Information Technology for Disaster Management (2001)
Kishi S., Song X., Li J.
Flood Detection in Changjiang 1998 from Landsat-TM Data
Shinkichi Kishi and Xiangfang Song*, Jiren Li**
*National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan
**Ministry of Water Resources, Beijing, China
Abstract
NIED/STA, Japan and RSTAC/MWR, China have conducted a joint research study on the
utilization of remote sensing data during floods in China. This paper outlines the research conducted
on flood detection as regards the middle reaches basin of Changjiang in the summer of 1998. NIED
provided the spatially mosaic images which made it easier to delineate the flooded areas.
Prior to the detailed analyses of TM data, the mapping of the near-daily extension of flood water
was conducted by interpreting multi-temporal pictures from several kinds of satellite.
TM data of the overlapping area of the adjacent landsat paths in nine days during the flood was
effectively used to examine the alteration of river water based upon the spectral characteristics of
turbidity. Additionally, TM data taken before the flood was also timely used to specify the land cover
condition in the area. The results of the study were supported by the examination of the MMR based
on the daily discharge data represented by the hydrographs.
As a result, TM data was again practical to grasp the land cover condition in the flooded area and
transition of turbidity of flood water. On the other hand, the synthesized observation frequency by
several kinds of satellites was not enough in practical use to monitor the daily transition of flooding
areas.
Keywords: Flood detection; Remote sensing
1. Introduction
nine days during the flood and by
conducting the supervised classification
for each image accompanied with the
examination of spectral characteristics in
the training areas.
Landsat TM data of the adjacent paths
covering the middle reaches basin of
Changjiang in the periods before and
during the flood were obtained. To grasp
the outline of the flood, two spatially
mosaic images were produced and
overlaid. In order to analyze the
characteristics of the TM data, the
overlapping areas of the adjacent paths
were designated as the study area. In the
areas, several kinds of multitemporal
satellite pictures were effectively used to
delineate the flooding water in near-daily
extension.
Using TM data in the area, the land
cover condition in the flooded areas was
examined by overlaying the images of the
2.
General view of the middle reaches
basin of Changjiang from landsat
TM data
In order to broadly grasp the flooded
area widely from TM data, two scenes of
adjacent paths covering the middle
reaches basin of Changjiang from the exit
of Three Gorge to Wuhan were mosaic
for the data of the summer season in 1995
three years before the flood, and of
August 1998, during the flood,
respectively. The flooding areas were
45
Information Technology for Disaster Management (2001)
Kishi S., Song X., Li J.
Date
Satelite
Sensor
Medium
Source
SAR
Printed
www/ESRIN/ESA
8.05RADARSAT SAR
Printed
JSPRS
8.06NOAA
AVHRR
Printed
CMA
8.11NOAA
AVHRR
Printed
CMA
8.12RADARSAT SAR
Printed
www/CCRS/CSA
8.14LANDSAT
TM
Degital
Beijing/CAS
8.23LANDSAT
TM
Degital
Beijing/CAS
9.12JERS-1
SAR
Degital
Kumamoto/NASDA
1998
8.01ERS-2
JSPRS :Japan Society of Photogrametry and Remote Sensing
CMA : China Meteorologist Administration
CSA : Chinese Academy of Science
clearly demonstrated by overlaying the
images of the near-infrared band as is
in Fig.1. In the figure, the flood areas
are shown in red color, according to the
assigned colors of red to the data before
the flood, and cyan to the data during the
flood.
The
authors
designated
the
downstream basin of Jinanli, which is
located in the northern part of Dangting
Lake, as the area of study. The site is
located in the central bottom portion of
the mosaic image, and overlaps the
adjacent paths observed by TM during
the 9 days of the study.
3.
Mapping of the extension of the
flooded area from satellite images
in time series
Prior to the digital analyses of TM data
observed by change after the spread of
flooding, aimed at grasping the daily
progress of flood water at the beginning
of August, printed images taken by
several kinds of sensors of observation
satellite such as NOAA/AVHRR,
ERS-2/SAR and RADARSAT/SAR were
46
Information Technology for Disaster Management (2001)
Kishi S., Song X., Li J.
been collected. The satellite data
during the flood which was used in the
study are listed in Table 1.
The data of observation by satellites
are also entered in Fig.2, which shows the
hydrograph compiled by the MWR
showing the daily discharge during the
flood at two major observation stations
located in the upper stream (Sarshi) and
lower stream (Chenlingji) with the study
area between. The discharge observed at
Chenlingji is combined with the data
from Dongting Lake.
The extended areas of inundation
interpreted from each satellite image
were plotted on the rough map of the
study area of about 40 km x 70 km, made
from TM images of 1995 as shown in
Fig.3. For an interesting example the
orange colored area was not recognized
as the inundation in the picture taken by
the AVHRR sensor at 15:00 on Aug. 11,
and appeared in the meaning of
comprehensive utilization of satellite
information in time series. In the study,
however, any SPOT data were not
available due to weather condition.
coded data of the inundated area
extracted by level slicing as shown in the
central column, and green and red are
respectively assigned to the data of TM
Band-4 and Band-3 in 1995 in the
left-central frame. In this color
composition, vegetation represented by
rice fields in the region appears in cyan,
and inorganic substances such as soil
appear in magenta respectively covered
by the inundated water. In the same way,
the permanent water areas of unmixed
water represented by the lake and old
river channel appear in pure blue, and
turbid water represented by main stream
of Changjiang appear in bright magenta.
