No abstract

The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is 123Surv Geophys (2010) 31:465-507 DOI 10.1007/s10712-010-9100-4 uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth's interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates.

ABSTRACT. Measurements derived from remote-sensing research and field surveys have provided new ice-velocity data for David Glacier--Drygalski Ice Tongue and Priestley and Reeves Glaciers, Antarctica. Average surface velocities were determined by tracking crevasses and other patterns moving with the ice in two sequential satellite images. Velocity measurements were made for different time intervals (1973-90, 1990-92, etc.) using images from various satellite sensors (Landsat 1 MSS, LandsatTM, SPOT XS ). In a study of the dynamics ofDavid Glacier-Drygalski Ice Tongue and Priestley and Reeves G laciers, global positioning system (GPS ) measurements were made between 1989 and 1994. A number of points were measured on each glacier: five points on David Glacier, three on Drygalski Ice Tongue, two on Reeves Glacier-Nansen Ice Sheet and two on Priestley Glacier. Comparison of the results from GPS data and feature-tracking in areas close to image tie-points shows that errors in measured average velocity from the featuretracking may be as little as ± 15-20 m a I. In areas far from tie-points, such as the outer part of Drygalski Ice Tonpue, comparison of the two types of measurements shows differences of about ± 70 m a -.

ABSTRACT. Talos Dome is an ice dome on the edge of the East Antarctic plateau; because accumulation is higher here than in other domes of East Antarctica, the ice preserves a good geochemical and palaeoclimatic record. A new map of the Talos Dome area locates the dome summit using the global positioning system (GPS) (72˚47' 14''S, 159˚04' 2'' E; 2318.5 m elevation (WGS84)). A surface strain network of nine stakes was measured using GPS. Data indicate that the stake closest to the summit moves south-southeast at a few cm a Airborne radar measurements indicate that the bedrock at the Talos Dome summit is about 400 m in elevation, and that it is covered by about 1900 m of ice. Snow radar and GPS surveys show that internal layering is continuous and horizontal in the summit area (15 km radius). The depth distribution analysis of snow radar layers reveals that accumulation decreases downwind of the dome (north-northeast) and increases upwind (south-southwest).The palaeomorphology of the dome has changed during the past 500 years, probably due to variation in spatial distribution of snow accumulation, driven by wind sublimation. In order to calculate a preliminary age vs depth profile for Talos Dome, a simple onedimensional steady-state model was formulated. This model predicts that the ice 100 m above the bedrock may cover one glacial-interglacial period.

Dome C was chosen by the European Project for Ice Coring in Antarctica (EPICA) as the site for the drilling of a deep ice core. This paper presents results from geodetic surveys of ice velocities (absolute and relative) at Dome C and along a transect to Terra Nova Bay. The purpose of the surveys was to provide accurate data for the study of ice dynamics, particularly a strain network comprising 37 poles surveyed in 1995 and again in 1999. Data indicate that the ice surface at the poles closest to the topographic summit moves horizontally by up to a few mm a–1 in a direction consistent with downslope motion of the ice sheet, while 25 km from the summit it moves up to 211 mma–1. The EPICA drilling site yields an interpolated velocity of about 15 ±10mma–1 in a north-northwesterly direction. Analysis of the velocity field and surface topography reveals that the surface flow centre is nearly co-located with the dome summit, and that both are in a steady-state condition. The measured horizontal velocities are consistent with the remote-sensing result and provide accurate ground-truth control for flow mapping. Seven snow–firn cores, up to 53m deep, were drilled during the Terra Nova Bay–Dome C traverse. Submerged velocity systems were installed at the borehole and measured using the global positioning system (GPS). First results show a steady-state condition. Measured (horizontal) ice velocities increase from the summit of the ice sheet to the coast, reaching about 28 ma–1 at site GPS2A.

The aim of this work is to evaluate UAV photogrammetric and GNSS techniques to investigate coastal zone morphological changes due to both natural and anthropogenic factors. Monitoring morphological beach change and coastline evolution trends is necessary to plan efficient maintenance work, sand refill and engineering structures to avoid coastal drift. The test area is located on the Northern Adriatic coast, a few kilometres from Ravenna (Italy). Three multi-temporal UAV surveys were performed using UAVs supported by GCPs, and Post Processed Kinematic (PPK) surveys were carried out to produce three-dimensional models to be used for comparison and validation. The statistical method based on Crossover Error Analysis was used to assess the empirical accuracy of the PPK surveys. GNSS surveys were then adopted to evaluate the accuracy of the 2019 photogrammetric DTMs. A multi-temporal analysis was carried out by gathering LiDAR dataset (2013) provided by the “Ministero dell’Ambiente e della Tutela del Territorio e del Mare” (MATTM), 1:5000 Regional Technical Cartography (CTR, 1998; DBTR 2013), and 1:5000 AGEA orthophotos (2008, 2011). The digitization of shoreline position on multi-temporal orthophotos and maps, together with DTM comparison, permitted historical coastal changes to be highlighted.

In order to make inferences on the geodynamics of Antarctica, geodetic and gravimetric maps derived from past and new observations can be used. This paper provides new insights into the geodynamics of Antarctica by integrating data at regional and continental scales. In particular, signatures of geodynamic activity at a regional extent have been investigated in Victoria Land (VL, Antarctica) by means of Global Navigation Satellite System (GNSS) permanent station observations, data from the VLNDEF (Victoria Land Network for Deformation control) discontinuous network, and gravity station measurements. At the continental scale, episodic GNSS observations on VLNDEF sites collected for 20 years, together with continuous data from the International GNSS Service (IGS) and Polar Earth Observing Network (POLENET) sites, were processed, and the Euler pole position assessed with the angular velocity of the Antarctic plate. Both the Bouguer and the free-air gravity anomaly maps were obtained by integrating the available open-access geophysics dataset, and a compilation of 180 gravity measurements collected in the VL within the Italian National Program for Antarctic Research (PNRA) activities. As a result, new evidence has been detected at regional and continental scale. The main absolute motion of VL is towards SE (Ve 9.9 ± 0.26 mm/yr, Vn −11.9 ± 0.27 mm/yr) with a pattern similar to the transforms of the Tasman and Balleny fracture zones produced as consequence of Southern Ocean spreading. Residual velocities of the GNSS stations located in VL confirm the active role of the two main tectonic lineaments of the region, the Rennick–Aviator and the Lillie–Tucker faults with right-lateral sense of shear. The resulting VL gravity anomalies show a NW region characterized by small sized Bouguer anomaly with high uplift rates associated and a SE region with low values of Bouguer anomaly and general subsidence phenomena. The East and West Antarctica are characterized by a different thickness of the Earth’s crust, and the relative velocities obtained by the observed GNSS data confirm that movements between the two regions are negligible. In East Antarctica, the roots of the main subglacial highlands, Gamburtsev Mts and Dronning Maud Land, are present. The Northern Victoria Land (NVL) is characterized by more scattered anomalies. These confirm the differences between the Glacial Isostatic Adjustment (GIA) modeled and observed uplift rates that could be related to deep-seated, regional scale structures.

No abstract