DOI: 10.5281/zenodo.11071898
title: Elevation bias due to penetration of spaceborne radar signal on Grosser Aletschgletscher, Switzerland - supplementary datasets

description: Introduction

We provide DEMs from Pléiades stereo images and TanDEM-X acquired in March 2021 and their difference DEM (dDEM) used to estimate the elevation bias due to radar penetration on Grosser Aletschgletscher, Switzerland. Additionally, we provide the reference DEM (i.e., swissALTI3D) used for the Pléiades DEM co-registration and TanDEM-X production, stable terrain masks used for the co-registration and the glacier outline

These are supplementary datasets associated to the publication by Bannwart et al., (2024a): “Elevation bias due to penetration of spaceborne radar signal on Grosser Aletschgletscher, Switzerland”, Journal of Glaciology. DOI: https://doi.org/10.1017/jog.2024.37

Datasets and Citation

The following datasets have been used and/or produced as part of the study above. Below you find a description of the individual datasets and their generation, including a citation example for each dataset. In general, when one or more datasets are used, both the individual dataset as well as the study (Bannwart et al. 2024) need to be cited. If you refer to the entire dataset, cite the Zenodo entry as well as the study.





TanDEM-X_DEM_6m_EPSG_32632_non_coreg.tif




TanDEM-X_DEM_6m_EPSG_32632_coreg.tif




Pleiades_DEM_2m_EPSG_32632_non_coreg.tif




Pleiades_DEM_6m_EPSG_32632_coreg.tif 




swissALTI3D_2m_EPSG_32632.tif




dDEM_non_corrected_6m_EPSG_32632.tif




dDEM_corrected_6m_EPSG_32632.tif




stable_terrain_mask_coreg_Pléiades_2m_EPSG_32632.tif




stable_terrain_mask_coreg_TanDEM-X_6m_EPSG_32632.tif




stable_terrain_mask_coreg_TanDEM-X_modified_6m_EPSG_32632.tif




glacier_outline_2021.shp



Data and Methods

TanDEM-X DEMs (non co-registered and co-registered):

We used an InSAR DEM generated from TanDEM-X Coregistered Single look Slant range Complex (CoSSC) data provided by the German Aerospace Center (DLR) through the project XTI_GLAC7746. The DEM originates from a single bistatic X-band (9.65 GHz) InSAR acquisition in the polarisations VV and HH from 30 March 2021 at 5:45 Central Europe Time. We used the operational processing system of the TanDEM-X mission to generate the DEM. The removal of artefacts resulted in data voids. The TanDEM-X DEM was then co-registered with the Pléiades DEM (see publication).

Resolution: 6 m

Coordinate reference system: EPSG:32632

Citation of individual dataset: 

TanDEM-X © DLR 2024

DLR-IMF: TanDEM-X Payload Ground Segment - CoSSC Generation and Interferometric Considerations, German Aerospace Center (DLR), Remote Sensing Technology Institute (IMF) Oberpfaffenhofen, Germany, Issue 1.0, available at: https://tandemx-science.dlr.de/ (last access: 3 May 2024), doc. TD-PGS-TN-3129.

DLR-EOC: TanDEM-X Ground Segment – DEM Products Specification Document, German Aerospace Center (DLR) – Earth Observation Center (EOC), EOC, DLR, Oberpfaffenhofen, Germany, 3.2 Edn., available at: https://tandemx-science.dlr.de/ (last access: 3 May 2024), doc. TD-GS-PS-0021, 2018.

Citation example:

“The TanDEM-X DEM (DLR 2024; DLR-IMF 2024; DLR-EOC 2024) from the study of Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY-NC-SA 4.0 International License (Attribution-NonCommercial-ShareAlike).

Pléiades DEMs (non co-registered and co-registered):

The stereo pair was acquired on 31 March 2021 at 10:40 Central Europe Time. The images were processed with the NASA Ames Stereo Pipeline (ASP, Beyer and others, 2018) to generate  the DEM with a ground-sampling distance of 2 m using the Semi-Global-Matching algorithm and the processing parameters from Deschamps-Berger and others (2020) without ground control points (GCPs). The Pléiades DEM was then co-registered with the reference DEM (see publication). To calculate the DEM differencing, the Pléiades DEM was resampled using bilinear interpolation to 6 m to match the resolution of the TanDEM-X DEM.

Resolution: 2 m (non co-registered), 6 m (co-registered)

Coordinate reference system: EPSG:32632

Citation of individual dataset: 

Pléiades © CNES 2023, distribution AIRBUS DS

Berthier, E., Lebreton, J., Fontannaz, D., Déprez, A., Michéa, D., Malet, J.-P., LEGOS-OMP / Data Terra (ForM@Ter-Theia) (2024). Pléiades Glacier Observatory Data Products. EOST. (Collection). doi: 10.25577/313a-a978

Citation example:

“The Pléiades DEM (CNES 2023; Berthier et al. 2024) from the study of Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY-NC 4.0 International License (Attribution-NonCommercial).

swissALTI3D: 

We used the swissALTI3D DEM from swisstopo (Swiss Federal Office of Topography (2021a) as a reference DEM for (a) the co-registration of the Pléiades DEM and (b) the generation of the TanDEM-X DEM (i.e., phase unwrapping). This swissALTI3D DEM has a resolution of 2 m and was  generated using aerial images acquired between July and September 2017. The downloaded version was provided in orthometric heights and swiss coordinate system CH1903+ / LV95 (EPSG:2056). Therefore, we converted to WGS84 UTM projection (EPSG:32632) using cubic interpolation and to ellipsoidal heights using the Swiss geoid model provided by swisstopo (Swiss Federal Office of Topography, 2021b). The geoid is provided in the geographic coordinate system (EPSG:4258), which was projected to UTM using the cubic method.

