K. Seitz (1), H. Bähr (1), F. Wild (1), B. Heck (1) and K. Roth (2)
(1) Geodetic Institute, Englerstraße 7, D76128 Karlsruhe
(2) State Office for KVK, Saarland
Definition of the Bouguer anomaly
The gravity value g(P) is determined gravimetrically (using measurement by weight), and it summarizes the gravity effect of all mass elements in the point P. It particularly looks at the surrounding masses, but local density contrasts also contribute to its variability in the high frequency range. If you take the measured gravity value g(P) and the freeair correction δg_{F}, and you attach the δgB correction for terrain, the equation δg_{top} = δg_{B} + δg_{G} continues to the geoid where you can then compare that with the normal gravity value γ_{0} on the ellipsoid, resulting in the refined Bouguer anomaly
Δg_{B} = g(P) + δg_{B} + δg_{G} + δd_{F}  γ_{0}.
Its interpretation in the context of the prospection permits the localisation of the deposits of raw materials (coal, salt deposits, metallic minerals etc.) which stand out by their density contrast in the Bouguer anomalies. In addition, the formation of gravity anomalies along with digital terrain models (DTM), is an essential database for the calculation of regional and global geoid and quasigeoid solutions.
Data Used
Digital Terrain Models (DTM)
Saarland  Datum: DHDN, DHHN  12.5 m x 12.5 m 
SRTM3  Datum: WGS84  3” x 3” 
SRTM30  Datum: WGS84  30” x 30” 
JGP95E  Datum: WGS84  5’ x 5’ 
→Interpolation of a DGM for the core zone (49° ≤ φ ≤ 49° 45’; 6° 10’ ≤ λ ≤ 7° 40’)
with a 0.4” x 0.6” grid spacing using the WGS84 coordinate system
Point gravity values (4606)
Saarland (820) 
RheinlandPfalz (249) 
Luxemburg (25) 
Bureau Gravimétrique International BGI (2582) 
Deutsches Schwerearchiv (930) 
Bouguer reduction

Freeair gravity anomaly δg_{F}
Correction for Terrain δg_{G}
Discretisation
For the calculation of the gravitational influence of the residual topography with respect to the referencepoint level, the terrain is based on DEMs approximated by suitable mass body:
 Tesseroide
 Cuboid (prisms)
 Point masses
 Weight lines
 Surface densities
s ≤ 10 km; Tesseroid  Quader 
5 km ≤ s ≤ 10 km; Tesseroid 
Reduction of the terrain influence δg_{G} on the gravity
With s ≤ 10 km 
Total core area 
5° border around the core area 
Total long range from JGP95E 
Calculation variants of the Bouguer anomoly Δg_{B} for the Saarland
δg_{G} with s ≤ 5 km; δg_{B} from planar Bouguer anomoly 
δg_{G} and δg_{B} from spherical cap with s ≤ 10 km 
δg_{G} global; δg_{B} of spherical shell 