economical it might currently be to obtain satellite imagery in comparison to airphotos. This
is not to imply that measurements of forest cover type should not or will not be made from
satellite images. However, the forestry profession may have to continue to depend upon
imagery from satellite sensors optimized and designed for other prime purposes.
The greatest potential for the sustained application of space systems in the forest management
process is the monitoring of areas where forest cover is subject to rapid alteration by either
natural or manmade activities. These alterations are widely varied in their nature and causes,
ranging from shifting cultivation, tropical forest exploitation, insect infestations, natural can-
opy closure, and many others. However, the majority result in a significant alteration in the
standing crop of leaf biomass present per unit area. Extensive research dealing with the grass-
land ecosystem2 3 has already clearly shown that the alteration of the amount of leaf material
per unit area is much more readily measured in the visible and photoinfrared spectral regions
currently available on spacecraft, than are the subtle spatial variations in spectroreflectance
due to variations in species composition in that ecosystem. Certainly the division of the for-
ested areas of the world into the two *'big" ecosystem classes consisting of areas dominated
by needle or broadleaf types can readily be made using Landsat satellite imagery. However,
within these two subdivisions, the determination of the status of the forest canopy based
upon variations in leaf biomass per unit area provides a much more viable alternative. It pro-
vides a much clearer justification for a forestry remote sensing program from space platforms
than to continue looking for the subtle variation in spectroreflectance needed to further sub-
divide the forest ecosystem into more specific cover types or species classes. The improved
management of the forest canopy which would result from using such information will
certainly require yearly imagery, if not imagery at several key seasonal points during the year.
Clearly, this requirement and associated techniques would provide a much more viable basis
for justifying a space program dealing with forestry applications.
Preliminary tests of the hypothesis that forest canopy alteration can be readily monitored
with digital processing of Landsat-type imagery have been completed. No large quasi-
operational program is yet underway, but this collection of small, individual research efforts
will be presented to illustrate the results achieved to date in a variety of geographic settings
around the world. All of the summaries which follow deal with digital analysis of the
Landsat imagery, but these examples vary considerably in their complexity and the analysis
procedures employed. Therefore, it is felt that as a group they serve as examples of the types
of forest canopy monitoring which can be undertaken, the approaches available, and the
potential results which can be achieved. Each of the summaries which follows has been delib-
erately briefed to conserve space. However, references to detailed reports on each topic are
provided and are readily available from the respective sources and/or researchers whose names
and addresses are included for this purpose.
2Pearson, R. L. and Miller, L. D., 1972. Remote mapping of standing crop biomass for estimation of the
productivity of the shortgrass prairie, Pawnee National Grasslands, Colorado. Proc. of the 8th International
Symposium on Remote Sensing of Environment, Univ. of Michigan, Ann Arbor. pp. 1357-1381.
3Tucker, C. J., 1978. Hand-held radiometer studies of vegetation in situ: a new and promising approach.
Proc. of the International Symposium on Remote Sensing for Observation and Inventory of Earth Re-
sources and the Endangered Environment, International Society of Photogrammetry and the International
Union of Forestry Research Organization, Freiburg, Germany. 6 p.
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