Information

Latest data update

September 20, 2023.

Contact

info@thegraceplotter.com

Grids computation

The time series are obtained from the unconstrained spherical harmonics coefficients provided by the datacenters. DDK filtering is then applied using our CNES reference field for RL05 grids as a reference field (see Kusche et al, 2009 for filtering info). This same reference field is thus applied for all groups, for both the DDK filtering process and the removal of a reference field to compute 1°x1° grids (geoid, equivalent water heights or gravity anomalies).

For CNES TSVD solutions (TSVD stands for "truncated singular value decomposition"), no filtering is applied.

Grid values are computed at the center of pixels, i.e. (89.5°,-179.5°) for the top-left grid point and (-89.5°,179.5°) for the bottom-right.

SLR

For all centers except CNES/GRGS, the conversion to grids takes into account spherical harmonic coefficients from degree 2 to degree 96, with C20 replaced by the official GRACE Technical Note 14 SLR time-series (and C30 starting November 2016). For CNES/GRGS, grids takes into account coefficients from degree 2 to 90, without C20 or C30 replacement since CNES/GRGS solutions already contain SLR data (Lageos 1&2 and others up to degree 30).

Geographical extraction

Single point extraction: barycentric computation from the values at the 4 surrounding grid points.
Rectangles and polygons: average over grid points situated inside the contour.
Basins: average over grid points from mask file (press "Show data" button for mask info).
In every case, grid values are weighted by cos(latitude), in order to obtain per surface unit values (cm/m²).

Regression

Analytic models are adjusted on time series through a least squares process. The so-called "Periodic model" includes a linear component, an annual component and a semiannual component. The "Advanced model" has a polynomial component instead of linear, and polynomial-modulated annual and semiannual components. In both case, components can be displayed using "Periodic+" and "Advanced+".

Background maps

GRACE gravity maps (trend, annual and semiannual amplitude of equivalent water heights) are obtained through a regression on the global series of harmonic coefficients. DDK5 filtered coefficients are used (except for CNES).

Google Maps Projection

Google Maps use Mercator Projection, which means that the poles are at the infinity upwards and downwards. Google cuts the map view at around +/- 85.01 degrees. However, one can still enter manually coordinates of points between 85 degrees and 89.5 degrees (+/-) in the form for data extraction.

Data centers

The data present on this website are produced by the following groups:
CNES/GRGS: French National Space Center / Research Group for Space Geodesy, in Toulouse, France.
AIUB: Astronomical Institute at the University of Bern, in Switzerland.
COST-G: Combination Service for Time-variable Gravity Fields consortium.
CSR: Center for Space Research in Austin, Texas.
GFZ: German Research Center for Geosciences in Potsdam, Germany.
JPL: Jet Propulsion Laboratory, in Pasadena, California.
LUH: Leibniz University of Hannover, Germany.
TUGRAZ: Technical University of Graz in Austria.

Notes

Current version: 7.0.4 (June 23, 2023).

Fonts used under SIL OFL License / Google Fonts / licensed by CC BY 3.0 oNline Web Fonts.

Highcharts used under single website License. jQuery used under MIT License.

This website is an extension of the CNES/GRGS website. See legal notice (in French).

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