Agricultural Science Digest
PURDUE UNIVERSITY
Vol. 11, May and June, 1969

ECOLOGICAL POTENTIALS IN SPECTRAL
SIGNATURE ANALYSIS

Aerial photographs have long been used by
ecologists to map, plant communities, study
changes, and identify species. In recent
years the increased use of color, and color
infrared photography has placed a greater
emphasis upon the spectral differences and
the changes that occur among plant species.

The researcher should be cautioned that
color infrared film is sensitive to both vis-
ible and infrared wavelengths, and therefore
the interpretation of this photography is more
difficult and can be erroneously read. Re-
cent developments in remote sensing systems
aim at solving this difficulty by allowing one
to record reflected or emitted energy in
wavelengths far outside those to which film
emulsions are sensitive.

To better understand the factors effecting
reflectance and emittance for various plant
conditions, one must study the differences
in these materials under controlled condi-
tions. Purdue researchers studied over
2, 300 spectra of different plant leaf samples
taken under a variety of growth conditions.
Studies were conducted from these measure-
ments to determine the effects of pigmenta-
tion and moisture content on leaf reflectance.
Additionally spectral measurements of over
250 soil samples were obtained to determine
effect of moisture content on soil reflectance.

Remote sensing offers an excellent method
for covering large geographic areas in a rela-
tively short period. In the Purdue program,
data recognization techniques are being ap-
plied to automatically identify and map vari-
ous agricultural data collected from aircraft
altitudes.

Data from an optical mechanical scanner
are obtained from an altitude of 3, 200 feet over
Central Indiana. The data were used in the
classification of vegetation, bare soil, and wa-
ter with a high degree of accuracy. From the
test areas selected along the flight line, 97%
classification accuracy was obtained for these
categories.

The advantages and disadvantages of differ-
ent remote sensing systems are explained. It
would appear that an operational remote sensing
system of the future should incorporate unique
advantages of several instrument systems in-
cluding photographic sensors, optical mechani-
cal scanners, radar, and perhaps laser altime-
ters and other instruments.

Journal Paper 3479, R. M. Hoffer and C. J.
Johannsen, Principal Researchers of Laboratory
for Agricultural Remote Sensing in cooperation
with the Department of Forestry and Conserva-
tion, and Department of Agronomy, respectively

DOWEL JOINT DESIGN

While dowel joints have been used in furni-
ture construction for centuries, there has never
been an exact engineering method for designing
them. Recent studies in the theories and tech-
niques of furniture frame analysis have made
it possible to design furniture capable of with-
standing any desired load or use level.

However, these theories and techniques
are applicable only when the elastic behavior
and strength of the joints can be predicted.
Purdue University researchers studied and de-
veloped a tentative design formula which can
be used to predict the ultimate strength of
dowel joints.

The experiments consisted of testing
single-pin, axially-loaded dowel joints, using

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