geodesy, geophysics, geophysical method, gravity method

1. Physical geodesy
BY
K.NELSIA PRIYA DHARSINI
AP/CIVIL

29. Materials
Relative gravimeter
Sensor Technology
1. Fused quartz - has high strength, remains almost perfectly elastic up to its breaking
stress, can be welded into compact structures, free of tares when transported, accurate
and quick and easy to operate
2. Metal - very low long-term drift and low temperature coefficient, high accuracy, more
prone to tares in response to transportation
3. Superconducting – uses magnetic levitation, extremely low drift
4. Inertial-grade accelerometer – excellent dynamic performance on moving platforms,
very compact Relative gravimeters

40. Methodology
Data correction and reduction
If station is next to valley, there is an absence of the downward force on gravimeter
assumed in Bouguer correction, which reduces free-air anomaly too much.
TIDAL CORRECTIONS •Pull of Sun and Moon large enough to affect gravity reading.
Changes gobs with period of 12 hours or so.
•Earth tide corrections can be corrected by repeated readings at same station. Data
Correction/Reduction

44. Methodology- t Data
Correction/Reductio
Airy Isostasy
•Airy proposed that crust is thicker beneath mountains and thinner beneath the oceans.
•topographic highs are supported by deep crustal roots, while topographic lows are found
above thinned crust Pratt Isostasy
•Pratt proposed that observation could be explained by lateral changes in density within a
uniform thickness crust. •mountains occur where there's less-dense crust, and basins
where there's more-dense crusn