Overview
The CSR Monthly SLR Low-Degree (5×5) Gravity Harmonics product provides monthly estimates of Earth’s gravity-field spherical harmonic coefficients through degree and order 5, together with the C(6,1) and S(6,1) terms. The solutions are derived from Satellite Laser Ranging observations to five, and in later years six, geodetic satellites.
This is an experimental product intended for experienced users who want to examine and assess the quality of low-degree gravity solutions derived from SLR.
Scientific Background
The degree-2 coefficients have direct physical interpretations. C(2,0) is associated with Earth’s oblateness. C(2,1) and S(2,1) describe the position of the principal figure axis relative to the rotation axis, while C(2,2) and S(2,2) describe Earth’s equatorial ellipticity.
Product Characteristics
The coefficients are supplied as variations relative to the GGM05C mean gravity field, which is included in the data file. All coefficients are fully normalized. To reconstruct the full monthly signal, the estimates with the Atmosphere and Ocean De-aliasing contribution restored should be added to GGM05C.
Solution quality improves noticeably beginning in early 2012, when LARES became available as a sixth SLR satellite. The estimates also benefit from forward modeling of higher-degree terms using GRACE and GRACE-FO information.
File Content and Processing
Each monthly record begins with header information giving the epoch and the degree/order 5 variations, including the C(6,1) and S(6,1) terms. The following 19 lines contain the delta C and delta S coefficients both without and with the GRACE Atmosphere and Ocean De-aliasing product restored; the AOD model was included during processing.
The coefficient variations and their formal uncertainties are scaled by 1.0e10. The file header documents the format and content. The monthly midpoint epoch is repeated for each degree-and-order pair in both Modified Julian Date and decimal year to simplify extraction of selected harmonics.
Degree-1 terms are no longer distributed with this product and will be provided separately.
Annual Variation
Data Access
Download the CSR Monthly SLR Low-Degree (5×5) Gravity Harmonics product using the link below.
CSR_Monthly_5x5_Gravity_Harmonics.txt
Format: Plain-text monthly spherical harmonic coefficients with descriptive metadata included in the file header.
Acknowledgement and Citation
This research is sponsored by the NASA GRACE Science Team (NASA Grant NNX16AF20G) and the NASA MEaSUREs program (JPL contract JPL1616713). When using these data, please acknowledge receiving the data from "https://grace.jpl.nasa.gov/data/get-data/ ", and cite:
Cheng, M., J. C. Ries, and B. D. Tapley (2011) Variations of the Earth's figure axis from satellite laser ranging and GRACE, J. Geophys. Res., 116, B01409, 2011, DOI:10.1029/2010JB000850.