Greenland ice velocity maps from the PROMICE project

Abstract

Abstract. We present the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) Ice Velocity product (https://doi.org/10.22008/promice/data/sentinel1icevelocity/greenlandicesheet, Solgaard and Kusk, 2021), which is a time series of Greenland Ice Sheet ice velocity mosaics spanning September 2016 through to the present. The product is based on Sentinel-1 synthetic aperture radar data and has a 500 m grid spacing. A new mosaic is available every 12 d and spans two consecutive Sentinel-1 cycles (24 d). The product is made available within ∼ 10 d of the last acquisition and includes all possible 6 and 12 d pairs within the two Sentinel-1A cycles. We describe our operational processing chain from data selection, mosaicking, and error estimation to final outlier removal. The product is validated against in situ GPS measurements. We find that the standard deviation of the difference between satellite- and GPS-derived velocities (and bias) is 20 m yr−1 (−3 m yr−1) and 27 m yr−1 (−2 m yr−1) for the components in an eastern and northern direction, respectively. Over stable ground the values are 8 m yr−1 (0.1 m yr−1) and 12 m yr−1 (−0.6 m yr−1) in an eastern and northern direction, respectively. This is within the expected values; however, we expect that the GPS measurements carry a considerable part of this uncertainty. We investigate variations in coverage from both a temporal and spatial perspective. The best spatial coverage is achieved in winter due to the comprehensive data coverage by Sentinel-1 and high coherence, while summer mosaics have the lowest coverage due to widespread melt. The southeast Greenland Ice Sheet margin, along with other areas of high accumulation and melt, often has gaps in the ice velocity mosaics. The spatial comprehensiveness and temporal consistency make the product ideal both for monitoring and for studying ice-sheet-wide and glacier-specific ice discharge and dynamics of glaciers on seasonal scales.

Range Geolocation Accuracy of C-/L-Band SAR and its Implications for Operational Stack Coregistration

“…14b and c). Similar bias observations of ∼15 cm have been reported by Solgaard et al [52] and Gisinger et [16] after the Extended Timing Annotation Dataset (ETAD) correction. Since the ETAD correction is designed to correct the effects of focusing approximations, the presence of the bias after the ETAD correction in [16] implies that the bias may not be due to the focusing approximations applied during the Sentinel-1 SAR processing.…”

Greenland ice sheet mass balance from 1840 through next week

“…Discharge across flux gates is derived with a 200 m spatial resolution grid but then summed and provided at glacier resolution. Temporal coverage begins in 1986 with a few velocity estimates and is updated each time a new velocity product is released, which is every ∼ 12 d with a ∼ 30 d lag (Solgaard et al, 2021;data: Solgaard and Kusk, 2021).…”

“…Some changes have been implemented since the last publication describing the discharge product (i.e., Mankoff et al, 2020b). These are minor and include updating the Khan et al (2016) (data: Khan, 2017) surface elevation change product from 2015 through 2019, updating various MEa-SUREs velocity products to their latest version, updating the PROMICE Sentinel ice velocity product from Edition 1 (https://doi.org/10.22008/promice/data/sentinel1icevelocity/ greenlandicesheet/v1.0.0) to Edition 2 (Solgaard et al, 2021;Solgaard and Kusk, 2021), and updating from BedMachine v3 (supplemented in the SE with Millan et al, 2018) to use only BedMachine v4 (Morlighem et al, 2021).…”

“…Temporally, D at daily resolution comes from ∼ 12 d observations upsampled to daily, and those ∼ 12 d resolution observations come from longer time period observations (Solgaard et al, 2021). Because the velocity method uses feature tracking, it is correct on average but misses variability within each sample period (e.g., Greene et al, 2020).…”

“…However, that spatial resolution is generally reduced in the final output to sector or region scale -typically higher than GMB but now lower resolution than VC. The IO temporal resolution (when) is limited by ice velocity data updates, which for the past several years occur every 12 d year-round after the launch of the Sentinel missions (Solgaard et al, 2021). The primary issue with the IO method is unknown ice thickness in some locations (e.g., Mankoff et al, 2020b).…”