1998 Burnett County Gandy Dancer

GPS Benchmark Project

Introduction

This report covers a GPS control survey project to establish geodetic coordinates of latitude and longitude, along with ellipsoidal heights on a series of benchmarks in the Gandy Dancer Trail corridor.

The benchmarks were sited by surveyor Mike Norton and he performed the level work to provide elevations in 1997. The benchmarks consist of 12 inch or more diameter concrete monuments that are 6 feet or deeper in the ground. Two reinforcing bars were set in the monument and a brass cap stamped with a BCBM number was set in the top.

A report on the elevation computations and least squares adjustment was filed with the Burnett County Office of Land Information (BCLIO) in early 1998.

Most of these benchmarks were constructed in areas suitable for GPS observations and so it was decided by Kathy Swingle, Burnett County Surveyor, to perform the GPS observations on these monuments. North Country Surveying, Inc. (NCS) of Siren has done most of the GPS work for Burnett County and was selected to perform the work.

It is anticipated that this data will be used in an upcoming flood study proposed by FEMA on the Yellow River basin. When ellipsoidal heights are correlated to true elevations, established by spirit levels, we can attain much higher quality elevations when converting GPS ellipsoidal heights to elevations.

Planning

Notes from the Norton survey were obtained and examined to compile a list of the benchmarks and their descriptions. We also pulled out descriptions of other benchmarks in the corridor. A file was started for each station containing Norton's notes and the final elevation listing from the elevation report. William G. Anderson of the NCS staff performed reconnaissance to determine if the monuments were suitable for GPS observations. Horizon diagrams were prepared for each benchmark and placed in the file. These files will be copied by BCLIO to create a record for the county.

It was determined that we could observe 10 benchmark stations in the project including BCBM 189-198 and also NGS station Heidi. One station, BCBM 199, was rejected due to tree canopy. It is located at the South or upstream dam facility at Danbury.

We decided to perform two independent observations from two different stations of the Burnett County Geodetic Control Network into each benchmark. We designed the observation scheme to keep all shots less than 5 km (3 miles).

Survey

Burnett County's two Leica SR299 dual frequency receivers were used to perform the observations. A rapid static survey was conducted.

Field observations were performed on June 29 and a clean up shot was done on July 2. Field observations were performed by Craig Hinzman, R.L.S. and William G. Anderson.

Six control stations of the Burnett County Geodetic Control Network were used to anchor the survey. These included: Helen, Overlook South, Echo, Webster, Paul, and Hotel.

A total of 24 baselines were observed from the 6 control stations into the 10 new benchmark stations and NGS station Heidi. Each new station had two shots into it, each from a different control station. One station BCBM197 had three shots into it from two different control stations. One the first day, one baseline would not resolve from HELEN to 0192. This baseline was not included in the final adjustments and an additional baseline from 0191 to 0192 was observed on July 2 to clean this up.

The receivers were downloaded each day upon completion of the fieldwork and the baselines were processed with Leica's SKI 2.0 software package by Douglas R. Crane, R.L.S.

Adjustment

The baselines were imported into Star*Net-GPS for a final adjustment. The preliminary adjustment ran so well that a minimally constrained adjustment was not performed. A fully constrained adjustment was performed holding the coordinates of the control stations fixed. The adjustment was scaled using a vector standard error factor of 10. The statistical results of the adjustment are as follows:
Statistical Summary
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Number of Stations = 17
Number of Observations = 69
Number of Unknowns = 33
Number of Redundant Obs = 36
Observation Count Sum Squares Error
of StdRes Factor
GPS Deltas 69 42.19 1.08
Total 69 42.19 1.08
Adjustment Passes the Chi Square Test at 5% Level

The files from the adjustment are submitted with this report on a diskette. These include the following file types:
File Type Description
98GANDY.DAT Input Data File
*.GPS GPS Vector Files Called for in the Input Data File
98GANDY.LST Output Listing File
98GANDY.PTS Final County Coordinates NOTE: (Elevations = Geoid 96 Conversions only)
98GANDY.POS Final Lat-Long values w/ellipsoid heights

Final Coordinate Values

For station descriptions and location information, see the BCLIO. The final values from the fully constrained adjustment are displayed below:

COUNTY COORDINATES GEOID 96 DERIVED ELEVATION NORTH EAST FEET (MSL)

Station Latitude Longitude Ellip Ht