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System outline

The benthic profiler NERIDIS III is a marine electro­magnetic profiler that has been developed for coastal and shelf operations in up to 500 m water depths. The system was designed to resolve subtle and gradual variations in silt and clay content, magnetic mineral concen-tration (e.g. titanomagnetite black sand), porosity and diagenesis state of marine sediments at a sub-meter scale.
Figure on the right: a CAD image of NERIDIS III profiler with open lid to show arrangement of control and battery units, EM sensor coil, CTD, recovery system and new high resolution still camera.

System specification

TypeMARUM build bottom towed vehicle
Depth rating1000 m (operated in 450 m off NW Spain)
Weight900 kg (in air), ~250 kg (in water)
Dimensions (L x W x H)5.2 x 1.2 x 0.8 m
Power2x 40 Ah Lithium Ion Battery Packs à 24V and 12V
TelemetrySHDSL (armored coax cable) or Ethernet
Tow cable length~3.5 times water depth (~20° tow angle)
Tow speed2 - 4 knots
Scientific payload- Frequency Domain EM (1m transmitter and concentric-coaxial receiver coil)
- Conductivity-Temperature-Depth and Turbidity probe
- Motion control (heading, roll, pitch, 3D acceleration)
- Camera and video observation
- Digital color macro photography (5 MP, 5 fps, 200 micro-s)
- Gammaray spectroscopy (Medusa MS SUB) - in prep.
Sampling ratesEM (25 Hz), CTD (10 Hz), motion (50 Hz), Photo (5 fps)
Application- Bottom towed (ground contact) by mid-size or large research vessels
- Integrated flotation system (e.g. transit and recovery)
- A-frame or crane deployment
- Real time data via tow cable
Mission durations [max distance]~ 12 h or ~7 h incl. Photography [80 or 45 km respectively]
Modular conceptSensor configuration is based on 3-8 specific modules (each module provides a loading space of 0.7 x 1.2 x 0.5 m - length x width x height)
Specific modules can be designed to meet custom needs

CSEM Imaging Concept

The non-magnetic and non-conductive NERIDIS III fully encases a state of the art broadband frequency domain EM sensor with horizontal coplanar arrangement of concentric 96 cm transmitter, bucking and receiver coil (modified and marinized Geophex GEM-3). Superimposed frequencies of the transmitted waveform between 25 Hz and 20 kHz allow to determine target specific EM spectra (UXO, cables, ferrous objects) and the magnetic susceptibility and electric conductivity of the sub-surface. Measurements are performed at sampling rates up to 25 Hz (approx. 0.1 meter resolution at 4 kn speed).

Optical Imaging Concept

The optical imaging concept is based on a AVT Prosilica GC2450C high-speed industrial quality digital color camera (5 frames per second, 5 Megapixel) and electronic high-speed shutter. Two rugged high-performance LED flash units synchronized with the camera shutter will permit rapid flashing with exposure times of a few µs.
Camera typeProsilica GC2450C (5 MP, up to 15 fps, 2448 x 2050)
Flashes2x 24 LED Cree flashes (4 channels à 8 A each)
Data recordingDFKI rock environment on Linux PC with 500 GB SSD
Optical resolution1900 x 1900 pixel over an area of 40 x 40 cm; sub-mm resolution
Illumination time (at 3.5 kn tow speed)100 - 200 µs
Data volume per km10 GB / km
InspectionLow resolution jpg's at desired time intervals
The availability of sharp and numerous images offers many research opportunities from object/specimen counting over ripple analysis to habitat mapping and sediment identification by automatic algorithms. At track crossings, these photos even permit to detect, evaluate and (hopefully) exclude eventual seabed scouring by the operation of the EM profiler itself.