Koarai, Mamoru
D e v e l o p m e n t o f t h e Te c h n o l o g y o f U t i l i z a t i o n o f
Airborne Synthetic Aperture Radar (SAR)
Mamoru Koarai, Kouichi Moteki, Nobuyuki Watanabe,
T a k a k i O k a t a n i , Y o u k o Ya m a d a a n d K a o r u M a t s u o
Geographical Survey Institute, Ministry of Construction, Japan
E-mail: koarai@gsi-mc.go.jp
K E Y W O R D S : A i r b o r n e S A R , X b a n d , D E M , Ve g e t a t i o n , S o i l M o i s t u r e , D i s a s t e r
Information
ABSTRACT:
Geographical Survey Institute (GSI) has observed various area such as urban, flat and
mountain, Central Japan, using Airborne SAR (X- band). The authors introduce several
results, such as, visualized SAR images, DEM and counter maps and so on. Then, they also
introduce results of accuracy validation of DEM. and application plans for national land
management.
1. INTRODUCTION
It is very important to grasp the situation as soon as possible when a disaster occurs, but
it is very hard to get information from the ground because there are a lot of things which
prevent us from getting such important data such as clouds and volcanic eruptions. In case
using a optical sensor, large amount of information is shut out by such barriers. On the
other hand, SAR (synthetic aperture radar) is a very useful method to collect information
even if an observation area is covered with such obstacles or an observation is executed
in nighttime because SAR uses micro waves and these waves are radiated by the sensor
itself. Though SAR sensor is installed in some satellites, J -ERS, ERS, RADARSAT and so
on, and observes the surface of the earth, but the sensor doesn't have enough resolution and
interval between two observations is not so short to get appropriate information which is
fast enough in case of emergency.
F r o m t h e s e p o i n t s o f v i e w, a n o b s e r v a t i o n b y a i r p l a n e s h a s l o t s o f a d v a n t a g e s , s u c h a s ,
resolution and quickness compared with observations by existing satellites. In the future,
some satellites with higher resolution will be launched, and it is very important to
investigate beforehand how much information we can get about a disaster from future
satellites and how much we can use these information for map production.
Geographical Survey Institute (GSI) of Japan has installed Airborne SAR (X band) in order
to research and develop technology for those things in fiscal 1996 and 1997. And GSI
observed some places in Japan using our Airborne SAR in fiscal 1998 and 1999, and made
visualized images and DEMs.
In this paper, the authors report the results of the observation and the accuracy validation
of DEM and survey results for national land management.
2. OBSERVATION
The information about the GSI-SAR sensor is shown in Table 1.
GSI also observed various areas in last fall and winter. Urban area, mountainous area and
flat area in Kanto Plain (Japan), such as, Tokyo Metropolitan, Mt. Tsukuba area,
Tsukuba-City and so on, are included in this observation. Table 2 is the list of observation
areas. The objects of observation are topography related environment and disaster, such
as landslide, collapse, volcano, marsh land.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Supplement B1. Amsterdam 2000.
Koarai, Mamoru
Lots of experiments were going to be done during this observation. First, observations
with various off-nadir angles and directions were done. Second, observations were done
a few times in different season. Third, observed soil conditions are different among
observations because the condition depends on the weather and the moisture. As the
weather and the moisture strongly depend on the season, the condition must be different.
Besides producing visualized images and DEMs, catalogue for the features which helps
people to identify the object that is shown in visualized SAR images will be made, and
some researches will also be done.
Table 1
Information of GSI-SAR
Item
Performance
Frequency
9.555GHz (X band)
Band Width
100MHz
Off Nadir Angle
55~75° (must be set beforehand)
Unit Bit Number
4bit / 8bit
PRF
3~2000Hz
Polarization
HH
Sender Pals Width
1 0 µs e c
Swath Width
~5km
Resolution
Azimuth 1.5m / Range 1.5m
Table 2 Observed area, Season and Off-nadir angle
Area name
Object
Season & Off-nadir angle
Fall
Winter
55°
65°
75°
65°
W
Urban area
Shinjyuku
Building
W
N S E W
Tokyo
Farm area
Tsukuba city
Flat land
E
N S E W
E
E
Mt.Tsukuba
Mountain
E
N S E W
E
E
Ito
Hill
3directi
on
Kutisakamot Land slide
NE
Mountain
o
area
Shizuoka
Himekawa
Collapse
NE
Nagano
SW
Jinnnosuket
Land slide
ani
Mt.Hakusan
Mt.Asama
Vo l c a n o
E
Marsh land
Koga
Soil
E
E
moisture
N:northa,S:south,E:east,W:west, SW:southwest, NE:northeast,
3direction:observe Mt komuro from 3 direction
Area
3. PRODUCE OF DEM AND ITS ACCURACY VALIDATION
3.1 DEM of ITO CITY (hill area)
I n F e b r u a r y, 1 9 9 9 , G S I o b s e r v e d I z u P e n i n s u l a a r e a , C e n t r a l J a p a n , w h i c h h a s h i g h
potential for disasters and which is expected to detect the crustal movement. The
observation was done using two and three dimension mode, and the visualized images a nd
DEM were produced.
The visualized SAR image of Ito City which is located in northeast area of Izu Peninsula
is shown in Figure 1. The DEM is made by the interferometry of two SAR data which were
observed at the same time. The DEM expressed by gradations is shown in Figure 2. The
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Supplement B1. Amsterdam 2000.
