Pacific Northwest Geodetic Array
Central Washington University

Short Drill-Braced Monument

The short drill-braced geodetic monument

  • Remote locations with limited access
  • Environmentally sensitive sites
  • Rapid deployment following large earthquakes
  • Insufficient funds for a deep-anchored drilled-braced monument

The short, drill-braced monuments is a smaller, hand-drilled geodetic monument design that we use for rapid installations of continuous GPS sites. The monument consists of 1-inch diameter stainless-steel rods forming a quad-pod that stands about 3 feet above the ground surface and is anchored 3 to 6 feet into bedrock. A generator-powered handheld rotary drill using a 1.5-inch diameter drill bit is used to prepare the holes. Epoxy is used to anchor the stainless-steel rod in the holes.

This page provides installation instructions for the SCIGN short, drilled-braced monument. The original design was a collaborative effort between S. Dockter, D. Elliot, and F. Wyatt (UCSD/SIO), and J. Galetzka and K. Hudnut (USGS Pasadena). Below are links to the USGS/SCIGN installation guide.

USGS/SCIGN Short Drilled-braced Monument Design

Installation and Guide

In the aftermath of the 2001 Nisqually earthquake, PANGA used this monument design because of its low cost and ease of installation. It takes about two days to install the monument and ancillary electronic equipment. Each site uses a FreeWave radio modem or a land-line telephone for data communications and a solar panel array with eight gell-cell batteries for power.

Materials, Costs and Drawings

Ancillary Equipment

We used Trimble SSI or Ashtek Z12 receivers and choke ring antennas with stainless steel recoverable antenna mounts. The antenna mount is the standard SCIGN-type anentta adapter, using SCIGN-type radomes.

All of our sites have secure and covered facilities. We use NEMA/EEMAC Type II enclosures with bulkhead fittings. The enclosures contains the GPS receiver, U.S. Robotics 56 kbs modem or Freewave radio modem and heavy duty surge protectors. The surge protectors isolate all components from lighting strikes or AC power surges.