Dynamic Monitoring of Changing and Evolvement in Kumtag Desert Based on Remote Sensing Images

ZHANG Huai-qing Institute of Forest Resource Information Techniques

Chinese Academy of Forestry, CAF Beijing, 100091, China

zhang@caf.ac.cn

LING Cheng-xing Institute of Forest Resource Information Techniques

Chinese Academy of Forestry, CAF Beijing, 100091, China

lingcx@caf.ac.cn

Abstract—Lansat MSS and Landsat TM data of the Kumtag desert research area in four periods from 1975, 1990, 2000 to 2007 were chosen to dynamic monitor the changes of desert area. An images interpretation system was established after data preprocessing. The desert changing data for the Kumtag desert research area in the past 32 years were acquired through the combination of maximum likelihood classification with visual interpretation. The results showed that the desert area of the Kumtag research area kept increasing from 1975 to 2007, specifically, the area rose from 22,712.58km2 in 1975 to 23,352.33km2 in 2007. The period from 2000 to 2007 was the period with the maximum dynamic desert change in the research area. The comprehensive analysis of the transition probability matrixes of desert, gobi, saline land, vegetation area, mountain bodies and water bodies in these three periods reflected that the dynamic-degree variation trend and the transition characteristics in the Kumtag desert area were mainly resulted from the laws of nature evolution, involving temperature, precipitation, evaporation, humidity, the changing characteristics of vegetation distribution and surface wind-erosion. From integrated analysis, it shows that main reason of desert development characteristic is natural selection and evolution.

Keywords-dynamic monitoring; Kumtag desert; remote sensing)

I. INTRODUCTION The Kumtag desert is extremely arid with thick and dry

sand beds. There is hardly any vegetation distributed in the hinterland of the desert, and the sand dunes have great fluidity. The desert is under the most rigorous nature conditions in the arid area of northwest China [1]. Present studies in this area mainly involve the morphologic observation of featherlike dune ridges, the distribution of plant communities as well as geological elements and structures, etc., while it has been lack of detailed studies on the dynamic changing mechanism of the desert evolution characteristics and the changing trend of the Kumtag desert in recent decades [2]. The RS images of the Kumtag desert research area from 1975 to 2007 were interpreted based on the RS technique, with which the inner mechanism of desertification and evolution of the Kubuqi desert and its dynamic changing process were explored from the angles of the dynamic degree and the land-type transition probability

based on the area data of the desertification land in the research area in 1975, 1990, 2000 and 2007.

II. RESEARCH AREA Located in Northwest China, the Kumtag desert is

bordered by the Lop Nor region in Xinjiang Tarim Basin to the west, the Dunhuang city to the east, the eastern section of the Tian Shan mountains to the north, and the Altun mountain to the south. It has the total area of about 23,400km2 and is known as the sixth largest desert in China. It is within 89° 57' 49" - 94° 54' 08" E and 39° 07' 50" - 41°00' 03" N, and within the borders of Xinjiang and Gansu. Its main area is distributed in the southeast part of the Ruoqiang county in Xinjiang province ， while distributed in the Dunnhuang city and the Aksay Kazak autonomous county of Jiuquan city within the borders of Gansu. The word “Kumtag” in the Uighur language means “sand hills”, and the Kumtag desert possesses the world-unique featherlike dune ridges.

Figure 1. TM images of research area (R:TM4 G:TM3 B:TM2).

III. RESEARCH METHOD

A. Remote Sensing Interpretation and Information Extraction Four periods (1975, 1990, 2000 and 2007) of Lansat

MSS and Landsat TM data for the Kumtag desert research area over three decades were chosen for this study. Through RS data preprocessing, the false-color images in the band combination MSS 3, 2 and 1 in 1975 and TM 4, 3 and 2 in

2010 International Conference on Artificial Intelligence and Computational Intelligence

978-0-7695-4225-6/10 $26.00 © 2010 IEEE

DOI 10.1109/AICI.2010.308

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2010 International Conference on Artificial Intelligence and Computational Intelligence

978-0-7695-4225-6/10 $26.00 © 2010 IEEE

DOI 10.1109/AICI.2010.308

336

1990, 2000 and 2007 in the research area were obtained as the information sources [3][4].

