Interferometric synthetic aperture radar data from 2021 for landslides at Barry Arm Fjord, Alaska

Subaerial landslides at the head of the Barry Arm fjord remain a tsunami threat for the Prince William Sound region in southern Alaska. Tasked RADARSAT-2 synthetic aperture radar (SAR) data from two ultrafine beam modes (2 m), U19 and U15, were used to measure landslide movement of slopes near the toe of the Barry Glacier between 21 May 2021 and 5 November 2021. Data were acquired every 24 days, with U19 beginning on 21 May 2021 and U15 beginning on 28 May 2021. For a few planned acquisition dates, scenes were not captured because of technical issues. Interferometric synthetic aperture radar (InSAR) deformation maps (interferograms) are provided in wrapped phase (line-of-sight (LOS) phase in radians between 0 and 2π). For landslide areas of interest (Landslides A and B, Figure 1) with more than 25% pixels with coherence values > 0.25, unwrapped phase deformation maps are also provided with displacement in centimeters. These products were created following the same methodology as described in Schaefer et al. (2020), which provides InSAR data for the same landslides in 2020. See methodology file in Schaefer et al. (2020) for processing details. All scenes were filtered by averaging values over 4 lines in both the range and azimuth direction, resulting in 8 m pixel interferograms. For removing topographic phase contributions, this data release uses a different digital terrain model (DTM) than the one that was used in Schaefer (2020). Herein, we use a spliced DTM which combines the 5 m-horizontal resolution IFSAR DTM acquired in 2010, and a 1-m horizontal resolution lidar-derived DTM acquired by the Alaska Division of Geological and Geophysical Surveys (DGGS) on 26 June 2020 (Daanen et al., 2020). In contrast, Schaefer et al. (2020) used the 5 m IFSAR DTM. Non-negligible phase contributions from topography likely remain in areas outside of the lidar-derived DTM (Figure 1).

For each time frame between SAR acquisitions, we describe interferogram results for Landslide A and Landslide B on the western slope of the Barry Arm fjord near the terminus of the Barry Glacier (Figure 1). The kinematic elements of both landslides are adopted from mapping by Coe et al. (2020); Landslide A is composed of four kinematic elements (Kite, Prow, Core, Tail) and Landslide B is composed of one kinematic element (Wedge), which are referred to in the scene descriptions below. All displacement values provided in the descriptions of individual interferograms are given in the LOS direction. 
 
Data are provided in Geostationary Earth Orbit Tagged Image File Format (GeoTIFF) and Keyhole Markup Language (KMZ) formats. For each time frame, a Tagged Image Format (TIF) image is provided that shows an aerial image acquired by ©Planet 2021 on 28 August 2021 overlain with the landslide kinematic elements, the wrapped and unwrapped (when available) interferograms, scale, and satellite look direction information. All coordinates provided are in the World Geodetic System 1984 (WGS84) coordinate system.

Summary of movement during the 2021 monitoring period: We present InSAR detected deformation for two landslides on the southeast-facing slope at the Barry Arm fjord between 21 May and 5 November, 2021. Early (21 May – 21 June) and late (12 October - 5 November) scenes contained substantial noise, likely because of differences in snow cover or adverse atmospheric conditions. These environmental conditions resulted in very few coherent pixels and thus insufficient data to detect landslide displacement during these times.
 
During time periods with moderate-to-extensive coherent pixels (28 May – 18 September), four areas had apparent LOS movement: (1) Areas in the upper part of the Core ranging between 0.005 - 0.05 km2 (near -148.159°, 61.153°) moved downslope a total of ~2 cm between 28 May and 21 June, increased to ~5 cm between 15 July and 8 August, and then back to ~ 2 cm between 25 August and 18 September. (2) A 0.3 km2 area in the upper part of the Kite (centered on -148.170°, 61.140°) moved consistently throughout the summer and early fall, totaling ~ 8 cm of cumulative movement between 21 June and 1 September. This area was incoherent outside of this time frame. (3) Small amounts of movement (