DETECTING INVASIVE PLANTS USING HYPERSPECTRAL AND HICH
RESOLUTION SATELLITE IMAGES
Fuan Tsai ^, Chi- Fan Chen
Center for Space and Remote Sensing Research, National Central University, Zhong- Li, Taoyuan
320, Taiwan - (ftsai, cfchen)@csrsr.ncu.edu.tw
KEY WORDS: Hyper spectral, High Resolution, Identification, Mapping, Vegetation
ABSTRACT:
The rapid spread of nonnative plant species have caused considerable negative impact to the biodiversity and
ccosystems in Taiwan. To better understand the status and to support researchers and decision makers to
develop strategies and remedies for this problem, it is necessary to obtain accurate spatial information and
the progression about the invasions of foreign species into native ecocommunity. The availability of
hyperspectral and high resolution satellite data provides researchers an opportunity to pursue more complex
analysis and have a great potential to achieve better performance and results in an invasive plants
investigation. High resolution images provide detail spatial information about the target areas but are often
limited to single or few spectral bands. On the other hand, hyperspectral data consist of tens to hundreds of
contiguous bands but lack of spatial details. Therefore, a combination of both types of data is likely to be an
optimal approach to the mapping of alien plants. However, with the large data volume and high data
dimensionality, the major challenge of using hyperspectral and high resolution data together is to extract
useful information effectively and efficiently. This paper presents a work in progress of developing a
systematic method to use hyperspectral and high resolution satellite images to identify an invasive plant
(horse tamarind, Leucaena Leucocephala) that is spreading in an alarming rate in southern Taiwan. The
developed method first locates "areas of interest" where target species is likely to populate most densely.
Then a two- level analysis procedure is implemented using hyperspectral and high resolution satellite images
to identify and map the distribution of target species. The first phase of the procedure is to analyze
hyperspectral images with selected (helpful) features to obtain a preliminary result. The second phase is to
isolate the areas where discrimination of target plant species is not satisfactory and to improve the accuracy
of discrimination with the analysis of canopy structures in high resolution satellite images. Verification with
ground truth samples indicates that the developed method of combining high resolution and hyperspectral
images analysis is an effective and efficient approach to detect invasive plants in a large area.
1 INTRODUCTION root- toxic tree has completely replaced original
native tropical forests and become the only
Being an island surrounded by oceans, Taiwan has a vegetation type (Liu & Chen, 2002).
natural barrier to prevent foreign species from
invading the local ecosystems. The botanic Reducing the impacts to local ecosystems and
ecosystems and biodiversity in Taiwan has been in biodiversity caused by alien species and employing
good preservation status for hundreds of years. restoration and other remedy actions has become a
However, in the past decades, intentionally or not, a trend in conservation (Stein & Flack, 1996). To better
considerable amount of alien species have been understand the status and to support researchers
brought into local environment because of the need and decision makers to develop strategies and
to prosper economic development and the increase remedies for this threatening problem, it is
of international travel and trading. According to a necessary to obtain accurate spatial information and
previous investigation (Lai, 1995), the number of the progression about the invasions of alien species
known nonnative plant species had reached a into native ecocommunity. Unlike field- based
record- high 4,500 species in 1995. The rapid spread investigations, remote sensing provides an timely
of alien plant species, especially those with and economical approach for discriminating
aggressively invasive capability, have caused invasive plant species from local botanic
considerable negative impact to the biodiversity and community, especially in a large- scale investigation.
ecosystems in Taiwan. Among them, horse tamarind Until relatively recently, aerial photographs and
(Leucaena Leucocephala) is one of the most serious multispectral satellite images are the primary
invasive plant species and have colonized a large sources of remote sensing applications to vegetation
portion of southern Taiwan, in particular, the mapping and have attained mixed success (for
Kenting National Park located in the Hen- Chun example, Lins et al, 1996; McCormick, 1999).
peninsula of southern Taiwan (Jiang & Xiu, 2000). In However, because these types of data can provide
some of the areas inside the national park, this Only limited spectral information, they may not be
Corresponding author.
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