Contributors: Lin Gilbert (University of Leeds), Sebastian B. Simonsen (Technical University of Denmark), Jan Wuite (ENVEO IT GmbH)
Issued by: Technical University of Denmark / Sebastian B. Simonsen
Issued Date: 04/05/2021
Ref: C3S_312b_Lot4.D1.IS.4_v3.0_GMB_Algorithm_Theoretical_Basis_Document_i1.0
Official reference number service contract: 2018/C3S_312b_Lot4_EODC/SC2
History of modifications
List of datasets covered by this document
Related documents
Acronyms
Scope of the document
This document is the Algorithm Theoretical Basis Document for Gravimetric Mass Balance (GMB) as part of the Copernicus Ice Sheets and Ice Shelves service. It describes the organisation of the data processing system and how product updates are implemented.
Executive summary
The service addresses three essential climate variables (ECVs) by providing four separate products.
- Ice velocity is given for Greenland in product D3.IS.4
- Gravimetric mass balance is given for Greenland and Antarctica in product D3.IS.5
- Surface elevation change is given for:
- Antarctica in product D3.IS.6.1
- Greenland in product D3.IS.6.2
In this document we describe the gravimetric mass balance. This gravimetric mass balance data is brokered from the Greenland and Antarctic CCI projects. The CCI project's ATBD (Forsberg, R., et al. 2020, Khvorostovsky et al. 2018; Nagler et al. 2018) provides a full description concerning the scientific approach underlying these products. Only output specifics will be given in the main text, other topics will refer to the relevant CCI project's ATBD.
1. Gravimetric mass balance
The gravimetric mass balance (GMB) is a brokered product from the ESA Climate Change Initiative (CCI). For details, the reader is referred to the to the GMB sections of the ESA Greenland_Ice_Sheet_cci and Antarctic_Ice_Sheet_cci products documentation (see Section 1.2)..
1.1. Instruments
The primary satellite source for generation of the GMB is the Gravity Recovery and Climate Experiment (GRACE) (Tapley et al., 2004) satellite mission launched in 2002. The GRACE mission allows fluctuations in ice-sheet mass to be estimated through measurement of their changing gravitational attraction. Advantages of the GRACE method is that it provides regional averages without the need for interpolation, measures the effect of mass fluctuations directly, and permits monthly temporal sampling. However, a key challenge is to discriminate fluctuations in ice-sheet mass from changes in the underlying crust and mantle. The spatial resolution of GRACE observations derived from global spherical harmonic solutions of about 300 km in the Polar Regions is coarse in comparison to that of other geodetic techniques. Hence, a further complicating factor is that signals may leak into regional GRACE solutions as a consequence of remote geophysical processes.
Velicogna and Wahr (2005) published for the first time the possibility of using data from the GRACE mission to determine the mass balance of the Greenland ice sheet. Since then many mass balance estimates of both Greenland and Antarctica have been published, both on ice sheet scale (Chen et al., 2006; Ramillien et al., 2006; Forsberg and Reeh, 2007; Barletta et al., 2008; Velicogna, 2009; Shepherd et al. 2012) and drainage basin scale (Luthcke et al., 2006; Wouters et al., 2008; Schrama and Wouters, 2011; Sasgen et al., 2012; Barletta et al. 2013, Groh and Horwath 2016).
1.2. Input/auxiliary data and algorithms
Information on the data-use and specific algorithms can be found in the following references:
- For the Antarctic Ice sheet: ESA Climate Change Initiative (CCI) Essential Climate Variable (ECV), Antarctic Ice Sheet (AIS) Algorithm Theoretical Basis Document (ATBD) – see Nagler et al 2018 (v3), Nagler 2016 (v1).
- For the Greenland Ice sheet: see Forsberg, R., et al. 2020, Khvorostovsky et al. 2018
1.3. Output data
The brokered data from the two ice sheet CCIs have been interpolated onto a common timeframe to provide a consistent product for both hemispheres. The GMB are given as a single NetCDF-file. Table 1 gives a brief description of the output fields, and a data sample.
