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G-858 MagMapper System with a DGPS Option

The already successful G-858 MagMapper System has now become even more versatile with the addition of Sub-metre Differential GPS Positioning!!

Features

• In conjunction with Trimble Navigation and Fugro Omnistar, Geometrics now offer a NON-MAGNETIC SUB-METRE DIFFERENTIALLY CORRECTED GPS SYSTEM to accompany the G-858 Fast-Sampling MagMapper Magnetometer System.
  
  
• TRIMBLE AG-132 GPS Receiver :- The AG-132 is a high-performance GPS receiver that uses a subscription based differential correction service to calculate sub-metre positions in real-time.
  
  
• INTEGRATED BACKPACK :- Includes a fully customised non-magnetic backpack that incorporates the specially modified AG-132, a vertically mounted GPS antenna and an optional lightbar arm strategically positioned in full view of the operator.
  
  
• ONLINE STEERING :- An option for real-time cross-track error indication on a light bar, mounted on an arm extending from the G-858 Mag/GPS backpack. This navigates the operator down the line with sub-metre accuracy. No longer is there a need to survey lines before recording starts!!

• UPDATED SOFTWARE
  Significant improvements have also been made recently to MagMap96, the software included with all G-858 systems, which now includes the ability to plot the GPS position and magnetometer data on screen, contour the data with GPS locations, convert the lat/long to UTM Coordinates with various Datum, and export the data in Surfer or Geosoft format for further contouring and analysis.
  
  
• SPECIAL MODIFICATIONS
  Significant alteration to the basic GPS receiver and antenna is required to replace the magnetic components with non-magnetic materials. This DGPS Option to the G-858 MagMapper represents a major breakthrough in Mag/GPS system integration and we feel confident that this system will offer significant performance improvements which will quickly justify the purchase.
  
  

Geometrics measured the magnetic signature of a modified Trimble AG-132 where all of the steel shielding had been removed from the main console and antenna. The system was not operational so the measurements were made with the unit unpowered. The results from the two GPS systems are as follows:

COMPONENT	UNIT TYPE	SIGNAL @ 0.6M	SIGNAL 1.2M	SIGNAL 3.0M
Antenna	Normal	24 nT pp	3 nT pp	(0.2 n Tpp)
	Modified	2 nT pp	(0.3 nT pp)	( <0.05 nT pp)
Main Unit	Normal	100 nT pp	20 nT pp	(1.3 n Tpp)
	Modified	5 nT pp	(0.6 nT pp)	( <0.05 nT pp)

Numbers in parentheses are calculated values using an inverse cube relationship from results measured at other distances.

As can be seen there is quite an improvement. Results indicate that the system will perform very well in a single-man portable configuration and will therefore not materially affect the system heading errors.

TYPICAL SURVEY PROCEDURES

• Typical Survey Procedures Using the Geometrics/Trimble AG-132 DGPS System