Qingzhen City is the experimental site of this project, which is typical in terms of natural geography and karst rocky desertification development. It is located in the central part of Guizhou Province, neighboring Guiyang City in the east, Pingba in the south, Zhijin in the west, and Qianxi and Xiuwen in the north (Fig. 3-3), with a total area of 1,492.4 km2, of which mountainous areas accounted for 33.3%, hilly areas accounted for 52.9%, and intermountainous flat dams area accounted for 13.8%, whereas, from the point of view of the current status of its land use in terms of sub-topographic categories, the area of arable land of Qingzhen accounted for 30%, the area of parkland accounted for 0.66%, the area of forest land accounted for 31.30%, the area of 19.22% of pasture land, 4.29% of construction land, 0.35% of transportation land, 5.72% of water, and 8.46% of unused land.

Figure 3-3 Geographic location map of Qingzhen City

Qingzhen has an average elevation of 1,350m, and in the natural geographic region, it is located in the Qianzhong mound plain and the north side of the Miaoling mountain range. The terrain is high in the northeast and southwest, and low in the center and south. Qingzhen city belongs to the central subtropical monsoon climate, the climate is cool and warm, the average annual temperature of 14 ℃ or so, the river valley area slightly higher than the average annual precipitation of 1200 mm. Qingzhen city within the territory of the complex types of landforms, mainly for the hilly mountainous terrain, the development of karst is strong, the water surface of the artificial lake is wide, the province's largest artificial lake is located in the southern part of the city of Qingzhen. The city of Qingzhen has 10 townships with a total population of 434,125, and there are Miao, Buyi, Dong, Yi, Shui, Hui, Gelao, Bai and other ethnic minorities in the county.

Qingzhen City, like other karst areas in the province, is an ecologically fragile area, and in the past development, the destruction of ecology was used to obtain basic subsistence, which led to the common problems in karst areas: agro-ecological degradation of the environment, the poor agricultural base, the low level of agricultural production; the rural industrial structure is unreasonable; and the development of the inter-geographical imbalance and so on. The strata and rocks exposed on the surface of Qingzhen City include metamorphosed sandstone, metamorphosed tuff and slate of the former Aurignacian System, tuff, dolomite and shale of the Aurignacian System, Cambrian System, Carboniferous System, Permian System, Triassic System and Jurassic System, conglomerate of the Tertiary System, accretionary materials of the Quaternary System, and basalts of the Hercynian Period, etc. The city is also home to a large number of rocks of the Hercynian Period. In the city's outcrops, carbonate rocks are the most widely distributed, ***1014km2, accounting for 67.94% of the city's total area, so karst landscape has become the main feature of the city's geomorphology type. Especially in the northwestern part of the flow long, horse field, hualong, Wangzhuang, new store, duck pool, Hanjiaba, dark flow, wood carving and the west of the sand geese, beat the drums and other places of the most typical karst landforms. The non-karst area is smaller, mainly distributed in the east, southwest and south of Qingzhen City, i.e., Xiaoba-Wenshui-Tiechang-Yungui along the line, Mai roll-Small Indigo Mountain-Luomang-Breaking Rock along the line, Zhongzhai-Breaking Rock along the line, Mazhou-Small Indigo Mountain-Luomeng Zhongzhai-Breaking Rock along the line, along the line of Liwuo-Hexidong-Shiguan-Zhoujiaqiao, Yinfang, Yangba and a few areas in the west side of Qingzhen City and the east side of Hongfeng Lake, and the rest of the areas are karst areas with a vast area. At the same time, repeated man-made cutting of vegetation and reclamation of steep slopes have caused the loss of vegetation cover and serious soil erosion, which eventually led to rocky desertification.

I. Remote sensing image interpretation of karst rocky desertification intensity level

The remote sensing image interpretation of karst rocky desertification in Qingzhen City is the same as the operation process of the whole province, and it follows the workflow and technical route of rocky desertification interpretation in karst areas, and it has a certain degree of independence and representativeness in the establishment of remote sensing interpretation indexes.

1. Characteristics of lithology and geological structure interpretation

There is a close relationship between the lithology of karst areas and non-karst areas and rock desertification. Areas with carbonate rock lithology are karst areas, and the degree of rock desertification is higher, and the degree varies according to the situation of rock exposure.

