Digital Processing and Information Extraction of the Remote Sensing Images in the Yangtze Three Gorges Project Region, China



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Towards Digital Earth

Proceedings of the International Symposium on Digital Earth



Science Press,1999

Digital Processing and Information Extraction of the Remote Sensing Images

in the Yangtze Three Gorges Project Region, China

Wunian Yang1 Zhengquan Cui2 F. Cauneau3 T. Ranchin3 J. P. Paris4 Guoliang Pu1
1 Institute of Remote Sensing & GIS, Chengdu University of Technology, Chengdu 610059, P. R. China.

Tel: (86)(28)4078820 / Fax: (86)(28)4078816 Email: ywn@cdit.edu.cn
2 Bureau of Investigation and Survey of Changjiang Water Resources Commission,

Wuhan 430010, P. R. China. Tel: (86)(27)82829507 / Fax: (86)(28)82829505

3 Centre d’Energétique, Groupe Télédétection et Modélisation, Ecole des Mines de PARIS,
BP. 207, F-06904 Sophia Antipolis Cedex, France. Tel:(33)493957460/Fax:(33)493957535,
Email: francois.cauneau@cenerg.cma.fr / thierry.ranchin@cenerg.cma.fr


4 G. D. T. A. Parc Technologique du Canal 8-10 Rue Hermes. F-31526 Ramonville-St Agne Cedex

France. Tel: (33)5 61 39 49 50/ Fax: (33)5 61 39 49 59. Email: jpp@gdta.cnes.fr
ABSTRACT Multi-time-phase of SPOT images, ERS-SAR image Radarsat images and Landsat TM images were applied in the study. The ARSIS method was mainly used to make fusion of the SPOT XS and Panchromatic images, achieving high quality of image results. many new geological, structural features and hazard phenomenon are found, achieving remarkable results:

(1) In the study of Wanxian-Wushan test region, with the theory and method of phase-separation analysis of remote sensing information field, geological and structural features were systematically interpreted with remote sensing images and the linear and circular structures were quantitatively analyzed. With a synthesizing analysis of the combined folds, faults and related major joint systems, four periods of structural deformation and the resulted deformation fields were determined. As a result, four tectonic stress fields produced successively during the Yanshanian to Himalayan period were recovered.

(2) In the study of Xiangxi-Yichang district, using the resulting images of fusion of multi-time-phase of SPOT images and ERS-SAR image, an imaging-geological map and a geological interpretation map were finished.

(3), In the study of Wanxian-Yunyang district, through fusion’s of the Landsat TM 4,5,3 images and SPOT P image, a lot of the best image results with high spatial resolution of 10m and being affluent in colors were obtained. Many 3-D viewing maps of remote sensing images of the landform relief, with a high resolution and being projected from different directions, were established. With which, quantitative analysis as drawing a section of landform and detecting DEM of some objects can be done directly and rapidly.



KEY WORDS SPOT image, ERS SAR image, Landsat TM images, Radarsat image, fusion of images, 3-D viewing maps, phase-separation analysis of remote sensing information field, landslide, geological application, Yangtze Three Gorges Project, China

1. Introduction


The Three Gorges Project (TGP) is the largest water conservancy project ever built in China, and so in the world. The reservoir is of a canyoned and river-like reservoir with a total length of about 600km and average width of 1.1 km which is less than twice the width of natural alluvial channel, and which has the storage capacity of the reservoir of 39.3 billion with the normal pool level (NPL) at 175m. The TGP is a multi-purpose hydro-development project, producing comprehensive benefits mainly in flood control, power generation and navigation improvement.

As the biggest water conservancy project all over the world, the Three Gorges Project becomes the focus of the world attention. The length of the reservoir bank, the reservoir capacity, the number of resettlement and ecological influence are matchless. Especially a great number of the geological hazards as landslides and rockfalls were developed along the banks of the Yangtze River, many of them are in an active stage at present. These may have a far-reaching influence on ecological environment. The world pays attention to the future of this project, especially to the geological, ecological and atmospheric environment variations after the storage. It is necessary to study and detect the present situation of the Three Gorges Project area by geological, geophysical and geochemical techniques, and to prepare an integrated approach for monitoring and understanding the process of modifications of the landscape and terrain characteristics under a so huge pressure.


