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					                                            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
   Landsat TM data of the adjacent paths                   for each image accompanied with the
covering the middle reaches basin of                       examination of spectral characteristics in
Changjiang in the periods before and                       the training areas.
during the flood were obtained. To grasp
the outline of the flood, two spatially                    2.   General view of the middle reaches
mosaic images were produced and                                 basin of Changjiang from landsat
overlaid. In order to analyze the                               TM data
characteristics of the TM data, the
overlapping areas of the adjacent paths                       In order to broadly grasp the flooded
were designated as the study area. In the                  area widely from TM data, two scenes of
areas, several kinds of multitemporal                      adjacent paths covering the middle
satellite pictures were effectively used to                reaches basin of Changjiang from the exit
delineate the flooding water in near-daily                 of Three Gorge to Wuhan were mosaic
extension.                                                 for the data of the summer season in 1995
   Using TM data in the area, the land                     three years before the flood, and of
cover condition in the flooded areas was                   August 1998, during the flood,
examined by overlaying the images of the                   respectively. The flooding areas were




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                                  Information Technology for Disaster Management (2001)
                                                                  Kishi S., Song X., Li J.




       Date          Satelite   Sensor       Medium        Source
              1998
               8.01ERS-2        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


       JSPRS :Japan Society of Photogrametry and Remote Sensing
       CMA : China Meteorologist Administration
       CSA : Chinese Academy of Science


clearly demonstrated by overlaying the            3.   Mapping of the extension of the
images of the near-infrared band as is                 flooded area from satellite images
  in Fig.1. In the figure, the flood areas             in time series
are shown in red color, according to the
assigned colors of red to the data before            Prior to the digital analyses of TM data
the flood, and cyan to the data during the        observed by change after the spread of
flood.                                            flooding, aimed at grasping the daily
   The      authors      designated    the        progress of flood water at the beginning
downstream basin of Jinanli, which is             of August, printed images taken by
located in the northern part of Dangting          several kinds of sensors of observation
Lake, as the area of study. The site is           satellite such as NOAA/AVHRR,
located in the central bottom portion of          ERS-2/SAR and RADARSAT/SAR were
the mosaic image, and overlaps the
adjacent paths observed by TM during
the 9 days of the study.




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                                 Information Technology for Disaster Management (2001)
                                                                 Kishi S., Song X., Li J.




   been collected. The satellite data             coded data of the inundated area
during the flood which was used in the            extracted by level slicing as shown in the
study are listed in Table 1.                      central column, and green and red are
   The data of observation by satellites          respectively assigned to the data of TM
are also entered in Fig.2, which shows the        Band-4 and Band-3 in 1995 in the
hydrograph compiled by the MWR                    left-central frame. In this color
showing the daily discharge during the            composition, vegetation represented by
flood at two major observation stations           rice fields in the region appears in cyan,
located in the upper stream (Sarshi) and          and inorganic substances such as soil
lower stream (Chenlingji) with the study          appear in magenta respectively covered
area between. The discharge observed at           by the inundated water. In the same way,
Chenlingji is combined with the data              the permanent water areas of unmixed
from Dongting Lake.                               water represented by the lake and old
   The extended areas of inundation               river channel appear in pure blue, and
interpreted from each satellite image             turbid water represented by main stream
were plotted on the rough map of the              of Changjiang appear in bright magenta.
study area of about 40 km x 70 km, made              Comparing the picture of the inundated
from TM images of 1995 as shown in                area in the central column over time, in
Fig.3. For an interesting example the             mid-September the water level is
orange colored area was not recognized            estimated to become lower due to the
as the inundation in the picture taken by         appearance of parts of land surface such
the AVHRR sensor at 15:00 on Aug. 11,             as road and banks. In fact, this is
and appeared in the meaning of                    supported by the hydrograph in Fig.2 as
comprehensive utilization of satellite            the reflux period of the flood. However, a
information in time series. In the study,         problem in the simple comparison of the
however, any SPOT data were not                   data without calibration between TM and
available due to weather condition.               SAR still remains.

