BOCA: Beaufort-Chukchi Altimetry for Dynamic Topography and Geostrophic Currents

When using this dataset, please cite the BOCA Zenodo record.

1. Summary

BOCA (Beaufort–Chukchi Altimetry for Dynamic Topography and Geostrophic Currents) is a high-resolution multi-mission satellite radar altimetry dataset for the Beaufort and Chukchi Seas (65–88°N and 170°E–240°E) covering 2002–2024. It provides sea level anomaly (SLA), absolute dynamic topography (ADT), and eastward and northward surface geostrophic current components on a level-10 icosahedral grid with approximately 8 km spatial spacing. Each daily mapped field is based on observations within a ±5-day window around its reference date. Gaps due to insufficient data are retained.

Version 1.0.

2. Data Processing

The processing methodology used for BOCA builds on the Arctic satellite-altimetry processing described in Pisareva et al. (2025) and extends it to a cross-calibrated multi-mission record covering 2002–2024.

BOCA combines observations from Envisat (European Space Agency, ESA), CryoSat-2 (ESA), and SARAL/AltiKa (Centre national d’ études spatiales, CNES, and the Indian Space Research Organisation, ISRO).

In ice-covered regions, sea-surface-height (SSH) observations were retrieved from radar echoes classified as leads or open water, while sea-ice returns were excluded using an unsupervised sea ice/lead/open-water classification (Müller et al., 2017). Altimeter ranges for Envisat and SARAL/AltiKa were processed with ALES+ (Passaro et al., 2018), enabling a bias-free transition between lead, sea-ice, and open-ocean surface conditions. Atmospheric and geophysical corrections were applied using data from DGFI-TUM's Open Altimeter Database (OpenADB, Schwatke et al., 2024).

The three satellite missions were cross-calibrated following the method of Bosch et al. (2014), adapted to the Arctic as in Passaro et al. (2020) and referenced to CryoSat-2. A spatially varying offset correction was additionally applied to Envisat SLA observations retrieved from leads.

To remove erroneous SSH from the dataset, an outlier-rejection strategy similar to that of Passaro et al. (2020) was performed. Afterward, ADT was obtained following the methodology proposed in Rio (2010) and Johannessen et al. (2014) by reducing the along-track SSH by the mean sea surface (DTU21MSS used; Andersen et al., 2023) and by adding the corresponding mean dynamic topography (DTU22MDT used; Knudsen et al., 2022): ADT = SLA + MDT = SSH − MSS + MDT.

The filtered along-track observations were mapped by least-squares adjustment with Gaussian distance weighting onto the level-10 icosahedral grid. Surface geostrophic currents were derived directly from the fitted ADT slopes.

3. Data Format and Variable Description

BOCA is distributed as a single NetCDF-4 file following the CF-1.13 and ACDD-1.3 metadata conventions.

point
Index of the Level-10 icosahedral grid point.

latitude
Latitude of the grid point [degrees north].

longitude
Longitude of the grid point [degrees east].

time
Reference date corresponding to the middle of the mapping interval [days since 1970-01-01 00:00:00 UTC].

time_bounds
Start and end dates of the observation interval associated with each mapped field.

sla
Sea level anomaly [m].

adt
Absolute dynamic topography [m].

ugos
Eastward surface geostrophic velocity [m s⁻¹].

vgos
Northward surface geostrophic velocity [m s⁻¹].

Missing data are represented by NaN.

4. References

Andersen O. B., Rose S. K., Abulaitijiang A., Zhang S., Fleury S. (2023). The DTU21 global mean sea surface and first evaluation. Earth System Science Data, 15(9), 4065–4075. https://doi.org/10.5194/essd-15-4065-2023

Bosch, W., Dettmering, D., Schwatke, C. (2014). Multi-mission cross-calibration of satellite altimeters: Constructing a long-term data record for global and regional sea level change studies. Remote Sensing, 6(3), 2255–2281. https://doi.org/10.3390/rs6032255

Johannessen, J. A., Raj, R. P., Nilsen, J. E. Ø., Pripp, T., Knudsen, P., Counillon, F., Stammer, D., Bertino, L., Andersen, O. B., Serra, N., Koldunov, N. (2014). Toward improved estimation of the dynamic topography and ocean circulation in the high latitude and Arctic Ocean: the importance of GOCE. Surveys in Geophysics, 35(3), 661–679. https://doi.org/10.1007/s10712-013-9270-y

Knudsen, P., Andersen, O., Maximenko, N., Hafner, J. (2022). A new combined mean dynamic topography model – DTUUH22MDT. Paper presented at the ESA Living Planet Symposium, Bonn, Germany. https://doi.org/10.24400/527896/a03-2022.3482

Müller, F. L., Dettmering, D., Bosch, W., Seitz, F. (2017). Monitoring the Arctic seas: how satellite altimetry can be used to detect open water in sea-ice regions. Remote Sensing, 9(6), 551. https://doi.org/10.3390/rs9060551

Passaro, M., Rose, S. K., Andersen, O. B., Boergens, E., Calafat, F. M., Dettmering, D., Benveniste, J. (2018). ALES+: Adapting a homogenous ocean retracker for satellite altimetry to sea ice leads, coastal and inland waters. Remote Sensing of Environment, 211, 456–471. https://doi.org/10.1016/j.rse.2018.02.074

Passaro, M., Müller, F. L., Dettmering, D. (2020) Baltic+ SEAL: algorithm theoretical baseline document (ATBD), version 2.1. Technical report delivered under the Baltic+ SEAL project. ESA. https://doi.org/10.5270/esa.BalticSEAL.ATBDV2.1

Pisareva, M. N., Müller, F. L., Passaro, M., Schwatke, C., Dettmering, D., Seitz, F. (2025). Chukchi Sea circulation and Bering Strait flow reversals from reprocessed satellite altimetry. Ocean Dynamics, 75, 26. https://doi.org/10.1007/s10236-025-01672-9

Rio, M. H. (2010). Absolute Dynamic Topography from Altimetry: Status and Prospects in the Upcoming GOCE Era. In: V. Barale, J. F. R. Gower, & L. Alberotanza (Eds.), Oceanography from Space: Revisited (pp. 165–179). Springer, Dordrecht. https://doi.org/10.1007/978-90-481-8681-5_10

Schwatke, C., Dettmering, D., Passaro, M., Hart-Davis, M., Scherer, D., Müller, F. L., Bosch, W., Seitz, F. (2024). OpenADB: DGFI-TUM's open altimeter database. Geoscience Data Journal, 11(4), 573–588. https://doi.org/10.1002/gdj3.233