Comparing the picture of the inundated
area in the central column over time, in
mid-September the water level is
estimated to become lower due to the
appearance of parts of land surface such
as road and banks. In fact, this is
supported by the hydrograph in Fig.2 as
the reflux period of the flood. However, a
problem in the simple comparison of the
data without calibration between TM and
SAR still remains.
4. Land cover conditions in the
flooded area
5.
In order to grasp the land cover
condition in the flooded area, the
inundated areas extracted from TM data
of mid and latter August and JERS-1
SAR data of mid-September were
respectively overlaid onto the TM data in
1995, according to the standard method
used internationally to understand the
situation through color representation.
The
results
are
assembled
chronologically from the top to the
bottom in Fig.4.
In the overlaid images on the right
column, blue is assigned to the binary
Consideration of the transition of
turbidity of flooded water through
TM data
As an attempt to estimate the
movement of the flooding water from the
transition of the turbidity using TM data
on two occasions during the interval of
nine days at the peak of the flood,
supervised classifisation by the most
likelihood method for each occasion was
conducted, and the overlaid image of
these visible band was made as shown in
Fig.5, accompanied with the training
areas and their spectral signature. The
turbidity here is considered as a relative
quantity of sediment included in the flood
47
Information Technology for Disaster Management (2001)
Kishi S., Song X., Li J.
water, and characterized by the intensity
of Tm band-3 in the red region. In the
case of the main stream of Changjiang, it
is characteristic that the river water be so
muddy that it has almost near intensity to
the city area covered by typical inorganic
substances even in Band-4 in the
near-infrared region.
In the overlaid images in the bottom
column, in Band-3 the red area indicates
relatively high turbidity on Aug.14, and
the blue area indicates high turbidity on
Aug. 23. In Band-4, as mentioned above,
the main stream represents some
brightness at both times in the darkness
of the surrounding water area.
From those images it was found that
the area of low turbidity in the latter part
of August through one of peaks of the
flood as seen in the hydrograph, due to
effects such as overflow, which sign was
detectable along the natural levee on the
left bank in the central part of the images
of August.14, and on the contrary, the
turbidity of surrounding areas of the old
river of the settlement of movement of
the flooded water.
sensing to disaster monitoring, the
comprehensive recurrent period of
several observation satellites would be
required to be at the most one day,
assuming the use of an all-weather type
sensor to complement the optical sensors.
Combined use of all-weather type SAR
with optical VNIR images in time of
peace is most practical to delineate the
damaged areas, and combined use will
make it possible to observe the same spot
on Earth constantly.
To realize the operational use in
disaster monitoring of orbital satellite
remote sensing, it is necessary to
establish an international cooperation
system for timely observation and quick
data distribution on natural disasters.
Acknowledgement
The authors acknowledge Mr.M.Hara of Vision Tech
Inc, Japan, for his quick retrieval and procurement of
LANSAT TM data from the Beijing Ground Station and
Dr. A. Kondoh of Chiba University for offering JERS-1
SAR data in cooperative research with NASDA.
6. Conclusion
References
Landsat TM data with its geometric
and radiometric characteristics was again
practical for us to grasp the land cover
condition in the flooded area and the
transition of turbidity of flood waters.
In term of the practical sensitivity of
satellite data to monitor the extension of
flood area, the observation frequency of
at most a few days was found to be
inadequate, despite synthesizing various
types of observation by several kinds of
satellites
after
considering
the
dependency of some satellites on
weathers.
In the application of remote satellite
S. Kishi, T. Morohoshi, X. Song, J.Li & M.
Hara: Flood Monitoring in China in
International Cooperation, IAF-97-C.3.05,
48th International Congress in Turin.
S. Kishi: Potentiality of Space borne SAR Data
for Monitoring of Natural Disaster,
IAF-96-C.1.04, 47th International Congress
in Beijing.
Y. Suga, S. Takeuchi & S. Kishi : Flood
Monitoring in China using JERS-1/SAR and
LANDSAT/TM Data IAF-99-C.2.06, 50th
International Congress in Amsterdam.
S. Kishi: Development of the Database of the
Examples of Application of Satellite Data to
Disaster Monitoring, IAF-93-B.5.101, 44th
International Congress in Graz.
48
Information Technology for Disaster Management (2001)
Kishi S., Song X., Li J.
STA:
Science and Technology Agency,
Japan
RSTAC:
Remote
Sensing
Technology
Application Center
MWR: Ministry of Water Resources, China
Abbreviations
NIED: National Research Institute for Earth
Science and Disaster Prevention
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