DOI: 10.11583/dtu.21369129.v2
title: CRYO2ICE radar/laser freeboards, snow depth on sea ice and comparison against auxiliary data during winter seasos 2020-2022

description: We investigated the near-coincident radar and laser altimetry observations from the CryoSat-2 and ICESat-2 Resonance (CRYO2ICE) campaign, which was initiated in July 2020, for the winter seasons of 2020-2022. We extracted Arctic radar and laser freeboard (the elevation of sea ice above the local sea level depending on scattering horizon), and binned the ICESat-2 observations (r005, ATL10) to the CryoSat-2 observations using a search radius of 3500 m and applied inverse-distancing-weightning. From ICESat-2, both strong and weak beams from all three beam pairs were included. For CryoSat-2, we make use of the Baseline-E from the European Space Agency (ESA), and include two further products using two other retrieval methodologies (CCI+ and LARM). We further derived snow depth from the difference in penetration of the radar and laser (using the freeboards), and this high-resolution orbit-based snow depth estimates were compared with nearest-neighbouring observations from basin-scale snow depth composites using either passive-microwave-radiometry (AMSR2) or a reanalysis-based model estimate (SMLG). Orbit-based snow depth estimates were also compared with buoy estimates (acoustic or thermistor string buoys). The study has also investigated drift and individual CryoSat-2 ESA Baseline-E crossover, where the data to those two analyses can be freely downloaded from the relevant providers (see Fredensborg Hansen et al., 2023 - Open Research Section).This dataset includes the CRYO2ICE tracks + coincident buoy data computed for Fredensborg Hansen et al. (2023), where the code is available here): https://github.com/reneefredensborg/CRYO2ICE-Arctic-freeboards-and-snow-depth-2020-2022The files/folders are as follows:File: <b><i>cryo2ice_tracks_{season}.csv</i></b> ---- information (IDs of CryoSat-2/ICESat-2 tracks along with start/end times of the tracks) for others to compare and identify CRYO2ICE tracks for future studies for both winter seasons.Files <i>(...)_smooth.h5 </i>in <b><i>CRYO2ICE_individual </i></b><b>ZIP-folder</b> (individual CRYO2ICE tracks identified)<i>: </i>CRYO2ICE individual tracks after binning (search radius of 3500 m, inverse-distancing-weighting etc., following the methdology presented in Fredensborg Hansen et al. (2023)) available as .h5-files.Files <i>(...)_smooth_test.csv </i>in <b><i>CRYO2ICE_individual_comparison </i></b><b>ZIP-folder</b> for<i>: </i>Includes all of the CRYO2ICE track with additional re-trackers (LARM (Landy et al, 2020) and CCI+ (Rinne and Hendricks, 2023, only available for 2020-2021), along-track snow depth of Warren et al. (1999) with modifications (mW99) extracted from ESA's CryoSat-2 product, as well as nearest-neighbour daily composite observations from SMLG (Liston et al., 2018) and AMSR2 (Meier et al., 2018), available as .csv-files.Files: <i>(....)_gridded_smooth_25km.csv</i> in <b><i>CRYO2ICE_25km_segments </i></b><b>ZIP-folder</b>---- all CRYO2ICE tracks (after processing, filtration and binning) computed as 25-km orbit segments for both winter seasons..Files: <i>(...)_semivariogram.csv </i>in <b><i>CRYO2ICE_semivariogram</i></b><i> </i><b>ZIP </b><b>f</b><b>older</b>(76 tracks investigated, November 2020 as example) ---- the analysis of tracks to identify the search radius to use when binning CS2 and IS2 to comparable observations.<b>SIMBA buoy comparison (ZIP folder): </b>Computed daily snow depth estimates are available for both SIMBA buoys (<i>FRIC0607 </i>and <i>PRIC0906</i>) (and a buoy estimated created by combining the two original buoy observations). Coincidident CRYO2ICE observations are available for each of these three daily buoy estimates.<b>ASSIST comparison: </b>one example of coincident CRYO2ICE/ASSIST data (presented in Supporting Information in Fredensborg Hansen et al., 2023) using IceWatch observations, https://icewatch.met.no/, last access: 06-01-2023 (observations-108/109/110 were investigated, but very little coincident data. )<b>AWI buoy comparisons (ZIP folder):</b><i> </i>buoy data from the following buoys <i>2020S98, 2020S105-108 </i>with the acoustic snow depth buoy data from the Alfred Wegener Institute (AWI) by Nicolaus et al. (2017) were used. Averaged daily snow depth estimates (<i>buoyID_daily.csv</i>) using all four sensors and the initial snow depth provided in the buoy deployment documents for each buoy are provided along with coincident CRYO2ICE/AWI buoy observations.<b>CRYO2ICE tracks</b>We refer to the code/READ ME-files/additional descriptions available in the Github repository, where descriptions of what the data entails are provided.<br><b>References</b>Fredensborg Hansen et al. (2023): Arctic freeboard and snow depth from near-coincident CryoSat-2 and ICESat-2 (CRYO2ICE) observations: A first examination during winter 2020-2021. <i>ESS Open Archive.</i> https://doi.org/10.22541/essoar.168614619.96485405/v1Landy, J. C., Petty, A. A., Tsamados, M., & Stroeve, J. C. (2020). Sea ice roughness overlooked as a key source of uncertainty in CryoSat-2 ice freeboard retrievals. <i>Journal of Geophysical Research: Oceans</i>, 125, e2019JC015820. https://doi.org/10.1029/2019JC015820Liston, G. E., Polashenski, C., Rösel, A., Itkin, P., King, J., Merkouriadi, I., & Haapala, J. (2018). A distributed snow-evolution model for sea-ice applications (SnowModel). <i>Journal of Geophysical Research: Oceans</i>, 123, 3786- 3810. https://doi.org/10.1002/2017JC013706Meier, W. N., T. Markus, and J. C. Comiso. (2018). AMSR-E/AMSR2 Unified L3 Daily 12.5 km Brightness Temperatures, Sea Ice Concentration, Motion & Snow Depth Polar Grids, Version 1 [Data Set]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/RA1MIJOYPK3P . Date Accessed 06-01-2023.Nicolaus, M.; Hoppmann, M.; Arndt, S.; Hendricks, S.; Katlein, C.; König-Langlo, G.; Nicolaus, A.; Rossmann, L.; Schiller, M.; Schwegmann, S.; Langevin, D.; Bartsch, A. (2017): Snow height and air temperature on sea ice from Snow Buoy measurements. Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Bremerhaven,https://doi.org/10.1594/PANGAEA.875638Rinne, E., & Hendricks, S. (2023). CCI+ Sea Ice ECV Sea Ice Thickness Product User Guide (PUG) . (Reference D4.2, Phase 1).