Real-time visualization of taxa-specific plankton distributions

Reported by: Carin Ashjian

During the 1997 GLOBEC field season the Video Plankton Recorder group (PIs: Davis, Gallager, Ashjian) obtained distributions of plankton taxa and associated hydrography in real-time using the Video Plankton Recorder. Highlights of these distributions were discussed during this presentation; further details may be found in Davis et al. (submitted). Briefly, image processing consists of in-focus object detection and image identification. In-focus images are extracted from the raw video fields using an image processing system and saved as tagged image format (TIF) file. These files then are analyzed using an image classification system (Tang et al., 1998) and identified to taxa or species. During the 1997 cruise, approximately 1 image per second was extracted and identified to taxa; recent advances in both hardware and the classification software have increased the speed of this process considerably so that several images may be processed per second. The automated identification system was 90-95% accurate for the taxa encountered.

Data from two segments of the cruise during which real-time plankton distributions were obtained were shown. The first segment was collected during a diel study conducted in the Great South Channel; the VPR was towed undulating from surface to near bottom around a drifter for 24 hours. Calanus finmarchicus was concentrated near the pycnocline during daylight hours but much more diffuse and extending from the surface to the pycnocline during night. The timing of this change in distribution coincided well with changes in downwelling light that had been measured by the light sensor on the VPR. The second segment was collected over a 24 hour period along repeated surveys of a 40 km transect oriented east-west from Georges Bank into the Great South Channel. Elevated concentrations of the diatom Chaetoceros socialis were observed in association with isolated parcels of high density water which appeared to have been advected across the transect line near the western end at least twice during the 24 hour period. Subsequent examination of the N-S velocity records from the acoustic Doppler current profiler confirmed that the presence of C. socialis and high density water was associated with northward and southward movement of water under the transect line during the tidal cycle. During the 1999 GLOBEC Phase III field season the VPR group plans to obtain similar real-time distributions of plankton, hydrography, and velocity which then will be utilized in real-time models.

Davis, C.S., S. M. Gallager, X. Tang, L. Vincent, and C. J. Ashjian. Real-time visualizaton of taxa-specific plankton distributions. Submitted.

Tang, X., W. K. Stewart, L. Vincent, H. Huang, M. Marra, S. M. Gallager, and C. S. Davis. 1998. Automated Plankton Image Recognition. Artificial Intelligence Review, 12(1).