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EXTRACTION OF FOREST STANDS PARAMETERS FROM ASTER DATA IN OPEN
FOREST
M. Abbasi*, H.R. Riyahi Bakhtyari°
“Department of Forestry, Faculty of Natural Resource and earth science, University of Shahre-kord, Charmahal & Bakhtyari, Iran.
"Desert Region Management Department, College of Agriculture, Shiraz University, Shiraz, Iran.
mozhgan.abbasi(@nres.sku.ac.ir, reza reyahi@yahoo.com
Commission IV, WG IV/3
KEY WORDS: Forest inventory, Tree crown area, QuickBird, ASTER, Zagros, Iran
ABSTRACT:
Tree crown size (CS) and stem number per hectare (SN) has become increasingly important for forest management and ecosystem
monitoring. Tree crown size is also strongly related to other canopy structural parameters, such as diameter at breast height, tree
height and biomass. For both issues, remote sensing data are attractive for their large-area and up-to-date mapping capacities. The
QuickBird and ASTER imagery used in this study was acquired over Zagros Forests in southern Zagros region, Fars province of Iran
on | August 2005 and 1 July 2005, respectively. For the forest site investigated in this study, we concentrated on stands of Quercus
Persica which is the dominant species in Zagros region. This study was conducted to investigate the capabilities of ASTER-LIB data
to estimate some of forest parameters at individual tree and stand level in dry area. The forest stand parameters are crown area,
crown density, average crown area. Obtaining the accuracy of classification the ground truth map was prepared by tree crown
delineation using the panchromatic band of QuickBird data. Individual tree crowns were automatically delineated by color
segmentation of QuickBird imagery. Simple linear regression procedure was used to show the relationships between spectral
variables and the individual trees and forest stand parameters. With decreasing the crown density the effects of background will
increase. Our results indicated that crown size could be accurately extracted from panchromatic band of QuickBird images especially
for open forest stands. This paper demonstrates that using high-resolution satellite imagery in the open forest offers a unique
opportunity for deriving single tree attributes and allowing reliable ground truth map to estimate stand structure. ASTER data and its
indices showed good capability to estimate crown area in this study.
1 INTRODUCTION Eriksson (2004) in his study found that the delineation
procedure often has difficulties when the forest is open and
There is a growing need to easily extract forest biophysical ground patches can be seen in the images since there is no
parameters, particularly for supporting sustainable forest reducing rule for non-treelike segments. To overcome this
management. These parameters are traditionally estimated using limitation, colour image segmentation gives access to colour
inventory data from field sample plots. However, the cost of space and leads to a robust approach to obtain accurate tree
conventional methods limits the intensity and frequency of the crown boundaries. Many vegetation indices (VIs) have been
estimates over large areas. A potential solution to reduce high proposed to reduce non-vegetation effects and enhance the
costs is application of remote sensing techniques to extract responsively to the variations of canopy biophysical
forest parameters. The increasing availability of high spatial characteristics (Wu et al., 2007). However, the stability and
resolution remotely sensed imagery provides viable sensitivity of VIs are affected by soil optical properties (Huete,
opportunities for developing automatic forest inventories at fine 1989) and illumination geometry. Soil optical properties may be
scale. Delineation of the individual tree crowns is usable to
estimate the tree crown size (CS) and stem number per hectare
(SN). Tree crown size is also strongly related to other canopy
structural parameters, such as diameter at breast height, tree
height and biomass.
Manual interpretation of images is often labor and time
consuming. Thus, automatic methods for interpretation can
lower the work load and speed up the interpretation time
(Eriksson, et al., 2006). Various studies have been done to
delineate tree crowns using different methods such as valley
following, template matching and region growing (Pinz, 1989;
Gougeon, 1995; Culvenor, 2002; Pouliot et al., 2002; Erikson,
2003). Most of these segmentation techniques have been
applied in dense coniferous forests using black and with or gray
images.
well represented by defining a soil line with respect to the
specific soil type (Richardson and Wiegand, 1977; Baret et al.,
1989; Qi et al, 1994). Using multispectral images of the
ASTER it is possible to use infrared bands to reduce the effect
of non-vegetation or background.
Zagros forest ecosystem is one of the main destroying forest
ecosystems in Iran. Quercus Persica is the most important
woody species in these forests. The objective of this research is
to evaluate the capability and suitability of the Advanced
Spaceborne Thermal Emission and Reflection Radiometer
(ASTER) satellite data, to estimate average crown area per ha.
For this purpose, the ASTER and QuickBird images of Dasht-e
Barm region located in the Fars province were analyzed. The
QuickBird imagery was applied as the reference image for
geometric correction of the ASTER data as well as for
delineation of individual tree crowns in this study.
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