Non-Magnetic DGPS System for Hi-Res Mag Surveys

Geometrics is pleased to announce that in conjunction with Trimble Navigation and Fugro Omnistar, they are offering a non-magnetic sub-meter differentially corrected GPS system based on the model AG132.

Improvements to MagMap96 Magnetic vs. Non-Magnetic GPS Comparison Trimble AgGPS Info OmniSTAR Info

Note that Geometrics will be offering only GPS with Subscription Services from Omnistar and not the "Coast Guard Beacon" services which use a magnetic ferrite antenna.  See coverage on Worldwide Coverage Map below.

Geometrics are also investigating the ability to use the "Parallel Swathing Option" which will provide real time cross track error indication on a light bar that will be mounted on an arm extending from the Mag/GPS backpack.  This option will not be immediately available, but will be an add-on option, depending upon interest level.
Significant alteration to the basic receiver and antenna is required to replace the magnetic components with non-magnetic materials.  Geometrics are offering an introductory price for the Modified AG132 system which has been tested to comply
with high sensitivity Cesium Mag single man portable applications. 
In addition, Geometrics have made significant improvements to MagMap96 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 Corrdinates with various Datum and export the data in Surfer format for futher contouring and analysis.
Geometrics believe this represents a major breakthrough in Mag/GPS system integration and they feel confident that this system will offer significant performance improvements which will quickly justify the purchase.  Delivery of the systems is approximately 60 to 90 days ARO.

Please contact Terry Odgers at Red Dog Scientific Services for additional information

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Comparison of "de-steeled" Trimble AG-132 vs a normal unit

Lynn Edwards, Cesium Engineering Manager, 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 done unpowered.  Results from the "normal" AG-132 didn't show much of a difference between powered and unpowered, but the unmodified unit was so magnetic that we wouldn't see these moderate effects anyway.
Here are the results from the two GPS systems:
  Note: Numbers in parentheses are calculated values using an inverse cube relationship from results measured at other distances.  The inverse cube relationship doesn't hold true exactly for calculations going to or from a two foot distance, but it is reasonably close for ball park numbers.

Part Unit Sig @ 2 FT Sig @ 4 FT Sig @ 10 FT
Antenna Normal (24 nTpp) 3 nTpp (0.2 nTpp)
  Modified 2 nTpp (0.3 nTpp) (<0.05 nTpp)
Main Unit Normal 100 nTpp 20 nTpp (1.3 nTpp)
  Modified 5 nTpp (0.6 nTpp) (< 0.05 nTpp)

As can be seen there is quite an improvement.  Results indicate that the system will perform well in a single-man portable configuration and will therefore not materially affect the system heading errors.
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Trimble AgGPS 132 Info

The AgGPS 132 is a high-performance GPS receiver that uses either free public or subscription-based private differential correction services to calculate sub-meter positions in real-time. Trimble's AgGPS Parallel Swathing Option is a light bar that plugs directly into the AgGPS and which works under any condition - day or night, dust or fog, wind or rain - providing equipment operators with precision guidance information for navigating straight, parallel lines.

More information is available at - click on Agriculture to go to the AG132.

AgGPS 132 Picture (14KB)
AgGPS Parallel Swathing (14kB)

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OmniSTAR Information

OmniSTAR has over 70 reference stations worldwide, allowing 24-hr DGPS coverage for over 90% of the world. New reference stations are constantly being set up to cater for OmniSTAR's expanding coverage. DGPS correction data is logged and archived on a routine basis providing a capability for post-processing and data analysis.

Each reference station is equipped with low noise, 12 channel GPS receivers transmitting RTCM data back to the network control centres. Reference station redundancy is achieved through back-up systems and station network density.

The worldwide OmniSTAR infrastructure of reference stations, network control centres and communication links is maintained locally by OmniSTAR offices.

OmniSTAR Coverage Map (40870 bytes)

For more info on OmniSTAR please visit