n 
Reprinted from 
PHOTOGRAMMETRIC ENGINEERING 
March 
1960 
  
Quantitative Photography 
A Geologic Research Tool 
*4 
RICHARD G. RAY, Geologist, and 
WILLIAM A. FISCHER, Geologist, 
U. S. Geological Survey, 
Washington 25, D. C. 
ABSTRACT: Various measurements useful in geologic research may be made 
from aerial photographs. These measurements include not only height and. dis- 
tance determinations that relate to the common meaning of the term PHOTO- 
GRAMMETRY but in addition involve colorimeter and densitometer measurements, 
all of which are herein grouped under the term QUANTITATIVE PHOTOGRAPHY. 
This paper reports briefly on techniques of obtaining quantitative data from 
aerial photographs, on some results of data collection, and on possible uses of 
quantitative photography in geologic research. 
INTRODUCTION 
Ne of experimental or obser- 
vational data is a facet of research that 
is fundamental to all scientific fields. Among 
the many sources of quantitative information 
in geologic studies the aerial photograph 
stands out as a potentially significant research 
tool because of the wealth of measurable data 
it can provide from the photographic expres- 
sion of surface features of the earth. The 
variety of measurements that can be made 
from aerial photographs—ranging from sim- 
ple height and distance measurements to 
densitometry and colorimetry—are best in- 
cluded under the term quantitative photogra- 
phy, as distinguished from the classical and 
restrictive use of the term photogrammetry, 
which is generally taken to refer to plani- 
metric and topographic map compilation. 
Quantitative photography provides the 
geologist with relative or absolute measure- 
ments useful in describing terrain features in 
objective terms rather than commonly em- 
ployed subjective terms (ie., moderately- 
steep slope, rolling hills), which may be so 
poorly definitive as to be misinterpreted. 
More important, it provides relative or abso- 
lute measurements that give a mathematical 
basis for comparison of different geologic 
features or conditions. 
If the term quantitative photography is 
broadly defined to include measurements 
made prior to taking the photographs so that 
photographic systems can be designed that 
will emphasize specific geologic information, a 
wider field of research will be encompassed. 
Recent studies indicate that certain measure- 
ments made prior to taking photographs— 
such as spectral reflectance determinations of 
rocks—may be particularly significant in se- 
lecting films and filters for emphasizing 
geologic features so that they can be meas- 
ured on the subsequently obtained photogra- 
phy. 
This paper describes some results and po- 
tential uses of quantitative photography in 
geologic research. 
QUANTITAVE GEOMORPHOLOGY 
Quantitative geomorphology—an analysis 
of measurements related to surface features 
of the landscape—is based primarily on sim- 
ple linear, area, and slope measurements to- 
gether with number and direction determina- 
tions. Many of these data are readily obtained 
from aerial photographs and include such 
measurements as stream length, basin area, 
and azimuths and lengths of fractures. Com- 
binations of simple measurements in turn 
yield ratios such as drainage density that may 
be useful in comparing land forms regardless 
of their scale. The data used in quantitative 
geomorphology commonly are time-con- 
suming and difficult to obtain in the field. 
Topographic maps are a source of many of 
these measurements but the vertical aerial 
photograph is a more abundant source. 
Research studies based on measurements 
* Publication authorized by the Director, U. S. Geological Survey. 
t Prepared as a contribution to Commission VII of the International Society of Photogrammetry in 
connection with the International Congress of Photogrammetry Sept. 1960, at London, England. Similar 
papers for this and other Commissions are in this issue and also in Vol. XXIV, 4 and XXV, 1 and 5— 
EDITOR 
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