Application of RS and GIS in natural disaster survey: a case study
of mountainous landslide caused by the herb typhoon
Spatial Analysis
The spatial pattern of newly happened barelands (patches) after the Herb typhoon was analyzed
with GIS spatial analysis techniques. Figure 1 shows the conceptual diagram of such spatial
analysis. Eq. (2) described the set logic of overlay analysis, where A set represents patches {N}
in a polygon feature of forest cover type or slope coverage {P}. Eq. (3) determined the patches
{N} intersected with a line feature of stream or road
coverage {L}, B set; while the patches connected to the
preexistent bareland patches {E} in T1 map (states before
the Herb visited day), C set, were determined by Eq. (4).
a.Overlay analysis
A={x | x={N
Ç P}} (2)
b. Intersecting analysis
B={x | x={N
É L}} (3)
c. Connectivity analysis
C={x | x={Distance(E,N)=0}} (4)
Figure 1. Conceptual Diagram of Spatial Analysis.
Results and Discussion
Accuracy Assessment of Classified Thematic Map
Transformed divergence among the bareland, vegetation, and water showed that these three
classes could be distinguished very well. The overall accuracy of T1 and T2 thematic maps were
greater than 95 percent, and their kappa coefficient of agreement were greater than 88 percent.
Detail assessment of classification accuracy refers to table 2.
Table 2. Confusion table for T1 and T2 classified thematic map
|
| T1 ** | |
T2 *** |
| |
|
| Class* |
Ba | Veg |
Wa | Sum | |
Class1) |
Ba | Veg | Wa |
Sum |
| Ba |
536 | 36 |
135 | 707 | |
Ba | 757
| 104 |
44 | 905 |
| Veg | 265
| 5208 | 0
| 5473 |
| Veg |
44 | 5140 |
0 | 5184 |
| Wa |
0 | 0 |
1765 | 1765 | |
Wa | 0 | 0
| 1856 | 1856
|
| |
|
| Sum | 801 |
5244 |
1900 | 7945 | |
Sum |
801 | 5244 |
1900 |
7945 |
|
* Symbols Ba, Veg, and Wa stand for the bare land, vegetation, and water class respectively.
** Classified map T1 stands for the state before the Herb typhoon, which has a 95.57% and
88.64% of overall accuracy and kappa coefficient of agreement respectively.
*** Classified map T2 stands for the state after the Herb typhoon, which has a 97.58% and
95.19% of overall accuracy and kappa coefficient of agreement respectively.
|
Change of Land Covers Nearby the Herb Typhoon
Change of the land covers, bare land, water,
and vegetation, nearby the Herb typhoon was
derived from T1 and T2 thematic map. Figure 2
demonstrates the spatial distributions of nine
classes (paths) among three major land covers
of the study site. Area (pixel counts) of each
class was also calculated and described in detail
in Table 3. It showed that the site has 7,165,707
pixels (111,964 ha), in which the bare land and
water has increased 3405 ha and 861 ha, while
the vegetation decreased 4266 ha between T1
and T2.
Change Map of Land Cover of Chiayi Slope Land Area nearby Herb Typhoon.
Figure 2. Change of Land Covers of the
Site nearby the Herb Typhoon.
Table 3. Area statistics for the change of land covers nearby the Herb typhoon *
|
|
To the state after Herb (T2) |
|
| Bare land | Vegetation |
Water | Sum |
|
From the
state before
Herb
(T1) | Bare land | 365498
| 359274 |
46765 | 771537 |
| Vegetation |
623700 |
5712185 |
8619 | 6344504 |
| Water |
260 | 27 |
49379 | 49666 |
|
| Sum |
989458 | 6071486 |
104763 |
7165707 |
|
|
* Counting unit is pixels, and a pixel stands for an area of 12.5 12.5 square meter.
|
Relations among the New Bareland and Stream and Road System
There was a linearly distributed spatial pattern for the newly happened bareland patches in T2
thematic map after the Herb
typhoon, especially alone the
streams and roads. Figure 3 has
demonstrated this spatial pattern.
By the area statistics view,
2836.77 ha, i.e. 29 % of new
bareland patches happened closed
to the streams and roads, in which
900.63 ha were located on the site
where the streams and roads pass
through. This phenomenon
demonstrated the importance and
necessity of conservation for the
land nearby the stream bank and
road.
Figure 3. New Bareland Patches nearby the Stream or
Road.
Table 4. Area statistics of new bareland which connected to and/or intersected with the stream or
road
|
| Stream |
State road | County road | the Other road |
Net area |
|
| Stream | 2510.31
| (110.23) * |
(121.70) |
(668.70) | 1609.68 |
| State road |
(110.23) | 306.91 |
(0) | (24.56) | 172.12 |
| County road |
(121.70) | (0) | 352.19 | (70.80) | 159.69 |
| the Other road |
(668.70) | (24.56) |
(70.80) |
1659.34 | 895.28 |
| Net area ** |
1609.68 | 172.12 | 159.69
| 895.28 | 2836.77 |
|
|
* Area includes in parentheses are the duplicated ones in each entry. ** Net area is derived by subtract the parenthesized areas from the one in diagonal entry in that
column. Areas were presented in ha.
|