With the data from the scientific field survey in the Kumtag desert in Sep. 2007 as the auxiliary data, the RS images in the four periods were interpreted through human-machine interaction, and the research regions were classified into six types: desert, Gobi, saline land, vegetation region, mountain body and water body. The range of the Kumtag desert research area was determined, including the chief region of the desert (small Gobi regions deep in the desert were taken as parts of the desert body), the desert in the Mingsha mountain area to the east of Danghe, the scattered sheet-shaped flat sand land in the Aqik valley, and the southern margin of the Lop Nor region. It extended to the Dunhuang Oasis in the east, the Altun Mountain in the south and the Aqik valley in the north. Based on the established interpretation key, the variation data of the desertification land and other land types in the research area during different periods were extracted with Arcgis 9.3 software. The principal research target in this study, namely the desert, appeared yellow-white in MSS images with common hues and exhibited the texture quality of sand with characteristics of desert texture and patchiness, while in TM images, it appeared brown-yellow with slightly brighter hues and exhibited the texture quality of sand with characteristics of desert texture and patchiness. Both of them shared the distinguishable boundaries with mountains, Gobi and saline land [6].

According to the resolution characteristics of RS images, it was prescribed that the minimum picture spot should be composed of 10×10 pixels during the information extraction. The error of the contour line of a picture spot during the interpretation was controlled within three pixels (100 m×100m on the spot), and the precision of the picture-spot interpretation was controlled [7][8]. Eventually, the data of the land type distribution in the Kumtag desert research area during the four periods were acquired through interpretation

[12][14].

B. Calculation of Dynamic Degrees of Desertification The area of the desert and other land types in the research

area during the four periods were obtained according to the statistics. The dynamic desertification degrees and the area variation in the desert area during the four periods were calculated. The formula (1) for calculating the dynamic desertification degrees was adopted [5]:

%101 ××−=tAi

AiAjSD (1)

Where SD is the dynamic changes for some region or desertification land of a certain type, Ai is the area of the desertification land in the first year, Aj is the area of desertification land in the last year and t is the interval years. A positive value represents that the area of desertification land is increasing, and a negative value represents that the area of desertification land is decreasing [5][13].

C. Calculation of transition probability matrixes of desert changes The four historical periods of the Kumtag desert research

area were divided into three time segments: 1975-1990, 1990-2000 and 2000-2007. The land types in the research area, such as desert, gobi, mountains, vegetation area, water bodies and saline land, were summed to obtain the changing degrees of the desertification land during nearly three decades and the distribution of other land types in the research area [10]. Afterwards, the changes of various land types were divided into a series of discrete evolution states, and the proportion of the transition from one state to another, namely the transition probability can be obtained based on the transition rates of a certain land type in different time segments. For instance, parts of the desert were transited into other land types from 1975 to 1990, such as gobi and vegetation cover area. The proportion of the former to the latter equaled to the transition probability. Through the calculation of the transition probability matrixes, the characteristics of the desert type transition and the trend of the dynamic desert changes in the Kumtag desert research area in different time segments within the three decades were obtained [9].

TABLE I. DESERT CHANGES IN RESEARCH AREA FROM 1975 TO 2007

Time segment Desert area

（km2）

Changing rate (%)

Dynamic degree

(%)

Ratio of desert

area (%) 1975 22712.58 38.846 1990 23005.22 39.346

Changes (1975-1990)

292.64 0.624 0.859

2000 23207.59 39.692 Changes

(1990-2000) 202.36 0.880 0.879

2007 23352.33 39.940 Changes

(2000-2007) 144.74 1.288 0.891

Total changes (1975-2007)

639.74 2.817 0.881

Figure 2. Changing trend of desert area from 1975 to 2007

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IV. ANALYSIS OF DESERTIFICATION DISTRIBUTION CHANGE INFORMATION

In the investigation of the changes of the Kumtag desert, the desertification process and the changing trend of the area can be analyzed scientifically based on the desert distribution in different periods since 1970s. Analysis was conducted based on the desert distribution data for the Kumtag area in the four periods (1975, 1990, 2000 and 2007), which was extracted from RS information. The data in Table 1 showed that the area of the Kumtag desert was 22,712.58km2 in 1975 and increased to 23,352.33km2 in 2007, and the net increment in these thirty-two years was 639.74km2, the total changing rate was 2.82%, the mean annual net increment was 19.99km2, and the annual increasing rate was 0.09%. The desert area accounted for 38.85% of the whole research area in 1975 and increased to 39.94% in 2007. The desert in the whole research area expanded slightly with time. Spatially, the changes were mainly distributed on the boundaries of the Altun mountains and the desert in the south as well as the sandy land with bush and brushwood newly emerged in the alluvial plain on the site of the Jade Gate in the east, the basic reason of which was that the desert changes in the research area exhibited the trend of nature evolution with less human interference, and thirty years of time was not long in comparison with the nature changes in the whole desert and did not bring about many changes in geological characteristics and distribution situation.

