THE EARTH SEEN
FROM THE AIR
[Illustration: FIG. 1--The National Capitol, Washington, D. C. A view
obliquely downward from a position over the National Botanical Garden,
showing the western front of the Capitol at the approach to it from
Pennsylvania Avenue. In the background, at the right, can be seen a part
of the Library of Congress and, at the left, a part of the Senate Office
Building. The radiating avenues of approach are of interest as well as
the character of the district surrounding the Capitol, as indicated by
the apartment houses and tree-lined streets.]
AMERICAN GEOGRAPHICAL SOCIETY
SPECIAL PUBLICATION NO. 4
W. L. G. JOERG, _Editor_
THE FACE OF THE EARTH
AS SEEN FROM THE AIR
A Study in the Application of Airplane
Photography to Geography
BY
WILLIS T. LEE
U. S. Geological Survey
[Illustration]
AMERICAN GEOGRAPHICAL SOCIETY
BROADWAY AT 156TH STREET
NEW YORK
1922
COPYRIGHT, 1922
BY
THE AMERICAN GEOGRAPHICAL SOCIETY
OF NEW YORK
CONDÉ NAST PRESS GREENWICH, CONN.
CONTENTS
CHAPTER PAGE
INTRODUCTION ix
I THE VIEWPOINT 1
II FAMILIAR SCENES FROM A NEW ANGLE 7
III ARCHITECTURE, LANDSCAPE GARDENING, AND ENGINEERING 11
IV THE MOSAIC 20
V GENERAL ASPECTS OF THE SURFACE AS SEEN FROM THE AIR 22
VI MARSHES AND MARSH DRAINAGE 27
VII COASTAL MUD FLATS 41
VIII SUBMERGED LAND FORMS 45
IX THE PLAIN FROM THE AIR 50
X MOUNTAIN FEATURES 57
XI AIR CRAFT IN THE STUDY OF ROCKS AND ORES 69
XII MAPPING AND CHARTING FROM THE AIR 72
INDEX 105
LIST OF ILLUSTRATIONS
_(o) indicates an oblique_, _(v) a vertical airplane photograph_
FIG. PAGE
THE VIEWPOINT, AND FAMILIAR SCENES FROM A NEW ANGLE
1 The National Capitol, Washington, D. C. (o) Frontispiece
2 Symbols of automatic register in the Eastman mapping camera (v) 3
3 The United States Military Academy, West Point, N. Y. (o) 8
4 The United States Naval Academy, Annapolis, Md. (o) 9
ARCHITECTURE, LANDSCAPE GARDENING, AND ENGINEERING
5 Monument Avenue, Richmond, Va. (o) 12
6 The United States Naval Observatory, Washington, D. C. (o). 13
7 Shipyards at Newport News, Va. (o) 14
8 The New York Connecting Railroad Bridge (o) 15
9 A part of Washington, D. C. (o) 16
10 Part of Rockaway Beach, Long Island, N. Y. (v) 17
11 Part of Long Branch, N. J. (v) 18
12 Benning, D. C., and the Anacostia River (v) 22
13 The land along the Anacostia River on the eastern edge of Washington,
D. C. (v) facing 22
14 Map of the same area as in Fig. 13 facing 22
GENERAL ASPECTS OF THE SURFACE
15 Southeastern part of Mulberry Island on the lower James River,
Maryland (v) 24
16 Map of the same area as in Fig. 15 25
17 Columbus, Ga. (v) facing 26
18 Map of the same area as in Fig. 17 facing 26
MARSHES AND COASTAL MUD FLATS
19 Tidal marsh and ocean beach at Corsons Inlet, New Jersey (v) 28
20 Details of marshland, Lee Marsh, lower Pamunkey River, Virginia
(v) 30
21 Details of marshland, Cousaic Marsh, lower Pamunkey River,
Virginia (v) 31
22 Barrier beach from Corsons Inlet to Atlantic City, N. J. (v) 32
23 A river system in miniature near Hampton, Virginia (v) 33
24 Sweet Hall Marsh on the lower Pamunkey River, Virginia (v) 34
25 Map of the same area as in Fig. 24, with cross section 35
26 Eltham Marsh on the lower Pamunkey River, Virginia (v) 36
27 Map of the same area as in Fig. 26, with cross section 37
28 A stream system of the mud-flat area off the Eastern Shore of
Virginia (v) 42
29 Mud-flat streams (v) 43
SUBMERGED LAND FORMS
30 Stove Point Neck at the mouth of the Piankatank River, Virginia
(v) 46
31 Gwynn Island at the mouth of the Piankatank River, Virginia (v) 46
