Last modified on Jun 27, 2024 17:32

Contributors:  Lin Gilbert (University of Leeds), Sebastian Simonsen (Technical University of Denmark), Jan Wuite (ENVEO IT GmbH)

Issued by: University of Leeds / Lin Gilbert

Issued Date: 18/11/2020

Ref:  C3S_312b_Lot4.D3.IS.7-v2.0_202001_Product_User_Guide_Specification_i1.2

Official reference number service contract:  2018/C3S_312b_Lot4_EODC/SC2

Note: This document provides the following three deliverables:
D3.IS.7-v2.0 Product User Guide and Specification - Ice Velocity
D3.IS.8-v2.0 Product User Guide and Specification – Gravimetric Mass Balance
D3.IS.9-v2.0 Product User Guide and Specification – Surface Elevation Change

History of modifications

List of datasets covered by this document

Related documents

Acronyms

Scope of the document

This document is the Product User Guide and Specification for the Copernicus Ice Sheets and Ice Shelves service. It describes the datasets produced, and their specifications.

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

We provide the descriptions of each CDR v2 with a guide to their usage and specifications.

1. Greenland ice sheet velocity – D3.IS.4

1.1. Product description

The product contains an annually averaged ice velocity (IV) map of Greenland derived from Sentinel-1 (S1) SAR data (Figure 1). The surface velocity is derived by applying advanced iterative feature tracking techniques. The primary processor for IV generation is the ENVEO software package (ESP v2.1), see the related ATBD D1.IS.2-v2.0 . The system's core module performs coherent and incoherent offset tracking utilizing long stripes of S1 data acquired in interferometric wide (IW) swath mode. The ESP v2.1 is a state-of-the-art IV retrieval algorithm designed for SAR sensors (e.g. Sentinel-1, TerraSAR-X, ALOS PALSAR, Cosmo-SkyMed), and has been tested rigorously through intercomparisons with other packages and extensive validation efforts.

Feature tracking is a technique capable of acquiring ice flow velocity data over short (days) and longer time spans (years) and in regions with fast flow, as no coherence is required. The method uses the displacement of surface features such as crevasses or rifts and edges that move approximately with the same speed as the ice and are identifiable on two co-registered satellite images to derive velocity. The ice velocity is derived using feature tracking on repeat pass SAR images. The velocity grid for a given file represents the average ice surface velocity over the repeat pass period. For Sentinel-1 acquisitions in Greenland the repeat pass period is 6 to 12 days. The C3S Greenland Ice Sheet Velocity combines all ice velocity maps acquired over a full year in an annually averaged product provided at 500 m grid spacing. The averaging year runs from Oct 1st until September 30th, roughly mimicking a glaciological year.

Figure 1: C3S ice velocity map of the Greenland Ice Sheet based on Sentinel-1 data acquired from October 2018 to September 2019.

1.2. Target requirements

Table 1 shows the C3S IV product achievement versus the user requirements identified through an extensive user survey within the glaciological community as part of the Ice Sheets CCI project (Hvidberg, et al, 2012). The C3S product fulfills all minimum requirements for spatial and temporal resolution and falls well within the optimum accuracy range.

Table 1: C3S IV product achievement versus Ice Sheets CCI user requirements (*)

1.3. Data usage information

1.3.1. Product Data Format and Content

The product is provided as a NetCDF file with separate layers for the velocity components: v_x, v_y, v_z and v_v (magnitude of the horizontal components), and maps showing the valid pixel count and uncertainty (std) (Table 2). The ice velocity map is annually averaged and provided at 500m grid spacing in North Polar Stereographic projection (EPSG: 3413, defined at https://epsg.io/3413). The horizontal velocity is provided in true meters per day, towards easting (v_x) and northing (v_y) direction of the grid, and the vertical displacement (v_z), is derived from a digital elevation model (TanDEM-X 90m DEM; Rizzoli et al., 2017). For all maps a nodata value of 3.4028235e+38 is used.

Table 2: IV main data variables

1.3.2. Product Known Limitations

The following lists some known product limitations:

1) The IV products contain separate layers for the horizontal (Easting, Northing) and the vertical components of velocity. This is, however, not the true 3D velocity, which requires both ascending and descending image pairs acquired close in time. The vertical component is derived from the difference in height of start and end position of the displacement vector taken from a DEM.

2) The IV products do not have a time stamp for a single date, but give the average velocity over the time-period covered.

3) For various reasons, the tracking software sometimes fails to find matching features leading to gaps in the velocity fields. This can be caused by a lack of surface features or when features, for example crevasses, rapidly change due to shearing leading to low correlation. Other reasons for gaps in the IV maps can be areas affected by radar shadow or anomalous pixels that are filtered out. A simple distance-weighted averaging filter is applied to get rid of outliers and to fill small gaps in the data (<5 pixels), further filtering/gap filling is left to the user if required. The annual map has only a few gaps.

4) Due to different acquisition modes, sensor type, resolution and processing strategy there can be differences between S-1 IV products and IV products derived from other sensors that complicate a direct comparison between the data sets. Because of differences in resolution, the image patches used for feature tracking have different dimensions impacting the type of features that can be resolved. S-1 can for instance not capture the high velocity gradients that may be found in shear zones with the same detail as for example TerraSAR-X (TSX). On the other hand, due to the regular repeat acquisition the temporal sequence of S-1 is much higher than that of TSX and the covered area of the IV maps is much larger.

5) In-situ GPS data for validation of ice velocity are only sparsely available. In absence of this, velocity products are compared with ice velocity maps retrieved from other sensors (e.g. S-1 vs TSX) to estimate product performance and uncertainty. As an additional quality test, velocity results on stable terrain (rock outcrops), where no movement is expected, are analysed.

