Geoscience Reference
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We see that the rectii ed image has black areas at the corners. We can remove
these black areas by cropping the image using imcrop .
I11 = imcrop(I10);
subplot(2,1,1), imshow(I1), title('Original Image')
subplot(2,1,2), imshow(I11), title('Rectified and Cropped Image')
h e function imcrop creates displays of the image with a resizable rectangular
tool that can be interactively positioned and manipulated using the mouse.
At er manipulating the tool into the desired position, the image is cropped
by either double clicking on the tool or choosing Crop Image from the tool's
context menu. h e result of our image enhancement experiment can now be
used in the next section to analyze the colors of individual sediment layers.
8.9 Color-Intensity Transects Across Varved Sediments
High-resolution core logging has, since the early 1990s, become popular as
an inexpensive tool for investigating the physical and chemical properties of
marine and lacustrine sediments. During the early days of nondestructive
core logging, magnetic susceptibility and grayscale intensity transects were
measured on board research vessels to generate a preliminary stratigraphy
of marine cores, since the cyclic recurrence of light and dark layers seemed
to rel ect glacial-interglacial cycles during the Pleistocene. Paleolimnologists
adopted these techniques to analyze annually-layered (varved) lake sediments
and to statistically detect short-term variabilities such as the 11 year sunspot
cycle, the 3-7 year El Niño cycle, or the 78 year Gleissberg cycle. Modern
multi-sensor core loggers are now designed to log a great variety of physical
and chemical properties using optical scanners, radiograph imaging, and
x-ray l uorescence elemental analyzers.
As an example we explore varved sediments deposited around 33 kyrs
ago in a landslide-dammed lake in the Quebrada de Cafayate of Argentina
(Trauth et al. 1999, 2003). h ese lake sediments have been intensively studied
for paleoclimate reconstructions since they document episodes of a wetter
and more variable climate that eventually fostered mass movements in the
NW Argentine Andes during the Late Pleistocene and Holocene. Aside from
various sedimentological, geochemical and micropaleontological analyses,
the colors of the sediments have been studied as a proxy for rainfall intensities
at the time of deposition. Color-intensity transects were analyzed to detect
interannual variations in precipitation caused by the El Niño/Southern
Oscillation (ENSO, 3-7 year cycles) and the Tropical Atlantic Sea-Surface
Temperature Variability (TAV, 10-15 year cycles) using linear and nonlinear
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