A Brief Introduction to Gravity . UT Intro to Geophysics Class March 10, 2009 Austin-Bergstrom Airport Theresa Diehl, Ph.D. Research Geodesist NOAA National Geodetic Survey. The Acceleration due to Gravity. Newton’s Law of Gravitation. Newton’s Law of Motion.
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UT Intro to Geophysics Class
March 10, 2009
Theresa Diehl, Ph.D.
NOAA National Geodetic Survey
Newton’s Law of Gravitation
Newton’s Law of Motion
For reference mass and a spherical earth:
g ≈ 10 m/s2
Mean sea level
The change in gravity from place to place
.01 m/s2 = 1 Gal (Galileo)
10-3 Gal = 1 milliGal (mGal)
e.g. 9.82394 m/s2 = 982.394 Gal = 982,394 mGal
gravity changed by 10 mGals between two places
The gravity is exactly this at this point
10-6 Gal = 1 microGal (μGal)
e.g. 9.82394228 m/s2
= 982,394.228 mGal
= 982,394,228 μGal
Pt. A: Gravity Marker
Pt. B: At the plane
Move from Pt. A to Pt.B
So: 982,455.555 mGal
Apply corrections for: shape of the earth, airplane motion, height above sea level, etc.
Difference: NAVD 88 – datum derived from GRACE
20-100 km gravity gaps along coast
Terrestrial gravity points
Current data distribution is non-uniform and of varying quality, particularly with respect to large data gaps in littoral regions.
Split into 2 groups- to see airborne gravimeter and GPS units