32 Map showing the location of Figs. 31 and 32, with cross section 47
33 A drowned valley: Lambs Creek, Chesapeake Bay, Virginia (v) 48
THE PLAIN FROM THE AIR
34 The Chattahoochee River south of Columbus, Ga. (v) facing 50
35 Map of the same area as in Fig. 34 facing 50
36 A river channel in the Great Plains: The Red River northeast of
Wichita Falls, Tex. (v) 51
37 A glacial drift plain in southwestern Michigan (v) 52
38 Map of the same area as in Fig. 37 53
39 Schoolcraft, Mich. (v) 54
40 Map of the same area as in Fig. 39 55
41 Kettleholes in glacial till southwest of Schoolcraft, Mich. (v) 56
MOUNTAIN FEATURES
42 Mt. Shasta, California (o) 58
43 A glacial gorge on the northeastern face of Mt. Shasta (o) 59
44 Yosemite Valley, California (o) 60
45 Map showing the angle of vision of Fig. 44 61
46 Cinder Cone on the eastern edge of the northern Sierra Nevada,
California (o) 62
47 Map showing the angle of vision of Fig. 46 63
48 The top of Cinder Cone (o) 64
49 Simi Hills northwest of Santa Monica, Cal. (v) 65
50 Part of Santa Monica Mountains north of Santa Monica, Cal. (v) 66
51 Map of the region between the center of Los Angeles and Santa
Monica, Cal., showing the location of Fig. 50 67
52 A young mountain gorge in the San Joaquin Hills, a coastal range
in Southern California (v) 68
53 Canyon in sedimentary rocks near the mouth of the Pecos River,
Texas (v) 70
MAPPING AND CHARTING FROM THE AIR
54 View across the western end of Lake Erie (o) 73
55 Map showing the angle of vision of Fig. 54 73
56 Rochester, N. Y. (v) facing 74
57 Map of the same area as in Fig. 56 facing 74
58 Index map showing the location of the airplane photographs in
this book taken on the Atlantic seaboard of the northeastern
United States 75
59 Marshlands on Chesapeake Bay south of the mouth of the York
River, Virginia (v) 76
60 Left shore of the York River northwest of Gloucester Point, Va.
(v) 77
61 The northwestern tip of Sandy Hook, New Jersey (v) 78
62 Beach cusps under water near Beach Haven, N. J. (v) 80
63 First stage in the formation of an inlet through a barrier beach:
near Beach Haven, N. J. (v) 81
64 A tidal delta in Shark River Inlet, Belmar, N. J. (v) 82
65 A tidal delta, Popes Creek on the lower Potomac River, Virginia
(o) 83
66 A double tidal delta at Barnegat Inlet, New Jersey (v) 84
67 A tidal inlet through the barrier beach south of Beach Haven,
N. J. (v) 85
68 Beach between Brigantine and Little Egg Inlets, New Jersey (v) 86
69 A simple spit: Lower Cedar Point, Maryland, on the lower Potomac
River (o) 87
70 A recurved spit south of Brigantine Inlet, New Jersey (v) 88
71 A recurved spit showing interference with natural growth: The
northern end of Ocean City, N. J. (v) 89
72 New Point Comfort at the tip of the York-Rappahannock peninsula,
Virginia (v) 90
73 Spit at Tucker Beach, New Jersey (v) 91
74 A land-tied island: Napatree Point, near Watch Hill, R. I. (v) 92
75 Powells Creek, Virginia, on the lower Potomac River (o) 93
76 Roberts Creek, a drowned river valley southeast of Yorktown, Va.
(v) 94
77 The underwater channel in Quantico Bay on the lower Potomac
River, Virginia (v) 95
78 Natural channels and shoals near Miami. Fla. (o) 96
79 A dredged channel at Miami, Fla. (o) 97
80 A shoal in Hereford Inlet north of Wildwood, N. J. (v) 98
81 Sand bars at Cape Charles, Va. (v) 99
82 Bars, channels, beaches, and marsh near Far Rockaway, Long
Island, N. Y. (v) 100
_All of the airplane photographs in this book, both oblique and
vertical, were taken by the United States Army Air Service, except Figs.
