September is coming

I am so excited about our first meeting in September! We have a great programme and exciting discussions ahead of us. Also, I received great interested from several scientists around the world. Please let me know if there is anyone else who is interested in our work and I will add them to the email list!

Device details

Hi everyone,

For those of you who use a specific optical device, could you write a short section about it on the ‘Device’ page?
It would also be great to have some technical details (though they could be added later), incl.

  • min and max particle size that can be captured
  • volume of water that is captured
  • raw output format (e.g. image as .jpg, etc.)
  • level of identification; e.g. broad categories (particle, zooplankton), fine identification (down to genus level)
  • deployment details (towed, vertically lowered, on autonomous platform, etc)
  • deployment restrictions (depth? temperature?)
  • power consumption
  • need for calibration

Any other ideas?




Q5. What are the most useful ways of presenting size distributions?

And How should slope determinations be made?

George’s comment ( Here, I see that alot of observations are presented with incorrect units assigned to the observations. It makes results difficult to interpret. I also see that people are locked into ways of presenting data that mask the trends. I personally think that differential number spectra mask alot of important information because the values span such a large range of values. Plus, not all values are equally certain. The small number of large particles in a given set of measurements makes their values more uncertain than the small, which affects how one should calculate slopes to the data.

#sizespectrum #sizedistribution

Q4. The next step is to measure multiple properties of individual particles

Q4. What would we like to know? What are the most promising techniques for doing so? What will we do with the data?

George says ( Way back when, Vern Asper measured both particle size and settling velocity on the same particles. More recently, Andrew McD has been measuring particle concentrations and fluxes on two different sets of particles and using the results to infer velocity as a function of size. Is there a way to measure both properties on the same particles so that we could perform more sophisticated analyses?

Q3. How do we calibrate different instruments?

My idea: ideally in two steps.

  1. On shore, using a tank filled with balls of a known size (or size range/consecutively different sizes)
  2. At sea, mounted on the same frame

Can we come up with calibration protocols?


Q2. How do we convert between measurements made by different instruments?

Further to George’s comment ( This is one of the central questions I would like this working group to resolve. It starts with the simple question: What is #esd? Different people have different ideas about how to extrapolate their data into a 3D object. For example, I calculated ESD for each particle assuming faecal pellets are cylindrical and all other particles are prolate ellipsoids. But is that what everyone does? And how do you cope with aggregates that are made of different things stuck together? For example:

mixed aggregate

Further to that, how do you determine where a particle ends? I suspect most of us use automatic algorithms, but again, it would be important to make sure that we all use the same threshold. When dealing with 3D objects, even a small error in estimated ESD will have a large effect on final volume (e.g. POC content) calculations!

Maybe we can come up with definitions for each device, all of which are internally consistent?

Q1. How do we determine/distinguish the distributions of different objects from the different instruments?

And how does the certainty vary with object size?

Further to George’s comment ( I think Sünnje and Klas have compared the LOPC and VPR data to distinguish marine snow and zooplankton, and it was pretty problematic. I think George’s idea to analyze and interpret the same data set using different view points is great: 1. ‘particle objects’ are zooplankton, 2. ‘particle objects’ are marine snow.

Just for fun, I’ve attached a couple of photos taken with a camera (particles from the MSC) and the VPR (courtesy of Klas!) . These highlight nicely the diversity we should expect.

Marine snow_small copy