4. Land cover conditions in the                   5.   Consideration of the transition of
   flooded area                                        turbidity of flooded water through
                                                       TM data
   In order to grasp the land cover
condition in the flooded area, the                   As an attempt to estimate the
inundated areas extracted from TM data            movement of the flooding water from the
of mid and latter August and JERS-1               transition of the turbidity using TM data
SAR data of mid-September were                    on two occasions during the interval of
respectively overlaid onto the TM data in         nine days at the peak of the flood,
1995, according to the standard method            supervised classifisation by the most
used internationally to understand the            likelihood method for each occasion was
situation through color representation.           conducted, and the overlaid image of
The       results      are      assembled         these visible band was made as shown in
chronologically from the top to the               Fig.5, accompanied with the training
bottom in Fig.4.                                  areas and their spectral signature. The
   In the overlaid images on the right            turbidity here is considered as a relative
column, blue is assigned to the binary            quantity of sediment included in the flood




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                                   Information Technology for Disaster Management (2001)
                                                                   Kishi S., Song X., Li J.




water, and characterized by the intensity           sensing to disaster monitoring, the
of Tm band-3 in the red region. In the              comprehensive recurrent period of
case of the main stream of Changjiang, it           several observation satellites would be
is characteristic that the river water be so        required to be at the most one day,
muddy that it has almost near intensity to          assuming the use of an all-weather type
the city area covered by typical inorganic          sensor to complement the optical sensors.
substances even in Band-4 in the                    Combined use of all-weather type SAR
near-infrared region.                               with optical VNIR images in time of
   In the overlaid images in the bottom             peace is most practical to delineate the
column, in Band-3 the red area indicates            damaged areas, and combined use will
relatively high turbidity on Aug.14, and            make it possible to observe the same spot
the blue area indicates high turbidity on           on Earth constantly.
Aug. 23. In Band-4, as mentioned above,                To realize the operational use in
the main stream represents some                     disaster monitoring of orbital satellite
brightness at both times in the darkness            remote sensing, it is necessary to
of the surrounding water area.                      establish an international cooperation
   From those images it was found that              system for timely observation and quick
the area of low turbidity in the latter part        data distribution on natural disasters.
of August through one of peaks of the
flood as seen in the hydrograph, due to
effects such as overflow, which sign was
                                                    Acknowledgement
detectable along the natural levee on the
left bank in the central part of the images           The authors acknowledge Mr.M.Hara of Vision Tech
of August.14, and on the contrary, the              Inc, Japan, for his quick retrieval and procurement of
turbidity of surrounding areas of the old           LANSAT TM data from the Beijing Ground Station and
river of the settlement of movement of              Dr. A. Kondoh of Chiba University for offering JERS-1
the flooded water.                                  SAR data in cooperative research with NASDA.


6. Conclusion
                                                    References
   Landsat TM data with its geometric
and radiometric characteristics was again           S. Kishi, T. Morohoshi, X. Song, J.Li & M.
practical for us to grasp the land cover              Hara: Flood Monitoring in China in
condition in the flooded area and the                 International Cooperation, IAF-97-C.3.05,
                                                      48th International Congress in Turin.
transition of turbidity of flood waters.
                                                    S. Kishi: Potentiality of Space borne SAR Data
   In term of the practical sensitivity of            for Monitoring of Natural Disaster,
satellite data to monitor the extension of            IAF-96-C.1.04, 47th International Congress
flood area, the observation frequency of              in Beijing.
at most a few days was found to be                  Y. Suga, S. Takeuchi & S. Kishi : Flood
inadequate, despite synthesizing various              Monitoring in China using JERS-1/SAR and
                                                      LANDSAT/TM Data IAF-99-C.2.06, 50th
types of observation by several kinds of
                                                      International Congress in Amsterdam.
satellites     after     considering     the        S. Kishi: Development of the Database of the
dependency of some satellites on                      Examples of Application of Satellite Data to
weathers.                                             Disaster Monitoring, IAF-93-B.5.101, 44th
   In the application of remote satellite             International Congress in Graz.




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                                  Information Technology for Disaster Management (2001)
                                                                  Kishi S., Song X., Li J.



                                                   STA:      Science and Technology Agency,
Abbreviations                                      Japan
                                                   RSTAC:      Remote   Sensing   Technology
NIED: National Research Institute for Earth        Application Center
Science and Disaster Prevention                    MWR: Ministry of Water Resources, China




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