78 and 79, which were taken by the United States Navy Air Service, and
Figs. 10, 65, 69, 75, 77, and 82, which were taken by the author. To
these two services the author is indebted for the permission to
reproduce their photographs, and this acknowledgment is made with the
same force as if made individually under each illustration._
_As a guide to the evaluation of the scale of the vertical photographs,
which is expressed under each photograph in the form of the natural
scale, or representative fraction, the following approximate equivalents
may be borne in mind_:
_1:10,000 = 800+ feet to the inch_
_1:16,000 = ¼ mile to the inch_
_1:21,000 = ⅓ mile to the inch_
INTRODUCTION
Scarcely a generation has passed during the evolution of the airplane
from a ridiculous dream to a practical factor in the work of the world.
Men who once read with derision, or only passive interest at best, of
the experiments of Langley, Chanute, and the Wrights have seen the
airplane developed suddenly into an indispensable instrument of war and
an agency of demonstrated value and of such diversity of application
that its future is hard to estimate.
The navigation of the air has accomplished much in many fields. Not only
does it offer a new means of efficiency in military reconnaissance,
rapid delivery of mail, fire patrol of forests, and the constantly
increasing number of commercial and scientific pursuits to which it is
being adapted; but it has also opened a new world to the geographer, the
physiographer, and the geologist.
AIRPLANE PHOTOGRAPHY: ITS DEVELOPMENT AND APPLICATION
Very early in the war the airplane was recognized as a useful, in fact a
necessary, means of observing enemy positions and movements. But the
speed of the airplane was found to preclude the taking of more than the
most hurried of notes during a flight, and notes written from memory are
not the most satisfactory. Photography was found to obviate this
difficulty. The ability of the camera to make instantaneous exposures
and fix a clear image on a photographic plate enabled the observer to
obtain a record not only of the scenes that he had viewed but also of
many that he might have missed while engaged in the necessary business
of watching the sky for the enemy--a record that for detail and accuracy
could not be approached by the most elaborate notes or the most graphic
description. Immediately inventive genius was set at work to adjust the
mechanism of the camera to the demands of air photography and to prepare
the rapidly working films and highly sensitized paper necessary for the
best results.
So satisfactory were the results and so great are the possibilities of
further adaptation that there is an unfortunate tendency on the part of
certain enthusiasts to make exaggerated claims that may react to retard
progress. This is particularly true in the use of the air photograph in
mapping. There are limitations to this use of air photography. It cannot
be reasonably expected to do away entirely with the ground work of the
surveyor. Rather, the camera is to be regarded as one of the instruments
of the surveyor. Observation from the air can never take the place of
close examination of the ground, but it can be of great use in the
location and study of land forms and geologic relations. Air photography
is only an added means of obtaining information, although it promises to
become a very important means.
Observations from the air described in numerous reports and articles in
geographic magazines during the war and since its close indicate that
air craft, especially in connection with air photography, can be of
great use in studying the physical features of the face of the earth. In
order to make a practical test of the use of the airplane in the study
of geography the writer spent about nine months during the year 1920
making flights, taking pictures from air craft, and gathering
information from various sources. This book embodies the chief results.
The material presented here is by way of illustrating the possibility of
using the airplane and airplane photography as a means of securing
information that should become increasingly useful in the study of
geography, and of showing geographic and geologic features better than
in any other way. The views have been chosen to illustrate the three
uses of air photographs with which this book deals--the presentation of
new views of subjects of popular interest and the practical value of
such views; the study of land forms from a new and advantageous point
of view; and the use of the air photograph as an aid in mapping.
In presenting these illustrations there is no intention that the list of
types should be considered in any sense complete. Physiographic
observation from the air is a relatively new undertaking, and results
are limited and imperfect. As improvements in mechanism and technique
are made, observations will be extended and better photographs and a
greater variety of them will be secured. Such as are presented here,
however, serve to demonstrate that the air photograph will come to be
recognized as a valuable source of information for the student of
geography and geology.