1.4. Product Nomenclature

The Filename of the IV Products consists of:
C3S_GrIS_IV_500m_S1_<Startdate><Enddate><Version>.<Format>

Table 3: Product nomenclature

Example: C3S_GrIS_IV_500m_S1_20181001_20190930_v1_2.nc Explanation: Annually averaged Greenland Ice Sheet surface velocity derived from Sentinel-1 for Oct 1^st 2018 – Sept 30^th 2019 provided at 500 m grid spacing, processing version 1_2 for C3S.

1.5. Structure of NetCDF files

The product metadata is included in the NetCDF file and is shown in Table 4. The NetCDF file contains 6 sub-datasets. Table 5 shows as an example the metadata for the "land_ice_surface_easting_velocity" sub-dataset.

Table 4: Example metadata for Greenland Ice Sheet Velocity product

NC_GLOBAL#comment=Ice velocity map of Greenland derived from Sentinel-1 SAR data acquired from 2017-10-01 to 2018-10-31. The surface velocity is derived applying feature tracking techniques. The ice velocity map is provided at 500m grid spacing in North Polar Stereographic projection (EPSG: 3413). The horizontal velocity is provided in true meters per day, towards EASTING(vx) and NORTHING(vy) direction of the grid, and the vertical displacement (vz), is derived from a digital elevation model. Provided is a NetCDF file with the velocity components: vx, vy, vz and vv (magnitude of the horizontal components), along with maps showing valid pixel count and uncertainty (std.). The product was generated by ENVEO.
NC_GLOBAL#contact=www.c3s.com
NC_GLOBAL#Conventions=CF-1.7
NC_GLOBAL#creation_date=2019-01-11
NC_GLOBAL#history=Initial product version 1.0
NC_GLOBAL#institution=Copernicus Climate Change Service
NC_GLOBAL#keywords=EARTH SCIENCE CLIMATE INDICATORS CRYOSPHERIC INDICATORS GLACIAL MEASUREMENTS ICE SHEET VELOCITY CRYOSPHERE GLACIERS/ICE SHEETS
NC_GLOBAL#license=C3S general license
NC_GLOBAL#project=C3S_312b_Lot4_ice_sheets_and_shelves
NC_GLOBAL#reference=Main: Nagler, T.; Rott, H.; Hetzenecker, M.; Wuite, J.; Potin, P. The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations. Remote Sens. 2015, 7, 9371-9389.
NC_GLOBAL#source=Copernicus Sentinel-1A and Sentinel-1B
NC_GLOBAL#summary=Ice velocity derived for Greenland Ice Sheet gridded at 500m averaged from 2017-10-01 to 2018-10-31.
NC_GLOBAL#title=Ice Velocity of the Greenland Ice Sheet
Subdatasets:
SUBDATASET_1_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_easting_velocity
SUBDATASET_1_DESC=[5401x2992] land_ice_surface_easting_velocity (32-bit floating-point)
SUBDATASET_2_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_northing_velocity
SUBDATASET_2_DESC=[5401x2992] land_ice_surface_northing_velocity (32-bit floating-point)
SUBDATASET_3_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_vertical_velocity
SUBDATASET_3_DESC=[5401x2992] land_ice_surface_vertical_velocity (32-bit floating-point)
SUBDATASET_4_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_velocity_magnitude
SUBDATASET_4_DESC=[5401x2992] land_ice_surface_velocity_magnitude (32-bit floating-point)
SUBDATASET_5_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_measurement_count
SUBDATASET_5_DESC=[5401x2992] land_ice_surface_measurement_count (32-bit integer)
SUBDATASET_6_NAME=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":land_ice_surface_velocity_stddev
SUBDATASET_6_DESC=[5401x2992] land_ice_surface_velocity_stddev (32-bit floating-point)

Table 5:Example metadata for land_ice_surface_easting_velocity subdataset.

