Opticallv photographed stereo pairs of. imagery are the
most commonly used photogrammetric source: for DTM!s.
Optical photogrammetric techniques have developed since
the second half of theil8Sth -century;rand the Fourth Edition
of the Manual “of Photogrammetry is probably the- best ref-
erence on this topic. Without going into further detail
about -opticai photosrammetry as a. source of. DTM's, it should
be emphasized that most if not all of the modern day ana-
lytical stereoplotters^collect'either eievation point)or
profile data in an electro-optical environment based upon
rigorous geometrical and mathematical principles.’ Digital
correlation and production of DIM's:wilil ber:discussed
o side-looking and synthetic aperture radar (SAR) may
be'-o' viable: source for DTM's; :lLeberliet. al. 19982)
omik et. al. (1983) provide good mathematical develop-
for radargrammetry, and Elachi et: al (1992) provide
& good discussion on SAR techniques. : Crude DTM's have been
produced using SÉASAT-SAR, and the recent support given to
new research efforts should produce SAR based DTM's in the
near future. An interesting proposal has been made by
Breshears et. al. (1982) to use interferometric SAR to pro-
duce contour information, and a preliminary experiment was
conducted,
The use of non-stereo imagery sensed with multi-spectral
bands by ‘Landsat as & source for DTM's'iMas been presented
by Haralick (see Wang, et.:al.] ina variety of :papers.
Basically, the concept is to automatically cluster similar
reflectance classes and then subcluster the image into a
reflectance image using multi-spectral ratios and a.topo:
graphic modulation image from which a DTM is produced using
an elevation growing technique.
Data Collected in DTM Compilation
Ui
The purpose of producing a DTM is-to obtain:.a numerical
representation of a landform.. As previousiy mentioned,
commonly collected information includesocontour:or iso-
elevation data, spot elevations, and elevation profiles.
Alternative information that might:be collected inciude
slope, curvature, ridge and drainage patterns, fractals,
power spectrum, and surface polynomial descriptors.: The
non-stereo Landsat approach mentioned collects reflectance
information which is a function of the slope information.
It. is important not to confuse the method of; representation
of the DIM with the data collected,.as.the.qualitv.of. the
DTM ‘is highly dependent upon the information inherent in
the model, as well‘ as to data degradation resultant. fron
the method of representation.