ACKNOWLEDGMENTS
The results here presented were secured by the co-operation of the Air
Services of the United States Army and Navy. Hydroplanes were placed at
my disposal on several occasions, and a number of flights were made over
water bodies, particularly over the Potomac River, Chesapeake Bay, and
New York Harbor. But the information was gathered chiefly through the
Army Air Service. Many flights were made in army planes, some for
general observation, others for photographing specific objects. Also the
army photographers, particularly those at Langley Field, near Newport
News, Va., made several photographic trips at my request, and a large
number of prints were furnished from negatives stored at this and other
flying fields.
In this connection I wish to express appreciation for the many
courtesies extended by Major General C. T. Menoher, U. S. A., Chief of
Air Service at the time the work was done, and by Major J.W. Simons,
Jr., A.S., Acting Administrative Executive, Air Service. These officers
placed at my disposal every facility of the service that I could use. It
would be a pleasure, if space allowed, to mention the names of the
numerous pilots and other officers to whom I am directly indebted for
the safe completion of some of the most thrilling adventures of my life.
I must, however, mention the officer to whom I am perhaps more indebted
than to any other. My introduction to this study was through Major J.W.
Bagley of the United States Army Engineering Corps, who has done much
toward making the camera a valuable instrument in mapping.[1] Through
his active interest I became acquainted with the officials of the Army
Air Service, who gave the necessary authorization for flights and for
securing most of the photographs used to illustrate this book. During
the time spent at this work I retained my position as geologist of the
United States Geological Survey. Hence the work is one of co-operation
chiefly between the United States Army Air Service and the United States
Geological Survey, and to a lesser degree with the United States Navy
Air Service.
CHAPTER I
THE VIEWPOINT
(FIGS. 1 TO 4)
OBLIQUE AND VERTICAL AIRPLANE PHOTOGRAPHS
Air photographs are, in general, of two sorts, depending upon whether
the photograph was taken with the camera pointing vertically or
obliquely downward. In either case the air photographer is free from the
limitations that hamper the ground photographer in choosing a point of
view. For he can ascend to any desired height and not only select an
advantageous position from which to photograph the feature which he
wishes to emphasize but also, at the same time, avoid obstacles which
might obstruct his view from the ground. Vertical photographs are
preferable where the accurate location of objects is desired. When
properly taken they serve many of the purposes of maps and are, in many
ways, even more useful than maps. They furnish the untrained mind with
much of the information that the trained mind reads from a topographic
map and, in addition, supply details and relations that a map cannot
depict. Exact accuracy, however, cannot be claimed for them until they
have been corrected for distortion and adjusted to some system of
controls.
Where the photograph is to be used as a means of securing a more
advantageous view of a subject than can be had from the ground rather
than as a map on which distances are to be scaled off, the oblique
photograph is probably the more desirable, since it is as easily
intelligible as a photograph taken laterally. The advantage of such
photographs is obvious. To the architect, the landscape gardener, the
city planner is given the opportunity to study their projects free from
all obstructions yet in such perspective that their relations to their
surroundings are brought out as would be possible by no other means.
Views like that of West Point (Fig. 3) are occasionally to be had from
some hilltop, but the limited choice of position on the ground contrasts
sharply with the unlimited choice in the air.
ELEMENTS TO BE RECORDED
Air photography is by no means simple. Much still remains to be done by
way of adapting the camera to its peculiar demands. Its present degree
of perfection, of course, is largely due to the impetus given its
development during the war because of its great importance in military
reconnaissance. The adaptation of the camera to operation from the
airplane might be described with profit but will be passed with slight
mention because it is the results of air photography rather than the
mechanism that are to be considered here. Technically, a photograph of
the earth’s surface may not be a map, but, given certain means of
interpretation, it can be made to serve as such. In using air
photographs, particularly the vertical ones, it is desirable to know the
scale, which is dependent upon the altitude at which the exposure is
made; the angle of the lens; and the variation from the vertical, in
order to make corrections for distortion. Therefore, it is desirable
that each photograph show the altitude, date, time of day, and position
of the lens at which the exposure was made. Cameras have been
constructed that automatically record these data on each negative. This
information is illustrated in Figure 2. The circular symbol at the left
in the white strip at the top of the photograph represents a circular
level, or inclinometer. The small round dot close to the center of the
inclinometer indicates that, at the time the exposure was made, the axis
of the lens was very nearly vertical. The symbol in the center of the
white strip indicates an altitude of about 9,800 feet, and that at the
right, that the exposure was made 7 seconds after 11 A.M. The other
symbols record that this photograph was No. 13 of a series made at
Rochester, N. Y., October 23, 1920, with an Eastman mapping camera known
as K-2. The symbol 8-P is non-essential and records that this negative
is No. 8 of panchromatic film.