Since the Three Gorges Project was stared to run in 1994, five years had passed and a great change had happened in this area. Because it covers a very large area where the traffic is very inconvenient, it is very available to choose the remote sensing technique as a main method for monitoring, studying and assessing rapidly and economically the impacts of the geological hazards on the Three Gorges Project and the project on natural environment.

2. Geological Background and Landform



2.1. The Stratigraphy and Petrography

The strata from the Sinian System to the Quaternary System are exposed rather completely in the Yangtze Three Gorges area, but the Upper Silurian Series, the Lower Devonian Series and the Upper Carboniferous are lacunal.

Geologic Structures The folds in the Yangtze Three Gorges region were quite developed, which consist of several structural zones. In the west, they mainly consist of the eastern Sichuan folding zone of the Sichuan Basin, and in the east, consist of Huangling anticline and Badoing-Fengjie folding zone. The mantle folds are characterized by a series of long closed anticlines alternating with gentle synclines. The sedimentary covers from the Sinian to the Jurassic were folded and faulted in the Yanshanian movement, establishing the regional tectonic framework. From Chongqing to Yichang, Yangtze River flows through 8 anticlines and 11 synclines
2.2. Characteristics of the Geomorphology

T
he Yangtze Three Gorges area is crisscrossed by valleys and gorges with the mountain rang and falling, and is complex of geomorphic types. Characteristics of geomorphology in this region are



Fig.1 Distribution of typical large-scale landslides and rockfalls in the Yangtze Three Gorges area

(from Chen Maoxun,1992)



controlled obviously by structures: anticlines form mountains and synclines form valleys, representing tectonic landform predominates. The landforms in the Yangtze Three Gorges area can be divided into mountains and hills, where landscapes of gorges, karst caves and tectonic terrace landform are the most magnificent.
2.3. Landslidesand Rockfalls

In the Yangtze Three Gorges area, geological and structural background is complex. Owing to the strong neotectonism, downcutting of the Yangtze River and plentiful rainstorm as well as human engineering activities, rockfalls and landslides occur frequently in this region. According to the investigation, there are 404 rockfalls and landslides with each volume of 10 000 m3 and total volume of 3 060 000 000 m3 on the two banks of the Yangtze and its tributaries. Among them there are 283 rockfalls and landslides on the trunk stream with volume of 1 500 000 000 m3, 121 on the tributaries with volume of 1 560 000 000 m3. There are 34 large-scale landslides and 4 rockfalls, with each volume of over 10 000 000m3 and total volume of 1 330 000 000 m3. The landslides are mainly distributed over the broad valley sector, especially from Chongqing to Fengjie, for example, Gaoqiaolu Landslide in Chongqing; Jipazi, Baota and Gaojiazui landslides in Yunyang; the landslide group in Wanxian and Baihuanping landslide in Fengjie. From Fengjie to Yichang, there are a lot of large-scale landslides, such as Huanglashi and Daping landslides in Badong; Fanjiaping and Xintan landslides in Zigui. The rockfalls are distributed mainly over the gorge sectors, especially in the Wuxia Gorge. For example, Yaqianwan, Baiheping, Xiangjiawan and Zuoyituo rockfall (Fig.1).

The development and distribution of rockfalls and landslides in the Yangtze Three Gorges Project area are controlled by the lithologic characteristics, geological structures and landform, and is restricted and effected by meteorological phenomena, hydrology, earthquake and human engineering activities.

3. Digital Processing and Information Extraction of the Remote Sensing Images




3.1. The Data Available


Multi-time-phase of SPOT images, ERS-SAR image, Radarsat images and Landsat TM images are applied in the study. The parameters of these images can be seen in the table 1.

