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Along much of our coastline the depth of penetration by
color photography will not be so great as in the area just
illustrated. However, there will be many instances where
color photography of bottom features to depths of but a few
feet will be extremely helpful.
It is always helpful to position channels
and shoals on the boat sheet prior to hydrography.
We have always done this insofar as practicable
on the maps that we prepare for the hydrography,
but our panchromatic photography left much to
be desired. Color photography clearly shows the
limits of channels and the extent of shoals.
Rocks awash and those slightly submerged
at low water are particularly important when
close to traffic lanes and it is not always
easy to locate these features either by photo-
grammetry with panchromatic photography or by
sounding. Color photography providing some
penetration of the water will no doubt be
extremely helpful for this purpose.
We have many small inlets that shift and
change with storms. We customarily revise the
shoreline after such changes from panchromatic
photography, and this is done quickly and
readily. However, hydrography to detect changes
in the channels at such inlets 1s a slower more
tedious job. Color photography will often detect
the fact that a channel has changed position and
show the new position even though it can give us,
thus far, only approximate information about the
depth.
Our methods of plotting with color photography are thus
far quite crude. We are using color transparencies. These
are cut to individual photographs for stereoscopic viewing
on a light table. When locating aids to navigation, radial
templets are made on a light table and plotted to passpoints
located by photogrammetric bridging with higher altitude
panchromatic photography.
We have not yet been able to satisfactorily project the
color transparencies on the Kelsh Plotter as we have not been
able to provide sufficient light for satisfactory projection
with polaroid filters. Consequently, we had to adopt an
