Evening star., 1939-01-15
Years Needed
ToConplete
Portrait
Soil Erosion Study
And Flood Plans
Combined
Bv Louis E. Reichard.

IL AOttbO ~ W.
The good old U. S. A. is posing for
mammoth portrait. The pho
tographic studio is away up in the
sky, and the photographers, dressed
In electrically heated suits, are
swapping pictures from an elevation
of approximately $4,000 feet.
Because there are 100000 square
miles of territory to be photo
graphed, the portrait, though it
cannot be called a long time eX-
posure," will be years in the making.
After it has been completed, Uncle
Sam may sit at an imposing desk
in Washington, call for such seq
ments of the huge picture as par
ticularly interest him at the mo-
ment and ponder over his plans
for improving America. Each OF
these segments will show him every
stream, every highway, every noun
tain and valley-even every house
within the area covered by it.
With these laid out before him,
Uncle Sam will be in strategic po-
sition to find ways and means to
keep an eye upon at least two OF
the natural forces that seem to be
bidding for recognition as Amer
ica's public enemy No. 1-soil ero-
sion and flood control.
In connection with soil erosion
projects, the photographs are prov
ing wonderfully helpful. Areas that
have heretofore been able to hide
from surveyors cannot escape de-
lection by the sharp eyes of aerial
cameras. So data until recently un-
available are now being obtained
readily by the sky photographers
and will be used in combating soil
erosion.
AS to flood control, the photo
graphs are proving of great value
in showing how, where and why
unpredictable streams like the Mis-
souri, change their courses over
night, build up sandbars capricious-
ly and misbehave generally. 1nfor-
nation thus gained will aid engi-
neers in their efforts to put check
rein on these turbulent streams.
The making of this colossal pic
ture of the United States is a tre-
mendous undertaking even for Uncle
Sam, accustomed as he is to doing
things on magnificent scale.
Nothing really worthy of comparison
with it has been done before. The
lob calls for marvellous photography
and for precision in flying required
nowhere else.
On those days when weather con-
ditions permit, flock of planes
sometimes as many as 5O-start
off on their taking spree.
By the time the days work is over,
thousands of 7x9 shots will have
been taken.
But before the days stint is begun
the pilot ana photographer in each
plane must do some preliminary
spade work-check ground speed, al
titude, wind direction-and prepare
themselves for a monotonous grind.
Then, his eyes fixed upon mar
velous instrument that warns him
the moment he deviates from a
straight course, the pilot gets under
way, flying back and forth over a
given stretch of territory and lop-
ping off a bit of it at each turn, un-
til the whole has been covered.
Meanwhile the photographer, hav-
Ing determined at what rate pic
lures should be taken, makes proper
camera adjustments, and the camera
begins clicking, automatically taking
pictures at the rate of one about
every 40 seconds.
The Government requires that the
photographs be made to the scale
of one inch to every 1855 feet OF ter
rain. This means flying at an alti-
tude Of about $4,000 feet.
Not all of the Photographic output
can be used. Approximately SO per
cent of each print, perhaps even
more, may go to waste because OF
distortion which begins just outside
the central portion Of the print and
grows more and more marked toward
its edges.
When the prints are cut down
is obviously impossible for even the
most expert flyer to hold his ship
constantly at one level, there are
certain to be deviations from scale,
owing to unavoidable rises and dips
AS consequence an inch. on one
photograph may represent either
more or less than an inch on an
other. This deviation is corrected
in the mapping room, where experts
take the known distance between
two points and, using that as a
yardstick. make the necessary ad-
justments. Then by some sort .of
legerdemain understood only by the
initiated, errors are wiped out dur
ing the rephotographing and Ell
larging process, and the photograph
brought back to scale.