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Koarai, Mamoru
features in the DEM by airborne SAR, such as, valleys and hills almost correspond with
the positions of these features shown in the topographical map.
Next, the authors inspected the accuracy of the DEM. This inspection was done by
comparing two DEMs, one was made from aerial photograph and the other was made by the
airborne SAR data. However, we didn't compare the area where the data was missing
because of invisibility from the airplane, such as, rear side of hills, buildings and so on.
The compared DEM was made by scanning aerial photographs and matching these photo
images with digital photogrammetric workstation. The using aerial photographs were
taken in November 1994, with the scale of 1:25,000.
The result of comparison between the DEM by airborne SAR and by aerial photos is shown
in Figure 3. This is histogram for the height difference between the DEM by airborne SAR
and aerial photos at validation points. The averaged height difference is 7.5m and the
standard deviation for the difference
Figure 1. Visualized SAR image (Ito)
Figure 2. DEM image (Ito)
Frequency(/1703pts.)
400
350
300
250
200
150
100
50
0
-25 -20 -15 -10
-5
0
5
10
15
20
25
Residual(m)
Figure 3. Comparison between SAR DEM
and Air-photo DEM (Ito)
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Figure 4. Visualized SAR image (Tsukuba)
(upper side = east)
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Supplement B1. Amsterdam 2000.
Koarai, Mamoru
is 9.7m. This result shows that we can get an accurate DEM whose residual is around a half
of interval between two contours that are shown in 1:50,000 basic topographical maps.
3.2 DEM of MT. TSUKUBA (Mountain area)
In this case, the authors inspected the accuracy of DEM in the mountain area. The
visualized SAR image taken from east direction is shown in Figure 4. And the each DEMs
made by SAR data from single direction (N,S,E,W) are shown in Figure 6. In the SAR image
taken from east direction (Figure 4 and 5), the west side of mountain body is shadow area,
then the ratio of DEM coverage is under 50%
(Figure 6).
For improvement of the coverage of elevation dates, we combine the four DEMs taken from
single directions shown in figure 5. As the results, the ratio of DEM coverage is over 80%
(Figure 6).
The result of comparison between the compos DEM by airborne SAR and by aerial photos
is shown in Figure 7. This is histogram for the height difference between the DEM by
a i r b o r n e S A R an d a e r i a l p h o t o s a t v a l i d a t i o n p o i n t s . T h e a v e r a g e d h e i g h t d i f f e r e n c e i s
7.4m and the standard deviation for the difference is 9.0m. The accuracy of the composed
DEM is better than the each DEMs taken from single direction. This result is almost same
a s t h e r e s u l t o f I t o C i t y, t h e a c c u r a c y o f D E M i s e q u a l t o 1 : 5 0 , 0 0 0 b a s i c t o p o g r a p h i c a l
maps.
Figure 5. Single and composed DEM images
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Supplement B1. Amsterdam 2000.
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Koarai, Mamoru
76%
2-Directions
1-Direction
41%
Frequency(2445pts.)
600
94%
4-Directions
500
400
300
200
100
0
-30 -25 -20 -15 -10
-5
0
5
10
15
20
25
30
Residual(m)
Figure 6. Relationship between number
of directions of composed DEMs
and ratio of data coverage
Figure 7. Comparison between SAR DEM
and Air-photo DEM (Tsukuba)
4. APPLICATION FOR NATIONAL LAND MANAGEMENT
4.1 ENVIRONMENT MONITORING
Micro wave responds to vegetation and soil moisture. For investigation o f the possibility
on marsh environment monitoring using SAR, the authors measured soil moisture in
Watarase wetland, Koga, in the same time of SAR observation. As the results of field
measurement at wetland and grassland, the soil moisture of Koga in winter decrees
c o m p a r e d w i t h i n f a l l . N o w, t h e r e l a t i o n s h i p b e t w e e n t h e d i f f e r e n c e o f s o i l m o i s t u r e a n d
the deference of back scatter in SAR image on two seasons is considered.
4.2 DISASTER MONITORING
As the disaster monitoring, the authors are going to try the interpretation of fitures related
disasters in SAR image. For example,
Collapse: difference between vegetated area and waste area
extract characteristics of land slide topography
flood: extract the submerged area
earthquake hazard: difference of backscatter between buildings and damaged buildings
F i n a l l y, t h e a u t h o r s h a v e t h e p l a n f o r d e t e c t i o n o f l a n d s l i d e m o v e m e n t u s i n g r e p e a t p a s s
interfferometry method of airborne SAR. In last fall, GSI has done the first observation
on the Jin -nosuke landslide, which moves several centimeter par year, at Hakusan, Central
Japan. Next fall, GSI will do the second observation at Hakusan, and will detect the
m o v e m e n t o f l a n d s l i d e b y r e p e a t p a s s i n t e r f f e r o m e t r y.
5. CONCLUSIO N
G S I h a s r e s e a r c h ed t h e u t i l i z a t i o n o f a i r b o r n e S A R f o r n a t u r a l l a n d m a n a g e m e n t , s u c h a s
cartographic use, disaster monitoring and environment monitoring. Through the
observations of various areas, we found that the accuracy of DEM by the airborne SAR
is almost equal to 1:50,000 basic topographic maps. That technology is useful for the
monitoring of topographic changes in volcanoes, even clouds or volcanic eruptions
p r e v e n t u s f r o m o b s e r v i n g s u c h c h a n g e s d i r e c t l y.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Supplement B1. Amsterdam 2000.