The Cowlitz County GPS Control Network includes two surveys, recorded
in the Cowlitz County’s Auditor’s Office. The first survey was designed
to establish 29 new stations at 5-16 Km spacing connected to eight Washington
High Precision Network (HPN) stations (Arp, Castle, HC 08504 3,K 63,KLS,Toutle,
Woodair and Yale). Of the 29 new stations, two are existing NGS Order 1,
Class 2 NAVD 88 benchmarks, seventeen are driven stainless steel rods with
sleeves and access covers, four are brass disks set in concrete bridge
abutments and six are brass disks on ¾" steel pipe in concrete.
A Leica NA 2002 electronic level was used to establish NAVD 88 elevations
on six of the new stations. This survey is in compliance with the Federal
Geodetic Control Committee's Geometric Geodetic Accuracy Standards and
Specifications for using GPS relative positioning techniques version 5.0
dated May 11, 1988 for Group C, Order 1 surveys.
The second survey established nine new stations at approximately 5
Km spacing connected to four Washington High Precision Network (HPN) stations
(Castle, K63, KLS and Woodair). Of the nine new stations, three are existing
NGS order 1, Class 2 NAVD 88 benchmarks, three are driven aluminum rods
with disks and three are existing monuments. A Leica NA 2002 Electronic
Level was used to establish NAVD 88 elevations on five new stations. This
survey is in compliance with the Federal Geodetic Control Committee's Geometric
Geodetic Accuracy Standards and Specifications for using GPS relative positioning
techniques version 5.0 dated May 11, 1988 for Group C, Order 1 surveys.
To accomplish these surveys three Trimble 4000 SSE receivers with dual
frequency geodetic antennas, three Sokkia 7311-35 optical plummet tribrachs
and three eight foot Dutch Hill tripods. Independent baselines were processed
in GPSurvey Version 1.20, TRIMNET Plus Version 92.11b, using the precise
ephemeris calculated by the National Geodetic Survey. Loop closures were
checked and the vectors were loaded into TRIMNET Plus. A minimally constrained
adjustment was ran to check the quality of the measurements and then another
adjustment was ran constrained to the eight Washington HPN stations. Geoid
heights from the Geoid 93 model were entered and a final adjustment was
run with the vertical constraints to estimate orthometric heights for stations
without leveled elevations. The horizontal datum is NAD 83 (1991) and the
vertical datum is NAVD 88.