Investigation of Environmental Effects on Coherence Loss in SAR Interferometry for Snow Water Equivalent Retrieval

Abstract

Interferometric Synthetic Aperture Radar (InSAR) is a promising tool for the retrieval of Snow Water Equivalent (SWE) from space. Due to refraction, the interferometric phase changes with snow depth and density, which is exploited by the InSAR method. While the method was first proposed two decades ago, qualitative research using experimental data analyzing factors affecting retrieval performance remains scarce. In this work a tower-based 1-10 GHz, fully polarimetric SAR with InSAR capabilities was used to analyze the effect of meteorological events (air temperature, precipitation intensity, and wind) on the observed temporal decorrelation of interferometric image pairs, at L-, S-, C-and X-bands. These factors were found to be causes of decorrelation in snow, being the temperature the critical variable in the case of snowmelt events. Of the analyzed bands, L-band presented the best coherence conservation properties. Additionally, the phase change between pairs with sufficient coherence was applied to generate estimates of changes in SWE, studying the retrieval errors at different bands and over different temporal baselines. SWE accumulation was calculated from 6 hours up to 12 days temporal baseline over a non-vegetated area. SWE accumulation profiles were successfully reconstructed for short temporal baselines and low frequencies, while an increase in the retrieval error was observed for high frequencies and long temporal baselines, indicating the limitations of higher frequencies for repeat-pass InSAR retrieval. The analysis was also reproduced over a forested area at L-band with similar results as to the non-vegetated area.

Snow Water Equivalent Retrieval Over Idaho, Part A: Using Sentinel-1 Repeat-Pass Interferometry

“…The SWE profile retrieval using C-band data performs well using 12 hours and 1 day repeat-pass data. The retrieval is poor using the 12-day repeat-pass data at C-band (Ruiz et al, 2022). 6-day repeat pass C-band data showed good performance for small SWE changes but poor performance for large SWE changes between the interferometric pairs due to phase ambiguity caused by large SWE change (Ruiz et al, 2022).…”

“…A high temporal coherence is observed at L-band for dry snow with a month temporal baseline (Molan et al, 2018). Temporal coherence decreases with increasing frequency (Leinss et al, 2015;Nagler et al, 2022;Kellndorfer et al, 2022;Ruiz et al, 2022). A median temporal coherence of about 0.5 is observed at 10.2 GHz and 16.8 GHz even after 60 days (Leinss et al, 2015) for a controlled system.…”

“…This is probably due to random phase drifts over time that cannot be estimated and corrected in a spaceborne system compared to a ground radar. Vegetation cover decreases the temporal coherence significantly at high frequencies (Baduge et al, 2016;Kellndorfer et al, 2022;Ruiz et al, 2022). A tower-based fully polarimetric InSAR studied the effect of air temperature, precipitation intensity, and wind on the temporal decorrelation at L-, S-, C-, and X-bands (Ruiz et al, 2022).…”

“…Vegetation cover decreases the temporal coherence significantly at high frequencies (Baduge et al, 2016;Kellndorfer et al, 2022;Ruiz et al, 2022). A tower-based fully polarimetric InSAR studied the effect of air temperature, precipitation intensity, and wind on the temporal decorrelation at L-, S-, C-, and X-bands (Ruiz et al, 2022). The temperature was shown to be the most critical variable affecting the temporal coherence among other variables.…”

“…The phase change of specularly reflected signals from the snow-ground interface has been shown to be strongly dependent on SWE changes for dry snow (Leinss et al, 2015;Guneriussen et al, 2001;Ruiz et al, 2022) ; in wet snow the phase center is normally at the snow surface, and the phase change is related to depth changes (Yueh et al, 2017(Yueh et al, , 2021Shah et al, 2017).…”