3.2. Digital Processing of the Remote Sensing Images


These softwares of image processing as Minimage ( Ecole des Mines de PARIS ), Citystar V.2.0 (Beijing University,China), RS-OrthoMapper V.1.0 (Chengdu University of Technology, China) and ADOBE PhotoShop v.4.01 were used to process the images. According to the studied projects, different functions of image processing, such as the radiation enhancement of images, special filtering, textural extraction, image transform and so on, were selected in the using. Many high qualitative images were achieved, and much information on geology, environment and natural hazards was extracted (Fig.2 to Fig.6).

3.2.1. Geometric Correction of the Images


The data set of the images consist of multi-time-phase of SPOT images, SAR image, Radarsat image and Landsat TM images, among them, there are some deformation in the geometry. Because of lacking DEM data in the processing the images of the Xiangxi-Yichang district, the topographical map with a scale of 1:200000 was used to choose controlling points. 25 controlling points were chosen and the SPOT images in different time and the SAR image were corrected in geometry. In the Wanxian-Yunyang district, the DEM created with SPOT stereo-images is available, the geometric correction of SPOT images and SAR Radar image were done by the software of the RS-OrthoMapper V.1.0 (IRSGIS, CDUT, CN) in the image processing.

3.2.2. Enhancement of the Images


Because original image has lower quantitative grades, it is necessary to enhance and modify their luminance or gray level. Based on the differences of the images, many suitable processing functions of radiation enhancement of the images were selected in the using and a lot of image results with high quality were achieved.

Fig.2, 3 and Fig.4 are a comparison of the three panchromatic images which were enhanced in luminance. From these images, it can find what changes and how big of the changes had happened in the Three Gorges Project area at present years, especially at the dam in the middle of the images. Fig.5 is ERS-SAR image in the dam of Sandouping district. It shows the situation of the flood in the Yangtze River. Because the image was received in August 4,1998, it was that time the Yangtze River had a high park of the flood



Table 1 The parameters of the images used in the study

SATELLITE

ORBIT/FILE

PRODUCT TYPE

DATA

BANDS

REMARKS

SPOT-2

275/288

HRV, YICHANG

10/11/1998

XS+P

Good

SPOT-2

275/288

HRV, YICHANG

28/10/1997

P

Good

SPOT-2

275/288

HRV, YICHANG

22/06/1990

P

Good

ERS-2

17192

SAR, YICHANG

04/08/1998

PRI

Good

SPOT-2

266/291

HRV,CHONGQING

06/09/1995

XS+P

Good

LANDSAT-5

127/38

TM, DAXIAN

03/02/1987

TM 3,4,5

Good

LANDSAT-5

126/38

TM,SHENNONGJIA

04/06/1988

TM 3,4,5

Good

LANDSAT-5

126/39

TM, ZHONGXIAN

16/07/1989

TM 3,4,5

Good

RADARSAT 1

CD no. 405256


6930-ACS,C:N30

-58 /E108-49



S3, WANXIAN- YAN -YUNYAN

03/03/1997

10:44:27


S3-ASC

R.12530, C.13865



Good, wider area

Inc.angle:33.97

Interpixel 8M


RADARSAT 1

CD no. 405201



7094-DES,C:N30-57/ E108-37

F2, WANXIAN

NO YUNYANG



14/03/1997

22:42:10


F2-DES

R. 8737, C.6790



Inc.angle:39.42

Interpixel 6.25m



SPOT -1

/wanxian/fpxwanxi. tif

HRV, WANXIAN,

05/09/1986

03:25:57


XS+P

Good

Geocoded


SPOT-1

/wanxianfpwax25.tif

HRV, WANXIAN

05/09/1986

03:25:57


P

Smaller part.

Geocoded


SPOT-1

/Yunyan/ffpxyunya.tif

HRV, YUNYANG

05/09/1986

03:25:57


XS+P

Yunyang, Good

Geocoded


SPOT-1

/Yunyan2fpyunyan.tif

HRV, YUNYANG

05/09/1986

03:25:57


P

Yunyang, smaller part.