The strata and rocks exposed on the surface of Qingzhen City include metasedimentary rocks, metasedimentary tuffs and slates of the former Aurignacian System; tuffs, dolomites and shales of the Aurignacian System, Cambrian System, Permian System, Triassic System and Jurassic System; conglomerates of the Tertiary System; accumulations of the Quaternary System; and basalts of the Hercynian Period, etc. The strong Yanshan Movement successively brought about a series of changes in the rock structure of the area. Strong Yanshan movement, successively make the eastern rock formation near the north-south fold, the western rock formation into the north-east fold, the fold belt towards the development of faults, transverse and oblique intertwined into a network, each other into layers of soluble rocks and insoluble rocks, by folding was interlaced with the band, the interaction of internal and external camping force, and gradually formed a variety of karst and normal geomorphological formations. The Himalayan movement further activated the region, and the old Tertiary conglomerates were fractured and controlled several present-day terrestrial red sedimentary basins.

Since the Quaternary period, the crust is obviously uplifted, the ground within the region by two major orogenic movement and a series of dissolution, erosion and stripping, the rock is exposed over a large area, forming a typical karst landforms, in the terrain of the gentle zone is non-karstic zone. Geological structure is the dominant factor in the formation of the basic skeleton of landforms, and is also the main basis for the division of landform types and landform zoning. The geomorphic landscape also reflects the geological features of different tectonic systems. From the point of view of the spread of mountains and rivers, the direction of the major mountain systems and rivers in Qingzhen is almost the same as the direction of the tectonic line, and the direction of several major mountain ranges in the northeast, such as Yungui Mountain, Baota Mountain and Jiulong Mountain, is in the north-south direction. It is in complete agreement with the axial and rocky directions of the Laoheshan folded backslope and the Dawiling backslope. The same is true for the main rivers of the children, the Dark River, Dry River and Longtan River are all oriented in north-south direction, and the Cat Jump River is oriented in northeast direction, all of which are almost the same as the rock layer direction and the fracture direction.

2. Characteristics of geomorphic slope interpretation of rocky desertification grade

The degree of rocky desertification is also closely related to the slope. Generally speaking, the higher the slope is, the more intense the scouring is, the more serious the soil erosion is, the faster the process of rocky desertification is, and the higher the degree of rocky desertification is. On the contrary, if the slope is gentle, the scouring is slower and the soil and water conservation is better, the degree of rocky desertification is low.

When other indicators such as surface texture and vegetation condition are certain, the grade of rocky desertification is mainly determined by the slope of landform. Geomorphology interpretation mainly uses graphics, color tone and shading. The graphics of geomorphology image include plane contour and the features of high and low rise and fall of the ground surface, while the color tone and shading can help to observe and analyze various geomorphology forms and obtain the information of geomorphology and its constituent materials. Mountain in the sunlight, the sunny slopes are more exposed to light, high brightness value, light tone; shaded slopes brightness value is small, darker tone.

So the color tone of the mountain image is very uneven, the high mountain shadow patch is smaller, the low hills image color tone difference tends to slow down the change. The shape of the mountaintop and the steepness of the mountain slopes are mainly based on the hue changes to read. Such as the south side of the mountain top to the sun is generally triangular protruding in the shadow, the apex of the triangle that is the top of the mountain, such as the top of the mountain hue change is more soothing or obvious, it is indicated that the lighted surface of the rounded or gently mountain tops. The two slopes of the color depth of the intersection line is the ridge, the ridge of the shadow slope of the color also has the depth of the difference between the tone of the light and uniform distribution of the slope said that the slope is slow, the tone of the deep or shadowed that the steep slopes of the two ridges between the low-lying part of the valley. Canyons and broad valleys can be clearly distinguished on the image. The slopes on both sides of the canyon are steeper, and the bottom of the canyon is often covered by shadows, and the color of the image is mostly dark, while the bottom of the wide valley is flatter, and there are often farmland and residents. The image of a karst basin is characterized by being surrounded by mountains, while the middle shows a low, flat basin-like terrain, with a more even tone in the flat areas.

Karst landforms are characterized by alternating positive and negative terrain, and the terrain appears disorganized. In the karst landform area, there are often lone peaks and peak forests, dissolving funnels, falling holes, dissolving depressions, dissolving basins, vadose streams, blind valleys, and other unique geomorphological patterns, in the gently sloping limestone layers are distributed with a number of funnels, there are single, or distributed in clusters, the funnels are mostly rounded and oval shaped. Some of them are filled with loose sediments, with lighter tones. Lone peaks and peak forests are karst positive topography, and the images are in darker tones; dissolved depressions are negative topography, in lighter tones; they constitute a collection of alternating dark and light shades and cluttered atlases. According to the above image features, the basic geomorphology can be roughly judged, for the interpretation of the slope grade to obtain, in addition to reference to the depth of the image shading to obtain, more importantly, from the 1/200,000 Qingzhen City slope vector map superimposed on the 1/50,000 topographic maps.

