Starting in 2017 all SediMeters measure the turbidity by two different methods, straight and oblique backscatter. This has two effects, first an increase of resolution to 0.5 cm, and second that there are two kinds of measurements that behave in different ways in some cases: When it comes to measure moderate levels of turbidity they will give near identical readings, but when the sensor is blocked by the bottom they may differ a little, and when exposed to air, they will differ a lot. By plotting the two channels in color, as if it were a color photo, we create a color image with 0.5 cm resolution.
The SediMeter instrument measures a vertical turbidity profile through the bottom of lakes, rivers, or the sea, in order to monitor sedimentary processes. Since it uses light (near infra-red) it has to stay reasonably clean to function properly, something that can be a challenge in some environments. For that reason we have version SM3B with a built-in mechanical cleaner. Apart from being costly, this has the disadvantage of creating a possibility for failure, by having a moving part in a liquid that sometimes is full of suspended sand particles. A method of keeping clean without moving parts is needed.
The SM3C model that we now announce has a vibrator ‚ÄĒ as in a mobile phone ‚ÄĒ that shakes briefly but intensely at preset intervals. The video shows the effect: particles and bubbles dislodged from the sensor.
Another novelty of 2017 is that we are doubling the resolution by measuring both straight backscatter and oblique backscatter. We will return to that topic¬†in a later post since it has wide-ranging implications for the usefulness of the instrument.
Much more to come in 2017, never before have we have so many new features in the pipeline!
Before a SediMeter is shipped it is run for a while in stand-alone logging mode, and in real-time monitoring. This screen capture¬†shows one such logging test file, for instrument SM3A-0041. It was inserted in a tank with Formazin that had been settling for a while, which explains the higher turbidity in the lower part of the sensor. The turbidity sensor mounted 11 cm higher up than the main array (“Turbidity (FBU”)¬†was passed by the top of the main turbid cloud¬†soon after the logging started.
In the following two delivery tests, the instruments were placed next to each other half submerged in the Formazin tank.
Note that the top of the Formazin cloud is visible as it settles. In the early part the two instruments are causing interference one with the other since they were synchronized and adjacent to one another. The separate turbidity sensor was in air and it’s value only represents the backscatter in the sensor air interfase.
This firmware update fixes several bugs. One of them could cause the instrument to freeze during a measurement, or cause malfunction only in reading the turbidity detectors. Another could cause the yellow LED to turn on even if the cable was not connected. A third bug could cause the instrument not to react when plugging in the cable.
Each of these malfunctions has been observed, but we were not able to reproduce them. We therefore reviewed the code line by line looking for any possible¬†malfunction, deduced what the consequences would be, and when we found a consequence¬†that matched an observed bug¬†we celebrated. We believe that between these three bugs all observed malfunctions have got their explanation (and that the fixes haven’t introduced any new bug!).
As a side effect we also found some areas of code that could be made more efficient, but we did not want to introduce any new features this time. It’s all about stability and perfection in this update.
All instruments delivered from now, and all instruments returned for service, will be updated with these bug fixes.
The next software update will include code for synchronized radio sleep in the SediLink radio modem. This means that remote monitoring in real time can be made with both the SediMeter instrument(s) and the SediLink radio modem in sleep most of the time, thus limiting the power drain. The small built-in solar panel of the SediLink gives enough power to keep this system charged even in low light conditions, if the duty cycle is limited to a reasonable value. In most cases one measurement can be taken per minute without running out of battery.
During the design phase, when deciding the size of the solar panel and the battery capacity the worst case scenario was defined as a high-latitude winter storm lasting for a week, meaning no charging at all for one week. The test shows that the battery capacity is adequate for running the system for one week. It also shows that even a little sunlight every day is enough to gradually charge the battery up again (this was measured indoors to simulate high latitude low light levels).
More than one SediMeter can be hooked up to each SediLink radio modem, but the effect on power has yet to be tested. In many cases it is estimated that up to 3 units can be powered, and this is by design; using 3 SediMeters in the same general spot is a desirable tactic¬†for estimating both the average siltation,¬†and the¬†uncertainty of the estimate.
Miami 2016-05-18 – The latest SediMeter‚ĄĘ models were developed based on feedback received from the USACE, in order to create an instrument that stands up to the demands of the army corps of engineers in their toughest field deployments.
A few years ago the USACE tested the previous (second) generation SediMeter, SM2, which was developed in 2007. It was a huge improvement over the first commercial generation from the 1990’s,¬†but it was still not tough enough. So based on the feedback from the researchers of the army corps of engineers, we created the specs for the third generation:
It was to be designed to survive the toughest environment where it would be meaningful to deploy it, i.e. a beach with breaking waves. So it must have a minimal cross-section, which meant that we did away with the instrument house ‚ÄĒ all electronics was made to fit on the sensor board.
Units equipped with a cleaner had to survive continuous use for years in the ocean, why the motor hardware was made of the best possible materials with no concern for cost. And it was tested for years in salt water.
