Towards ice thickness inversion: an evaluation of global DEMs by ICESat-2 in the glacierized Tibetan Plateau

Abstract

Abstract. Accurate estimates of regional ice thickness, which are generally produced by ice-thickness inversion models, are crucial for assessments of available freshwater resources and sea level rise. Digital elevation model (DEM) derived surface topography of glaciers is a primary data source for such models. However, the scarce in-situ measurements of glacier surface elevation limit the evaluation of DEM uncertainty, and hence its influence on ice-thickness modelling over the glacierized area of the Tibetan Plateau (TP). Here, we examine the performance over the glacierized TP of six widely used and mainly global-scale DEMs: AW3D30 (30 m), SRTM-GL1 (30 m), NASADEM (30 m), TanDEM-X (90 m), SRTM v4.1 (90 m) and MERIT (90 m) by using ICESat-2 laser altimetry data while considering the effects of glacier dynamics, terrain, and DEM misregistration. The results reveal NASADEM as the best performer, with a small mean error (ME) of −1.0 and a root mean squared error (RMSE) of 12.6 m. A systematic vertical offset existed in AW3D30 (−35.3 ME and 34.9 m RMSE), although it had a similar relative accuracy to NASADEM (~ 13 m STD). TanDEM-X also performs well (−0.1 ME and 15.1 m RMSE), but suffers from serious errors and outliers on steep slopes. SRTM-based DEMs (SRTM-GL1, SRTM v4.1, and MERIT) (all ~ 36 m RMSE) had an inferior performance to NASADEM. However, their errors were reduced in the ablation zone when glacier variations were excluded. Errors in the six DEMs increased from the south-facing to the north-facing aspect and become larger with increasing slope. Misregistration of DEMs relative to ICESat-2 footprint in most glacier areas is small (less than one pixel). An intercomparison of four ice-thickness models: GlabTop2, Open Global Glacier Model (OGGM), Huss-Farinotti (HF), Ice Thickness Inversion Based on Velocity (ITIBOV), show that GlabTop2 is sensitive to the accuracy of both elevation and slope, while OGGM and HF are less sensitive to DEM quality, and ITIBOV is the most sensitive to slope accuracy. Considering the inconsistency of DEMs acquisition dates, NASADEM would be a best choice for ice-thickness estimates over the TP, followed by AW3D30, and TanDEM-X (if steep and high elevation terrain can be avoided). Our assessment figures out the performances of mainly global DEMs over the glacierized TP. This study not only avails the glacier thickness estimation with ice thickness inversion models, but also offered references for other cryosphere studies using DEM.

Glacier mass-balance estimates over High Mountain Asia from 2000 to 2021 based on ICESat-2 and NASADEM

“…The larger uncertainty in higher altitude regions is associated with the small number of laser footprints collected in glaciated areas. The larger uncertainty may also be attributed to the larger errors in the NASADEM on steeper slopes (Chen and others, 2022) and the relatively larger percentage of voids compared to lower-slope regions.…”

“…Compared with the C-band SRTM 1 arc-second v3 product, this processing scheme can deal with strong offsets and ramps occurring in regions where the acquisition strips cross each other (Crippen and others, 2016). It has the best performance among the open-access DEMs (Chen and others, 2022), and has few voids remaining. We masked out the void-fill regions in the NASADEM data (Braun and others, 2019), as the fill-in data have a completely different time stamp and may not be inherently consistent with the original radar data on glaciers, or the data used to fill in could have already originated from optical data like ASTER Global Digital Elevation Model (GDEM) (NASA JPL, 2021).…”

“…The ICESat-2 ATL06 (Land Ice Elevation) product has been applied to study the ice mass balance of Greenland and Antarctic ice sheets (Smith and others, 2020), small glaciers such as those in Svalbard (Sochor and others, 2021) and glacier elevation changes in steep and rugged regions such as HMA (Wang and others, 2021; Shen and others, 2022; Zhao and others, 2022). The ICESat-2 ATL06 product was also found to have a higher accuracy than other DEM products (Chen and others, 2022). Consequently, it is relevant to use ICESat-2 data collected over the HMA from 2018 to 2021 to study the spatiotemporal glacier mass variations.…”