Assessment of CryoSat-2 interferometric and non-interferometric SAR altimetry over ice sheets

Malcolm Mcmillan,Andrew Shepherd,Alan Muir,Julia Gaudelli,Anna E Hogg,Robert Cullen

doi:10.1016/j.asr.2017.11.036

Abstract

The launch of CryoSat-2 heralded a new era of interferometric Synthetic Aperture Radar altimetry over the Polar Ice Sheets. The mission’s novel SAR interferometric (SARIn) mode of operation has enabled monitoring of rapidly changing coastal regions, which had been challenging for previous low resolution altimeters. Given the growing requirement to continue the 25-year altimeter record, there is now a need to assess the differences between existing SAR and SARIn altimeter datasets, with a view to understanding the impact on ice sheet retrievals of the different radar hardware and processing methodologies. Uniquely, CryoSat-2 data can be processed both with and without interferometric information, offering the opportunity to directly compare the SAR and SARIn products generated by the current ground segment. Here, we provide a first comparison of these Level-2 datasets, and evaluate their capacity to measure ice sheet elevation and elevation change. We find that the current interferometric product has substantially improved precision, accuracy and coverage compared to its non-interferometric counterpart, yielding a ∼35% improvement in the root-mean-square-difference (RMSD) of elevations recorded at orbital cross-overs, and a ∼30% lower RMSD of elevation rates relative to Operation IceBridge airborne altimeter measurements. This analysis demonstrates the value that the interferometer adds to the current CryoSat-2 configuration, and highlights the importance for non-interferometric SAR Level-2 processing of the auxiliary data used to identify the location of the echoing point. These results provide a benchmark of the relative performance of the Level-2 interferometric and non-interferometric products currently produced by the ground segment, which will help to inform the design and implementation of a future polar radar altimeter mission.

Highlights

For the past quarter of a century, satellite radar altimeters have acquired measurements across Earth’s polar regions, mapping the ice sheets of Greenland and Antarctica at the continental scale, and establishing a near continuous record of ice sheet elevation evolution
In this study we have aimed to provide a first assessment of the relative performance of interferometric and noninterferometric CryoSat-2 Level 2 SAR altimetry products over ice sheets, as generated by the current ground segment
This study has provided a first comparison between CryoSat-2 interferometric and non-interferometric altimeter Level-2 products over ice sheets, and an indication of the benefits associated with the former

Summary

Introduction

For the past quarter of a century, satellite radar altimeters have acquired measurements across Earth’s polar regions, mapping the ice sheets of Greenland and Antarctica at the continental scale, and establishing a near continuous record of ice sheet elevation evolution These observations have provided systematic measurements of changes in ice sheet volume (Davis and Ferguson, 2004; Johannessen et al, 2005; Helm et al, 2014) and mass (Wingham et al, 2006b; Zwally et al, 2011; Shepherd et al, 2012; McMillan et al, 2014a, 2016), which have informed community assessments of global mean sea level rise (Vaughan et al, 2013). They have provided detailed topographic information (Remy et al, 1989; Bamber and Bindschadler, 1997; Bamber et al, 2009; Helm et al, 2014), which provides a boundary condition for numerical ice sheet models

Results

Discussion

Conclusion