Driver: netCDF/Network Common Data Format
Files: C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc
C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc.aux.xml
Size is 2992, 5401
Coordinate System is:
PROJCS["WGS 84 / NSIDC Sea Ice Polar Stereographic North",
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]],
PROJECTION["Polar_Stereographic"],
PARAMETER["latitude_of_origin",70],
PARAMETER["central_meridian",-45],
PARAMETER["scale_factor",1],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]],
AXIS["X",EAST],
AXIS["Y",NORTH],
AUTHORITY["EPSG","3413"]]
Origin = (-640000.000000000000000,-655500.000000000000000)
Pixel Size = (500.000000000000000,-500.000000000000000)
Metadata:
crs#false_easting=0
crs#false_northing=0
crs#grid_mapping_name=polar_stereographic
crs#latitude_of_projection_origin=90
crs#spatial_ref=PROJCS["WGS 84 / NSIDC Sea Ice Polar Stereographic North",
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]],
PROJECTION["Polar_Stereographic"],
PARAMETER["latitude_of_origin",70],
PARAMETER["central_meridian",-45],
PARAMETER["scale_factor",1],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]],
AXIS["X",EAST],
AXIS["Y",NORTH],
AUTHORITY["EPSG","3413"]]
crs#standard_parallel=70
crs#straight_vertical_longitude_from_pole=-45
crs#unit=metre
land_ice_surface_easting_velocity#coordinates=y x
land_ice_surface_easting_velocity#description=easting ice velocity
land_ice_surface_easting_velocity#grid_mapping=crs
land_ice_surface_easting_velocity#units=m/day
land_ice_surface_easting_velocity#_FillValue=3.4028235e+38
NC_GLOBAL#comment=Ice velocity map of Greenland derived from Sentinel-1 SAR data acquired from 2017-10-01 to 2018-10-31. The surface velocity is derived applying feature tracking techniques. The ice velocity map is provided at 500m grid spacing in North Polar Stereographic projection (EPSG: 3413). The horizontal velocity is provided in true meters per day, towards EASTING(vx) and NORTHING(vy) direction of the grid, and the vertical displacement (vz), is derived from a digital elevation model. Provided is a NetCDF file with the velocity components: vx, vy, vz and vv (magnitude of the horizontal components), along with maps showing valid pixel count and uncertainty (std.). The product was generated by ENVEO.
NC_GLOBAL#contact=www.c3s.com
NC_GLOBAL#Conventions=CF-1.7
NC_GLOBAL#creation_date=2019-01-11
NC_GLOBAL#history=Initial product version 1.0
NC_GLOBAL#institution=Copernicus Climate Change Service
NC_GLOBAL#keywords=EARTH SCIENCE CLIMATE INDICATORS CRYOSPHERIC INDICATORS GLACIAL MEASUREMENTS ICE SHEET VELOCITY CRYOSPHERE GLACIERS/ICE SHEETS
NC_GLOBAL#license=C3S general license
NC_GLOBAL#project=C3S_312b_Lot4_ice_sheets_and_shelves
NC_GLOBAL#reference=Main: Nagler, T.; Rott, H.; Hetzenecker, M.; Wuite, J.; Potin, P. The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations. Remote Sens. 2015, 7, 9371-9389.
NC_GLOBAL#source=Copernicus Sentinel-1A and Sentinel-1B
NC_GLOBAL#summary=Ice velocity derived for Greenland Ice Sheet gridded at 500m averaged from 2017-10-01 to 2018-10-31.
NC_GLOBAL#title=Ice Velocity of the Greenland Ice Sheet
x#axis=X
x#long_name=x coordinate of projection
x#standard_name=projection_x_coordinate
x#units=m
y#axis=Y
y#long_name=y coordinate of projection
y#standard_name=projection_y_coordinate
y#units=m
Geolocation:
LINE_OFFSET=0
LINE_STEP=1
PIXEL_OFFSET=0
PIXEL_STEP=1
SRS=GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]
X_BAND=1
X_DATASET=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":x
Y_BAND=1
Y_DATASET=NETCDF:"C3S_GrIS_IV_500m_S1_20171001_20181031_v1.nc":y
Corner Coordinates:
Upper Left ( -640000.000, -655500.000) ( 89d18'52.26"W, 81d33'27.74"N)
Lower Left ( -640000.000,-3356000.000) ( 55d47'48.66"W, 59d11'44.31"N)
Upper Right ( 856000.000, -655500.000) ( 7d33'22.15"E, 80d 4'16.22"N)
Lower Right ( 856000.000,-3356000.000) ( 30d41'27.32"W, 58d47'30.97"N)
Center ( 108000.000,-2005750.000) ( 41d55' 4.35"W, 71d36'38.37"N)
Band 1 Block=748x1351 Type=Float32, ColorInterp=Undefined
NoData Value=3.4028234663852886e+38
Unit Type: m/day
Metadata:
coordinates=y x
description=easting ice velocity
grid_mapping=crs
NETCDF_VARNAME=land_ice_surface_easting_velocity
units=m/day
_FillValue=3.4028235e+38

2. Gravimetric mass balance – D3.IS.5

2.1. Product description

The GMB relies solely on remote sensing data from the GRACE mission and its follow-on mission (GRACE-FO) to provide estimates of mass balance changes of the major drainage basins of Greenland and Antarctica. The GRACE-FO mission was launched on May 22, 2018, and the GRACE mission ended in October 2017, this resulted in a data-gap in the GMB record. The GRACE solution provided for the major drainage basins are brokered from the Greenland and the Antarctic ice sheet CCI projects. For both processing algorithms and uncertainty estimates we refer to Barletta, Sørensen and Forsberg (2013) and Groh and Horwath (2016). The Antarctic ice sheet CCI projects have not yet provided GMB solutions for the GRACE-FO and thereby only Greenland GRACE-FO data are brokered in the product. The brokering of Antarctic data from the Antarctic ice sheet CCI projects is expected to begin in 2021.

Specification summary:

• Sensors: GRACE and GRACE-FO (Greenland only)
• Grid: major drainage basins
• Time range: 2003 to 2016 and 2018-2020 (Greenland only)
• Time intervals: Monthly
• Validation frequency: N/A
• Quality flagging: N/A

In the following we will refer to both GRACE and GRACE-FO as GRACE if GRACE-FO is not explicitly mention.

2.2. Target requirements

The target requirements for the GMB are based on recommendations of both GCOS and C3S.

• Basin-level accuracy: 10km³/yr
• Stability: 10km³/yr

The requirements are given in terms of volume change, whereas what is measured is mass, a conservative volume to mass conversion in terms of target requirements are ice densities (917 kg/m³).

2.3. Data usage information

The product provides summed estimates at major drainage basins for both ice sheets. The basin definition is also provided in the file, in order to make the product more transparent for the end-user. The resolution of the GRACE measurement results in difficulties in separating mass changed across drainage boundaries.

2.3.1. Product Data Format and Content

The product is provided as a NetCDF file with separate layers for the individual drainage basins of the two ice sheets on Earth. For both hemispheres the drainage basin definition is included in the file. In Table 6 below we list the most important variables in the product files.

Table 6: GMB main data variables

2.3.2. Product known limitations

Limitations to the GRACE product include:

1. Spatial resolution. The real GRACE spatial resolution is around 200-250 km, but maps are provided at 50 km resolution. The higher resolution in the grid product is needed to properly reflect and compare to the mass domains solved for the "drainage basin" products. The GRACE mass measurements for Greenland are also given as 8 "Zwally Basins", using a subdivision going back in time to early satellite altimetry estimates. See Zwally et al 2012. In addition, a total mass change product for all of Greenland, including outlying ice caps and glaciers, is given.
2. Solution space: the GRACE mass change product is derived by two different methods: direct inversion and spectral estimation. The "leakage" of mass change from glaciers and ice caps from Canada is treated differently in these methods, and therefore the total Greenland mass change is different, as GRACE is "blind" to relocation of masses between NW Greenland and ice caps on the Canadian side. Furthermore, the spectral method estimates drainage basins independently, meaning that the mass loss sum of all basins does not sum to the best estimate for all of Greenland. Since signal leakage is one of the largest error sources in GRACE mass loss estimates, both methods are retained in C3S, and provide a measure of method-related errors.
3. Time resolution: The C3S GRACE data are based on monthly averages. The time stamp refers to the centre of the month.
4. For the first GRACE mission, the solution after 2014 is relatively degraded and the temporal resolution is also affected. That means that some solutions are actually for more than one month. This is not the case when the time series is continued by GRACE-FO

2.3.3. Product Nomenclature

The dataset filename as delivered to EODC is of the format
C3S_GMB_versx.nc, where:

• C3S is the overall project
• GMB is the ECV addressed, ie surface elevation change
• versx is the version number of the processing code

2.3.4. Structure of netcdf files

The header data for an example NetCDF data file is given in Table 7.