Geocoded


SPOT-1

dtm*.ima

DEM, Created by GDTA/IGN with SPOT images

05/09/1986

DTM data

Geocoded



3.2.3. Fusion of the SPOT Images with Landsat TM and the ERS-SAR Image


T
o detect some smaller bodies of the natural hazards as landslides and rockfalls and to extract information available, it is necessary to modify the quality of the images in their spatial resolution. In this study, the ARSIS method (Ranchin T. and Wald L., 1999) was chosen and used to make fusion of SPOT XS and Panchromatic images, achieving high qualitative images.

(Fig.2 SPOT Panchromatic image, acquired on June 22,1990. The dam of the Three Gorges Project should be built at the Sandouping, in the middle of the image. That time, the Three Gorges Project had not be launched. The image displays the original appearance of the area.)


(
Fig.3 SPOT Panchromatic image acquired on Oct. 28,1997, the dam area of the Three Gorges Project. That time the Three Gorges Project had been run for three years, many changes had happened from the image. The dam and some facilities such as Yangtze bridge, highway, residence buntings and so on, had been set up initiatively. The stream of the Yangtze River should be blocked in 10 days (on Nov. 8, 1997)).

Many methods to fusion sensor bands were used in the various applications of remote sensing. But most of them improve spatial resolution of image with a cast of losing spectral composition of original image, that is, the resulting image has a poor color. ARSIS method, from its French name-“Amélioration de la Résolution Spatiale par Injection de structures” (Ranchin T. and Wald L., 1999), is based on the wavelet transform and the multi-resolution analysis. It was designed to achieve the best synthesis result of images in a high spatial resolution and preserve spectral information of original image in the most extent.






(Fig.4 SPOT Panchromatic image received on Nov. 10,1998, the dam area of the Three Gorges Project. Because the Three Gorges Project had been launched for four years and the dam was blocked one year in that time, the dam and many facilities such as highway, residence buntings, shiplock channel and shiplift channel had been set up, a great change had happened in the image.)




(Fig.5 ERS-SAR image received on Aug. 4, 1998, the dam district of the Three Gorges Project. Progresses of engineering of the dam and the facilities related are shown clearly in the image. It shows too the situation of the flood in the Yangtze River, it was that time when the image was received the Yangtze River had a high park of the flood. These light points in the river are respondent of the ships.)

With ARSIS method, the fusion images with high quality were achieved in the study. The set of data available in the Xiangxi-Yichang zone, the Yangtze Three Gorges Project area is composed of three SPOT panchromatic (P) images from 1990,1997,1998 and a group of multispectral SPOT XS image (XS1, XS2 and XS3) from 1998. Among these images, some deformation in geometry is existed and needed to be corrected, because the fusion processing generally requires the images to be processed should be acquired at the same place and in the same time.


T
hree algorithms are under concern in the image processing: the High-Pass Filtering (HPF) algorithm (Chavez et al. 1991), model RWM within the ARSIS concept (ARSIS-RWM) (Ranchin and Wald, 1999) and the P+XS algorithm (Anonymous, 1986). They are applied to the three data sets. For the three sets of images and the three methods, nine synthesized multispectral images with a resolution of 10m. Following the protocol proposed by Wald et al. (1997), all of the P images are degraded to 20 m and all of the XS images are to 40m. Then, the application of the three algorithms selected is performed to these new sets of images. The synthetic XS images produced at 20m for all of the algorithms and sets of data can then be compared on a pixel-basis to the original XS images. Then the three methods are performed on these sets of degraded images providing nine synthesized multispectral images with a resolution of 20m.

In the first phase, the influence of the time lag between P and XS images is assessed for each method separately. We assume that the 10m synthesized images for 1998 (P1998 and XS1998) best represent the reality for 1998, thus they serve as a reference to which are compared the two other 10m synthesized images for 1990 (P1990 and XS1990) and for 1997 (P1997 and XS1998). The visual inspection over the site of the dam of the resulting images for the two first sets of images, achieved with the HPF and the P+XS methods, demonstrated the failure of these methods when the time acquisition of the images are different. On the contrary, the algorithm based on the ARSIS concept is able to fulfil the objectives of the end-users.

