dugongs in palau - C3

Preliminary surveys
The sel ected sites were visited and preliminary surveys were done to determine the overall composition of
the area. These surveys were very quick qualitative surveys. The techniques involved in the survey were
fairly simple. At the site, random points were chosen and the GPS coordinates were noted. At each
random point a diver swam around for about five or ten minutes and noted down observations such as
bot tom character, visibility and the absence or presence of seagrass. If there was seagrass present, the
estimated abundance and species was recorded. The information collected along with the satellite imagery
was then used later to determine the position and number of transects at the sites and also was used in the
classification of seagrass meadows.
Imagery used
The images used for the survey were IKONOS imagery. IKONOS is a satellite-based platform operated
by Space Imaging Inc. that captures digital images in four spectral bands as well as panchromatic images.
The four spectral bands are Red, Green, Blue and Near Infrared. Resolution for the spectral bands is 4
meters while the panchromatic band offers a resolution of 1 meter. The images were taken by the satellite
in November of 2000. Mainly because of their availability and their high resolution, IKONOS imagery
was used for this survey.
When provided, the images were already ortho-rectified and projected using the Universal Trans Mercator
(UTM) method with WGS84 datum. Therefore, preprocessing of the images was very limited. The only
processing needed was to subset the images of the selected sites and the conversion of the coordinate
system from UTM WGS84 to Lat/Long WGS84.
Transects
There are a variety of techniques and methods that can be used for ground-truthing. The techniques differ
according to the locality features, depth and mapping objectives. For this survey it was decided that a
combination of transects and points for the shallow areas (5 meters or less) would be used and GPS
tracking for deeper zones (greater than 6 meters).
A total of six transects were used on Ngederrak reef. These transects ran from east to west across the
entire extent of the reef with an approximate distance of 300 m between each. Deep-water surveys were
also conducted using SCUBA and GPS tracking along the inner channel and along the eastern and
western end of the reef flat (Figure 10).
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