Table 7: Sample of the structure of the provided NetCDF file for the Gravimetric mass balance.

netcdf C3S_GMB_GRACE_vers2.nc {
  dimensions:
    t = 180;
    AntB = 901322;
    GrisB = 272965;
    N = 3;
  variables:
    float time(t=180);
      :long_name = "Time";
      :standard_name = "time";
      :units = "hours since 1990-01-01T00:00:00Z";

    float AntBasin(N=3, AntB=901322);
      :long_name = "Antarctic_Basin_definition";
      :column_meanings = "Latitude, Longitude, basin_number";
      :units = "degrees_north degrees_east number";
      :reference = "Zwally antarctic basins https://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php";

    float GrISBasin(N=3, GrisB=272965);
      :long_name = "Greenland_Basin_definition";
      :column_meanings = "Latitude, Longitude, basin_number";
      :units = "degrees_north degrees_east number";
      :reference = "Zwally Greenland basins https://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php";

    float GrIS_total(t=180);
      :long_name = "Greenland_ice_sheet_total_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_total_er(t=180);
      :long_name = "Greenland_ice_sheet_total_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_1(t=180);
      :long_name = "Greenland_ice_sheet_basin_1_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_1_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_1_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_2(t=180);
      :long_name = "Greenland_ice_sheet_basin_2_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_2_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_2_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_3(t=180);
      :units = "Gt";
      :long_name = "Greenland_ice_sheet_basin_3_GMB";
      :_ChunkSizes = 180U; // uint

    float GrIS_3_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_3_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_4(t=180);
      :units = "Gt";
      :long_name = "Greenland_ice_sheet_basin_4_GMB";
      :_ChunkSizes = 180U; // uint

    float GrIS_4_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_4_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_5(t=180);
      :long_name = "Greenland_ice_sheet_basin_5_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_5_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_5_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_6(t=180);
      :long_name = "Greenland_ice_sheet_basin_6_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_6_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_6_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_7(t=180);
      :long_name = "Greenland_ice_sheet_basin_7_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_7_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_7_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_8(t=180);
      :long_name = "Greenland_ice_sheet_basin_8_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float GrIS_8_er(t=180);
      :long_name = "Greenland_ice_sheet_basin_8_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_1(t=180);
      :long_name = "Antarctic_ice_sheet_basin_1_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_1_er(t=180);
      :units = "Gt";
      :long_name = "Antarctic_ice_sheet_basin_1_GMB_error";
      :_ChunkSizes = 180U; // uint

    float AntIS_2(t=180);
      :long_name = "Antarctic_ice_sheet_basin_2_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_2_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_2_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_3(t=180);
      :long_name = "Antarctic_ice_sheet_basin_3_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_3_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_3_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_4(t=180);
      :long_name = "Antarctic_ice_sheet_basin_4_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_4_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_4_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_5(t=180);
      :long_name = "Antarctic_ice_sheet_basin_5_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_5_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_5_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_6(t=180);
      :long_name = "Antarctic_ice_sheet_basin_6_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_6_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_6_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_7(t=180);
      :long_name = "Antarctic_ice_sheet_basin_7_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_7_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_7_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_8(t=180);
      :long_name = "Antarctic_ice_sheet_basin_8_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_8_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_8_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_9(t=180);
      :long_name = "Antarctic_ice_sheet_basin_9_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_9_er(t=180);
      :units = "Gt";
      :long_name = "Antarctic_ice_sheet_basin_9_GMB_error";
      :_ChunkSizes = 180U; // uint

    float AntIS_10(t=180);
      :long_name = "Antarctic_ice_sheet_basin_10_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_10_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_10_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_11(t=180);
      :long_name = "Antarctic_ice_sheet_basin_11_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_11_er(t=180);
      :units = "Gt";
      :long_name = "Antarctic_ice_sheet_basin_11_GMB_error";
      :_ChunkSizes = 180U; // uint

    float AntIS_12(t=180);
      :long_name = "Antarctic_ice_sheet_basin_12_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_12_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_12_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_13(t=180);
      :long_name = "Antarctic_ice_sheet_basin_13_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_13_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_13_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_14(t=180);
      :long_name = "Antarctic_ice_sheet_basin_14_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_14_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_14_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_15(t=180);
      :long_name = "Antarctic_ice_sheet_basin_15_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_15_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_15_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_16(t=180);
      :long_name = "Antarctic_ice_sheet_basin_16_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_16_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_16_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_17(t=180);
      :long_name = "Antarctic_ice_sheet_basin_17_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_17_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_17_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_18(t=180);
      :long_name = "Antarctic_ice_sheet_basin_18_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_18_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_18_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_19(t=180);
      :long_name = "Antarctic_ice_sheet_basin_19_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_19_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_19_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_20(t=180);
      :long_name = "Antarctic_ice_sheet_basin_20_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_20_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_20_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_21(t=180);
      :long_name = "Antarctic_ice_sheet_basin_21_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_21_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_21_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_22(t=180);
      :long_name = "Antarctic_ice_sheet_basin_22_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_22_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_22_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_23(t=180);
      :long_name = "Antarctic_ice_sheet_basin_23_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_23_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_23_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_24(t=180);
      :long_name = "Antarctic_ice_sheet_basin_24_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_24_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_24_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_27(t=180);
      :long_name = "Antarctic_ice_sheet_basin_27_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_27_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_27_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_25_26(t=180);
      :long_name = "Antarctic_ice_sheet_basin_25_and_26_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_25_26_er(t=180);
      :long_name = "Antarctic_ice_sheet_basin_25_and_26_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntPeninsula_total(t=180);
      :long_name = "Antarctic_Peninsula_total_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntPeninsula_total_er(t=180);
      :long_name = "Antarctic_Peninsula_total_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float East_AntIS_total(t=180);
      :long_name = "East_Antarctic_ice_sheet_total_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float East_AntIS_total_er(t=180);
      :long_name = "East_Antarctic_ice_sheet_total_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float West_AntIS_total(t=180);
      :long_name = "West_Antarctic_ice_sheet_total_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float West_AntIS_total_er(t=180);
      :long_name = "West_Antarctic_ice_sheet_total_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_total(t=180);
      :long_name = "Antarctic_ice_sheet_total_GMB";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