3. Characteristics of Soil Layer and Vegetation Interpretation

Karst areas are different due to the thickness of soil layer and vegetation cover. Generally speaking, areas with thicker soil layer and high vegetation cover have less or no rocky desertification. On the other hand, the degree of rocky desertification is higher in areas with thinner soil layers and lower vegetation cover.

In remote sensing image TM4, 3, 2 bands, the reflection of vegetation is sensitive, when the texture, lithology and slope and other indicators are determined, the outline of polygonal patches and rocky desertification intensity level determination is the index of vegetation, vegetation cover, vegetation structure information from the image hue depth and color hue determination (Table 3-5).

4. Field operation verification

In remote sensing image investigation, field operation verification is an indispensable and important part. Through the supplementary investigation of the operation in this work area, the mark of remote sensing interpretation of rocky desertification intensity grading is established, and the corresponding field photos are taken at the same time, which are used for the interpretation and analysis of rocky desertification intensity. In order to correctly interpret the satellite images and ensure the accuracy of the survey, the locations traversed by the route were first marked on the remote sensing image map of Qingzhen as markers, which were combined with topographic and geological maps to check and contrast with each other along the route and test the results of the image prejudgement along the route. The actual location using GPS to locate, and then combined with the coordinates of the image to determine the end of the investigation that is the beginning of the satellite image interpretation.

Observation point 1: Bumping Village, Qingzhen City, satellite positioning: N26°38.005′,E106°25.65′. This point is a closed crested depression, typical karst landform, the west side of the image map is red with white, light or medium intensity rocky desertification, the type of vegetation is low scrub, the vegetation cover is less than 45%, it is difficult to utilize the rocky mountain, the rocky gully, the rocky shoots are not developed, the degree of utilization is low (Photo 3-2). On its southeast side, the image features red color, the vegetation cover is 90%, the slope is steep, it is potential rocky desertification, once the vegetation is destroyed, it is easy to form rocky desertification (Photo 3-3).

Observation point two: Guizhou Aluminum Plant, satellite positioning: N26°38.005′,E106°25.65′. The rock layer at this point is the rock layer exposed in the Lower Cambrian, which is a non-karstic area. Its image is characterized by white massive structure, which is not rocky desertification, mainly due to artificial mining, resulting in a large number of exposed rocks. The exposed rock layer on its east side is limestone, with the image feature of greenish-red color, with sporadic white dots of rock exposed, and the vegetation coverage rate is about 80%, and the vegetation type is low scrub, which is mild or potential rock desertification (Photos 3-4).

Observation point 3: Yuchi River Canyon, satellite positioning: N26°51.345′,E106°10.454′. The image feature of this point changes from yellow to red with white color. The soil layer on the terrace is thick, and the steep slope is heavily reclaimed, which is a karst area, a stage of rocky desertification process, and a hard-to-use land of potential rocky desertification (Photos 3-5).

Table 3-5 Characteristics of standard false-color image

Two, spatial data analysis of karst rocky desertification

1. Spatial distribution of rocky desertification intensity levels in Qingzhen

Through the deciphering of satellite remote sensing imagery, a spatial distribution map of rocky desertification intensity levels in karst area of Qingzhen was finally generated (Photo 3-6), and the data analysis function of GIS was used to statistically The area, map spots and percentage of each level were made (Table 3-6) for further analysis.

Table 3-6 Table of rocky desertification intensity levels in Qingzhen City

Calculated through statistical analysis, the non-karst areas in Qingzhen City are mainly distributed in the east and southwest of Qingzhen City, accounting for 14.38% of the total area of Qingzhen City, while the karst areas account for 85.62% of the total area of Qingzhen City, among which the non-rocky desertification areas are mainly distributed in the central part of Qingzhen City and the area around the southern Red Maple Lake, and the potential rocky desertification areas is mainly distributed in the northeast and north areas of Qingzhen City, light rocky desertification is mainly distributed in the west and southwest of Qingzhen City, medium rocky desertification is mainly distributed in the northwest of Qingzhen City, the west of Hongfeng Lake, and a small amount of it is distributed in the central area, and strong rocky desertification is mainly distributed in the central area of Qingzhen City, and a small amount of it is distributed in the east of Hongfeng Lake and the northwest of Qingzhen City. The area of rocky desertification in Qingzhen City accounts for 24.67% of the total area, of which 17.31% is light rocky desertification, 6.46% is medium rocky desertification, and 0.90% is intense rocky desertification (Figs. 3-4).

