SediSond™

All geologists are familiar with the method of sticking a sond into soft soil or sediments in order to get a feel for the stratification. What we feel in our fingers is the resistance, and the vibration from particles such as sand. But what if the depth is too large for a metal rod to be used? That is where the SediSond comes in.

The SediSond was envisioned by Dr. Ulf Erlingsson in the 1990’s as an electronic sond equipped with an accelerometer, that was allowed to fall freely into the sediments from a height of a few meters. The accelerometer would register the retardation and vibrations as it was brought to a standstill. Software would then calculate the altitude based on the accelerometer data.

This instrument is now finally commercially available, and the best thing is, that we just reprogrammed a SediMeter SM4P and put a tip on it, and a line attachment, to create the instrument. Please check back shortly for m,ore information (the release has been delayed due to our website having been infected with malware).

The SediSond™ is based on the SediMeter™ SM4P

By just reprogramming the firmware and adding some hardware, we managed to create a whole new instrument. The best thing is, that all existing owners of SM4P can have their instruments upgraded to firmware rev 2.

Firmware rev. 2 adds Burst Mode to SM4

The firmware upgrade enables burst mode with a rate from 1/8th to 20 Hz, and up to 255 measurements per burst, and this is equally useful for SM4 and SM4P instruments.

3D Acceleration Data at 400 Hz

By programming each measurement in the burst to contain twenty 3D-accelerometer measurements, and measuring bursts at 20 Hz, the SM4 rev 2 can measure acceleration at 400 Hz continuously for several seconds.

Burst Mode and SM4P hardware creates a SediSond

By programming the SM4P to start collecting 400 Hz acceleration data when it detects free-fall, we have a SediSond instrument that records the resistance in the sediments as the tip of the instrument penetrates layer after layer. At the same time the OBS detectors register the turbidity on their way down.

The SediMeter.exe 6.0 software converts these time-series data to a plot of sediment density and turbidity, with the vertical axis representing elevation (Z).

Fluid Mud

One of the trickiest tasks in studying soft sediments is to investigate fluid mud. It is often pushed away by the shock wave in front of a sediment sampler or corer. An echo-sounder may not detect it, because it has not got a density or sound velocity sufficiently different from that of water. Visually it is easy to detect, however, so the SediMeter may confuse it for the actual sea bed.

Thanks to the SediSond functionality, it is now a straightforward task to correlate SediMeter data with sediment density, since the software plots them together in the same graph.

Incidentally, it is possible to program the SediMeter so that it both acts as a SediSond and as a SediMeter in the same mission. It can be deployed by falling into the bed, recording the free-fall data, and then continue recording as a SediMeter every so often, until it is retrieved again. This gives an even better indication of what is taking place on the lake floor, or whatever environment you are studying.