Lagrangian developments from the initial activities to the latest developments. In addition to basic oceanography research applications, Lagrangian technological developments include prototypes for measuring surface and subsurface ocean properties, for tracking purposes in search and rescue operations and pollution events, and for monitoring ice motion and thickness in the Arctic. The paper emphasizes original and unpublished technical aspects related to the latest development, [ES] Desde mediados de la década de los 80, los oceanógrafos físicos en el Instituto de Ciencias del Mar se involucraron en el uso de boyas Lagrangianas como una tecnología complementaria para su investigación oceanográfica. A medida que las observaciones Lagrangianas se volvieron más factibles, los investigadores continuaron desarrollando sus propios flotadores en lo que se convirtió en la semilla de las actuales actividades tecnológicas llevadas a cabo en el Departamento de Oceanografía Física y Tecnológica. En este artículo se presenta una visión general del trabajo realizado durante los últimos 30 años, con especial énfasis en el uso de flotadores a la deriva y desarrollos propios desde su inicio hasta las aplicaciones más recientes. Además de estudios básicos de investigación oceanográfica, los desarrollos tecnológicos llevados a cabo incluyen prototipos para medir las propiedades superficiales y sub-superficiales, para tareas de seguimiento en operaciones de búsqueda y rescate y eventos de contaminación marina o para monitorizar el grosor de la capa de hielo y su movimiento en el Ártico. En este trabajo se hace hincapié en aspectos técnicos originales e inéditos relacionados con los últimos desarrollos

Small-scale (~100 to 200 m) deformations of an Arctic sea ice floe were detected from multiple GPS-equipped buoys that were deployed on the same ice floe. Over a nine-month period three deformation events were recorded. At each case the event was of limited duration, each lasting less than a day. The events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area. The strain rate during the deformation, of the order of 10−5 s−1, is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100 m in length. On the 2-day time scale, the strain rate became too small and none of the deformation events could be detected. This suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent, small-scale brittle failure of total deformation. Taken as a whole, our results show the influence that large-scale wind stress can have on small-scale deformation. However, it is important to note that the impact of large-scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process

Small-scale (~100 to 200 m) deformations of an Arctic sea ice floe were detected from multiple GPS-equipped buoys that were deployed on the same ice floe. Over a nine-month period three deformation events were recorded. At each case the event was of limited duration, each lasting less than a day. The events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area. The strain rate during the deformation, of the order of 10−5 s−1, is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100 m in length. On the 2-day time scale, the strain rate became too small and none of the deformation events could be detected. This suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent, small-scale brittle failure of total deformation. Taken as a whole, our results show the influence that large-scale wind stress can have on small-scale deformation. However, it is important to note that the impact of large-scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process

Small-scale (~100-200 m) deformations of an Arctic sea ice floe were detected from multiple GPS-equipped buoys that were deployed on the same ice floe. Over a nine-month period three deformation events were recorded. At each case the event was of limited duration, each lasting less than a day. The events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area. The strain rate during the deformation, of the order of 10-5s-1, is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100m in length. On the 2 day time scale, the strain rate became too small and none of the deformation events could be detected. This suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent, small-scale brittle failure of total deformation. Taken as a whole, our results show the influence that large-scale wind stress can have on small-scale deformation. However, it is important to note that the impact of large-scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process. © 2015

Slow slip events (SSEs) have been observed in GPS time series for many subduction zones worldwide but not in decade-long GPS time series from the Sumatran GPS Array (SuGAr). An outstanding question has been whether SSEs have simply not occurred on the Sunda megathrust or whether they have been obscured by the prodigious number of earthquakes and their ensuing postseismic deformation within the time of geodetic observation. We remove all known tectonic signals from the time series to search for evidence of SSEs. The residuals are essentially flat at the centimeter scale. To search for signals at the millimeter scale we test various filtering and visualization techniques. Despite these efforts, we conclude that it is difficult to confirm that SSEs exist at this scale using the current data, although we do see a few suspicious signals. The lack of evidence for events may reflect SSEs occurring at a magnitude, location, or timescale that renders them undetectable with the current resolution of the SuGAr, that the properties of this megathrust are not conducive to SSEs, or because the megathrust is in an active period of the earthquake cycle

We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg. The buoyancy stresses induced by such a foot may be sufficient to cause moderate-sized bergs to break off from the main berg. A mathematical model is developed to test the feasibility of this mechanism. The results suggest that once the foot reaches a critical length, the induced stresses are sufficient to cause calving. The theoretically predicted maximum stable foot length compares well to the data collected in situ. Further, the model provides analytical expressions for the previously observed “rampart-moat” iceberg surface profiles.

