This instrument was primarily developed to detect erosion and re-sedimentation processes at the bottom of marine environments (ocean/river locations). It is not recommend to be used with concentrations below 100NTU or 250mg/l SPM. It records the reflections and the dynamic parameters for high concentrations that are created in the measuring plane by solid particles moving in a multiphase current. It provides an independent contribution to the complex questions which arise from the context of transport of solids in the zones between the bottom, the fluid mud layer and the main body of water. Internal filters in the ASMA software shall be used below 100 NTU. Below 100NTU the data quality is limited

The instrument operates with backscatter infrared sensors embedded in a titanium body. The sensors are placed on an active board at a distance of 10 mm. This means that 100 sensors are mounted per meter.

Each sensor consists of an infrared transmitter and detector. The sample to be taken has a volume of approx. 10 cm³ at a distance up to 100 mm in front of the sensor.

The instrument contains three additional sensors.

  • An inclinometer for two directions will give the actual angle between ground and instrument. The maximum range is 60° in all directions.
  • A pressure gauge senses the actual depth of the location of the instrument and it gives information about tides.
  • A temperature sensor detects the temperature of the steel housing which is related to the water temperature.

Activation and power supply for the sensors as well as for the transmission of the signals are controlled by a battery powered central unit sealed-in the head of the instrument. It consists of a microprocessor, a data memory, the additional sensors and the energy supply.

The energy consumption of the instrument is very low ( < 6 mAs). That means one 9V block alkaline battery (lithium will double duration time) will provide the necessary energy for 2 months, assuming a sample rate of 10 measurements every 5 minutes, or the energy for a standby status of approx. 6 months. The capacity of 8 Mb will provide a measuring time of approx. 8 weeks in total, without weakening the battery at the sated rates above.

The microprocessor carries out all of the tasks necessary for control. Incoming data is processed by the microprocessor and stored in memory.

The ASMA 4.xx software runs on modern PC systems.

Specifications ASM-IV-TI (titanium body)


  • Measuring section: 0.96 m (Type S), 1.44 m (Type N), 1.92 m (Type L)
  • Minimum frequency: 1 Hz
  • Measuring intervals: 1 sec. ….no limit
  • Sampling rate: 1 … 255 samples per burst
  • Memory capacity: 8 MB standard
  • Energy supply:
    • Main supply: one alkaline 9V block battery minimum two lithium 9 V block battery for maximum energy source
    • Memory backup: gold cap
  • Standard lengths of the instrument: 1.9 m (Type S), 2.4 m (Type N), 2.9 m (Type L)
  • Dimensions of the instrument:
    • Sensor area: 30 mm (Type S, N), 35mm (Type L) diameter
    • Head: 60mm (diameter)
  • Weight: 4.5 kg (Type S), 5.5 kg (Type N), 8.5 kg (Type L)
  • Ambient temperature: -15…+45°C
  • Installation depth: 40 m water depth max.
  • Distances first OBS pressure sensor: 190 mm


  • Measuring method: optical
  • Sensors: back scatter infrared sensors (920nm)
  • Sensor distance: 10 mm
  • Number of sensors: 100 per meter
  • Measuring range:
    • 50….2000 NTU
    • 500..50,000 mg/l sand (d50=250µm)
    • 100…5,000 mg/l mud (d50=20µm)
  • Resolution: 5%
  • Accuracy: +/-10%
  • Linearity sensor to sensor: +/-5%


  • Measuring method: gravimetric
  • Sensors: 2-D integrated circuit
  • Measuring range: 0…60° all directions
  • Resolution:
  • Accuracy: +/- 1°

Water depth

  • Measuring method: piezoelectric
  • Sensor: stainless steel pressure housing & membrane
  • Measuring range: 0…5,000 hPa abs. other ranges on request
  • Resolution: 0.5%
  • Accuracy: +/- 0.3% (full range)


  • Measuring method: resitive
  • Sensor: silicon integrated circuit
  • Measuring range: -10…45 °C
  • Resolution: 1°C
  • Accuracy: +/- 0.5°C


!The most common cause of errors in ASM-OBS data is a failed calibration!

Calibration tank

For a proper calibration it is absolutely necessary to keep particles in homogenious suspension while running the calibration procedure. The design above had been created after checking with different particle sizes in the tank. A download drawing is available.
ARGUS will pre-calibrate ASM-IV instruments if requested. In this case the user has to provide sediments from the local environment.

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