A review of the applications of SAR polarimetry and polarimetric interferometry - an ESA funded study

International audienc

Bedmap2: improved ice bed, surface and thickness datasets for Antarctica

We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60° S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved data-coverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72 m lower and the area of ice sheet grounded on bed below sea level is increased by 10%. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets

Bedmap2: improved ice bed, surface and thickness datasets for Antarctica

We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60° S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved data-coverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72 m lower and the area of ice sheet grounded on bed below sea level is increased by 10%. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets

Pine Island Glacier ice shelf melt distributed at kilometre scales

By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise. Much of this ice loss is from Pine Island Glacier, which has thinned since at least 1992, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line. Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems. Here, a Lagrangian methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow. At the broad scale, melt rates of up to 100 m yr−1 occur near the grounding line, reducing to 30 m yr−1 just 20 km downstream. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr−1, in close agreement with 2009 oceanographically constrained estimates. At smaller scales, a network of basal channels typically 500 m to 3 km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt. Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them. Kilometre-scale variations in melt are a key component of the complex ice–ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very high resolution models, are required to predict the sea-level contribution of the region

The basal roughness of Pine Island Glacier, West Antarctica

We assess basal roughness beneath Pine Island Glacier (PIG), West Antarctica, based on a recent airborne radio-echo sounding dataset. We identify a clear relationship between faster ice flow and decreased basal roughness in significant parts of PIG. The central portion and two of its tributaries are particularly smooth, but the majority of the tributaries feeding the main trunk are rougher. We interpret the presence of a smooth bed as being a consequence of the deposition of marine sediments following disappearance of the West Antarctic ice sheet in the Pliocene or Pleistocene, and, conversely, a lack of marine sedimentation where the bed is rough. Importantly, we also identify a patchy distribution of marine sediments, and thus a bed over which the controls on flow vary. While there is a notable correspondence between ice velocity and bed roughness, we do not assume a direct causal relationship, but find that an indirect one is likely. Where low basal roughness results in low basal resistance to flow, a lower driving stress is required to produce the flux required to achieve mass balance. This, in turn, means that the surface in that area will be lower than surrounding areas with a rougher bed, and this will tend to draw flow into the area with low bed roughness. Since our studies shows that bed roughness beneath the tributaries of the trunk varies substantially, there is a strong likelihood that these tributaries will differ in the rate at which they transmit current velocity changes on the main trunk into the interior of the glacier basin

Study for the definition of ERS-1 SAR calibration performance assessment and quality assurance software system Task 1; ERS-1 SAR performance analysis, final report Algorithm specifications

ESA - European Space AgencyAvailable from British Library Document Supply Centre- DSC:3425.929(ESA-CR-(P)--2875/1) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Rutford Ice Stream, Antarctica

Rutford Ice Stream is in many ways a typical Antarctic outlet glacier. Constrained by a subglacial-bed trough to the east of the Ellsworth Mountains, it drains an area of 49,000 km2 of the West Antarctic Ice Sheet. Varying in width from 20 to 30 km, flowing fast (up to 400 m/a) for more than 150 km before it starts to float, and over 2000 m thick along most of its length, it discharges 18.5±2 Gt of ice per year across its grounding line. It has an average driving stress of 40 kPa, which is resisted by lateral shear stresses at the margins in boundary layers up to about 10 km wide, and by basal shear stress in the middle third of the ice stream. Seismic studies of the base reveal varied conditions, with soft deformable till and more competent sediments. Stresses in the margins of up to 160 kPa lead to fracturing and crevassing, highlighted as bright bands in satellite synthetic aperture radar (SAR) images. Shallow seismic refraction and radar measurements indicate that fracture is initiated at depths around 10–20 m, consistent with the SAR penetration depths. Indications of change come from SAR interferometry of the upstream shear margin, where decadal fluctuations in the velocity profile suggest the effective width of the ice stream is varying. The limit of tidal flexing has been accurately located with SAR interferometry and shows no change in position between 1992 and 1996. Downstream of the grounding line there is a strong pattern of ice thickness variation advecting with the flow. We do not have a good explanation for the pattern, but it could have been caused by fluctuations in the position of the grounding line as a consequence of changes in ice thickness advecting downstream. The extent of the pattern suggests that the changes were occurring between 100 and 400 years ago

Basal conditions beneath enhanced-flow tributaries of Slessor Glacier, East Antarctica

Radio-echo sounding data are used to investigate bed roughness beneath the three enhanced-flow tributaries of Slessor Glacier, East Antarctica. Slow-moving inter-tributary areas are found to have rough beds, while the bed of the northernmost tributary is relatively smooth. A reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary, and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times, so marine sediments may have accumulated here. Together, these factors are further support for the dominance of basal motion in this tributary, reported elsewhere. Conversely, although the other two Slessor tributaries may have water routed beneath them, they would not have been below sea level before the growth of the ice sheet, so cannot be underlain by marine sediments. They are also found to be rough, and, within the range of uncertainties, it is likely that basal motion does not play a major role in the flow of these tributaries. Perhaps the most interesting area, however, is a deep trough where flow rates are currently low but the bed is as smooth as the northern Slessor trough. It is proposed that, although ice deformation currently dominates in this trough, basal motion may have occurred in the past, when the ice was thicker

A systematic review of the safety and effectiveness of restraint and seclusion as interventions for the short-term management of violence in adult psychiatric inpatient settings and emergency departments

AIMS: The aim of this review was to assess whether restraint and seclusion are safe and effective interventions for the short-term management of disturbed/violent behaviour. Staff and service user perspectives on the use of these interventions were also considered. The review was undertaken as part of the development process for a national guideline on the short-term management of disturbed/violent behaviour in adult psychiatric inpatient settings and emergency departments in the United Kingdom. METHOD: An exhaustive literature search was undertaken. Systematic reviews, before and after studies, as well as qualitative studies were included. Searches were run from 1985 to 2002. FINDINGS: Thirty-six eligible studies were identified. However, none were randomised controlled trials. Most of the included studies had many limitations, such as small sample sizes, confounders not adequately accounted for, potential selection bias, poorly reported results, and lack of clarity as to whether mechanical restraints were used. This review must therefore be viewed as a mapping exercise, which illustrates the range and quality of studies that have been undertaken in this area to date. CONCLUSIONS AND IMPLICATIONS FOR PRACTICE: Insufficient evidence is available to determine whether seclusion and restraint are safe and/or effective interventions for the short-term management of disturbed/violent behaviour in adult psychiatric inpatient settings. These interventions should therefore be used with caution and only as a last resort once other methods of calming a situation and/or service user have failed