[Illustration: FIG. 2--Symbols of automatic register in the Eastman
mapping camera, photographed with the body of the picture showing roads,
streams, orchards, cultivated fields, etc. For explanation of the
symbols, see the text.]
The information given by the symbols is corroborated by the picture.
Orchard and shade trees appear as circular dots in place of the
elongated images characteristic of pictures taken obliquely downward,
and the short, squat shadows denote exposure near midday. Shocks of corn
standing in the fields show that the season is autumn.
HOW TO READ AIRPLANE PHOTOGRAPHS
Not all the features, however, are so easily recognizable. Oblique
photographs are often more readily interpreted than ordinary
photographs, since they combine with the usual view the essentials of a
plan; but in vertical photographs very few objects present an appearance
that is natural in the light of our experience as lateral observers. The
uninitiated, on attempting systematically to identify the features of a
vertical photograph, find a very large number that are foreign in
appearance. A necessary preliminary is an acquaintance with the ground
photographed or with similar regions and features. Without such a key
the air photograph is not always self-interpretative and is often
unintelligible. Military observers are carefully trained to recognize
features of military significance. It is not to be expected, however,
that they should be trained in the observation of land forms except such
as are of military importance. Consequently, whereas a great variety of
photographs is now easily obtainable at many flying fields, the
information that a scientist would desire concerning them is not so
easily available. Most of the photographs used in this paper were taken
by men who were not trained in observing land forms. Many were taken
simply as a requirement in practice flights and meant so little to the
observer that no record was made concerning them. For several not even
the location was recorded.
It is of primary importance that the picture be held in the right
position. Not only must the observer imagine himself looking directly
down on the scene but he must hold the photograph in the position in
which experience has shown that the image appears the most natural.
Otherwise a depression will appear as an elevation and an elevation as a
hollow. It is a well-known fact that in telescopic photographs of the
moon the craters appear like hollows when the print is held in one
position and like elevations when the position is reversed. Experience
shows that if the print is held _so that the shadows fall toward the
observer_ the objects appear natural. The reason is that the observer
sees only those shadows that are caused by light falling towards him.
Consequently, the only interpretation that the brain can give to shadows
on a photograph is that they are cast by an elevation between the eye
and the light. In a picture, therefore, in which shadows fall away from
the eye instead of towards it valleys are seen as hills and hills as
valleys. In the northern hemisphere this prescribed orientation
conflicts with the convention of placing the north side of a map at the
top of the page and also with the modern shaded map on which the light
is represented as coming from the upper left, or northwest, corner of
the map.
FAILURE OF AIR PHOTOGRAPHS TO SHOW RELIEF, AND MEASURES TO REMEDY THIS
DEFECT
In photographs taken from the ground the lights and shadows are such
that a high degree of naturalness is possible. But objects seen from
directly above, and even those viewed obliquely, though to a lesser
degree, are illuminated so uniformly that photographs of them are apt to
appear flat. To some extent this has been overcome by the use of
extra-sensitive emulsions, special ray filters, and printing papers
adapted for accentuating contrast. Many of the photographs used in this
book did not allow satisfactory reproduction till the contrast of the
negatives was greatly increased by the arts of the photographic
laboratory. But, even at its best, no photograph taken vertically
affords an adequate idea of the height of hills or the depth of hollows.
Only shadows that are particularly well defined can be distinguished as
shadows, while small elevations and depressions affect the negative no
differently than a difference in marking or color. In military defenses,
if the mere surface of the camouflage is sufficiently realistic, the
ordinary camera is even more easily deceived than the human eye. It is a
well-known fact that man and other animals of the higher order see
objects in relief, within a certain range of vision, because the eyes
convey to their respective retinas slightly different images of the same
object which the brain combines into a relief image. The stereoscopic
camera has long been used for the same purpose. Its principle, with
certain adaptations that need not be discussed here, has been to some
extent employed in airplane pictures, with such excellent results that
it is claimed by some that by further development actual contouring will
be possible by this means. It is reported that in military
reconnaissance stereoscopic pictures render ordinary camouflage useless
and that bridges, observation towers, gun emplacements, etc., are shown
in relief and, therefore, easily detected.[2]