Analyze observed gravity using robust geophysical correction workflows. Estimate anomalies for stations, profiles, and trends. Understand subsurface mass variations through clear outputs and formulas.
Use the form below to compute free-air, Bouguer, complete Bouguer, and residual gravity anomalies with an optional buried-sphere model.
The table below uses the built-in sample values shown in the form.
| Parameter | Example Value | Unit | Computed Outcome |
|---|---|---|---|
| Observed Gravity | 979,350.220 | mGal | Corrected observed gravity = 979,379.671 mGal |
| Latitude | 32.000 | degrees | Theoretical gravity = 979,484.376 mGal |
| Elevation | 450.000 | m | Free-air correction = 138.870 mGal |
| Rock Density | 2.670 | g/cm³ | Bouguer correction = 50.379 mGal |
| Terrain Correction | 1.850 | mGal | Complete Bouguer anomaly = -14.364 mGal |
| Regional Trend | 3.400 | mGal | Residual anomaly = -17.764 mGal |
| Density Contrast | 0.500 | g/cm³ | Modeled sphere peak = 2.426844 mGal |
| Sphere Radius / Depth | 250.000 / 300.000 | m | Peak position = 0.000 m |
This calculator combines standard gravity reduction equations with an optional buried-sphere forward model.
γ(φ) = 978032.67715 × [1 + 0.0053024 sin²φ − 0.0000058 sin²(2φ)]
Theoretical gravity as a function of latitude, with γ in mGal and φ in degrees.
gcorr = (gobs × calibration factor) + drift correction + tidal correction
Corrected observed gravity.
Free-Air Correction = 0.3086 × elevation
Elevation in meters, output in mGal.
Bouguer Correction = 0.04193 × density × elevation
Density in g/cm³ and elevation in meters.
Free-Air Anomaly = gcorr − γ + Free-Air Correction
Simple Bouguer Anomaly = Free-Air Anomaly − Bouguer Correction
Complete Bouguer Anomaly = Simple Bouguer Anomaly + Terrain Correction
Residual Anomaly = Complete Bouguer Anomaly − Regional Trend
Δg(x) = [G × (4/3)πa³Δρ × z] / (x² + z²)3/2
Buried-sphere profile, where G is the gravitational constant, a is radius, Δρ is density contrast, and z is depth to center.
A gravity anomaly is the difference between observed gravity and a reference value after selected corrections. It helps identify subsurface mass variations caused by density contrasts, structure, lithology, or voids.
Free-air anomaly corrects for elevation but not for the mass between the station and datum. Bouguer anomaly also removes the slab effect of intervening rock, giving a better estimate of subsurface density variation.
Gravity changes with latitude because Earth rotates and is not a perfect sphere. Latitude allows the calculator to estimate theoretical gravity at the station before anomaly corrections are applied.
The Bouguer correction depends on the assumed density of rock between the station and datum. A higher density increases the correction and can significantly change the anomaly result.
Terrain correction accounts for local hills, valleys, and nearby topography that distort the gravitational field. It is usually added after the simple Bouguer anomaly is computed.
The residual anomaly removes a broader regional trend from the complete Bouguer anomaly. It helps isolate shorter-wavelength local features that may correspond to targeted geological bodies.
The graph is a forward model, not a measured survey profile. It shows the anomaly expected from a buried spherical body using your density contrast, radius, depth, and profile geometry.
Yes. The calculator accepts negative values where physically meaningful, such as stations below sea level, negative regional trends, and negative residual anomalies from low-density zones.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.