    float AntIS_total_er(t=180);
      :long_name = "Antarctic_ice_sheet_total_GMB_error";
      :units = "Gt";
      :_ChunkSizes = 180U; // uint

  // global attributes:
  :Title = "GMB for Greenland and Antarctica ice sheets from the GRACE missions";
  :institution = "DTU Space - Geodesy and Earth Observations";
  :reference = "Baratta et al. (2016), Groh and Horwart (2016)";
  :file_creation_date = "Tue Nov 10 10:51:12 2020";
  :region = "Greenland and Antarctica";
  :missions_used = "For Antarctica GRACE only and for Greenland both GRACE and GRACE-FO";
  :time_coverage_start = "2003";
  :time_coverage_end = "2019 (2016 for Antarctica)";
  :Tracking_id = "24398bcd-4138-4414-8f66-deb6dfc5c879";
  :netCDF_version = "NETCDF4";
  :product_version = "2.0";
  :Summary = "This data set is prepared for the C3S project, and is brokered from the CCI+ projects of Antarctica and Greenland ice sheets";
}

3. Surface elevation change, Antarctica – D3.IS.6.1

3.1. Product description

The product contains surface elevation change rates and their uncertainties from the Antarctic ice sheet, ice shelves, ice rises and islands on a regular geographic grid at regular time intervals. The change rate is calculated over a 5-year period. An example plot from one data grid is shown in Figure 2 below.

Figure 2: Example data from Antarctic surface elevation change product D3.IS.6.1

The initial CDR input data is radar altimetry surface elevation measurements from ERS1, ERS2, Envisat, CryoSat-2 and Sentinel-3A.

The product is updated monthly and will always contain the whole-time range to date. There is a time lag of 2 months between new measurements being taken and their being added to the product.

Validation is performed with respect to observation campaigns by the Airborne Topographic Mapper, a scanning laser altimeter flown on board aircraft by Operation IceBridge (Studinger 2014). Each campaign lasts for one Antarctic spring season (October to December), and so validation is performed annually.

Specification summary:

• Sensors: ERS1 RA, ERS2 RA, Envisat RA-2 and CryoSat-2 SIRAL, Sentinel-3A SRAL
• Grid: 25km by 25km polar stereographic projection based on 0°E, 71°S on the WGS84 ellipsoid (EPSG: 3031)
• Time range: 1992 to present
• Time intervals: 5yr window moving in monthly steps
• Validation frequency: annual
• Quality flagging: flags provided for steep terrain and missing data

Details of the product file format and contents are below. Details of methodology may be found in the related document, the Algorithm Theoretical Basis Document.

3.2. Target requirements

Targets are set by two separate bodies. The Global Climate Observing System (GCOS) maintains definitions of Essential Climate Variables and their requirements at
https://gcos.wmo.int/en/essential-climate-variables/ice-sheets-ice-shelves/ecv-requirements The C3S project itself provides key performance indicator targets.

Details of the CDR v2 performances against these targets may be found in the Product Quality Assessment Report, a related document.

The requirements summarized for the SEC products, based on the combined GCOS and C3S performance indicator targets are shown in Table 8.

Table 8: SEC products targets and performance indicators

3.3. Data usage information

3.3.1. Product data format and content

The product is provided as a NetCDF file containing stacked grids of the surface elevation change rate and associated uncertainty, and validity flags. The grids cover the Antarctic ice sheets, shelves rises and islands at 25km x 25km resolution in a polar stereographic projection with centre longitude 0E and true scale latitude 71S. There is one grid per month, each cell containing the rate of surface elevation change derived from a 5 year period centred on that gird's timestamp. The change rate and its uncertainty are given in m/year. Missing data is indicated by a floating point NaN (not a number) value. Single-layer flag grids are provided for surface type (eg ocean, land ice, ice shelf, ice rise or island) and high slope (< 2⁰, 2⁰ <= slope <= 5⁰, > 5⁰), on the same projection as the data. The main variables are listed in Table 9 below.

Table 9: Antarctic surface elevation change main data variables.

3.3.2. Product known limitations

Please note: the gridded data and its uncertainties are well-defined at pixel level. If they are to be combined to drainage basin-level the user should be sure to consider the varying terrain and ice dynamics within the basin - a simple mean value will not be representative.

3.3.3. Product nomenclature

The dataset filename as delivered to EODC is of the format
C3S_AntIS_RA_SEC_versx_yyyy-mm-dd.nc, where:

• C3S is the overall project
• AntIS indicates the Antarctic ice sheet region
• RA indicates that the data source is radar altimetry
• SEC is the ECV addressed, ie surface elevation change
• versx is the version number of the processing code
• yyyy-mm-dd is the creation date of the dataset

The latest file created should always be used, as the files are accumulative – each one contains all previous data as well as its monthly updates.

