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Title
International cooperation and technology transfer
Author
Mussio, Luigi

AUTOMATIC FOREST AREA RECOGNITION USING GIS IMAGE ANALYSIS CAPABILITY
Marco Ciolli, Paolo Zatelli
Dipartimento di Ingegneria Civile ed Ambientale, Università degli Studi di Trento
via Mesiano 77, 38100 Trento, tei. 0461.882678 - fax 0461.882672
e-mail: Marco.Ciolli @ing.unitn.it - Paolo.Zatelli@ing.unitn.it
KEY WORD: digitai image, classification, orthoimage, forest area recognition, GIS.
ABSTRACT
In the higher part of many Italian alpine regions the population is rapidly decreasing. This fact directly influences
landscape and forest management criteria. In particular, large pastures and agricultured areas are being covered by
trees or bushes, which change the landscape. This is a well known trend but it is very difficult to evaluate the extension
and the evolution of these phenomena. A new approach to this problem has been developed at the Laboratorio Ambiente
e Territorio, with which it is possible to determine changes of the forested areas over time. Series of aerial photographs
taken in different years (1954, 1983, 1994) have been compared using automatic algorithms which exploit the GRASS
GIS (Grass GIS is a public domain Geographic Information System) image analysis capability. The aerial photographs
have been orthorectified to achieve images which can be directly superimposed to each other and to cartography.
An image classification is carried out for each image using the following steps: preprocessing to identify homogeneous
gray level areas; analysis of the gray level distribution in each area, filtering of the image to define boundaries of different
kind of vegetation. A supervised homogenization is carried out to recover small errors, in particular small gaps inside
wooden areas.
The forest coverage evolution is finally computed by comparing the boundaries of the wooden areas in different years.
A skilled operator is able to perform the whole operation in a very short time, especially compared to traditional
techniques. This method has proved to be effective for the automatic determination of the widening of the forested areas.
A precise knowledge of the forest coverage evolution is very precious to enhance forest and landscape management
criteria. It can also be combined with demographic informal
1. FOREST AREA RECOGNITION
1.1 Introduction
To carry out ecological landscape planning is necessary
to dispose of many information about the development of
the landscape through the years. The comprehension of
the economic, social and cultural reasons which are tied
to a landscape change gives to landscape planners and
the technicians a correct point of view in land
management. Sometimes it is very difficult to find
information about landscape changes. Photogrammetry
and Geographic Information System image analysis
capability can be used to give a dramatic improvement to
our knowledge of the land.
Landscape and forest management criteria are influenced
by the fact that in the higher part of many Italian alpine
regions the population is rapidly decreasing.
In particular, large pastures and agricultured areas are
being covered by trees or bushes, which deeply change
the landscape. This is a well known trend but it is very
difficult to evaluate the extension and the evolution of the
phenomena. This happens because foresters have no
measures or direct samples which quantify the
phenomena and which can be used to compare different
situations at different times.
A new approach to this problem has been developed at
the Laboratorio Ambiente e Territorio of the Faculty of
engineering of Trento making possible to determine
changes of the forested areas over time.
Ortho-photos are a very important historical document
because they permit to read the land changes comparing
different periods. The presence of aerial photographs
taken in the fifties is particularly interesting because this
was a period characterized by the most significant
changes.
to better explain landscape change.
Series of aerial photos taken in different years (1954,
1983, 1994) have been compared using automatic
algorithms which exploit the GRASS GIS image analysis
capability.
1.2 Study area
The study area has been chosen in Roncegno Mountain
in the Roncegno Municipality, in the south east of the
Trentino region (Italy). It is delimited by South by old
Brenta River (mean height above sea level: 400 m), by
East by Ceggio River, by North by Monte Gronlait and
Monte Cola (2200 m above sea level) and by West by
Larganza River. This region is rapidly changing both in
socio-economic characters and in landscape. In this area,
as well as in most of the Trentino region, a well known
reforestation trend is present. The area has been chosen
to verify that the available data are sufficient to carry out
the quantification of the forest change.
1.3 Tecniques
Since the reforestation trend has never been quantified,
this work is a first attempt to determine the extension of
this phenomena by a quantitative analysis.
Different solutions are possible. The first possibility is to
carry out field surveys which present some problems: they
are very expensive, they usually take a long time, they
lack of unifomity and they are able to depict only the
present situation.
A second possibility relies on remote sensing which could
be the best solution since data are collected in different
spectral bands. Therefore a better forested area
recognition can be exploited since the spectral signature
of each specie can be identified.