Table 1: Summary of variables in the output fields, as given in the NetCDF-file for GMB, C3S_GMB_vers1_2018-12-18.nc
Variable | Short description | Unit | Long description | Data sample |
AntBasin | Basin definition | None | Zwally definition of major drainage basins of the Antarctic Ice Sheet |
|
AntIS_x | Basin x GMB | Gt | Antarctic gravimetric mass balance for basin x | |
AntIS_x_er | Basin x GMB error | Gt | Error estimate of the Antarctic gravimetric mass balance for basin x | |
AntIS_total | Total GMB | Gt | Total Antarctic gravimetric mass balance | |
AntIS_total_er | Total GMB error | Gt | Error estimate of total Antarctic gravimetric mass balance | |
AntPeninsula_total | Total GMB | Gt | Total gravimetric mass balance for the Peninsula | |
AntPeninsula_total_er | Total GMB error | Gt | Error estimate of total gravimetric mass balance for the Peninsula | |
East_AntIS_total | Total GMB | Gt | Total gravimetric mass balance for the East Antarctica | |
East_AntIS_total_er | Total GMB error | Gt | Error estimate of total gravimetric mass balance for the East Antarctica | |
West__AntIS_total_er | Total GMB | Gt | Total gravimetric mass balance for the west Antarctica | |
West__AntIS_total_er | Total GMB error | Gt | Error estimate of total gravimetric mass balance for the West Antarctica | |
GrISBasin | Basin definition | None | Zwally definition of major drainage basins of the Greenland Ice Sheet | |
GrIS_x | Basin x GMB | GT | Greenland gravimetric mass balance for basin x | |
GrIS_x_er | Basin x GMB error | GT | Error estimate of the Greenland gravimetric mass balance for basin x | |
GrIS_total | Total GMB | GT | Total gravimetric mass balance for the Greenland ice sheet | |
GrIS_total_er | Total GMB error | GT | Error estimate of total gravimetric mass balance for the Greenland Ice sheet | |
time | Time | Hours since 01-01-1990 |
References
Barletta, V. R., Bordoni, A., and Sabadini, R.: Isolating the PGR signal in the GRACE data: impact on mass balance estimates in Antarctica and Greenland, Geophys. J. Int., 172, 18–30, doi:10.1111/j.1365- 246X.2007.03630.x, 2008.
Barletta, V. R., Sørensen, L. S., and Forsberg, R. (2013). Scatter of mass changes estimates at basin scale for Greenland and Antarctica. The Cryosphere, 7(5), 1411–1432.
Chen, J. L., Wilson, C. R., Blankenship, D. D., and Tapley, B. D.: Antarctic mass rates from GRACE, Geophys. Res. Lett., 33, L11502, doi:10.1029/2006GL026369, 2006.
Forsberg, R. and Reeh, N.: Mass change of the Greenland Ice Sheet from GRAC E, in: Proceedings, Gravity Field of the Earth – 1st meeting of the International Gravity Field Service, Harita Dergisi, Ankara, vol. 73, avaialble at: http://www.igfs.net, 2007
Forsberg, R., et al (2020), Algorithm Theoretical Baseline Document (ATBD) for the Greenland Ice Sheet CCI+ Project of ESA’s Climate Change Initiative, version 1.2, ST-DTU-ESA-GISCCI+ ATBD001,19-10-20 (https://climate.esa.int/media/documents/ST-DTU-ESA-GISCCI-ATBD-001_v1.2.pdf)
Groh, A., and Horwath, M. (2016). The method of tailored sensitivity kernels for GRACE mass change estimates. Geophysical Research Abstracts, 18, EGU2016-12065.