3.3.4. Structure of netCDF files

The header data for an example netCDF data file is given here:

netcdf C3S_AntIS_RA_SEC_vers1_2019-03-18 {
dimensions:
    x = 216 ;
    y = 180 ;
    t = 260 ;
    bounds = 2 ;
variables:
    float x ( x ) ;
        string x:long_name = "Cartesian x-coordinate - easting" ;
        string x:standard_name = "projection_x_coordinate" ;
        string x:short_name = "x" ;
        string x:units = "m" ;
        string x:axis = "X" ;
    float y ( y ) ;
        string y:long_name = "Cartesian x-coordinate - northing" ;
        string y:standard_name = "projection_y_coordinate" ;
        string y:short_name = "y" ;
        string y:units = "m" ;
        string y:axis = "Y" ;
    float longitude(y, x) ;
        string longitude:long_name = "Longitude" ;
        string longitude:standard_name = "longitude" ;
        string longitude:short_name = "lon" ;
        string longitude:units = "degrees_east" ;
    float latitude(y, x) ;
        string latitude:long_name = "Latitude" ;
        string latitude:standard_name = "latitude" ;
        string latitude:short_name = "lat" ;
        string latitude:units = "degrees_north" ;
    float time(t) ;
        string time:long_name = "SEC period central time" ;
        string time:standard_name = "time" ;
        string time:short_name = "time" ;
        string time:units = "hours since 1990-01-01T00:00:00Z" ;
        string time:calendar, 'gregorian'
    float sec(y, x, t) ;
        string sec:long_name = "SEC" ;
        string sec:standard_name = "surface_elevation_change" ;
        string sec:short_name = "sec" ;
        string sec:units = "m/year" ;
        sec:_FillValue = NaNf ;
        string sec:coordinates = "time x y" ;
        string sec:cell_methods = "area: mean time:linear_least_squares_fit" ;
    float sec_uncert(y, x, t) ;
        string sec_uncert:long_name = "SEC uncertainty" ;
        string sec_uncert:standard_name = "surface_elevation_change_standard_error" ;
        string sec_uncert:short_name = "sec_uncertainty" ;
        string sec_uncert:units = "m/year" ;
        sec_uncert:_FillValue = NaNf ;
        string sec_uncert:coordinates = "time x y" ;
        string sec_uncert:cell_methods = "area:mean area:uncertainty_sum

time:linear_least_squares_fit time:uncertainty_sum" ;
    byte sec_ok(y, x, t) ;
        string sec_ok:long_name = "SEC status flag" ;
        string sec_ok:standard_name = "surface_elevation_change status_flag" ;
        string sec_ok:short_name = "sec_status" ;
        string sec_ok:coordinates = "time x y" ;
        sec_ok:valid_range = 0b, 1b ;
        sec_ok:flag_values = 0b, 1b ;
        string sec_ok:flag_meanings = "no_data data_valid" ;
    byte surface_type(y, x) ;
        string surface_type:long_name = "Surface type mask" ;
        string surface_type:standard_name = "surface_type status_flag" ;
        string surface_type:short_name = "surface_type" ;
        string surface_type:coordinates = "x y" ;
        surface_type:valid_range = 0b, 3b ;
        surface_type:flag_values = 0b, 1b, 2b, 3b ;
        string surface_type:flag_meanings = "no_ice ge_95_percent_ice ice_shelf

ice_rise_or_island"
    byte high_slope(y, x) ;
        string high_slope:long_name = "Surface slope flag" ;
        string high_slope:standard_name = "high_slope status_flag" ;
        string high_slope:short_name = "slope" ;
        string high_slope:coordinates = "x y" ;
        high_slope:valid_range = 0b, 2b ;
        high_slope:flag_values = 0b, 1b, 2b ;
        string high_slope:flag_meanings = "slope_le_2_degrees slope_gt_2_and_le_5_degrees slope_gt_5_degrees" ;
// global attributes:
        string :Conventions = "CF-1.7" ;
        string :title = "Surface Elevation Change Rate of the Antarctic Ice Sheet" ;
        string :references = "Main: Wingham, Shepherd, Muir and Marshall, Phil Trans R Soc A, doi:10/rsta.2006.1792. Slope mask: Slater et al, The Cryosphere, 12,1551-1562, https://doi.org/10.5194/tc-12-1551- 2018" ;
        string :source = "ESA Radar altimeters: ERS-1, ERS-2, Envisat and CryoSat-2 " ;
        string :institution = "Copernicus Climate Change Service" ;
        string :contact = "www.c3s.com" ;
        string :project = "C3S_312b_Lot4_ice_sheets_and_shelves" ;
        string :creation_date = "2019-03-18T:13:11:55Z" ;
        string :comment = "Data is geophysically corrected, instruments 60 month power corrected. SEC uses crossover method, cross-calibration by elevation regression. Time coverage 1994.83 to 2016.42 using data from 2.5 years further at each end of the range. Longitude 0 to 360 degrees, latitude -90 to -57.664 degrees. Grid projection ESPG: 3031, ie PS 0E 71S WGS84, grid bottom left at -2.6e6m in x and -2.2e6m in y, grid cell width in x and y 25km" ;
        string :history = "Initial product version 1.0" ;
        string :summary = "Surface elevation change rate derived for Antarctica in 25km by 25km grid cells over a 5 year window moving at a monthly cadence." ;
        string :keywords = "EARTH SCIENCE CLIMATE INDICATORS CRYOSPHERIC INDICATORS GLACIAL MEASUREMENTS GLACIER ELEVATION/ICE SHEET ELEVATION, EARTH SCIENCE CRYOSPHERE GLACIERS/ICE SHEETS GLACIER ELEVATION/ICE ELEVATION" ;
        string :license = "C3S general license" ;}

4. Surface elevation change, Greenland – D3.IS.6.2

4.1. Product description

The product contains surface elevation change rates and their associated uncertainties for the Greenland ice sheet, and is provided on a regular grid at monthly resolution. The basis for the elevation change estimate for the older satellites (ERS-1, ERS-2 and Envisat) is a running 5-year mean, whereas the Cryosat-2 mission is based on monthly evaluation of a 3-year baseline. An example plot from one data grid is shown in Figure 3.