Resolution: 2 m

Coordinate reference system: EPSG:32632

Citation of individual dataset:  

Swiss Federal Office of Topography (2021). swissALTI3D. Das hochpräzise digitale Höhenmodell der Schweiz. Bundesamt für Landestopografie swisstopo, ed. Wabern. https://www.swisstopo.admin.ch/de/geodata/height/alti3d.html.

Citation example:

“The swissALTI3D (Swiss Federal Office of Topography 2021) as used in Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY 4.0 International License (Attribution).

DEM differencing (dDEM, non corrected and corrected):

We used DEM differencing to quantify the elevation difference (dh) between the TanDEM-X DEM and the Pléiades DEM. To calculate the dDEM we subtracted the Pléiades DEM from the TanDEM-X DEM (after co-registration). Values larger than ±50m in the dDEM are considered outliers and removed. Further, on the tongue of Grosser Aletschgletscher we encountered a bias in the dDEM originating from the phase unwrapping during the TanDEM-X DEM production. This resulted in unrealistic positive elevation differences at the tongue (up to 50 m). Therefore, on-glacier, we additionally removed positive differences larger than 5 m. For direct comparison of the elevation differences with the GPR, snow pit and snow core measurements one has to assume a signal propagation velocity within the snow and ice medium, which will lead to a smaller height of ambiguity in the snow volume and a reduced actual penetration depth. As a measure for the actual radar penetration depth the previously calculated dDEM due to signal penetration is scaled proportionally with  (approx. 78%). The resulting file is called “dDEM_corrected”. For more information we refer to the publication.

Resolution: 6 m

Coordinate reference system: EPSG:32632

Citation of individual dataset:  

Bannwart, J., Piermattei, L., Dussaillant, I., Krieger, L., Floricioiu, D., Berthier, E., Roeoesli, C., Machguth, H. and Zemp, M. (2024). Elevation bias due to penetration of spaceborne radar signal on Grosser Aletschgletscher, Switzerland - supplementary datasets [Data set]. Zenodo. https://doi.org/10.5281/zenodo.11071899

Citation example:

“The dDEM (Bannwart et al. 2024b) as produced in Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY-NC-SA 4.0 International License (Attribution-NonCommercial-ShareAlike).

Stable terrain masks:

The stable terrain masks have been used to co-register the Pléiades DEM to the swissALTI3D and the TanDEM-X DEM to the Pléiades DEM. The two masks were created using the Pléiades orthophoto and a supervised classification method following the approach by Deschamps-Berger C and others (2020). The masks consist of off-glacier areas where no changes are expected between the two DEMs, and only snow-free pixels were retained. The masks are a binary file with a resolution of 2m and 6 m, respectively, in UTM32N projection. To evaluate the sensitivity of the radar penetration bias to co-registration, we tested two co-registration algorithms on two stable terrain masks used to co-register the TanDEM-X DEM. In the modified stable mask, we manually removed pixels in the sparse forest and dark shadow areas based on a visual inspection of the Pléiades orthophoto. 

Resolution: 2 m (mask used to co-register Pléiades DEM to the swissALTI3D), 6 m (masks used to co-register the TanDEM-X DEM to the Pléiased DEM)

Coordinate reference system: EPSG:32632

Citation of individual dataset:

Bannwart, J., Piermattei, L., Dussaillant, I., Krieger, L., Floricioiu, D., Berthier, E., Roeoesli, C., Machguth, H. and Zemp, M. (2024). Elevation bias due to penetration of spaceborne radar signal on Grosser Aletschgletscher, Switzerland - supplementary datasets [Data set]. Zenodo. https://doi.org/10.5281/zenodo.11071899  

Citation example:

“The stable terrain mask to co-register the Pléiades DEM (Bannwart et al. 2024b) in Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY-NC 4.0 International License (Attribution-NonCommercial).

Glacier outline:

The outline as a shapefile of Grosser Aletschgletscher was manually adjusted to the glacier’s outline in 2021 based on the GLIMS outlines from 2015 (Paul and others, 2019) and the Pléiades orthophoto.

Citation of individual dataset:

Bannwart, J., Piermattei, L., Dussaillant, I., Krieger, L., Floricioiu, D., Berthier, E., Roeoesli, C., Machguth, H. and Zemp, M. (2024). Elevation bias due to penetration of spaceborne radar signal on Grosser Aletschgletscher, Switzerland - supplementary datasets [Data set]. Zenodo. https://doi.org/10.5281/zenodo.11071899

Paul, F. (submitter), Azzoni, R.S., Fugazza, D., Le Bris, R., Nemec, J., Paul, F., Rabatel, A., Ramusovic, M.; Rastner, P., Schaub, Y., Schwaizer (nee Bippus), G (analysts). (2019) GLIMS Glacier Database. Boulder, Co. National Snow and Ice Data Center.  http://dx.doi.org/10.7265/N5V98602.

Citation example:

“The glacier outline of Grosser Aletschgletscher in 2021 (Bannwart et al 2024b; Paul et al. 2019) as produced in Bannwart et al. (2024a)....”

Licence:

This dataset is licensed under a Creative Commons CC BY-NC 4.0 International License (Attribution-NonCommercial).

Acknowledgements

We thank swisstopo for providing the swissALTI3D and CNES for their support.