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Proceedings of the Symposium on Global and Environmental Monitoring

spectrally-bascd detection, but not necessarily identification, of areas or
stands containing damage of some type (Olsson 1990 and personal
communication). Workers (e.g., Wastenson and others, 1987) have not been
able to use these data to consistently detect or identify trees exhibiting
substantial needle loss. This result is due to the fact that affected trees tend to
occur singly and not in groups. Ekstrand's (1988) work with Norway spruce
in Sweden suggests that use of a geographic information system containing
current stand histories and other ancillary information in digital form could
enable satellite-based detection of significant needle loss in certain terrain
and species mix situations.
We have concluded that, beyond the aerial photography applications
mentioned above, significant additional research with both satellite and
aerially acquired data will be required before additional types of forest
damage can be detected and then reliably separated from one another using
this technology in Sweden.
Clear-Felled Area
With respect to cover type area and area change estimation, the range of
near-term applications of remote sensing data are larger. Clear-felled areas,
given late Spring and Summer Landsat or SPOT satellite data, are readily
detectable and identifiable in most situations found in Sweden using
technology available now (e.g., Jaakkola and Hagner 1988, Hame 1988,
Boresjo 1989, and Olsson and Sohlberg 1989).
Jaakkola and Hagner, for example, showed that digital Landsat TM and SPOT
XS scenes from different dates could be used to accurately detect and map
clear-felled areas down to 0.5 hectare or less in sizx. Olsson and Sohlberg
(1989) used two spatially registered scenes of SPOT-P digital data (from
succeeding years) to reliably map clear-felled areas as small as 0.2 hectare
over ten 5 by 5 kilometer areas in south-central Sweden. The difference
between the ground surveyed clear-felled area and that obtained from
interpretation of the digital image was approximately 3 percent — a figure
which could be reduced further by tuning the procedure (Olsson, personal
Thus, use of remote sensing for clear-felled area estimation is considered a
strong candidate for early test and evaluation in the Swedish NFI.
Forest Cover Area Mapping/Estimation
The next most-developed satellite survey capability of this type is general
forest cover type mapping and estimation. Jonasson (1987), Jaakkola (1987),
Hame (1988), Boresjo (1989), and Hagner (1989), among others, have shown
that cover type, certain cutting classes, and other vegetation or surface-
related information for Scandinavian conditions is available through the use
of Landsat TM and SPOT data. Jaakkola and others (1988) present a summary
of key findings for Landsat TM data in this regard for forestry over a broader
area in Europe. Medium scale (typically 1:30,000, panchromatic) aerial
photography for forest type, age, volume, and site class mapping is presently
being used by at least one government group in Sweden (e.g., Age, 1985).