Contributors: S. B. Simonsen (Technical University of Denmark), J. Wuite (ENVEO IT GmbH)
Issued by: Technical University of Denmark / Sebastian B. Simonsen
Date: 06/12/2022
Ref: C3S2_312a_Lot4.WP1-PDDP-IS-v1_202206_GMB_PQAD-v4_i1.1
Official reference number service contract: 2021/C3S2_312a_Lot4_EODC/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
General definitions
Brokered Product: A brokered product is a pre-existing dataset to which the Copernicus Climate Change Service (C3S) acquires a license, for the purpose of including it in the Climate Data Store (CDS).
Generated Product: A generated product is a dataset made specifically for C3S, for the purpose of including it in the CDS.
Gravimetric Mass Balance (GMB): The mass balance of an ice sheet is the net difference between mass gained from snow deposition and mass lost by melting or iceberg calving. This is essentially the same as the mass change of the ice sheet. When mass balance is derived from measured changes in the Earth's gravitational field, this is referred to as a gravimetric mass balance.
Scope of the document
The Copernicus Ice Sheets and Ice Shelves service addresses three essential climate variables (ECVs), by providing four separate products.
- Ice velocity is given for Greenland in product WP2-FDDP-IV-CDR
- Gravimetric mass balance is given for Greenland and Antarctica in product WP2-FDDP-GMB-CDR
- Surface elevation change is given for:
- Antarctic Ice Sheet (AIS) in product WP2-FDDP-SEC-CDR-AntIS
- Greenland Ice Sheet (GrIS) in product WP2-FDDP-SEC-CDR-GrIS
This document is the Product Quality Assurance Document for Gravimetric Mass Balance (GMB) as part of the Copernicus Ice Sheets and Ice Shelves service. It describes the validated datasets and the methods used for validation.
Executive summary
This document deals with gravimetric mass balance for Greenland and Antarctic ice sheets. Direct validation is not carried out on this brokered dataset, as it has been performed previously and documented. Relevant documentation is available at:
- Antarctic Icesheet (AIS): https://climate.esa.int/en/projects/ice-sheets-antarctic/key-documents/
- Greenland Icesheet (GrIS): https://climate.esa.int/en/projects/ice-sheets-greenland/key-documents/ 1
The main findings from these documents are as follows.
The primary satellite source for the generation of the Gravimetric Mass Balance (GMB) is the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions (D3). There is no other sensor that can directly observe changes in mass with comparable or even better spatial and temporal coverage. Hence, observations of alternative quantities related to mass changes have to be used for validation after applying an appropriate conversion. For example, changes in the ice sheet's surface elevation can be converted into mass changes using an assumption of density. The validation could also be based on the predictions of geophysical models. All these alternatives have assumptions and input data with their individual uncertainties. However, the GMB observations agree with derived ice sheet mass balance estimates from the mass-budget method, ice sheet's surface elevation, regional climate models and synthetic data tests.
1. Validated products
The GMB products provide estimates of mass balance changes of the major drainage basins of Greenland and Antarctica. The products are brokered from the European Space Agency’s (ESA) Antarctic ice sheets Climate Change Initiative (CCI) and the ESA Greenland ice sheets CCI projects. For further details, see the C3S Product User Guide and Specification (PUGS) document [D2] or the documentation of the CCI projects, namely:
- AIS: Section 5 of the Product User Guide (PUG), version 1.0, available at: https://climate.esa.int/media/documents/ST-UL-ESA-AISCCI-PUG-0001.pdf
- GrIS: Section 5 of the PUG, version 2.0, available at: https://climate.esa.int/media/documents/ST-DTU-ESA-GISCCI-PUG-001_v2.0.pdf 2
2. Description of validating datasets
Unfortunately, no sensor except GRACE(-FO) can directly observe changes in mass with comparable or even better spatial and temporal coverage. Hence, observations of alternative quantities related to mass changes have to be used for validation after applying an appropriate conversion.
A detailed description of the validation datasets is given in:
- AIS: Section 5.1 of the AIS Product Validation and Intercomparison Report (PVIR), version 1.3, available at (https://climate.esa.int/media/documents/ST-UL-ESA-AISCCI-PVIR-001_v1.3a.pdf).
- GrIS: Section 4 of the GrIS PVIR, version 1.0, available at (https://climate.esa.int/media/documents/ST-DTU-ESA-GISCCI-PVIR-001_v1.0.pdf) 3
3. Description of product validation methodology
The detailed description of the validation methodology is available at:
- AIS: Please see section 5.2 of the AIS PVIR (https://climate.esa.int/media/documents/ST-UL-ESA-AISCCI-PVIR-001_v1.3a.pdf)
- GrIS: Please see section 4.1 of the GrIS PVIR (https://climate.esa.int/media/documents/ST-DTU-ESA-GISCCI-PVIR-001_v1.0.pdf) 4
These documents proivide a full summary of the validation against:
- The mass-budget method
- Ice sheet's surface elevation
- Regional climate models
- Synthetic data tests.
4. Summary of validation results
A summary of the validation results is available at:
- AIS: Please see section 5.3 of the AIS PVIR (https://climate.esa.int/media/documents/ST-UL-ESA-AISCCI-PVIR-001_v1.3a.pdf)
- GrIS: Please see section 4.2 of the GrIS PVIR (https://climate.esa.int/media/documents/ST-DTU-ESA-GISCCI-PVIR-001_v1.0.pdf) 5
The GMB observations are in general agreement with derived ice sheet masse balance estimates from the mass-budget method, ice sheet's surface elevation, regional climate models and synthetic data tests.
Both the SEC and the mass budget time series were used to check for a seamless continuation of the GRACE time series by GRACE-FO and for the existence of a potential gap. These checks did not indicate a potential offset between the GRACE and GRACE-FO results in the GMB product.
