Geometrics G882 TVG Transverse Gradiometer

Description

The Geometrics G882 TVG is a transverse gradiometer based on the Geometrics G-882 cesium vapor marine magnetometer, which is used for surveys in shallow or deep water. The G-882 is used for detection and mapping of ferrous objects, including anchors, chains, cables, pipelines, ballast stones, shipwreck debris, munitions (UXO), aircraft and engines, and for geological studies. The datasheet lists the transverse gradiometer as an optional configuration of the G-882.

The G-882 uses a self-oscillating split-beam cesium vapor (non-radioactive) sensor with an operating range of 20,000 to 100,000 nT. Noise is <0.004 nT/√Hz rms (SX export version: <0.02 nT/√Hz rms), the max sample rate is 20 Hz and heading error is <1 nT over an entire 360° spin. The earth's field vector should be at an angle greater than 10° from the sensor's equator and greater than 6° away from the sensor's long axis, with automatic hemisphere switching. Output is RS-232 at 1,200 to 19,200 baud, and power is 24 to 32 VDC, 0.75 A at power-on and 0.5 A thereafter.

Each G-882 sensor fish is 7 cm in diameter and 137 cm long with fin assembly, and weighs 18 kg including sensor, electronics and one main weight; additional collar weights are 6.4 kg each, up to a total of five. The listed tow cable is 12 mm in diameter and 800 m long, weighs 7.7 kg with terminations, has a break strength of 1,630 kg and a bend diameter of 30 cm. The G-882 is O-ring sealed and rated to 4,000 psi (2,730 m), operates from −35 °C to +50 °C and can be stored from −45 °C to +70 °C. An internal CM-221 Mini-counter provides multi-sensor sync and data concatenation for side-by-side systems, and the system interfaces directly to side scan sonars from major manufacturers for tandem tow configurations.

According to the datasheet, standard accessories are an operation manual, shipping/storage container, ship kit with tools and hardware, power supply, MagLogLite, MagMap and MagPick processing software, depth transducer and altimeter. MagLogLite data logging software records and displays data and position with automatic anomaly detection. Optional items include steel tow cable to 6,000 m with telemetry, a plastic Pelican case, MagLogPro software and collar weights. Typical detection ranges given include 1 to 2 nT at 30 m for an automobile, 1 to 5 nT at 30 m for a 1000 lb bomb and 0.5 to 2 nT at 4 m for a 5-inch screwdriver.

Technical Specification

Base magnetometer

Geometrics G-882 marine magnetometer

Gradiometer configuration

Longitudinal or transverse gradiometer listed as optional

Operating principle

Self-oscillating split-beam cesium vapor (non-radioactive)

Operating range

20,000 to 100,000 nT

Operating zones

Earth's field vector at an angle greater than 10° from the sensor's equator and greater than 6° away from the sensor's long axis; automatic hemisphere switching

Noise

<0.004 nT/√Hz rms; SX (export) version: <0.02 nT/√Hz rms

Max sample rate

20 Hz

Heading error

<1 nT (over entire 360° spin)

Output

RS-232 at 1,200 to 19,200 baud

Power

24 to 32 VDC, 0.75 A at power-on and 0.5 A thereafter

Multi-sensor sync

Internal CM-221 Mini-counter (multi-sensor sync and data concatenation)

Sensor fish dimensions

7 cm Ø × 137 cm (with fin assembly)

Sensor fish weight

18 kg (includes sensor, electronics and 1 main weight)

Collar weights

6.4 kg each; total of 5 capable

Tow cable

12 mm Ø × 800 m; 7.7 kg with terminations

Tow cable break strength

1,630 kg

Tow cable bend diameter

30 cm

Housing

Rugged fibre-wound fibreglass housing

Operating temperature

−35 °C to +50 °C

Storage temperature

−45 °C to +70 °C

Altitude

9,000 m

Depth rating

4,000 psi (2,730 m)

Water tight

O-ring sealed for up to 4,000 psi depth operation

Standard accessories

Operation manual, shipping/storage container, ship kit with tools and hardware, power supply, MagLogLite, MagMap and MagPick processing software, depth transducer, altimeter

Optional accessories

Steel tow cable to 6,000 m with telemetry, longitudinal or transverse gradiometer, plastic Pelican case, MagLogPro, collar weights

Software

MagLogLite data logging (recording and display of data and position, automatic anomaly detection)

Side scan integration

Interfaces to major side scan manufacturers for tandem tow configurations

Typical detection range: ship, 1000 tons

0.5 to 1 nT at 244 m

Typical detection range: anchor, 20 tons

0.8 to 1.25 nT at 120 m

Typical detection range: automobile

1 to 2 nT at 30 m

Typical detection range: light aircraft

0.5 to 2 nT at 12 m

Typical detection range: pipeline (12 inch)

1 to 2 nT at 60 m

Typical detection range: pipeline (6 inch)

1 to 2 nT at 30 m

Typical detection range: iron, 100 kg

1 to 2 nT at 15 m

Typical detection range: iron, 100 lb

0.5 to 1 nT at 9 m

Typical detection range: iron, 10 lb

0.5 to 1 nT at 6 m

Typical detection range: iron, 1 lb

0.5 to 1 nT at 3 m

Typical detection range: screwdriver, 5-inch

0.5 to 2 nT at 4 m

Typical detection range: bomb, 1000 lb

1 to 5 nT at 30 m

Typical detection range: bomb, 500 lb

0.5 to 5 nT at 16 m

Typical detection range: grenade

0.5 to 2 nT at 3 m

Typical detection range: shell, 20 mm

0.5 to 2 nT at 1.8 m

Applications

Detection and mapping of ferrous objects (anchors, chains, cables, pipelines, ballast stones, shipwreck debris, UXO, aircraft, engines); geological studies

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