We also eliminated¬†all redundant features. The¬†less things that can¬†go wrong, the more reliable a product¬†is.¬†And we permanently seal them¬†to decrease the risk of water leakage. The version without cleaner is solid state, and the one with cleaner has one moving part: The reel for the line, driven by a shaft that is sealed by three o-rings;¬†and even if all three fail, there is a permanently sealed backup to protect the electronics from water.¬†This third generation of SediMeters, SM3, came out in 2013. By now the design¬†has been field tested and fine tuned for 3 years.
Says the inventor Dr. Ulf Erlingsson: “I spared no effort to make this the best SediMeter money can buy, and I am completely¬†pleased with¬†the result,” adding that there is nothing he wishes he would have done differently, neither in the instrument nor in the measurement system that it forms the heart¬†of.
You can now rent a SediMeter instrument for your sediment project, instead of buying. Maybe you have a research project involving measuring sedimentation, erosion, siltation, resuspension, scour, or near-bed turbidity, but you just need the instrument for a few days or maybe a couple of months? In that scenario renting makes economical sense.
Maybe you have been tasked with performing dredging monitoring, supervising sediment spill and making sure it does not accumulate on coral reefs, oyster beds, mussel banks, or in seagrass fields, and you need many instruments but only for a limited time. Here is a plan: Buy one or a few instruments for the background data collection, and to familiarize yourself with the instrument.
Less problems, more data
Then rent a slew of instruments for deployment during the actual works. Why buy them if you only need them a few weeks, right? Let us handle the maintenance, storage, make sure they always have the latest firmware and fresh batteries, and just rent again the next time you need them. It saves you a lot of trouble, and you’ll always have the “latest model”. Just make sure you book in time so that you don’t get without it when you need it.
Use the Contact form or call us to make a reservation.
A hundred years ago Physical Geography concerned itself with the description of landforms and processes, and deductions about how these processes had led to those landscapes. Then in the 1930’s a research student in Uppsala called Filip Hjulstr√∂m crossed the river called Fyris√•n every day on his way to the department. He stopped, took a water sample and measured the water level. He then analyzed the sediment concentration and made a quantitative estimation of soil loss through river runoff. Years later he became the professor of the department, and a series of research students dedicated themselves to the quantification of the geomorphological processes: √Öke Sundborg (who would succeed him as professor, studied fluvial processes in the river Klar√§lven), Anders Rapp (who would become professor in Lund, quantified mass transport in the Swedish mountains), John O Norrman (who succeeded Sundborg, studied coastal processes in the lake V√§ttern), Valter Axelsson (whose homepage is on a “museum domain”, studied delta deposition), and others.
To carry out quantitative geomorphological studies frequently requires inventing new instruments and methods. The department got a world-class Geomorphological Laboratory with flumes and a professionally staffed workshop. Valter Axelsson developed a method for quantification of recently deposited sediments using X-ray and¬†the rectangular Axelsson corer.¬†Bengt Nilsson developed a suspended sediment sampler for vertical integrated suspended sediment sampling, during the International Hydrological Decade. The sampler was widely used especially in remote parts of the world, and it is still available for purchase¬†– even though¬†it will soon turn 50 years!
I was lucky enough to have Rapp as professor during my undergraduate years in Lund University, and to then come to Uppsala University¬†for my PhD studies. Having access to the Geomorphological Laboratory and the workshop I was able to¬†develop the SediMeter. The purpose of the instrument¬†in my thesis was to determine the onset of bedload transport on nearshore bottoms, and to find out what happens off the “closing depth”. However, already during the initial field trials in 1986 (under the ice of a frozen lake; working near the Arctic Circle does tend to limit the time available for field testing) I found that the instrument had potential applications¬†that went far beyond those initially contemplated.
Since my career took a different path I didn’t continue using the instrument until I decided in 2007 to develop a new, better version. That second generation was again replaced by a third generation in 2013.¬†Electronics have developed tremendously, but the basic design of the sensor has stayed the same, because it works so well.
We now write¬†2016¬†and¬†30 years has passed since¬†the first¬†field deployment of the SediMeter. It has developed into the world’s arguably best system for monitoring siltation caused by sediment spill and pollution from dredging and other works. It is also used to monitoring sedimentation in reservoirs, harbors, and navigation channels, and in laboratory experiments, as well as for monitoring resuspension and erosion.
The Geomorphological Laboratory is, alas, gone, and the Department of Physical Geography has been merged and reorganized, but a number of¬†instruments and samplers developed in the Uppsala School of Physical Geography live on as commercial products – and the SediMeter is one of them.
Written by Ulf Erlingsson
The SediLink radio modem can be mounted directly on a SediMeter SM3A for lab use. This is useful for instance in a physical model of an engineering project where the objective is to study sediment transport. Later the same equipment can be used to verify the predictions in the field, but with an extension cable between the SediMeter and the radio modem‚ÄĒand a buoy so it gets up above the water surface!