Spaceborne Laser Altimetry Research Articles

Outlet glacier response to the 2012 collapse of the Matusevich Ice Shelf, Severnaya Zemlya, Russian Arctic

AbstractThe Matusevich Ice Shelf (MIS), located within the Severnaya Zemlya Archipelago in the Russian Arctic, rapidly broke apart between 10 August and 7 September 2012. We examine the response of the outlet glaciers that fed the MIS from local ice caps to the removal of the ice shelf. We use spaceborne laser altimetry and multiple optically derived digital elevation models to track ice surface elevation change rates (dh/dt) between 1984 and 2014. Glacier speeds are measured by pixel‐tracking from optical and RADAR imagery between 2010 and 2014 and interferometric synthetic aperture radar in 1995 to compare precollapse and postcollapse velocities. We find that the three main outlet glaciers that fed the MIS are thinning an order of magnitude more rapidly than most of the rest of Severnaya Zemyla, based upon ICESat data from 2003 to 2009. Recent, 2012 to 2014 thinning rates are three to four times faster than the 30 year average thinning rate, calculated between 1984 and 2014. The springtime speeds of the largest outlet glacier (Issledovateley) have increased more than 200% at the terminus between April 2010 and April 2014. To date, changes in surface elevation (dh/dt) and velocity at the outlet glaciers near MIS are smaller than glacier responses to ice shelf collapse in Antarctica. It is possible that the MIS was already very weak prior to the 2012 collapse and unable to support back stress. Further observations are required to assess whether the thinning and nonmelt season glacier speeds are continuing to accelerate.

星载激光测高技术发展现状

星载激光测高技术发展现状

Calibration of spaceborne laser Altimeters-an algorithm and the site selection problem

Meeting the accuracy demand of products derived from spaceborne laser altimetry requires post-launch calibration/validation procedures. Over general surfaces, such as the ones land or ice offer, calibration methods that suite undulating topography should be applied. Whereas the estimation of calibration parameters usually refers to the derivation of an error model, the problem here extends beyond that. Not knowing in advance the offsets between the recorded and actual footprint locations implies that the offsets and the calibration parameters should be estimated jointly. In addition, concerns arise regarding the reliability and quality of the estimates, namely avoiding convergence to a false solution and avoiding estimates that are highly correlated and with a low level of accuracy. The correlation and the accuracy can indeed be estimated in retrospect, but the preference is to learn in advance what factors affect them and under what circumstances they can be optimized. This paper analyzes the calibration problem along the lines of correctness and reliable estimation and shows that the error recovery model provides ample information that can lead to a solution that is both efficient and an integral part of a calibration model. Analysis of the model shows that over natural topography relatively short sites are sufficient for achieving a reliable calibration. The paper then shows that by applying optimization criteria on the estimation, rules for predicting the quality of the solution can be derived as well as general measures for evaluating sites considered for calibration.