International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 Inter 
  
  
  
be spatially located on the ground surface (Moffit and Mikhail, 3. OBJECTIVES distr 
1980; Lillesand and Kiefer, 1999). The ability to ‘detect’ and * reme 
classify features using different multispectral bands is a further, Remotely sensed data appear to have tremendous potential in acro: 
specific advantage of remote sensing data. natural terrain studies (landslide mapping and ecology scho 
management) in Hong Kong, but as yet, this potential has not been 
2.2 Vegetation Indices evaluated. The purpose of this paper is to describe a methodology 
developed for using remotely sensed data in landslide mapping 
Spectral indices of vegetation, based on satellite observations in and risk assessment studies in Hong Kong. Our specific objectives 
the near-infrared and visible (red) wave bands, are widely are to use remotely sensed data to depict small-scale natural Two 
employed as measures of green vegetation density (Jensen, 2000). terrain landslides, and to identify disturbed vegetation across land Geor 
Healthy vegetation reflects strongly in the near-infrared region of surfaces and relate these to landslide incidence. In Hong Kong, IKO 
the electromagnetic spectrum, whereas burnt, dying, or diseased over the past many decades, anthropogenic disturbance of forests 
vegetation has a decreased reflectance in this region. (principally tree cutting and burning) has resulted in an expansion LAN 
of degraded fire-prone grassland and shrub land hillsides (Hau and Mid- 
LANDSAT TM data, which uses near and mid-infrared is Corlett 2002, 2003). In Hong Kong, there may be a causal and mois 
therefore useful to establishing vegetation indices that distinguish temporal relationship between natural terrain landslides and struc 
burned area$, and to classifying these into damage classes (Siegert vegetation disturbance, including hill fires (e.g. Savage, 1974; indic 
and Hoffman, 2000; Rogan and Yool, 2001). Vegetation Dyrness, 1976; Cannon 1997). Such relationships are important to 200€ 
monitoring by remotely sensed data has been carried out using landslide prediction studies. norn 
vegetation indices that are mathematical transformations designed and 
to assess the contribution of green plants to multispectral 3.1 Study Area resol 
observations (Bannari et. al., 1995; Jensen 2000). Vegetation used 
indices (VI’s) are mainly derived from reflectance data from The area selected for study is the Pat Sin Leng Range (within Pat land 
discrete red (R) and near-infrared (NIR) bands. A commonly Sin Leng Country Park), which traverses the northeastern New [KO 
employed VI is the normalized difference vegetation index NDVI part of the Territories district of Hong Kong region (Fig. 1). In this 
= [NIR-R]/[NIR+R] (Bannari et. al., 1995). NDVI values fall area, optimum conditions exist (geology. topography, vegetation The 
between —1 and +1. Higher NDVI values (> 0) indicate more and hill fire history) for developing a methodology. (this 
green vegetation, and appear ‘bright’ in images. Soils have values and 
close to zero, and water bodies have values less than zero. a SH - Le RR M 
"^ en | 2 ur en? e 
"AMD 7 : ht : HIRR) int r^v m { PATSINIENG So 7 
Advanced Very High Resolution Radiometer (AVHRR) imagery yo A = RANGE p ral . 
from the National Oceanic and Atmospheric Administration gut ; ey LH T . 
(NOAA) satellite series (available since 1981) is also used to / Aes f ^ 
en ; ; ci NEW TERRITORIES fn > MY 
measure vegetation indices for global vegetation mapping. ef N. x . 
AVHRR thermal and optical data have been used to locate fires in 3 i x f "ME iu A 
real time (Li ef. al., 2000) and to detect recent fire scars of up to , emp E ENS . 
one year old (Eva et. al., 1998; Barbosa et. al., 1999). Detecting : ir a = P A 
older scars using optical data, is, however, difficult (Steyaert ef. Pr din] 4 E ' v A do 
al., 1997). SPOT mid-infrared vegetation reflectance values are fd Fg - 4 Tm V Y > 
useful in this regard (Fraser et. al., 2000) as an indirect measure of - 4 LANTAU Cd o 2 raison i, A 4 The 
fire-denuded surfaces. Mid-infrared reflectance values are ii ISLAND — ^ ISLAND M 4 LAN 
sensitive to canopy moisture such that any increase in the exposed p ^ w= >, An. A t : 
soil surface (e.g. post-fire) will realize increased values. Sc Sa n & qm . R XX 
Bi N LA Wm, d. 
2.3 Remote Sensing Applications in Landslide Studies et SA 
  
  
  
Remotely sensed data (LANDSAT TM; interferometric SAR Figure 1. Location of Pat Sin Leng Range (study area). 
[InSAR]) has found specific application in documenting landscape 
change through surface erosion (Metternicht and Zinck, 1998; The local geology comprises Lower Cretaceous sedimentary rocks 
Pickup and Marks 2000; Meyer et. al., 2001), landslide mapping of the Pat Sin Leng Formation. This Formation occupies a fault- 
(Lillesand and Kiefer, 1999; Singhroy and Mattar 2000) and in bounded block with beds dipping steeply to the northeast. A 
  
  
identifying causative factors in landsliding events (McKean et. al., prominent escarpment developed on the south side of the Range 51 
1991). marks the unconformable contact with the underlying Tai Mo 
Shan volcanics (Lai et. al., 1996; Fyfe et. al., 2000; Sewell et. al., ND 
To recognize small-scale, shallow landslides, data that provides at 2000. Numerous small landslide scars are evident (in the field and DO 
least 10 m spatial resolution is required. LANDSAT TM data can in aerial photographs) on the upper and mid-hill slopes of the fort 
be used (e.g. Metternicht and Zinck, 1998; McKean et. al., 1991) Range. Colluvial deposits flank the escarpment and upper reaches 
but higher resolution SPOT PAN (10 m) (Liao and Lee, 2000), of stream valleys. The lowland valleys are wooded, but upper hill Hen 
IKONOS (4 m) or InSAR (Singhroy and Mattar 2000) data is slopes are covered by fire-prone grasslands and shrublands. The fron 
preferred for this application. Agriculture, Fisheries and Conservation Department of Hong heal 
Kong keeps records of hill fires within the territory's Country valu 
Parks, although it does not provide specific information on fire disc 
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