In the second phase, a quantitative assessment is made as recommended by Wald et al.(1997). In this study, the nine 10m synthesized multispectral images and the nine 20m synthesized multispectral images are taken under concern. Different statistical parameters accessing the three properties defined by Wald et al. are computed. The parameters derived for the three sets of images and the three algorithms demonstrated the benefits of using the algorithm based the ARSIS concept whatever the date of acquisition of the high spatial resolution images.

Fig.6 to Fig.8 are respectively the fusion of the SPOT panchromatic (P) images from 1997 and1998 with multispectral SPOT XS images (XS1, XS2 and XS3) from 1998. Fig.9 is the fusion of the SPOT images (P+XS) from 1998 with the ERS-SAR image from 1998. The changes of the project area are displayed quite obviously on these images. You can even measure how much progress of the project was processed from these images. Many new geological and structural features and hazard phenomenon are found based on these images. An imaging-geological map and a geological interpretation map of the Three Gorges Project area were finished with these images

(Fig.6 The fusion of the SPOT panchromatic (P) images from 1997 with multispectral SPOT XS images (XS1, XS2 and XS3) from 1998. The changes of the project area are displayed obviously on this image. It not only give prominence to detail landform of the image from 1997, but also preserves the features of XS images from 1998.)






(Fig.7. The fusion of the SPOT panchromatic (P) images from 1998 with multispectral SPOT XS images (XS1, XS2 and XS3) from 1998. The correction of the image in the geometry was done. The changes of the project area are displayed more obviously in the image. Due to its best composition in color with a resolution of 10m, the image is taken as a basic image for extracting and interpreted geological and structural features as well as the natural hazards. Detail of the dam can be seen from Fig.8.)

(Fig.8. Remote sensing image of the dam-site, Sandouping, the Yangtze T.G.P. The fusion of the SPOT P and XS images from 1998.)







(Fig.9. The fusion of the SPOT images ( P+XS, from 1998 ) with ERS-SAR image (PRI, from 1998). The geometric correction of the images were done. Linear structures are shown more clearly in the image. It shows the situation of the flood in the Yangtze River. It was that time when the image was received the Yangtze River had a high park of the flood. Many light points in the river are respondent of the ships.)

3.2.4. Fusion of Multisource Information of Geological, Geochemical and Geophysical Data with RS, GIS and GPS Data






I
n the study of large-scale project, using the composite and alternate image processing of multisource information for a large quantity of geological, geophysical, an remote sensing materials, it can rapidly extract advantageous information and make some better representing for applications. The problem in this method is that generally used remote sensing images as Landsat images are rough corrected products which have geometrical distortion. There are some displacements between geological bodies and their geophysical or geochemical anomalies in the 3-D space. If these were used to composite a map, a false compound anomaly map would be produced. A method to solve the problem is that an orthographic image map is made with RS, GIS and GPS techniques, and then these multisource anomalies are precisely matched on the image map. The 2-D and 3-dimension multisource information maps are set up and then the composite feature information are quantitatively extracted. The author applied the method in the minerogenetic prediction and study of geological hazard, in China, achieving remarkable results (YANG Wunian, et al., 1997, 1998)

(Fig.10 The Landsat image (color composed image of TM4,5,3) in the Huangjinkou(HJK) district, Yangtze Three Gorges Project region, which was orthographically projected under the GPS controlling points.)


Figure 10 is the Landsat image (color composed image of TM 4, 5, and 3) in the Huangjinkou district, Yangtze Three Gorges Project region, which was orthographically projected under GPS controlling points. With DEM data, the 3-D display map of remote sensing image was done, many landslides and rockfalls can be found along the river valley (Fig.11, 12). Figs. 13 to 18 are the fusion’s of the Landsat TM images with the Spot P image and 3-D viewing of the relief of landforms (DEM) with different properties. Because Landsat TM images have better spectral resolution and color features, and SPOT P image has better spatial resolution of 10m, many best image results were obtained through fusion’s of the Landsat TM images and the Spot P image.


