The Geoid Slope
Validation Survey of 2013

Map screenshot of gsvs13 line across Iowa. Map data ©2012 Google.

The purpose of this page is to provide information regarding the upcoming Geoid Slope Validation Survey of 2013 (GSVS13) which will take place in Iowa. The survey will begin within 20 miles of Cedar Rapids, IA and end within 20 miles of Denison, IA. The exact end points of the survey have not yet been determined.

Definitions

In order to describe the survey, the following groups of points must first be defined:

"Official Points": These are exterior passive geodetic control marks, spaced approximately every mile along the survey route, capable of being occupied by a GPS fixed height pole tripod, a level rod and a Lacoste-Romberg relative gravimeter.
"Gravity Anchor Points": These are a subset of the "Official Points", and will be approximately every 7th point. They have all the capabilities of an "Official Point" but are further capable of being occupied by a g-pod (for gravity gradients) and an A-10 absolute gravimeter.
"Gravity End Points": These are separate from "Official Points", and are two special building-interior points, set within 1 km of the first and last "Official Points" of the survey. They are capable of being occupied by a g-Pod, an FG-5 absolute gravimeter, a Lacoste Romberg relative gravimeter and a level rod.
"Leveling Points of Opportunity": These are separate from "Official Points", and are exterior passive geodetic control marks which were not chosen to become "Official Points", but which are within 500 meters of the survey line and which have pre-existing NAVD 88 published heights.
"DIADEM Eccentric Camera Points": These are exterior passive geodetic control marks of a temporary nature (PK nail, spray paint or other) which lie within 100 feet of an "Official Point". They will be set by the DIADEM camera crew on-the-fly, when the DIADEM camera system cannot be driven directly over an Official Point. When the DIADEM can be driven directly over and Official Point, there will not be a "DIADEM Eccentric Camera Point" associated with it.

Project Surveys

Below is a list of surveys to be completed:

Lidar/Imagery over the entire line
Temporary CORS
Long Session GPS (Dual frequency carrier phase GPS in a multiple-setup, day-by-day leapfrog pattern, ala GSVS11) at Official Points
First order, class II geodetic leveling connecting the entire set of Official Points
Gravity to include:
- FG-5 absolute gravity at Gravity End Points
- A-10 absolute gravity at Gravity End Points and all Gravity Anchor Points
- Lacoste-Romberg relative gravity connecting Gravity End Points and also all Official Points
- Lacoste-Romberg based gradients of gravity at Gravity End Points and Gravity Anchor Points
Astro-geodetic deflections of the vertical using the DIADEM camera (preferably at Official Points, but realistically will be at many DIADEM Eccentric Camera Points)
Airborne gravity over entire line
Short Period Static GPS: Performed as 20 minute long static-pairs between Official Points and DIADEM Eccentric Camera Points.

GSVS13 Survey Line Specifications

Click the image for a larger version.

Minimal Trees (GPS)
No major bridges/water crossings (Leveling)
Along roads (ease of access)
Cheap travel/per diem
Mostly cloud-free nights
Under GRAV-D coverage (or will be)
Marks can be set within 40' of the shoulder of a road
With at least some existent bench marks/NAVD 88 level lines
A "significant enough" geoid slope to be interesting
For GSVS11, we wanted "low and flat" topography. For GSVS13 we'll want to step this up to "high and flat" or possibly "medium high, more-or-less flat and gravimetrically complex"
Begin and End at more-or-less populated areas, for a variety of P.R., travel, housing and other issues.
Availability of hotels at locations *along* the line, not just at the endpoints