NTEZTHIETEA:
a year in
ost and
ce and its
BLUE GREEN ALGAE IN THE SOUTH-WESTERN BALTIC
DETECTION FROM SATELLITE
K.A. Ulbricht, DFVLR-Institut für Nachrichtentechnik
8031 Oberpfaffenhofen, Post WeBling
U. Horstmann, Institut für Meerenkunde der Universität
Kiel, 2300 Kiel
Scanning through LANDSAT scenes of August 1975, we noticed irregular white traces
in the southwestern Baltic sea, after applying contrast enhancement as well as
other image processing modules on computer compatible tapes, supplied by the
EROS Data Center in Sioux Falls, USA. Patterns were rather irreqular in inten-
sity within same spectral region, and varied in appearance and intensity, when
comparing gray levels in the four multispectral LANDSAT channels MSS 4
(0,5 - 0.6 um), MSS 5 (0,6 — O,7 um) MSS 6 (0,7. —.0,8 um), and MSS 7
(0,8 - 1.1 'um). Discussions and a'review of literature {howed, that phenomena
refer to maSs accumulations of blue green algae, which was underlined by behaviour
of phenomena on consecutive days: an unstructurized white "cloud" in the water,
changing to distinct white lines the next day (s. fig. 1 and 2)” - 10).
There are two dominant species of blue green algae, developing blooms in the
Baltic, Aphanizomenon flos-aquae (fig. 3), and Nodularia spunigena (fig. 4).
Aphanizomenon flos-aquae is composed of bundles of filaments, the single cells
being 5 - 15 ,um long and 4 - 6 jum wide. Responsible for it's nitrogen fixing
capacity are feterocysts, scarcely longer than vegetative cells and lacking
pigmentation. Nodularia spumigena also are filamentous blue green algae, whosc
cells are 8 - 14 ,um long, while their width ranges from 10 - 16 ‚um. Their
heterocysts are also longer than their vegetative cells and are tfansparent:
We found mass appearances of blue green algae during August 1975' on several
LANDSAT scenes, i.e. parts of the Baltic. Traces on LANDSAT images north and
south of the Danish island of Alsen (fig. 2) were verified to be blue green
algae by Danish ground truth investigations 11y. An especially strong appearance
of the phenomenon was found on a LANDSAT scene of August 7, 1975, of the south-
western Baltic between the Danish Bornholm, Rügen and the German Democratic
Republic (fig. 5). On this image, covering an area of 185 km times 185 km, three
different regions of algal appearance can be distinguished,
1: an induction zone, where intensive blooms start near outlets and inside
bays, "Boddens" and "Haffs",
