SediMeter SM3

The SediMeter measures a vertical turbidity profile and calculates sedimentation and erosion with millimetre precision.

Instrument for Sediment Monitoring: Siltation, Erosion, Scour, Deposition

The Lindorm SediMeter is a "sediment meter". It measures a 35 cm long vertical turbidity profile - using 36 optical backscatter detectors (OBS) - through the bottom, and calculates the level with micrometer resolution. The SediMeter is ideal for erosion and sedimentation measurements. The SediMeter can be used for detect when erosion happens, analyze siltation, and measure sedimentation rate, the latter both in terms of sediment accumulation rate, and in terms of sediment settling from suspension. It can be used to get real-time data on the dynamics of the sea floor, and it is ideal for monitoring sediment spill from dredging in real-time.

The patented sedimeter sensor consists of an array of 36 infrared optical backscatter detectors. The turbidity is measured every 10 mm, and the bottom level is interpolated with a resolution of 0.001 mm. This may seem like an exaggeration, but it allows for the detection of change on a very minute scale, and thus of qualitatively correlating processes (waves, currents, dredging spill) to sediment accumulation and erosion on the bottom. It has been found that the sedimentation of as little as 100 g/m² can be detected (see this video).

There is also a dedicated 37th turbidity sensor mounted 11 cm higher up than the array of 36 OBSes. The calculated level, along with this turbidity, can be measured as "burst samples", up to 20 times for each measurement, at an interval of between 1 and 16 seconds. Thus the memory holds up to (20 x 16,384 =) 327,680 level and turbidity measurements. The turbidity data from the array of 36 OBSes is only saved once per measurement, though, and the same is true for temperature and battery data.

The SediMeter offers several deployment options. Both models, SM3A and SM3B, can be used either as a stand-alone logger, or connected to a cable, or both. The instruments support RS-485 at 9600 and 115,200 baud, and has a built-in rechargeable battery. The protocol supports daisy-chain networking, with hundreds of instruments along a single cable stretching over several kilometers. Radio telemetry can be used from a buoy to land, or via a satellite link. The required software is free.

Applications

Monitor...	In...	For...
Sediment Accumulation	Channels	Navigation Safety
Sedimentation	Bioherms	Dredging Spill Monitoring
Siltation	Reservoirs	Environmental Monitoring
Silt Deposition	Coral Reefs	Environmental Impact Assessment
Resuspension	Lakes	Pollution Monitoring
Scour	Rivers	Engineering
Erosion	Shores	Environmental Management
Near-Bed Turbidity	Seas	Research

 

Common Specifications for SM3
Data
Data output	Turbidity at 36 + 1 levels (FBU), Bottom level (cm), Temperature (cK), Battery voltage (mV)
Turbidimeter principle	180° optical backscatter (OBS)
OBS wavelength	945 nm (NIR)
OBS detectors	36 for sediment level + 1 for turbidity and cleaner operation
OBS spacing	36 at 10 mm + one at 110 mm
Bottom level accuracy	±2 mm (for a well defined the bottom)
Bottom level resolution	0.1 mm
Thermometer location	Between OBS #36 and #37
Thermometer resolution	0.1°C, calibrated to ±0.5°C
Logger
Measurement interval	User selectable from 1 second to 24 hours
Burst samples	Up to 20 subsamples per measurement
Burst channels	Level, and #37 turbidity
Burst interval	1 to 16 seconds
Memory capacity	16,384 measurements
Communication
Computer interface	RS-485 (a.k.a. RS485, TIA-485)
Baud rates	9600 baud; 115,200 baud (9600,N,8,1 after RESET)
Network	Up to 255 units in a daisy-chained cable
Protocol	LogDator Communication Protocol ver. 3.0
Power
Input voltage range	5 V ≤ Usupply ≤ 15 V
Charge time	ca 16 to 20 hours
Current, charging	Imax ≈ 110 mA
Current, on-line monitoring	Iaverage ≈ 10 mA
Battery life	Over one year
Battery type	Lithium (NiMH on special order)
User interface
Power status LED	Blue light when external power is connected
Battery charging LEDs	Red for charging, green for full, both for error
RS-485 LEDs	Yellow for listening, green for transmitting
Measurement indicator LED	One blink per measurement
Magnetic reed switches	Reset CPU; Battery charging error override
Recommended accessories
Mounting hardware	Anchor, holder tube, and handle to screw it down
Cable	USB to SediMeter cable, 1.8 m or 5.0 m standard lengths
Blind plug	Protects UW connector when used stand-alone
Software (free)	SediMeter.exe ver 3, and driver for the USB cable
Environmental
Depth rating	45 m (150') standard
Temperature	From 0ºC to 50ºC, not exposed to direct sunlight
Optical liquid medium	Purified saturated oil, odorless, combustible
RoHS	*Lead in shuttle counterweight is exempt from prohibition

Model versions

The SM3B is the first SediMeter with a built-in cleaner. This can enable it to operate for months on end, even in fouling environments.

Unique Specifications for SM3B
Cleaner	Yes
Length	ca 760 mm
Mass	ca 380 g + ca 230 g shuttle*
Diameter	15 mm sensor 20 mm motor house 60 mm shuttle
Battery Capacity	1800 mAh
Connector	Bottom end