Application of image cross-correlation to the measurement of glacier velocity using satellite image data

Altimeter measurements of ranges to modelled irregular surfaces are simulated and two correction schemes are used to reconstruct the modelled surfaces from the simulated data. When the cross-track slope is negligible, the problem can be treated as two-dimensional and the relocation method is preferred to the slope correction method. In a two-dimensional test case, 85 percent of the slope-induced rms error was removed by the relocation method. The mean error along profiles of about 75 km or longer is usually reduced more than the rms error. An alternative slope correction scheme, which uses the local slope to calculate the expected error, is less effective in the two-dimensional case. Over a simulated three-dimensional surface, where groundtracks are widely spaced and cross-track slopes are significant, the slope-correction method must be used in at least the cross-track direction.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JC088iC03p01617%4010.1002/%28ISSN%292169-9291.SEASAT2

Slope‐induced errors in radar altimetry over continental ice sheets

The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic-enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.

/pdf/the-sensitivity-of-the-antarctic-ice-sheet-to-a-changing-3xe5hbx6wc.pdf

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

Preliminary results from Seasat radar altimetry over Antarctica north of 72 deg S and Greenland south of 72 deg N are presented. Surface elevations of the ice sheets, obtained from computer retracking of the radar altimeter waveforms, are contoured at 50-m intervals for Greenland and at 100-m intervals for Antarctica. Elevation differences at orbital crossover points are analyzed to obtain a precision of 1.9 m; this figure is partly determined by radial errors of approximately 1.0 m in orbital determination and partly by noise due to ice surface irregularities. Adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small, relatively flat region reduces the rms difference to 0.25 m, which is indicative of the optimum precision obtainable over the ice sheets. However, the precision degrades as the slope of the surface or amplitude of the undulations increases, yielding an overall precision of + or - 1.6 m.

Surface elevation contours of Greenland and Antarctic ice sheets

The primary purpose of the GLAS instrument is to detect ice elevation changes over time which are used to derive changes in ice volume. Other objectives include measuring sea ice freeboard, ocean and land surface elevation, surface roughness, and canopy heights over land. This Algorithm Theoretical Basis Document (ATBD) describes the theory and implementation behind the algorithms used to produce the level 1B products for waveform parameters and global elevation and the level 2 products that are specific to ice sheet, sea ice, land, and ocean elevations respectively. These output products, are defined in detail along with the associated quality, and the constraints, and assumptions used to derive them.

/pdf/the-algorithm-theoretical-basis-document-for-the-derivation-192r7uqiwv.pdf

The Algorithm Theoretical Basis Document for the Derivation of Range and Range Distributions from Laser Pulse Waveform Analysis for Surface Elevations, Roughness, Slope, and Vegetation Heights

: Results are presented of spectral analyses of the surface and bedrock profiles along a flow line of the Wilkes ice cap and the surface along the Greenland E.G.I.G. profile. Although the bedrock appears irregular over all wavelengths studied, the ice-cap surface is typically characterized by a smooth curve with small-scale surface undulations superimposed on it. The following relations of Budd (1969, 1970) are confirmed. (Author)

An Analysis of the Relation between the Surface and Bedrock Profiles of Ice Caps

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An Analysis of the Relation between the Surface and Bedrock Profiles of Ice Caps