Fig.3 The results of recognition based on

multispectral features .

(Fig. 11 The DEM of the Huangjinkou (HJK) district, Yangtze Three Gorges Project region)










(Fig.12 The 3-D modeling and analysis of the remote sensing image, Huangjinkou (HJK) district, Yangtze Three Gorges Project region, which was orthographically projected under the GPS controlling points. Many landslides and rockfalls can be found along the river valley. Quantitative analysis of topography as a profile of the landform and demands of the DEM can be done directly with the image.)





(Fig.13 The fusion of Landsat images (TM 4, 5, 3) from 1987 and the SPOT P image from 1986 of Jipazi area, Yunyang, the Yangtze TGP region. The Jipazi landslide is displayed obviously in the image.)






(Fig.14 3-D viewing of the remote sensing image of the Jipazi landslide in the Yunyang, the Yangtze TGP region, with an angle of viewing is 203°.The Jipazi landslide is displayed obviously in the image. The data of the DEM was created by SPOT images. Surface image is the result of fusion of the Landsat TM 453 images from 1987 and the SPOT panchromatic image from 1986.)








(Fig.15 DEM of the Yunyang district, the Yangtze TGP region. The data of the DEM was created by the SPOT image couple.)








(Fig.16 3-D viewing of DEM of Yunyang district, The Yangtze Three Gorges Project region. The data of the DEM was created by GDTA / IGN with the SPOT image couple. Quantitative analysis of the topography as a profile of the landform and demands of the DEM can be done directly from the image.)



4. Geological Interpretation of the Remote Sensing Images




4.1. Linear Structures and Structural Stress Fields Related


The geological and structural appearances display- ed on remote sensing images are responsible to a

composed result of the earth crust's movements since geological history, containing much indicating information of tectonic movements and related







(Fig.17 3-D viewing of the Wanxian-Yunyang area, the Yangtze Three Gorges Project region, with an angle of viewing is 82°.The relief of the landform and some geological structures (anticlines, synclines and faults) are displayed obviously in the image. DEM was created with SPOT images. Surface image is Landsat TM 453 from 1987. Quantitative analysis of the topography as a profile of the landform and demands of the DEM can be done directly from the image.)


mineralization in different time and stages. Therefore, it is possible for us to decompose and extract related information from remote sensing images by means of the phase-separation analysis of remote sensing information field according to different time and structural layers (YANG Wunian, 1997) and then quantitatively describe and analyze the information with the geomathematic methods.
Most researchers have paid attention to the importance of time, scales, and space sizes of linear and circular structures in tectonic analysis and minerogenetic prediction, but there hasn't been an effective method to solve this problem. Many people often put these linear and circular structures in different time, scales, and structural layers together to quantitatively process, resulting in complexity of the problem, and it is very difficult to find out internal relations among the linear and circular structures, related geological bodies, and related minerals, final conclusion is uncertain.

After many years’ practices, the author proposed a new theory and method, Phase-Separation Analysis of Remote Sensing Images for Regional Tectonic Deformation and Stress Fields (YANG Wunian, et al., 1991,1997). The author suggests that the structural feature on a remote sensing image is a synthetic result of combination of the deformations produced during the geological history of an area, including characteristic information of previous tectonic deformations. Therefore, tectonic stress fields of different stages in the complex deformation of an area can be reconstructed by the following steps: (1) geological structures formed at different stages and in different times are distinguished using remote sensing images; (2) tectonic deformation fields at different stages are determined by analyzing relationships between microstructures (joints and fractures) and the related tectonics (folds and faults); and (3) Tectonic stress fields at different stages are respectively recovered through a study of the features of structural deformation fields in different periods. This method was applied in many places in different geological conditions, china and had achieved remarkable results (YANG Wunian, et al., 1991, 1994, 1995, 1996, 1997; YUE Guangyu et al. 1996).