We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg. The buoyancy stresses induced by such a foot may be sufficient to cause moderate-sized bergs to break off from the main berg. A mathematical model is developed to test the feasibility of this mechanism. The results suggest that once the foot reaches a critical length, the induced stresses are sufficient to cause calving. The theoretically predicted maximum stable foot length compares well to the data collected in situ. Further, the model provides analytical expressions for the previously observed “rampart-moat” iceberg surface profiles.

SATICE-type buoys are geodetic-quality GPS systems capable of collecting continuous high-precision GPS data while drifting on sea ice. The buoy core sensor is a dual-frequency, carrier-beat-phase GPS receiver that provides continuous (0.1 Hz), three-dimensional position estimates with cm-level precision in a well-defined geodetic reference frame. Besides highquality GPS measurements, other geophysical auxiliary observations such meteorological, ice, and upper ocean are also acquired. Heretofore, we have designed, built, deployed, and operated five SATICE buoys, in the Western Arctic (Chukchi Sea and Beaufort Sea), two of which are currently active in the Beaufort. Data from these buoys are helping us gain an improved understanding of Arctic sea ice physics and ocean dynamics. As part of our contribution to ICE-ARC, we will build a new series of improved SATICE buoys and deploy them pan-Arctic. SATICE buoy technology is described below

We have used tide-gauge data from near Helheim Glacier, East Greenland, and GPS data acquired on the glacier to investigate the spectra of tidal forcing and flow response. For both the tidegauge and GPS time series, we calculated amplitudes and phases for a harmonic expansion using a limited set of harmonic constituents. We find that the semidiurnal constituents of the glacier flow are well modeled using a single admittance and lag with respect to the tide-gauge data. However, diurnal variations in the glacier flow cannot be simply described using this model. We find an additional signal in glacier position, in phase with the S1 solar tide, with some modulations at other frequencies. These non-tidal variations account for a peak-to-peak variation in glacier flow speed at a site close to the terminus of ~0.7md-1, compared with a mean flow rate at this location of ~22md-1. The speed variations reach their daily maximum value ~6 hours after local noon. We hypothesize that these additional diurnal variations are associated with peaks in lubrication of the glacier bed due to surface melting driven by diurnal solar heating

We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg. The buoyancy stresses induced by such a foot may be sufficient to cause moderate-sized bergs to break off from the main berg. A mathematical model is developed to test the feasibility of this mechanism. The results suggest that once the foot reaches a critical length, the induced stresses are sufficient to cause calving. The theoretically predicted maximum stable foot length compares well to the data collected in situ. Further, the model provides analytical expressions for the previously observed >rampart-moat> iceberg surface profiles. Key Points Observational iceberg data from 2012 Baffin Bay field experiment Mathematical model of iceberg decay due to hydrostatic stresses Analytic expressions for iceberg profiles and breakup conditions developed © 2014. American Geophysical Union. All Rights Reserved

Slow-slip events were first discovered on the deeper Cascadia subduction interface about a decade ago. Since then, slow-slip events have been observed at various subduction environments including Cascadia, Nankai, Alaska, New Zealand, Mexico, and Costa Rica. Conspicuously absent from this list, however, is the Sumatran subduction zone, along which no slow-slip events have yet been discovered. As one of the most active subduction zones currently in the world, the Sumatran subduction zone has experienced a series of great earthquakes over the last decade, along with numerous moderate and smaller earthquakes. We conducted a systematic search for transient aseismic slip in time series from the Sumatran GPS Array (SuGAr) between 2002 and 2012. We reprocessed the time series using GIPSY 6.2, and included the most up-to-date atmosphere and ocean models in processing to reduce day-to-day scatter of the raw time series. The raw data are dominated signals from coseismic and postseismic deformation. In order to search for much smaller transient signals, on the order of a few millimeters, we estimated and removed long-term background rates simultaneously with a large number of earthquake parameters, thus generating daily residuals. After our careful inspection of the daily residuals, we concluded that no episodic slip events have been recorded. Regarding non-episodic slip events, one station (BSAT) recorded a rate change in a few months immediately after the 2004 Sumatra-Andaman earthquake. Some other nearby stations that were installed later recorded a portion of this change. However, there were no other independent observations to confirm if this signal was indeed slow-slip. Except this suspicious signal, no other positive evidence could provide support for the occurrence of slow-slip events in Sumatra. This may indicate that slow-slip events have not occurred on the Sunda megathrust over the last decade, but may also highlight the limitation of the SuGAr network to detect sl

