HIGH ACCURACY REFERENCE NETWORK

Primary Base Station Network

The current hybrid geoid model is based upon conversion of the gravitational geoid to NAVD88 using ellipsoid measurements on benchmarks, called the Primary Base Station Network (PBSN). Optimal spacing of the PBSN is 30 km. across the entire state. Existing benchmarks with precise ellipsoid heights are not evenly spaced and must be supplemented by additional Order A measurements as shown on the PBSN map. Ellipsoid heights will be measured on approximately 70 existing existing 1 st and 2 nd order benchmarks with optimal 30 km. spacing in 6 zones and tied into approximately 45 existing HARN stations and CORS.

Professional services contractors will GPS measure these marks. Each mark will be measured at least three times with different constellations for 6.5-hours per measurement. The data will be acquired and submitted to NGS following published NGS-58 and bluebook standards to produce precise ellipsoid heights on these marks for use by the NGS to improve the geoid conversion and incorporation into the NSRS. This network will also improve local geodetic work that has high quality height requirements, such as floodplain mapping.

The current SRCW work plan for the 6 projects zones are:

Project Zone 1 (Northwest Washington east of Puget Sound) is proposed for 2011.

Project Zone 2 ( Northeast Washington) monuments were located in 2008 and will be followed by surveying in 2009.

Project Zone 3 ( Southeast Washington) was surveyed in fall 2008.

Project Zone 4 ( South-Central Washington centered on the Tri-Cities) was surveyed in late 2007. The data for Project Zones 3 and 4 has been processed and is being merged together for submittal to NGS in early 2009.

Project Zone 5 (Southwest Washington centered on Mount St. Helens) is proposed for 2010.

Project Zone 6 (Western Washington west of Puget Sound) is proposed for 2012.

• Primary Base Station Network