Table 1 showed that the changing rate of the area of the desert was the highest during the seven years from 2000 to 2007, i.e., 1.29%. The mean annual increasing rate was 0.09% and also the highest among the three periods, which was followed by the mean annual increasing rate from 1990 to 2000, i.e., 0.09%, with the changing rate of 0.88%. The lowest changing rate emerged in the first period (1975-1990) with the rate of 0.62%, and the mean annual changing rate was the lowest, i.e., 0.09%. As shown in Fig. 4, the changes in the desert area in the three periods exhibited the trend of slow and slightly-intensified increase. The desert-area increasing rate was rather low before 1990 and became higher after 1990, and after 2000, the rate increased considerably. During the thirty-two years from 1975 to 2007, the desert-area changes in the Kumtag desert research area had been increasing without exceptions.

V. DYNAMIC ANALYSIS OF DESERTIFICATION Analysis and determination based on the distribution

situation of various land-use types from RS images in the research area as well as spatial changes and the variation characteristics of the dynamic desert transfer reflected effectively the process and states of the desertification and evolution in the area.

In order to further analyze the regional characteristics of the desert changes in the Kumtag desert research area, the typical regional RS images from different directions of the Kumtag desert research area were compared for analysis. Analysis showed that the area had not experienced much obvious overall change in nearly thirty years and maintained the primary morphologic characteristics. Since no great

natural change occurred, no great changes were observed in the general conformation and the distributing regions of the desert. Under the slight increase in the distribution area of the desertification land in the research area, the minute inner local changes indicated that some changes were occurring at the desert margins where the desert was bordered by the mountains, Gobi and saline land.

Table 1 showed that the dynamic degree of the desertification land from 1975 to 1990 was calculated as 0.859%, according to the dynamic degrees of the Kumtag desert in the three time segments that covered thirty-two years (1975-1990, 1990-2000 and 2000-2007). Although the interval time was the longest, i.e., fifteen years, it was the period with the lowest dynamic degree among the three periods. From 1995 to 2000, the dynamic degree of the desert in the research area increased somewhat to 0.88%, from which it can be seen that the period with the highest dynamic degree of the desert in the research area was from 2000 to 2007, and the dynamic degree reached 0.89%, indicating that the desert changes in the Kumtag desert research area were the most significant during the seven years.

VI. CONCLUSIONS (1) The desert area in the Kumtag desert research area

continued increasing from 1975 to 2007. According to the analysis on the scale and the rate of desert expansion during 1975-1990, 1990-2000 and 2000-2007, the largest area increment emerged in the period from 1975 to 1990 (as long as 15 years), i.e., 292.64km2. In terms of the desert expansion rate, however, the desert changing rate in this period was the lowest among the three periods, i.e., 0.62%, which was lower than the mean changing rate of the three periods and much lower than that during 2000-2007, i.e., 1.29%. Although the area increased during the seven years from 2000 to 2007 was 144.74km2, the period was the one with the largest and the most intensive desert changes among the three periods. According to the time analysis of the thirty-two years from 1975 to 2007, the desert area increased from 22,712.58km2 in 1975, which accounted for 38.85% of the total research area, into 23,352.33km2 in 2007, which accounted for 39.94% of the total area. During this period, the overall changing rate amounted to 2.82%, and the desert area increased at the mean annual rate of 0.09%. The desert area continued increasing without reversion.

(2) Because the Kumtag desert research area is in an extremely arid desert in the temperate zone of China, the varieties and the population of wild lives are extremely scarce, and the temperature difference between the night and the day is considerable. Due to the extremely severe conditions, the increasing trend of the desert area during the thirty-two years from 1975 to 2007 was mainly attributed to the nature evolution in the desert, while the influence of human activities appeared much unimportant. According to the analysis on the dynamic degrees of the desert in the research area and the transition probabilities of various land types, the dynamic degree of the whole desert increased slightly from 0.86% to 0.89% during the three periods which cover thirty-two years from 1975 to 2007.

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ACKNOWLEDGMENT This study was funded by the national science &

technology program in the 11th five-year plan period “Technology Integration and demonstration application for comprehensive monitoring of forest resources (project number: 2006BAD23B06)” and the national foundation work project “comprehensive scientific investigation of Kumtag desert (project number: 2006FY110800)”.

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