As of March 2009, network real-time kinematic (RTK) GPS surveying is available in GreatBritain with the aid of two commercial service providers, Leica's "SmartNet" and Trimble's "VRS Now", both

As of March 2009, network real-time kinematic (RTK) GPS surveying is available in Great Britain with the aid of two commercial service providers, Leica’s “SmartNet” and Trimble’s “VRS Now”, both of which rely largely on the Ordnance Survey’s “OS Net” network of around 120 continuously operating reference stations. With the aim of testing the performance of Network RTK under both ideal and less-ideal conditions (greater distances and elevation differences from the nearest reference stations, proximity to the edges of OS Net, and increased susceptibility to ocean tide loading effects), we have tested the positional accuracy of both commercial Network RTK systems by comparison with precise coordinates determined using the Bernese scientific GPS processing software, at six representative locations spanning England and Wales. We find that the coordinate quality measures provided by the Network RTK solutions are overall representative of the actual coordinate accuracy, which is typically 10-20 mm in plan and 15-35 mm in height, and can be successfully used to identify outliers. Positional accuracy tends to be poorest outside of the bounds of OS Net and at greater elevation differences from nearby reference stations. Averaging of coordinates over two short windows separated by 20-45 minutes can be used to achieve moderate improvements in coordinate accuracy without the need for single long occupations of sites.

[1] Sea ice thickness plays a critical role in global climate change, but it cannot be measured directly from space. Alternatively, sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow/ice densities. This paper investigates the relationship between snow-freeboard (ice-freeboard plus snow) and total thickness (ice thickness plus snow) and addresses the uncertainties that arise from the unknown snow depth and snow/ice densities. A unique data set of coincident measurements of snow-freeboard and total thickness was collected in the Arctic and Antarctic. Snow-freeboard was determined by laser altimetry, and total thickness was determined by electromagnetic induction with a helicopter-borne instrument. Obtained total thickness/snow-freeboard ratios range from 2 to 12 in the Arctic and from 2 to 8 in the Antarctic. The principal finding is that the ratios vary greatly within each region, and a fixed ratio per profile should not be used, as this can induce incorrect ice thicknesses. The ratio uncertainties can induce a relative thickness error of 5.4% and 4.9% in the first-year and multiyear ice mode. Additionally, the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements. To assess accuracy, calculated snow depths were compared to in situ measurements and agree within ±5 cm. This increases if measurements and calculations differ spatially. The method of deriving snow-freeboard from laser altimetry is briefly described, and the variability of the total thickness/snow-freeboard ratio is shown for one profile in the Lincoln Sea and one in the Weddell Sea.Citation: Goebell, S. (2011), Comparison of coincident snow-freeboard and sea ice thickness profiles derived from helicopterborne laser altimetry and electromagnetic induction sounding,

Modern space geodetic techniques enable deformation monitoring of continental plate interiors with high spatial and temporal coverage. Resolving data and results are currently evaluated for their application for the integrated assessment of seismic hazard and risk in Germany. This goes especially for regions where earthquakes are generally rare but high magnitudes are still not unrealistic while vulnerability of today's society is steadily growing. The present contribution deals with the continuous monitoring of tectonic fracture systems in Germany using the GPS. The estimation of the station velocities with GPS and the resulting geodetic strain is supposed to provide additional input to the earthquake hazard assessment. Unfortunately, the low expected and currently seen velocities (<1-2 mm/year) make it extremely difficult to distinguish between noise and a tectonic signal. Because of the short observation interval the velocity uncertainties are about 2 mm/year in the horizontal components. The essential goal of this program is to provide and model highly precise deformation data and to discuss its needs for a better assessment of geological hazard, especially for the most active tectonic regions in Germany, the Rhine-Graben, the Swabian Alb, the Alpine foreland, and the Vogtland. Here we present preliminary results from 2 years of measurements at currently 150 GPS stations throughout Germany. The time span of this program has proven to be too short and the density of the station network to be not dense enough yet for reliable significant horizontal station velocities and supporting the earthquake hazard assessment.