Space geodetic observations acquired on glaciers provide a detailed record of flow variations in response to a wide range of dynamic processes, including ocean-tidal forcing. Understanding a glacier's response to tides yields insight into its elastic and rheological properties as well as coupling to the glacier bed. We have used GPS data acquired on Helheim Glacier in East Greenland and tide-gauge data from its fjord to investigate the spectra of tidal forcing and flow response. For the semidiurnal tidal components, the observed glacier flow variations can be related to the tidal force by assuming a linear delayed response with a single admittance and time lag. However, we find that there are diurnal variations in the glacier flow that are not consistent with this model of glacier response to tidal forcing. The figure shows a phasor diagram of the observed S1 and M2 tidal components, as well as a prediction from the tide-gauge spectra based on the admittance and lag derived from the semidiurnal components. This figure illustrates the inconsistency of the tidal forcing and glacier flow at the S1 period of 1 day. We conclude that this inconsistency represents non-tidal diurnal velocity variations of the flow of Helheim Glacier that account for a peak-to-peak variation in glacier flow speed at a site located close to the terminus of ~0.8 m/d. At this site, the mean flow rate was ~20 m/d. The speed variations have a 9-day modulation and reach their daily maximum value 4.0–4.5 hours after local noon. Based on these results, we hypothesize that melting associated with solar heating causes diurnal lubrication of the glacier bed

On November 2, 2009, the European Space Agency's (ESA) launched the Soil Moisture and Ocean Salinity (SMOS) satellite carrying a microwave synthetic aperture radiometer working at 1.4 GHz (wavelength of 21 cm). The main objective of the mission is to provide Sea Surface Salinity (SSS) and Soil Moisture (SM) observations, with a spatial resolution of 30-50 km, and an accuracy suited for climate studies. Many studies have been performed studying the quality of the retrieved SSS and the SM measurements. However, SMOS can also measure the ice thickness, over ice, with good accuracy for a thin sea ice layer (less about 0.5 cm). These measurements could be complementary to CryoSat, which can best measure ice thickness for thicker ice. This work will present a comparison between ice thickness measured by SMOS and in situ measurements from buoys and other satellite measurements. Moreover, the comparison will also be performed with Aquarius NASA's radiometer, launched on June 2011, which has three real aperture radiometers at 1.4GHz. The insitu dataset used for the comparison and validation of the methodology will be one obtained with Ice Mass Balance (IMB) and other buoys deployed as part of the SATICE project (http://satice.icm.csic.es/) in the western Arctic Ocean. SSMI data and CryoSat data will also be used for comparison

A network of geodetic markers for high-precision Global Positioning System (GPS) surveying was established in 2001 in the island of São Jorge, at the Azores triple junction, where the North America-Eurasia-Nubia plates meet. The aim was to monitor tectonic, volcanic, and landslide-induced surface deformation in an active tectono-volcanic region. The network consisted of 17 stations, and was occupied in 2001, 2004, and 2010. GPS observations from the three episodic campaigns were analyzed using the latest geophysical models and geodetic procedures to generate a velocity field for São Jorge Island. Surface velocities estimated at 15 inland locations reveal that São Jorge is moving neither with Eurasia nor with Nubia and presents two sectors with different behavior. The NW sector of the island is moving at a rate of 2.2 ± 0.3 mm/yr to N82° ± 6° while the SE sector is moving at a rate of 1.4 ± 0.3 mm/yr to N109° ± 11°, when compared to the velocity of Nubia predicted by ITRF2008-PMM. This velocity field cannot be explained by slip along the active faults that cross the island, nor is compatible with volcanic deformation on the active volcanic rift zones. It is suggested that the velocity differences that are measured represent deformation related to local sub-surficial magmatic/volcanic processes occurring near the island. This intra-island deformation may also be related to the stress field and seafloor spreading occurring in an area situated on the western sector of the Azores Plateau, reflecting the presence of WNW-ESE volcanic structures, along which magma intrusion produces NE-SW dilatation, bounded to the East by a NE-SW trending structure, probably of tectonic nature, working as a dextral transfer zone

Single-frequency GNSS data has not generally been used for high-accuracy geodetic applications since the 1990s, but there are significant advantages if single-frequency GNSS receivers can be usefully deployed for studies of fast-moving outlet glaciers. The cost for these receivers is significantly lower (~50%) than for dual-frequency receivers, a significant benefit given the high spatial density at which these system are deployed on the glacier and the high risk for damage or loss in the glacial environment. In addition, the size of the data files that need to be transferred from extremely remote locations, often at very slow transmission rates, is significantly reduced. Consideration of single-frequency systems for this application is viable because of the relatively small extent (< 50 km) of the entire network to be deployed. Unfortunately, the availability of research-quality software that can perform kinematic solutions on single-frequency data is limited. We have developed the BAKAR software employing a stochastic filter to analyze single-frequency GNSS data. The software can implement a range of stochastic models for time-dependent site position. In this presentation, we describe the BAKAR software, and discuss its strengths and weaknesses. On one hand, chief among the challenges we have encountered are determination of accurate prior positions, and bursts of polar ionospheric activity that impede cycle-slip detection, even over intersite distances as short as 10 km. On the other hand, use of a single-frequency observable is theoretically less sensitive to multipath and signal scattering. We will quantitatively assess these effects, and assess the accuracy of BAKAR in a range of situations and applications