Geoscience Reference
In-Depth Information
Chapter 13
Hypercube Sampling
Yu-Pin Lin, Hone-Jay Chu, Cheng-Long Wang, Hsiao-Hsuan Yu, and
Yung-Chieh Wang
INTRODUCTION
This study applies variogram analyses of normalized difference vegetation index
(NDVI) images derived from SPOT HRV images obtained before and after the Chi-Chi
earthquake in the Chenyulan watershed, Taiwan, as well as images after four large
typhoons, to delineate the spatial patterns, spatial structures, and spatial variability
of landscapes caused by these large disturbances. The conditional Latin hypercube
sampling (LHS) approach was applied to select samples from multiple NDVI im-
ages. Kriging and sequential Gaussian simulation (SGS) with sufficient samples were
then used to generate maps of NDVI images. The variography of NDVI image results
demonstrate that spatial patterns of disturbed landscapes were successfully delineated
by variogram analysis in study areas. The high-magnitude Chi-Chi earthquake created
spatial landscape variations in the study area. After the earthquake, the cumulative
impacts of typhoons on landscape patterns depended on the magnitudes and paths of
typhoons, but were not always evident in the spatiotemporal variability of landscapes
in the study area. The statistics and spatial structures of multiple NDVI images were
captured by 3,000 samples from 62,500 grids in the NDVI images. Kriging and SGS
with the 3,000 samples effectively reproduced spatial patterns of NDVI images. How-
ever, the proposed approach, which integrates the conditional LHS (cLHS) approach,
variogram, kriging, and SGS in remotely sensed images, efficiently monitors, sam-
ples, and maps the effects of large chronological disturbances on spatial characteristics
of landscape changes including spatial variability and heterogeneity
.
The infl uences of large physical disturbances on ecosystem structure and func-
tion have garnered considerable attention (Foster et al., 1998; Millward and Kraft,
2004; Swanson et al., 1998; Turner and Dale, 1998). Fires, hurricanes (typhoons),
tornados, ice storms, and landslides are examples of such large disturbances (Mill-
ward and Kraft, 2004). Earthquakes have long been recognized as a major cause of
landslides (Keefer, 1984; Lin et al., 2008a). However, landslides are only the fi rst in
a series of processes by which materials are removed from slopes and transported out
of a region by fl uvial action (Keefer, 1994; Lin et al., 2008a). Additionally, typhoons
are extremely important natural disturbances that characterize the structure, function,
and dynamics of many tropical and temperate forest ecosystems (Lee and Lin, 2008).
Taiwan, which is located in a subtropical region, sits on the Philippine plate at the
Euro-Asian Plate junction (DeMets et al., 1990). Plate convergence occasionally gener-