Khvorostovsky, K. et al., 2018, Algorithm Theoretical Baseline Document (ATBD) for the Greenland Ice Sheet CCI Project of ESA’s Climate Change Initiative, version 3.2 (http://esa-icesheets-greenland-cci.org/index.php?q=webfm_send/170)
Luthcke, S. B., Zwally, H. J., Abdalati, W., Rowlands, D. D., Ray, R. D., Nerem, R. S., Lemoine, F. G., McCarthy, J. J., and Chinn, D. S.: Recent Greenland ice mass loss by drainage system from satellite gravity observations, Science, 314, 1286–1289, 2006.
Nagler, T. et al., 2018, Algorithm Theoretical Baseline Document (ATBD) for the Antarctic Ice Sheet CCI Project of ESA’s Climate Change Initiative, version 3.0. (Contact CCI project for this document: https://climate.esa.int/en/projects/ice-sheets-antarctic/contacts/)
Nagler;T., M. Bässler, D. Floricioiu, A. Groh, M. Horwath, A. Kusk, A. Muir, J. Wuite. Algorithm Theoretical Basis Document (ATBD) for the Antarctic_Ice_Sheet_cci project of ESA's Climate Change Initiative, version 1.0, 18 January 2016 (https://dap.ceda.ac.uk/neodc/esacci/ice_sheets_antarctica/docs/ST-UL-ESA-AISCCI-ATBD-001_v1.0.pdf)
Ramillien, G., Lombart, A., Cazenave, A., Ivins, E. R., Llubes, M., Remy, F., and Biancale, R.: Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE, Global Planet. Change, 53, 198–208, doi:10.1016/j.gloplacha.2006.06.003, 2006.
Sasgen, I., Broeke, M. v. d., Bamber, J. L., Rignot, E., Sandberg Sørensen, L., Wouters, B., Martinec, Z., Velicogna, I., and Simonsen, S. B.: Timing and origin of recent regional ice-mass loss in Greenland, Earth Planet. Sci. Lett., 333–334, 293–303, doi:10.1016/j.epsl.2012.03.033, 2012.
Schrama, E. J. O. and Wouters, B.: Revisiting Greenland ice sheet mass loss observed by GRACE, J. Geophys. Res., 116, B02407, doi:10.1029/2009JB006847, 2011.
Shepherd, A., Ivins, E. R., Geruo, A., Barletta, V. R., Bentley, M. J., Bettadpur, S., Briggs, K. H., Bromwich, D. H., Forsberg, R., Galin, N., Horwath, M., Jacobs, S., Joughin, I., King, M. A., Lenaerts, J. T. M., Li, J. L., Ligtenberg, S. R. M., Luckman, A., Luthcke, S. B., McMillan, M., Meister, R., Milne, G., Mouginot, J., Muir, A., Nicolas, J. P., Paden, J., Payne, A. J., Pritchard, H., Rignot, E., Rott, H., Sorensen, L. S., Scambos, T. A., Scheuchl, B., Schrama, E. J. O., Smith, B., Sundal, A. V., van Angelen, J. H., van de Berg, W. J., van den Broeke, M. R., Vaughan, D. G., Velicogna, I., Wahr, J., Whitehouse, P. L., Wingham, D. J., Yi, D. H., Young, D., and Zwally, H. J.: A Reconciled Estimate of Ice-Sheet Mass Balance, Science, 338, 1183–1189, 2012.
Tapley, B. D., Bettadpur, S., Watkins, M., and Reigber, C. (2004). The gravity recovery and climate experiment: Mission overview and early results. Geophys. Res. Lett., 31, L09607.
Velicogna, I. and Wahr, J.: Greenland mass balance from GRACE, Geophys. Res. Lett, 32, L18505, doi:10.1029/2005GL023955, 2005.
Velicogna, I.: Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE, Geophys. Res. Lett, 36, L19503, doi:10.1029/2009GL040222, 2009.
Wouters, B., Chambers, D., and Schrama, E. J. O.: GRACE observes small-scale mass loss in Greenland, Geophys. Res. Lett., 35, L20501, doi:10.1029/2008GL034816, 2008.
