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
Lecture 7 – Gravity and Related Issues
11 February 2008
Lab 2: Problem
How do I get this to work?
Two models provide similar but not identical results. Difference is 1 mgal.
Review of Height Systems
Terrestrial and marine gravity data in NGS data base.
Note the discontinuity at the shoreline.
Orbit inclination: 89.048 degrees
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
Image from Featherstone, W, “Height Systems and Vertical Datums” Spatial Science, Vol 51 No. 1, June 2006
Leveled Height vs. Orthometric Height
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
NAD 83 datum
global geopotential surface
Average of 52 cm
NAVD 88 datum
NOTE: heights are not to scale