New SediMeter features in 2015

Miami, FL, 2015-01-23 – The third generation SediMeter released in 2013 is getting some exiting improvements in 2015, in response to feedback from customers. Although none of the improvements is visible on the outside, they are significant.

The only physical change is that the cleaner version SM3B is getting a doubled battery capacity, up to 1800 mAh from 900 mAh. Considering that the idle current is the same, this represents more than a doubling of the available power for measurements and cleanings. The firmware has also been tweaked to minimize unnecessary current drain.

The second big improvement is a doubled memory capacity, from 8192 measurements to 16,384 measurements. That’s over 5 months with one measurement per 15 minutes.

However, the biggest improvement for some users may be the (re-) introduction of burst samples. In the previous SediMeter, SM2, the burst samples were avaialble for optional sensors such as pressure and light. In the 2015 version of SM3, the burst samples are available for the two key parameters: Bottom level, and near-bottom turbidity. For each measurement, each of these parameters can now be measured not just once, but up to 20 times, with an interval of 1 to 16 seconds between the burst samples.

Why are the burst samples such a big deal? It’s got to do with statistics. How do you know that a single measurement is representative of the time when it was taken? It’s easy to visualize this on the bottom off a beach, where the waves stir up the sediment during part of the wave period, while at other parts all the sand falls back on the bottom. If we measure once per hour we cannot know in which part of the wave period we measure. The short-time variation may be larger than that from measurement to measurement. But if we take a few samples at a short time interval, we can see what the short-time variability is. This is equivalent to the “nugget effect” in geostatistics.

Combining the larger memory and the burst sampling, it’s now possible to take 327,680 measurements of bottom level and near-bed turbidity. That’s the equivalent of one measurement per 15 seconds for almost 57 days (which can be accomplished with a burst interval of 15 s, and a measurement interval of 5 minutes).