The G-858 MagMapper Magnetometer is a high-sensitivity, fast-sampling ‘walking’ cesium vapor magnetometer. Its console includes a graphical interface that’s easy to learn and makes survey design and data review simple and efficient. The G-858 provides various modes of operation to allow the user to custom design a survey grid for their particular needs, or skip the grid entirely and use GPS! G-858 data acquisition offers either continuous or discrete station recording. The high sampling rate of the instrument in continuous mode allows the operator to survey an area at a fast walking pace. A lightweight data acquisition package enables you to survey large areas without having to stop for rest. A wider search zone and measurement of the magnetic field gradient can be achieved by adding a second sensor. The G-858’s internal firmware has been streamlined to include those features important for UXO, archaeological, environmental, utility, and mineral exploration.

The G-858 MagMapper is an industry proven magnetometer that you know you can rely on, both in the field and also through our world-class support department.


Features and benefits

  • Single or Dual Sensor Modes Easily go from a single sensor survey to either a vertical or horizontal gradiometer survey.
  • Fast Sampling: Save money and time on large-scale surveys. Eliminate gaps in the data.
  • Low AC Field Interference: Survey next to power lines when necessary.
  • Easy-to-use Interface: Useable by inexperienced personnel.
  • Rugged and Reliable: Weatherproof. Survives three-foot drop onto hard surface.
  • Long Battery Life: Each battery pack allows for 6 hours of surveying with single sensor and 4 hours with gradiometer.

Technical Details

G-858 Magnetometer Specification List

    G-858 Magnetometer


  • Operating Principle: Self-oscillating split-beam Cesium Vapor (non-radioactive Cs-133) with automatic hemisphere switching.
  • Operating Range: 20,000 nT to 100,000 nT.
  • Operating Zones: For highest signal-to-noise ratio, the sensor long axis should be oriented at 45°, ±30 to the earth’s field but operation will continue through 45°, ±35°. Sensor is automatic hemisphere switching.
  • Noise: < 0.008 nT/ Hzrms (SX (export) version: 0.02 nT/ Hzrms).
  • Heading Error: < 1.5 nT including backpack and GPS.
  • Gradient Tolerance: > 500 nT /in (>20,000 nT/m).
  • Temperature Drift: < 0.05 nT/°C.
  • Max Sample Rate: 10 Hz.
  • Data Storage: Non-volatile RAM with capacity for 8 to 12 hrs of magnetometer, time, event marks, field notes and XYZ or GPS locations.
  • Audio Output:
  • Audio tone of field variation; pitch and volume adjustable. (Search mode).
  • Audio pulse each 1 second (pace metronome).
  • Alarm for loss of signal, low battery or quality control setting exceeded.
  • Data Output: Three-wire RS-232 standard serial port, optional continuous real-time transmittal of data via RS-232 to PC. Total memory output transfer time less than 5 min at 115,200 baud.
  • Visual Output: 320 x 200 graphic liquid-crystal display, daylight-visible with selectable outputs for:
  • Display of up to 5 stacked profiles, real time or review mode. Survey grid showing boundaries and position.
  • All system set-up functions, e.g., memory status, data transfer, sample time.
  • All survey set-up functions, e.g., survey profile number and direction, station number or GPS data transfer protocol, line number.
  • Survey monitoring functions, e.g. total field, noise level, profile number or x-y coordinates.
  • Internal Clock: Resolution of 0.1 sec, drift: < 1 sec/day.
  • Power: 24 VDC rechargeable gel cell, 5 hrs for Mag w/GPS. Magnetic effect less than 1.5 nT at 4 ft. Internal backup battery for clock and non-volatile RAM.
  • Operating Software:
  • Survey Modes: Search survey - Simple survey - Mapped survey, station or continuous - Base station
  • Data acquisition/display: Acquire and store data and survey functions. Display profiles, total field to 0.1 nT resolution, survey / map parameters and diagnostics.
  • Post-acquisition Software: MagMap software for installation on customer’s computer.
  • 1. Data transfer and corrections: a. Transfer of data from field Magnetometer, GPS, or Base station to PC. b. Diurnal correction using base station data. c. Processing the corrected data into ASCII values of X-Y-Z.
  • 2. Data processing functions include spike editing, spline filtering, repositioning of X, Y, Z or GPS Lat/Long, conversion to UTM coordinates, profile and contour map plotting.


  • Sensor: DIA: 6 cm; L: 15 cm; Weight: 340 grams (2-3/8x6-3/4 in; 12 oz).
  • Backpack: 4.3 kg (9.5 lb).
  • Console: L: 28 cm; W: 15 cm; H: 8 cm; Weight: 1.6 kg (11x6x3 in; 3.5 lb). Magnetic effect less than 1 nT at 4 ft.


  • Operating Temperature: -25°C to +50°C (-13°F to + 122°F).
  • Storage Temperature: -35°C to + 60°C (-30°F to + 140°F).
  • Water Tight: Weatherproof in driving rain.
  • Shock: Survives a 3 ft drop onto a hard surface.
  • Warranty: 1 year on G-858 and sensor, 1 year on accessories.


  • G-858AP: Includes ergonomic backpack and Tallysman GPS.


  • Code and carrier phase tacking with 1Hz Position, velocity, time output.
  • SBAS capable and designed for harsh environments.
  • RS-232 compatible interface.
  • Size and Weight: DIA: 66.5mm; H: 21mm; Weight: 60 g (2.6x0.8 in; 2.1 oz).
  • Input Voltage: +9 to +16 VDC.
  • Power Consumption: 1.2W (typical).
  • Com Ports: 1 RS-232 (optional 2 RS-232) at up to 19,200 baud.
  • Operating Temperature: -40°C to +85° C (-40°F to +185°F).
  • Position Accuracy: Single point L1 <2 m CEP; WAAS L1 <1 m CEP.
  • Data Rates: Measurements 1 Hz; Position 1 Hz.
  • Time to First Fix: Cold start 39 sec; warm start 34 sec; hot start 2.5 sec.
  • Signal Reacquisition: <1 sec typical.
G-858 Magnetometer Shipping Weights & DIMS

Shipping Weights & DIMS

Contents Dimensions (L x W x H) Weight
Case 1 - G-858 Magnetometer 32in x 21in x 13in
81cm x 54cm x 33cm
Case 2 - Gradiometer Assembly + Extras 22in x 15in x 28in
56cm x 38cm x 71cm


  • Environmental: Find abandoned wells, pipes, and storage tanks quickly.
  • Archaeology: Perform basic magnetic archeology surveys.
  • Geology: Survey for regional variations in the magnetic field for mining and oil and gas applications.
  • UXO Detection: Collect data at high speed with a fast sample rate, making detection and delineation of UXO quick and easy.