From Glacier Facies to SAR Backscatter Zones via GPR

Abstract

Abstract-We present a comparison between data acquired with frequency-modulated ground-penetrating radar (GPR) and satellite synthetic aperture radar (SAR). Both radars are polarimetric and operate at a center frequency of 5.3 GHz. The field site is the polythermal glacier Kongsvegen, Svalbard. Along glacier GPR profiles cover the ablation area and the accumulation area, where the latter consists of superimposed ice (SI) and firn. The glacier facies are clearly identifiable on the GPR profiles, although we show that the copolarized response is better for distinguishing different ice zones, whereas the SI-firn boundary is most obvious in the cross-polarized response. A calibrated backscatter coefficient is calculated for the GPR data and compared with the SAR backscatter coefficient. The SAR zones are in very good agreement with the GPR-derived glacier facies. We show that, in the ablation area, the SAR response is dominated by backscatter from the previous summer surface. In the SI and firn areas, it is dominated by sources below the previous summer surface.

Monitoring glacier zones and snow/firn line changes in the Qinghai–Tibetan Plateau using C-band SAR imagery

“…In C-band, both surface scattering and volume scattering occur in the superimposed ice area due to the air bubbles in the ice (Langley et al, 2009). Superimposed ice is detectable by using cross-polarized ground penetrating radar (Langley et al, 2008); however, whether the superimposed ice is detectable on SAR imagery is controversial. In Brandt et al (2008) and Langley et al (2007), the authors give the backscatter coefficient extent of superimposed ice in C-band co-polarization.…”

Unlocking annual firn layer water equivalents from ground-penetrating radar data on an Alpine glacier

“…Therefore, studies have focused on the mapping of facies zones and other general glaciological characteristics (Pälli et al, 2003;Langley et al, 2008;Eisen et al, 2009;Dunse et al, 2009). On the other hand, GPR not only could accompany ongoing monitoring programmes to complement the sparse accumulation measurements with high spatial resolution but also could be used to retrospectively extend newly initiated time series into the past.…”

Changes in glacier facies zonation on Devon Ice Cap, Nunavut, detected from SAR imagery and field observations

“…2; Bardel et al, 2002;Engeset et al, 2002;Wolken et al, 2009). As discussed in more detail in the Results (Section 5.1), the glacier ice and superimposed ice zones typically have the lowest σ 0 of all facies due to the lack of reflectors at depth, the saturation and percolation zones have high σ 0 due to extensive ice layers and pipes within the firn, while the dry snow zone has low σ 0 due to the lack of internal reflectors (Partington, 1998;Langley et al, 2008). The presence of fresh dry snow above the last summer surface has a negligible impact on the reflected signal due to its low density and small crystal structure, so winter imagery is usually assumed to represent facies formed during the previous summer (Wang et al, 2007).…”

“…For example, Casey and Kelly (2010) were able to identify the glacier ice zone, saturation/percolation zone and transient snow line on Devon Ice Cap using Radarsat-1 data. Langley et al (2008) and Engeset et al (2002) used Envisat ASAR and ERS 1/2 SAR imagery, respectively, to distinguish between firn and ice facies on Kongsvegen, Svalbard. The SAR-derived firn line (area where the nearsurface density structure of an ice cap transitions from ice to firn) and the equilibrium line altitude (ELA) were found to have a significant relationship, suggesting that changes in the location of the SAR-derived firn line could be used as a proxy for detecting changes in relative mass balance (Engeset et al, 2002).…”