Zooglider is a specialized glider to study mesozooplankton. Thanks to a public website, everybody can follow it in real time while it samples waters around the Balearic Islands in the BioSWOT-Med campaign.
By Sven Gastauer
Where is Zooglider and what is it doing? Zooglider is a specialized glider that is used in the BioSWOT-Med campaign to further the understanding of mesozooplankton. Sven Gastauer, senior acoustic scientist at the Thünen Institute for Sea Fisheries, Germany and visiting scholar at the Scripps Institution of Oceanography (University of California San Diego), USA, is in charge of Zooglider in the BioSWOT-Med campaign. Here, it explains how it is possible to follow it though a public website.
Whenever Zooglider comes to the surface, it stretches one of its wings towards the Mediterranean sun. This allows it to connect to satellite and send us some summary information, that we display on the web. The plots are fully interactive, to allow for a better impression of what Zooglider encounters on its mission.
– Select Mission
Here you can select any Mission Zooglider has performed so far. We have 2 Zooglider in total, so the most recent mission is called 2023_03_0051, because if was started in March 2023 (2023_03) and it is the Zooglider with the serial number 51. Once completed, the mission will get a more sensible name (as you can see in the list).
The map shows the GPS track of the selected Zoogldier mission. Points in black and yellow represent day (yellow) or night (black). The green lines represent the calculated surface drift between two dives. The (orange) Next Waypoint is the point Zooglider is given as its destination. First Dive (blue) is the first dive of the mission.
The Environment tab shows plots for temperature, salinity, chlorophyll and the density of the water, as measured by the glider. The y axis represents the ambient pressure (or Depth where 1 dbar is app. 1m). The x axis represents time (left the start of the mission, right the last dive). The color scale can be adjusted by the different threshold settings (located on top of the plots). Scale y-axis allows to scale the y axis in ‘normal’ linear scale or square root. Square root with transform the pressure information into a square root scale, i.e. stretching the measurements closer to the surface and compressing the deeper values. This can be helpful to detect fluctuations happening in the near surface waters, difficult to detect otherwise. Each of the plots can also be overlayed with the contours of any of the available environmental variables (Contour Select box on top of the plots) the number of contours to be displayed is dictated by # contours.
If you click on any of the dives in any of the plots, the detailed profile of the measured variables will be displayed in the lower plot panels. The Range threshold allows you to adjust for any depth range you might want to focus on.
The contours, profile display, y axis scaling and thresholding is the same for Environment, Zoocam and Zonar.
In the Zoocam and Zonar plots, the top bar represents day or night (yellow=day and black = night).
For the current mission, the camera was switched off for most of the dives, to preserve some disk space while Zooglider is not in close proximity to the main features. ROI are region of interest. Zooglider has a simple onboard processing algorithm, which detects particles on the captured images. It measures the size of these particles and then gives us a summary of what it detected as numbers per size class. This gives us an impression of concentrations of organisms or particles of a given size class in the water column. Sometimes you will see a dive that is red for all size classes. This is usually caused by a tentacle or something similar stuck on the camera. The white – black line below the plot is a measurement of mean grayscale of the plots, a proxy for the density of particles observed. The line below represents the sampling rate of the camera, which is 0 if the camera is switched off. Otherwise, we generally sample at 1 or 2 images per second.
Zonar is the active acoustic device on Zooglider, operated at 1000 and 200 kHz. We show the so-called Volume Backscatter, which is a measure of the observed acoustic intensity expressed in dB. The measure is in dB, so a difference of 3 dB is equal to almost double the amount of acoustic energy. From left to right, we show the 1000 kHz, 200 kHz and the difference of the 1000 and 200 kHz data. In very general term, the higher frequency will be dominated by smaller particles, while the lower frequency will be dominated by larger particles. Hence more backscatter on the 1000 kHz compared to the 200 kHz, hints towards a dominance by smaller organisms (positive values – blue on the right plot), while stronger values at the 200 kHz hint towards a dominance of larger organisms (negative values – red on the right plot). If you squint your eyes a bit of zoom in, you will see some stronger values in the surface waters during the night and stronger values a bit deeper during the day, which can be explained by the daily vertical migration of organisms.