# 地球重力场——Earth Gravitational Model EGM2008

a=6378137.00 m (WGS 84 地球半径)
GM
=3.986004418 x 1014 m3s-2 (地球重力常数)
ω
=7292115 x 10-11 radians/sec (地球角速度)

PS：不知道是不是遭遇屏蔽了，我在教研室登录不上这个网站,都是找朋友帮我下载了拷贝过来的，感谢下羊40同学

Introduction

The official Earth Gravitational Model EGM2008 has been publicly released by the U.S. National Geospatial-Intelligence Agency (NGA) EGM Development Team. This gravitational model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159. Full access to the model's coefficients and other descriptive files with additional details about EGM2008 are provided herein.

Those wishing to use EGM2008 to compute geoid undulation values with respect to WGS 84, may do so using the self-contained suite of coefficient files, FORTRAN software, and pre-computed geoid grids provided on this web page. For other applications, the previous release of the full 'Geoscience' package for EGM2008 can be accessed through the link at the bottom of this web page.

The WGS 84 constants used to define the reference ellipsoid, and the associated normal gravity field, to which the geoid undulations are referenced are:

• a=6378137.00 m (semi-major axis of WGS 84 ellipsoid)
• f=1/298.257223563 (flattening of WGS 84 ellipsoid)
• GM=3.986004418 x 1014 m3s-2 (Product of the Earth's mass and the Gravitational Constant)
• ω=7292115 x 10-11 radians/sec (Earth's angular velocity)

All synthesis software, coefficients, and pre-computed geoid grids listed below assume a Tide Free system, as far as permanent tide is concerned.

Note that the harmonic synthesis software provided below applies a constant, zero-degree term of -41 cm to all geoid undulations computed using EGM2008 with the height_anomaly-to-geoid_undulation correction model (also provided). Similarly, all pre-computed geoid undulations incorporate this constant zero-degree term. This term converts geoid undulations that are intrinsically referenced to an ideal mean-earth ellipsoid into undulations that are referenced to WGS 84. The value of -41 cm derives from a mean-earth ellipsoid for which the estimated parameters in the Tide Free system are: a=6378136.58 m and 1/f=298.257686.

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