In this study, Wanxian - Wushan area in the Three Gorges Project region was selected as an important test area for its typical structural characteristics. Folds and faults were very developed in the area. In the northern part of the area, it is Dabashan folding belt, which consists of a series of closed folds and faults with inside winding arcs toward the south. The Wanxian folding belt in the southern part of the area consists of a lot of parallel folds with winding arcs toward the north. The two folding belts in arcs-type are converged near the Wuxi in the east and dispersed at the Haungjinkou in the west, respectively developing a transverse tensional joint system which is of particular characteristics on them, forming a complicated tectonic pattern (Fig.18). The mechanism of tectogenesis in this area has been debated for a long time. In this study, using the phase-separation analysis method of remote sensing information field (YANG Wunian, 1997), geological and structural features were systematically interpreted with remote sensing





(Fig.18 Orthography map of Kaixian area [H-49-(1)], with a scale of 1:250000 and the interval of Contour lines of 240m, in the Three Gorges Project region. It was mosaic of 3 Landsat scenes and Color composed with TM 4, 5 and 3. The map was created by IRSGIS, CDUT, CN, 1997, with its software of OrthoMapper V1.0)

(Fig.19 The linear and circular structure systems in the Kaixian area, interpreted with Fig.18.)

Legends: 1, the first period major transverse tensional joints which are related to the folds having the axis in the NW direction (early period); 2, the second period major transverse tensional joints which are related to Dabashan arc-type folding belt and Chuandong arc-type folding belt; 3, the third period major transverse tensional joints which are related to the folds having the axis in the SN direction; 4, the fourth period major transverse tensional joints which are related to the fold having the axis in the NW direction (later period); 5, main fault; 6, general fault; 7, main fault which is concluded or in concealed condition; 8, circular structure and its number; 9, geological contact.


images (Fig.19), and quantitative analysis of the linear and circular structures were done (figures were omitted). Through an analysis of the combined folds, faults and related joint systems, four periods of structural deformation and the resulted deformation fields were determined. As a result, four tectonic stress fields produced successively during the Yanshanian to Himalayan period were recovered (4 figures were omitted).
The study result shows that the structural stress fields controlled the structural deformation and changes of the ancient environment in the area, which had some effect on the modern landform. The Yanshanian movement 70Ma ago strongly acted on the Yangtze paraplatform and had Yangtze Three Gorges area fold and uplift to become mountains, forming a series of folding mountains and downwarping basins in NE direction.

4.2. Geological Interpretation and Mapping






In the study, owing to obtain high qualitative image results by fusion processing of the SPOT panchromatic image and the multispectral XS images as well as with the ERS SAR image, the geological and structural features in the Xiangxi-Yichang district were systematically interpreted. Fig.20 is the imaging geological map interpreted with SPOT images and SAR image, and Fig.21 is the geological map related. From these image and map, you can obviously see the development of magmatic rocks and the distribution of the strata from Cretaceous to Sinian as well as the developmental characteristics of linear structures in the district. The imaging features of several bigger faults in the western district and a great deal of remote sensing bigger joints are displayed obviously in the image (Fig.20). Xintan landslide and Lianziya deformed rock mass are quite clearly shown in the image (Fig.20). All of the other features such topography and water systems as well as the actions of the Three Gorges Project are displayed very distinctly. The image and map can be exported in a scale of 1:50 000 to 1:200 000.

The result of image interpretation shows that the strata in the studied area from the Sinian System to the Quaternary System are exposed. The strata consist mainly of clastic rocks, such as sandstone and siltstone, and carbonate rocks as limestone. Magmatic rocks and metamorphic rocks were developed in the middle part and northern part of the district. The Magmatic rocks consist mainly of such intrusions as granite (γ) and diorite (δ). The metamorphic rocks consist mainly of schist, gneiss, migmatite and marble. The loose sediments are scattered over the terraces and the foot of slope along the Yangtze River and its tributaries, and consist mainly of alluvial-proluvial clay, subclay, sand and gravel. The folds were developed and are mainly distributed in the western district. The faults and the bigger joints were quite developed, especially the joints, which has a bigger density.