2. Analysis of the relationship between the intensity level of rocky desertification and lithology

Geologically, the area around Duck Pond in Qingzhen belongs to the Upper Permian System, which is an interbedded layer of flint limestone and shale, and the development of moderate rocky desertification is typical due to the dense and hard flint rock. The eastern part of Jiutou Dapo belongs to Triassic Yelang Formation, with shale in the upper part, tuff in the middle part and shale in the lower part, which is soft and weak in resistance to weathering, but it is still a strong solidified rock among clay rocks, so that there is a mild rocky desertification development, and the surrounding areas and the areas extending to the eastern part of Weicheng belong to the Lower Permian, with tuff and flinty limestone as the main ones, and shale is seen a little bit at the bottom, and then it is further to the east to the Cat-jumping River and the northeastern part of Weicheng. It belongs to the Carboniferous System, dominated by sandstone and shale, all of which are potential rocky desertification areas.

From the east of Weicheng township to the south of Xinfa and other places for the lower Triassic Maocaopu Formation, the upper part of the dolomite, the central part of the gray dolomite, the lower part of the gray rock, due to this dolomite layer is unstable, the lateral transition is often for the dolomite tuff or grey rock, so most of the area is no rocky desertification area. To the east of it and near the horse field is the upper Triassic Songzikan Formation, with gray dolomite and muddy dolomite interspersed with shale, and the development of moderate rocky desertification is typical. Around Liuchang, the Lower Triassic Maocaopu Formation and Yelang Formation, and the Upper Permian and Lower Permian are the main ones, so the potential rocky desertification and mild rocky desertification are intermixed and distributed. The area around Hongfeng Lake belongs to Hongfeng Subgroup of Huaxi Formation of Anisik Stage of the Middle Triassic, mainly dolomite sandwiched with shale, occasionally containing solution collapse breccia and gypsum interbedded, except for the west, which is dominated by potential rocky desertification and mild rocky desertification. The lithology is not the same, will lead to the intensity level area and degree of rock desertification has been different (Table 3-7).

Figure 3-4 Proportion of rocky desertification intensity level in Qingzhen City

Table 3-7 Distribution area of rocky desertification intensity level of each lithology in the karst area of Qingzhen City (unit: m2)

Based on the comparative analysis, the proportion of the distribution of each lithology (Fig. 3-5) and the proportion (Fig. 3-6) can be derived. It can be seen that the distribution of lithology in Qingzhen plays a dominant role in the distribution of rocky desertification, in which rocky desertification is mainly distributed in the area of gray dolomite, whose rocky desertification area accounts for 42% of the total area of Qingzhen Karst, followed by rocky desertification mainly in the area of gray shale, whose rocky desertification area accounts for 19% of the total area of Karst, and the area with the least amount of rocky desertification is the distribution area of dolomite, whose rocky desertification area accounts for 10% of the total area of Qingzhen Karst. The least area of rocky desertification is the dolomite distribution area, whose rocky desertification area accounts for 10% of the total karst area in Qingzhen. And in the gray dolomite area, the potential rocky desertification is most widely distributed, accounting for about 62% of its area, followed by the area without rocky desertification, accounting for 16%, and the least intense rocky desertification, accounting for 1% (Figure 3-7).

Potential rocky desertification is most widely distributed in gray shale areas, followed by mild rocky desertification and no intensity rocky desertification distribution (Figure 3-8). No rocky desertification, potential rocky desertification, and mild rocky desertification are all more in dolomite areas, while intensity rocky desertification only accounts for 1% (Figure 3-9). Potential rocky desertification is 58% in limestone areas, followed by mild rocky desertification at 26%, potential rocky desertification at 12%, moderate rocky desertification at 1%, and intense rocky desertification at 3% (Figure 3-10). In the area where dolomite and limestone are distributed alternately, potential rocky desertification is dominant, with no rocky desertification and mild rocky desertification accounting for more or less the same proportion, while moderate rocky desertification and intense rocky desertification are more frequent (Figure 3-11). Taking the above comparisons together, no rocky desertification is mainly distributed in dolomite areas, followed by grayish shale, mixed dolomite and limestone areas, and limestone areas are the least; potential rocky desertification is mainly distributed in grayish dolomite areas, and dolomite areas are the least; mild rocky desertification is the most distributed in dolomite and limestone areas, and grayish dolomite areas are the least; moderate rocky desertification is mainly distributed in mixed dolomite and limestone areas, and the limestone areas account for only 1% of the total area of the region; intense desertification is most widely distributed in limestone areas, while it is almost undistributed in grayish shale areas.

Figure 3-5 Proportion of rocky desertification distribution in each lithology

Figure 3-6 Proportion of rocky desertification intensity level in each lithology

Figure 3-7 Proportion of rocky desertification intensity level in grey dolomite

Figure 3-8 Proportion of rocky desertification intensity level in grey shale

Figure 3-9 Proportion of rocky desertification intensity level in dolomite

Figure 3-10 Proportion of intensity level of rocky desertification in limestone

Figure 3-11 Proportion of intensity level of rocky desertification in dolomite, limestone