Figure 3: Example accumulated surface elevation change map produced from product D3.IS.6.2

The version 1 CDR input data is radar altimetry surface elevation measurements from ERS1, ERS2, ENVISat and CryoSat-2. The new version 2 CDR adds the use of observations from Sentinel-3A. The expected additions for version 3 are baseline upgrades for ENVISat and CryoSat-2, and an improved land ice product for Sentinel-3A, if they become available. Like the version 1 product, the current version 2 CDR will be updated monthly as iCDRs, with a time lag of 2 months between new measurements being taken and them being added to the product. As for validation this is performed once a year, as new validation data are only available from spring campaigns by the Airborne Topographic Mapper, a scanning laser altimeter flown on board aircraft by Operation IceBridge (Studinger 2014).

4.1.1. Specification summary:

Sensors:

• ERS1 RA, ERS2 RA, Envisat RA-2 CryoSat-2 SIRAL, and Sentinel-3A SRAL

Grid:

• 25km by 25km polar stereographic projection (EPSG 3413)

Time range:

• 1992 to present

Time intervals:

• 5-year window moving in monthly steps (3-year in the CryoSat-2 era and Sentinel-3)

Validation frequency:

• Annual

Quality flagging:
Flags are provided for steep terrain, missing data and nearest distance to the original RA-altimeter measurement.

4.2. Target requirements

The target requirements are generic for the surface elevation change. Hence, the same as listed for the Antarctic surface elevation change, in Section 5.2 above. Table 8 applies.

4.3. Data usage information

4.3.1. Product data format and content

The product is provided as a NetCDF file containing stacked grids of the surface elevation change rate and associated uncertainty, and validity flags. Given in a north polar stereographic projection, with centre longitude 45W and latitude 70N, the grids cover the Greenland ice sheets at 25km x 25km. Solutions for the Greenland surface elevation change are given at a temporal resolution of one month, which combined with the 25 km grid gives a parameter-dimension of (63x103x307)¹. The change rate and its uncertainty are given in m/year. Missing data is indicated by a floating-point NaN (not a number) value. Single-layer flag grids are provided for surface type (0 for Land/Ocean and 1 for an ice cover of more than 95%) and high slope (< 2⁰, 2⁰ <= slope <= 5⁰, > 5⁰). All single-layer flags are gridded using the north polar stereographic projection as the data. The main variables are listed in Table 10 below.

Table 10: Greenland surface elevation change main data variables.

4.3.2. Product known limitations

Please note:

• The gridded data and its uncertainties are well-defined at pixel level. If they are to be combined to drainage basin-level the user should be sure to consider the varying terrain and ice dynamics within the basin - a simple mean value will not be representative.
• The performed kriging procedure has the capability of extrapolating data over undesired distances and the distance-flag should be consulted before any averaging of elevation change is performed.

4.3.3. Product nomenclature

The dataset filename as delivered to EODC is of the format
C3S_GrIS_RA_SEC_versx_yyyy-mm-dd.nc, where:

• C3S is the overall project
• GrIS indicates the Greenland ice sheet region
• RA indicates that the data source is radar altimetry
• SEC is the ECV addressed, ie surface elevation change
• versx is the version number of the processing code
• yyyy-mm-dd is the creation date of the dataset

The filename is changed within the CDS to fit their information storage system.

The latest file created should always be used, as the files are cumulative – each one contains all previous data as well as its monthly updates.

4.3.4. Structure of NetCDF files

The header data for an example NetCDF data file is given in Table 11.

Table 11: Sample of the structure of the provided NetCDF file for the Greenland Surface elevation change and exemplified by the March 2019 dataset.

netcdf C3S_GrIS_RA_SEC_25km_vers2_2020-01-03.nc {
  dimensions:
    x = 73;
    t = 316;
    y = 116;
  variables:
    float x(x=73);
      :long_name = "Cartesian x-coordinate - easting";
      :standard_name = "projection_x_coordinate";
      :units = "m";

    float y(y=116);
      :long_name = "Cartesian y-coordinate - northing";
      :units = "m";
      :standard_name = "projection_y_coordinate";

    float time(t=316);
      :long_name = "SEC period central time";
      :standard_name = "time";
      :units = "hours since 1990-01-01T00:00:00Z";

    float start_time(t=316);
      :standard_name = "time";
      :long_name = "SEC period start time";
      :units = "hours since 1990-01-01T00:00:00Z";

    float end_time(t=316);
      :standard_name = "time";
      :long_name = "SEC period end time";
      :units = "hours since 1990-01-01T00:00:00Z";

    char grid_projection;
      :ellipsoid = "WGS84";
      :false_easting = 0.0; // double
      :false_northing = 0.0; // double
      :grid_mapping_name = "polar_stereographic";
      :latitude_of_projection_origin = 90.0; // double
      :standard_parallel = 70.0; // double
      :straight_vertical_longitude_from_pole = -45.0; // double
      :EPSG = "3413";

    float lat(y=116, x=73);
      :_FillValue = 9999.0f; // float
      :units = "degrees_north";
      :grid_mapping = "grid_projection";
      :long_name = "Latitude";
      :_ChunkSizes = 116U, 73U; // uint

    float lon(y=116, x=73);
      :_FillValue = 9999.0f; // float
      :units = "degrees_east";
      :grid_mapping = "grid_projection";
      :long_name = "longitude";
      :_ChunkSizes = 116U, 73U; // uint

