the sensys approach to uxo surveys in marine environment ... · the sensys approach to uxo surveys...
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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
About SENSYS Who we are
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About SENSYS Whom we serve
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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.
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