Monitoring Bedfast Ice and Ice Phenology in Lakes of the Lena River Delta Using TerraSAR-X Backscatter and Coherence Time Series

Abstract

Thermokarst lakes and ponds are major elements of permafrost landscapes, occupying up to 40% of the land area in some Arctic regions. Shallow lakes freeze to the bed, thus preventing permafrost thaw underneath them and limiting the length of the period with greenhouse gas production in the unfrozen lake sediments. Radar remote sensing permits to distinguish lakes with bedfast ice due to the difference in backscatter intensities from bedfast and floating ice. This study investigates the potential of a unique time series of three-year repeat-pass TerraSAR-X (TSX) imagery with high temporal (11 days) and spatial (10 m) resolution for monitoring bedfast ice as well as ice phenology of lakes in the zone of continuous permafrost in the Lena River Delta, Siberia. TSX backscatter intensity is shown to be an excellent tool for monitoring floating versus bedfast lake ice as well as ice phenology. TSX-derived timing of ice grounding and the ice growth model CLIMo are used to retrieve the ice thicknesses of the bedfast ice at points where in situ ice thickness measurements were available. Comparison shows good agreement in the year of field measurements. Additionally, for the first time, an 11-day sequential interferometric coherence time series is analyzed as a supplementary approach for the bedfast ice monitoring. The coherence time series detects most of the ice grounding as well as spring snow/ice melt onset. Overall, the results show the great value of TSX time series for monitoring Arctic lake ice and provide a basis for various applications: for instance, derivation of shallow lakes bathymetry, evaluation of winter water resources and locating fish winter habitat as well as estimation of taliks extent in permafrost.

Transient modeling of the ground thermal conditions using satellite data in the Lena River delta, Siberia

“…Almost three quarters of the grid cells feature water fractions of less than 20 %. However, relatively shallow thermokarst lakes dominate in the LRD, which at least partly freeze to the bottom in winter (Schwamborn et al, 2002a;Antonova et al, 2016), so microwave emission becomes similar to land areas, although in particular the wavelength dependency of the effect may be complex (Gunn et al, 2011). Furthermore, the winter discharge of the Lena River is very low compared to other northern rivers, as the catchment is largely located in the continuous permafrost zone (Yang et al, 2002).…”

Circumpolar Mapping of Ground-Fast Lake Ice

“…The talik depth is expected to be higher for smaller terraces. Higher spatial resolution SAR missions such as TerraSAR-X could also be used (Jones et al, 2013;Antonova et al, 2016) to identify these smaller littoral terraces, as well as to identify any subtle changes locally. However, the application of such data over larger regions across the Arctic is not possible due to their limited spatial coverage.…”

Thermokarst pond dynamics in subarctic environment monitoring with radar remote sensing

“…More detailed water‐depth information could be obtained from continuous time series of SAR images. Antonova et al (2016) used time‐series backscatter intensity data to derive the timing of ice grounding of thermokarst ponds/lakes with grounded ice . The ice thickness (water depth) of thermokarst ponds/lakes with grounded ice can be retrieved by combining the timing of ice grounding and a model of ice growth.…”

“…Therefore, radar remote sensing can distinguish between these two ice-cover regimes due to the difference in the backscatter intensities between grounded and floating ice. [17][18][19][20][21][22][23] On radar images acquired during winter, ponds/lakes with floating ice exhibit high backscatter intensity, whereas those with grounded ice exhibit remarkable lower values. Jeffries et al (1996) used synthetic-aperture radar (SAR) imagery to determine thermokarst lake depth and water availability in the Barrow area, Alaska.…”

“…In contrast, in the case of grounded lake ice, the microwaves pass through the snow and lake ice, and most of the radar signal is transmitted below the lake bed, resulting in low‐intensity backscatter. Therefore, radar remote sensing can distinguish between these two ice‐cover regimes due to the difference in the backscatter intensities between grounded and floating ice . On radar images acquired during winter, ponds/lakes with floating ice exhibit high backscatter intensity, whereas those with grounded ice exhibit remarkable lower values.…”