Lecture 7 – Gravity and Related Issues. GISC-3325 11 February 2008. Scheduling Issues. Next class and lab will be on OPUS and GPS processing using OPUS. Next week I will be out. Monday or Wednesday (18 and 20 Feb) will be first exam. Chapters 1-4 and all lectures and labs
11 February 2008
How do I get this to work?
Two models provide similar but not identical results. Difference is 1 mgal.
Review of Height Systems Difference is 1 mgal.
Terrestrial and marine gravity data in NGS data base.
Note the discontinuity at the shoreline. Difference is 1 mgal.
Orbit inclination: 89.048 degrees Difference is 1 mgal.
Semi-major axis: 6,849,706.754m
Distance between satellites: 222,732.810 m
GRS 80 defined not only by geometric but also physical parameters (gravity).
Gravity defines the plumb line – the local vertical parameters (gravity).
Image from Featherstone, W, “Height Systems and Vertical Datums” Spatial Science, Vol 51 No. 1, June 2006
Leveled Height vs. Orthometric Height Datums” Spatial Science, Vol 51 No. 1, June 2006
h = local leveled differences
H = relative orthometric heights
HAChAB + hBC
Reference Surface (Geoid)
Observed difference in orthometric height, H, depends on the leveling route.
NAVD 88 and dynamic heights differ by only 1 mm at this station.
NAVD 88 = 2026.545 m
DYN Hght= 2023.109
Difference = 3.436 m
Error condition: input position is inconsistent with predicted one.
ITRF96/GRS-80 ellipsoid surface predicted one.
NAD 83 datum
global geopotential surface
Average of 52 cm
NAVD 88 datum
NOTE: heights are not to scale