Additionally, the geological interpretation map shows distinctly that the dam of the Three Gorges Project is set on a complete rigid landmass of crystalline rock (granite) and no bigger active fault in the surrounding area, with a stable geological environment.

5. Conclusion and Discussion


The Yangtze Three Gorges Project is the largest water conservancy project built in the world. The investigations have shown that hundreds of the geological hazards as landslides and rockfalls were developed along the banks of the reservoir, many of

them are in an active stage at present. These may have a far-reaching influence on the stability of the bank slopes of the reservoir and the environment. It is very available to choose the remote sensing technique as a main method for monitoring their changes and assessing rapidly the impacts on the project and on natural environment.

A remote sensing image is a stereoscopic miniature of natural landscape. It objectively records information on shapes and physical characteristics (tones and colors) of structural deformations, both the individual parts and the overall pattern, and is of a high quality summary. It also records some information on concealed structures. All of this information reflects the differences between geological bodies in composition, texture/structure, and physical properties under dynamic influences inside and out. The information on concealed

structures can be revealed by deformation of the earth crust, and by modifications of the geophysical and geochemical fields, or by abnormal changes in the atmosphere and biosphere above them. Apart from such information, much information on remotely sensed multispectral images is invisible to the human eyes, such as infrared or microwave radar images, and much of this information is useful in analysis of geological features out of sight. Using remote sensing images to analyze the deformation of geological bodies and extract information related not only provides useful data, but also is helpful for combining fracture systems of rocks and structural deformation with geological formations very well, so as to achieve conclusions that coincide with objective reality. Further more, a synthesizing application of new techniques and methods, such as the fusion of multi-type images, the composite processing of multisource information of geological, geochemical and geophysical data with RS, GIS and GPS data and the 3-dimension display, greatly enhances actual effect of useful information.

Multi-time-phase images of SPOT, ERS-SAR, Radarsat and Landsat TM were applied in the study. The ARSIS method was chosen and used to make a fusion of SPOT XS and P. Images. The ARSIS method is based on the wavelet transform and the multi-resolution analysis which was designed to achieve the best synthesis result of images in a high spatial resolution and preserve spectral information of original image in the most extent.

Through a digital processing and information extraction of remote sensing images, many new geological, structural features and hazard phenomenon were found, achieving remarkable results.

(1), In the Wanxian - Wushan test region, using the theory and method of phase-separation analysis of remote sensing information field, geological and structural features were systematically interpreted with remote sensing images , and quantitative analysis of the linear and circular structures were done. Through an analysis of the combined folds, faults and related joint systems, four periods of structural deformation and the resulted deformation fields were determined. As a result, four tectonic stress fields produced successively during the Yanshanian to Himalayan period were recovered .





(2), In the Xiangxi-Yichang district, using the resulting images of fusion of multi-time-phase of SPOT images and ERS-SAR image, an imaging-geological map and a geological interpretation map were finished.

(3), In the Wanxian-Yunyang district, through fusion’s of the Landsat TM 4,5,3 images and SPOT P image, a lot of the optimal image results with high spatial resolution of 10m and being affluent in colors were obtained. Many 3-D viewing maps of remote sensing images of the landform relief, with a high resolution and being projected from different directions, were established. With which, quantitative analysis as drawing a section of landform and detecting DEM of some objects can be done directly and rapidly.



Acknowledgment


Sincerely thanks to the French Ministry of Foreign Affairs,the Midi-Pyrenees Regional Council and the Committee of Development Foundation of Sciences and Technology for Geology and Minerals, Ministry of Land and Resources(MLR), China, which supported the finance for attending in an advanced studies of remote sensing and GIS techniques at GDTA (Groupement pour le Développement de la Télédétection Aérospatiale), Paris VI University and Ecole des Mines de Paris.

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