SENSYS Sensorik & Systemtechnologie GmbH

How mass measurement data improve UXO detection The SENSYS approach to UXO surveys in marine environment.

Founded in 1990 by Dr. Andreas Fischer

Manufacturer of magnetic and electromagnetic survey systems and components

Developer of customer specific electronics, software and systems

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How mass measurement data improve UXO detection

Today‘s demands Efficiency vs. Accuracy?

Economy demands Single runs High survey speed

Wide survey swath

Low profile, few requirements to the vessel

Safe altitude of sensor

Today‘s demands Eficiency vs. Accuracy?

Physics demands High density of data points High accuracy in referencing

Multi-channel surveys Controlled and stable distance between sensor and object (seabed) Go as close to the object as possible

The „right“ approach? Land vs. Sea

Same thing from physics POV No differences in detection method No remarkable differences in detection range

Sea: often less environmental noise Sea: referencing less accurate/harder

The „right“ approach? Land vs. Sea

Result of 25years experience Multi-channel

high data density

The „right“ approach? Land vs. Sea

Multi-channel

high data density

controlled

The „right“ approach? Why multi-channel?

The more channels the better the data quality

… generates line of measurement dots

Typical towfish with slow single probe …

… generates a measurement grid at the same time

MAGRay with fast multiple probes …

The „right“ approach? Why multi-channel?

The more channels the higher the chance of surveying a large part or even a complete anomaly in one swath.

The „right“ approach? What channel spacing?

Object not clearly visible operator could ignore/oversee weak objects

The „right“ approach? What channel spacing?

No clear object separation/dipol object’s calculation misleading

The „right“ approach? What channel spacing?

Distortion of data object misinterpretation in size and depth

The „right“ approach? Distance between Tracks.

Bomb SD70 (66kg), 24 kg explosives depth 2,3m, max 43 nT, min -4.3 nT Grid size 1m x 1m Contour line 10 nT

Could easily be missed by a single sensor and a track distance >5m

Could barely be missed with a 4m array and a track distance of 10m

The „right“ approach? Sample rate.

Every value that has been measured doesn’t need to be guessed. High sample rates allow for filtering (e.g. 50/60Hz interference)

The „right“ approach? Sample rate.

The higher survey speed the higher the sample rate needs to be

Example for 7 knots (3.60 m/s) Cesium-vapor Overhauser Fluxgate

typical 40 Hz (1 Hz @highest sensitivity)

Typical 4 Hz 200 Hz

Point distance 9 cm (3.6 m)

Point distance 90 cm Point distance 1.8 cm

The „right“ approach? The right sensor. Scalar resonance mags (Overhauser, cesium-vapor, protons)

Total field Resolution 0.01 nT (one magnitude better than fluxgates), decreasing at higher sample rates

Vectorial mags (fluxgates)

Measure one or more component of Earth magnetic field in a particular direction Resolution 0.1 nT, same at all sample rates up to 2kHz

Both types are equally effective

Better resolution of scalar mags barely come into play due to noise

The „right“ approach? Avoid noise.

Movement noise is the most important source of noise Caused by moving the sensor through the Earth magnetic field ranges from 0.5 …1.5 nT

Not depending on sensor type

maintain a stable height stable platforms/arrays to be preferred

The „right“ approach? The height above ground. Field decreases with 3rd power of distance (4th power for gradiometer)

Example: Object simulation diameter 0.5 m

2 m 2.5 m 3 m 4 m 5 m

44 nT 20 nT 10 nT 3.6 nT 1.5 nT

SNR >>1 SNR>>1 SNR>1 SNR>1 SNR~1

The „right“ approach? The height above ground.

Be as close as possible. Maintaining a certain survey level avoids movement noise. Maintaining a constant distance to seabed (follow seabed) allows for object calculation.

Alternative: know your height at any time

Be aware of your noise level.

Conclusion

Put many sensors in a stable array with a spacing <= 1m

Work with high sample rates

Maintain feasible track distances according to the swath (<10m)

Control the altitude and follow the seabed

Produce as less noise as possible

Go as close as possible

The SENSYS approach.

… to increase chances to find objects

… to rise the quality of your data

… to increase chances to find objects

… in order to minimize noise and allow for object calculations

… in order to detect even faint objects

… in order to increase signal to noise ratio

Conclusion The SENSYS approach.

SENSYS GmbH Technologiezentrum Rabenfelde 5 15526 Bad Saarow

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