Lecture 2b - Gravity Anomaly Modelling

Flashcards about gravity data processing and interpretation, covering magnitudes, gradients, corrections, and survey techniques.

What is the approximate magnitude of the Earth's mass in microgals regarding gravity measurements?

Around 10 to the power of 9 microgals.

What gravity signal can a human being produce at a distance of one meter?

Approximately 5 microgals.

What is the typical resolution of a microgravimeter?

About 1 microgal with a standard deviation of less than 5 microgals.

Why is the gravity gradient value negative?

It indicates that gravity decreases with increasing distance from the Earth's center.

What is the approximate value of the gravity gradient?

Minus 300 microgals per meter.

What does the gravity gradient represent in gravity surveys?

The free air correction.

What is the value of the free air correction in GU units?

About -3 GU per meter.

What does the Bouguer correction account for?

The additional mass under the instrument with increasing elevation.

What is the approximate value of the combined free air and Bouguer correction?

About -2 GU per meter.

To achieve measurement accuracy to around 0.1 GU, what level of uncertainty in height is acceptable according to the Bouguer correction?

An uncertainty of about 0.05 meters (5 centimeters).

What height accuracy of the gravimeter is needed to achieve a measurement accuracy of 0.1 GU?

The height must be known to better than 5 centimeters.

What was the target height accuracy of the geoid in the GOCE satellite mission?

Less than 2 centimeters.

What methods were used to achieve high-quality position measurements for the GOCE satellite?

Continuous GPS and laser-based measurements.

What type of field is gravity considered to be?

A vector field.

What components of gravity can ground-based instruments measure?

Only the magnitude of the field.

What can gravity surveys be used to estimate?

Subsurface density variations.

What methods can be used to analyze gravity survey data?

Forward modeling based on simplified geometric components.

What other processes can affect anomaly magnitudes, besides subsurface density variations?

Water table variations.

What critical step must be taken to ensure accurate gravity data interpretation?

Ensuring corrections have been appropriately applied.