    float dh(y=116, x=73, t=316);
      :long_name = "Elevation change";
      :grid_mapping = "grid_projection";
      :units = "m";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    float dh_uncert(y=116, x=73, t=316);
      :long_name = "Elevation change uncertainty";
      :grid_mapping = "grid_projection";
      :units = "m";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    float dhdt(y=116, x=73, t=316);
      :long_name = "Rate of elevation change";
      :grid_mapping = "grid_projection";
      :units = "m/year";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    float dhdt_uncert(y=116, x=73, t=316);
      :grid_mapping = "grid_projection";
      :units = "m/year";
      :long_name = "Rate of elevation change uncertainty";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    float dhdt_stabil(y=116, x=73, t=316);
      :long_name = "Stability of rate of elevation change fit";
      :grid_mapping = "grid_projection";
      :units = "m/year";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    byte dhdt_ok(y=116, x=73, t=316);
      :long_name = "SEC valid flags";
      :grid_mapping = "grid_projection";
      :flag_values = 0B, 1B; // byte
      :flag_meanings = "no_data data_valid";
      :_ChunkSizes = 116U, 73U, 316U; // uint

    float dist(y=116, x=73, t=316);
      :long_name = "Distance to observational node";
      :grid_mapping = "grid_projection";
      :unit = "m";
      :_ChunkSizes = 58U, 37U, 158U; // uint

    byte land_mask(y=116, x=73);
      :ref = "ESA Glacier CCI Greenland ice cover";
      :flag_values = 0B, 1B; // byte
      :flag_meanings = "0_LandOcean 1_IceCover";
      :grid_mapping = "grid_projection";
      :long_name = "Land cover";
      :_ChunkSizes = 116U, 73U; // uint

    byte high_slope(y=116, x=73);
      :flag_values = 0B, 1B, 2B; // byte
      :flag_meanings = "0Slope_leq_2degrees 1Slope_geq2leq5degrees 2Slope_geq_5degrees";
      :ref = "Slope of the GIMP Greenland DEM";
      :long_name = "Slope flag";
      :grid_mapping = "grid_projection";
      :_ChunkSizes = 116U, 73U; // uint

    float area(y=116, x=73);
      :grid_mapping = "grid_projection";
      :units = "m^2";
      :long_name = "Grid_area";
      :_ChunkSizes = 116U, 73U; // uint

  // global attributes:
  :Title = "Surface Elevation change of the Greenland ice sheet from Radar altimetry";
  :institution = "Copernicus Climate Change Service, DTU Space - Div. of Geodynamics";
  :reference = "Simonsen and Sørensen (2017), Sørensen et al. (2018)";
  :contact = "www.c3s.com";
  :file_creation_date = "Fri Jan  3 13:19:17 2020";
  :project = "C3S_312b_Lot4_ice_sheets_and_shelves";
  :region = "Greenland";
  :missions_used = "ESA Radar altimeters: ERS-1,ERS-2, Envisat and CryoSat-2";
  :power_corrections = "ERS-1, ERS-2 and Envisat 5-years, CryoSat-2 3-years";
  :grid_projection = "EPSG:3413";
  :grid_minx = -832025.1172356805; // double
  :grid_miny = -3337070.476431791; // double
  :grid_nx = 73L; // long
  :grid_ny = 116L; // long
  :grid_cell_width_x = "25000 m";
  :grid_cell_width_y = "25000.0m";
  :Latitude_min = 58.695983374298976; // double
  :Latitude_max = 85.73589403067308; // double
  :Longitude_min = -105.95411605334395; // double
  :Longitude_max = 19.48215412699801; // double
  :model_type = "ERS-1, ERS-2 and Envisat combined crossovers and repeat-track, CryoSat-2 plane fit";
  :cross_cal_method = "Elevation regression, and weighted mean";
  :time_coverage_start = "1992-01-15 00:00:00";
  :time_coverage_end = "2018-04-15 00:00:00";
  :Tracking_id = "1410ec13-233b-4d97-9a7f-5b3bfeca78bd";
  :Internal_ref = "C3S_GrIS_RA_SEC_vers2_2020-01-03.nc";
  :netCDF_version = "NETCDF4";
  :product_version = "2.0 - test";
  :Conventions = "CF-1.7";
  :keywords = "EARTH SCIENCE CRYOSPHERE GLACIERS/ICE SHEETS/GLACIER ELEVATION/ICE SHEET ELEVATION";
  :license = "C3S general license";
  :summary = "Surface elevation change rate derived for Greenland in 25km by 25km grid cells over a 5/3 year window moving monthly cadence.";
}

5. Data access information

5.1. All products

Data will be made available through the Copernicus Climate Data Store (CDS), which is the sole data distributor. Registration (free) is required to access the CDS and its toolbox software suite. The CDS is a web-based service, with its homepage at https://cds.climate.copernicus.eu/cdsapp#!/home

Data can be downloaded from the website and used under the License to Use Copernicus Products (included on download page). Data may also be viewed online.

All requests for information or further data should be channelled through the CDS Knowledge Base at https://confluence.ecmwf.int//display/CKB/

References

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, 1411-1432

Groh, A., and Horwath, M. (2016). The method of tailored sensitivity kernels for GRACE mass change estimates. Geophysical Research Abstracts, 18, EGU2016-12065.

Hvidberg, C.S., et al., User Requirements Document for the Ice_Sheets_cci project of ESA's Climate Change Initiative, version 1.5, 03 Aug 2012. Available from: http://www.esa-icesheets-cci.org/

Rizzoli, P., Martone, M., Gonzalez, C., Wecklich, C., Tridon, D.B., Bräutigam, B., Bachmann, M., Schulze, D., Fritz, T., Huber, M. and Wessel, B., (2017). Generation and performance assessment of the global TanDEM-X digital elevation model. ISPRS Journal of Photogrammetry and Remote Sensing, 132, pp.119-139

Studinger, M. (2014). IceBridge ATM L4 Surface Elevation Rate of Change, Version 299 1, Antarctica subset. N. S. a. I. D. C. D. A. A. Center. Boulder, Colorado, USA. DOI: 10.5067/BCW6CI3TXOCY

H.J. Zwally, M.B. Giovinetto, M.A. Beckley, J.L. Saba (2012). Antarctic and Greenland drainage systems, GSFC cryospheric sciences laboratory. Available at
http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php

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