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SCATTER PLOTS FOR RED POLYGON AREA
| SCATTER PLOTS
FOR RED POLYGON AREA
inner lagoon waters
| plots below were obtained using PCI Geomatica |
- The area under red polygon offers a straightforward exposure of bright shallow bottoms at all depths for studying the Brightest Pixels Line (BPL) in all three of Green/Red, Red/Nir and Green/Nir pairs of wavebands.
- Top three scatter plots for raw radiances
- in all three scatterplots, the exponential decay is represented in a pure form by the outer exponentially-shaped limit of shallow pixels.
- an extremely gently sloping of very homogeneous and bright shallow bottoms, starting with pixels with just a very few centimeters of water, is the reason why the exponential decay is so self-explanatory in these Red/Nir and Green/Nir scatter plots.
- Middle three scatterplots are for smoothed-deglinted radiances
- Glintm_GlintM: deglinting interval: deglinting has been applied only up to a maximum radiance Ls nir=20:
- pixels where Ls nir>20 have been left un-deglinted.
- please note in the scatter plot of band 1 vs band 2, that the majority of pixels around Ls1=55 Ls2=19 are much less scattered in this scatter plot than in the raw scatter plot just above:
- this is the result of smoothing_deglinting.
- Bottom three scatter plots are for smoothed-deglinted-linearized scatter plots
- the exponential decay has become linear, with slopes K1/K3, K2/K3 or K1/K2 which are easily measured using this kind of display.
- these slopes are best estimated as the slope of the outer edge of shallow pixels
- i.e. rather than through a procedure of sampling and regressing of a number of training sites as proposed by Lyzenga.
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SCATTER PLOTS FOR GREEN POLYGON AREA
| SCATTER PLOTS FOR GREEN POLYGON AREA
inner lagoon waters
where we witness the intrusion
of very clear waters from the reef rim
into the much less clear
inner lagoon waters
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plots below obtained using PCI Geomatica
 - The green polygon is an area of the inner lagoon which receives crystal-clear oceanic waters through the reef rim system
- over a short distance, these waters mix with much less clean lagoon waters.
- Tarawa is home to 50,000 persons.
- In the scatterplots for raw data, it can be seen that the maximum radiance exceeds that of red polygon by approximately 20 DN in all three bands.
- For some reason, the very shallow bottom is even brighter here than under the red polygon, which complicates things further:
- this must be caused, somehow, by the intrusion of clear oceanic waters into lagoon waters
- a unique study case
- indeed, it can be seen in scatter plots of Ls1 versus Ls3
- that for a maximum radiance of pixels Ls3=50
- Ls1=205 in the green polygon is significantly higher
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