Characterization of Snow Facies on the Greenland Ice Sheet Observed by TanDEM-X Interferometric SAR Data

Abstract

This paper presents for the first time a detailed study on information content of X-band single-pass interferometric spaceborne SAR data with respect to snow facies characterization. An approach for classifying different snow facies of the Greenland Ice Sheet by exploiting X-band TanDEM-X interferometric synthetic aperture radar acquisitions is firstly detailed. Large-scale mosaics of radar backscatter and volume correlation factor, derived from quicklook images of the interferometric coherence, represent the starting point for applying an unsupervised classification method based on the c-means fuzzy clustering algorithm. The data was acquired during winter 2010/2011. A partition of four different snow facies was chosen and interpreted using reference melt data, snow density, and in situ measurements. The variations in the stratification and micro-structure of firn, such as the variations of density with depth and the presence of percolation features, are identified as relevant parameters for explaining the significant differences in the observed interferometric signatures among different snow facies. Moreover, a statistical analysis of backscatter and volume correlation factor provided useful parameters for characterizing the snow facies behavior and analyzing their dependency on the acquisition geometry. Finally, knowing the location and characterization of the different snow facies, the two-way X-band penetration depth over the whole Ice Sheet was estimated. The obtained mean values vary from 2.3 m for the outer snow facies up to 4.18 m for the inner one. The presented approach represents a starting point for a long-term monitoring of ice sheet dynamics, by acquiring time-series, and is of high relevance for the design of future SAR missions as well.

Height Accuracy and Data Coverage for the Final Global TanDEM-X DEM Data

“…Thus one sees, as expected, that the absolute height accuracy over ice regions significantly increases to 6.372 meters and that the mean absolute height error drops down to -2.83 meters with some geocells going below -5 meters. Figure 3 shows the mean height difference and one clearly sees the signal penetration offset between the laser-based ICESat data and the radar-based TanDEM-X height technology over Greenland [9] and Antarctica (negative) as well as the various forest regions (positive). It should be mentioned that the final three rows of DEM tiles, namely latitudes from -90 to -88 degrees, over Antarctica have no ICESat data points for validation as the ICESat system did not cover this region.…”

GNSS-R Ice Sheet Altimetry in Greenland Using TDS-1 Data

“…A recent analysis of data taken by the radar Tandem-X (TDX) mission [44], provides information on the ice refractive index in Greenland showing variations in the range [1.3-1.4] and an average penetration depths on the order of 4 meters for the dry-snow facie. This range of values for the refractive index is consistent with the values near the surface (TDX penetration) in Figure 8.…”

“…Reference [44] compares ICESat laser altimetric measurements h ICESat , which essentially sense the external air-snow interface, and the X-band microwave DEM measured with Tandem-X (TDX), h TDX . The differences ∆h TDX = h ICESat − h TDX , for different facies, are in the range [3.54 − 6.82] meters with standard deviations in the order of two meters.…”

Repeat-pass SAR interferometry for land cover classification: A methodology using Sentinel-1 Short-Time-Series

“…and to use it as input feature for the classification. In this framework, examples are given by the global TanDEM-X Forest/Non-Forest Map [18] [19], or the classification of Greenland snow facies in [20].…”