Digital Signal Processing Reference
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shores where floating mats of vegetation are manually constructed by fishermen as traps for fish. This
is despite the fact that the average expected values at this time of the year (during the summer season
the average concentration is 58 μg/l in the mid area of the lake, and 7.58 μg/l in the western region of
the lake, according to (Siam et al, 2000) and the values deduced from field work conducted on May
2005 showed an increase in the average concentration to 61 μg/l in the mid of the lake. It is obvious
from the field observations that during this period of the year there is an effect by the floating and
submerged vegetation on the CHL-a concentrations retrieved from the image.
Comparing the readings from the image at specific locations where it was possible to take field
measurements (LO11, LO12, LO13, LO14, LO15, and LO21) where the readings range from 31.14 -
86.7 μg/l to the limited measured values (11.3-24.4 μg/l) it is deduced that the concentrations from the
image were reasonably higher.
Figure (8-30)
shows the locations where CHL-a samples were
measured. In recent publication by (Ossman et al, 2010), concentrations of CHL-a within lake Edko
recorded higher values that ranges between (28-99 μg/l). Taking into account the limited number of
measured values in 2006 and the values from earlier field work in 2005 and published CHL-a
concentrations in Lake Edko, it is concluded that the CHL-a in open water is in the range of 40-76 μg/l
in the middle region of the lake. The following uncertainty sources should be highlighted; the image
taken was 11 days later than the measurements values, no samples were taken in the middle area of the
lake, submerged and floating vegetation may result in higher CHL-a readings.
Figure (8-30): The locations where CHL-a samples were measured
The average concentration of CHL-a within the (ROI) is 31.4 μg/l within the whole (ROI) in both the
easernt and western areas of lake water body this is shown in
Figure (8-31)
.
Figure (8-31): Concentrations of CHL-a within the selected (ROI)
It can be concluded from the analysis of the SPOT image, that the CHL-a concentration in the open
water area of the lake was in the same range as it is expected from the data published in the literature.
The high spatial resolution of the SPOT image proved that there are small islands of floating
vegetation and submerged vegetation areas;
Figure (8-31)
, which will give increased estimated Chl-
values in the images of coarser resolutions. This single SPOT image provided a good insight into the
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