Tianxiang Yue

Landscape change detection of the newly created wetland in Yellow River Delta

Four models are employed in the landscape change detection of the newly created wetland. The models include ones for patch connectivity, ecological diversity, human impact intensity and mean center of land cover. The landscape data of the newly created wetland in Yellow River Delta in 1984, 1991, and 1996 are produced from the unsupervised classification and the supervised classification on the basis of integrating Landsat TM images of the newly created wetland in the four seasons of the each year. The result from operating the models into the data shows that the newly created wetland landscape in Yellow River Delta had a great change. The driving focus of the change are mainly from natural evolution of the newly created wetland and rapid population growth, especially non-peasant population growth in Yellow River Delta because a considerable amount of oil and gas fields have been found in the Yellow River Delta. For preventing the newly created wetland from more destruction and conserving benign succession of the ecosystems in the newly created wetland, six measures are suggested on the basis of research results.

High-accuracy surface modelling and its application to DEM generation

An innovative method, high-accuracy surface modelling (HASM), is presented, which is based on the fundamental theorem of surfaces. The fundamental theorem of surfaces makes sure that a surface is uniquely defined by the first and second fundamental coefficients. Numerical tests of a Gaussian synthetic surface show that the Root Mean Square Error of the HASM method is much less than the ones of classical methods, such as the Triangulated Irregular Network, Spline, Inverse Distance Weight and Kriging methods. The HASM method gives a solution to the error problem that has long troubled generations of digital elevation models. All the methods for surface modelling are used to simulate a Digital Elevation Map (DEM) of Qian-Yan-Zhou Experimental Station for Red Soil and Hilly Land, which has a great topographical variety. Shaded relief maps of the simulated DEMs are developed to represent the terrain relief of Qian-Yan-Zhou Experimental Station, which shows that simulation results of the HASM method are much better than the ones of classical methods.

A method of DEM construction and related error analysis

The concept and the computation of terrain representation error (ETR) are investigated and total DEM error is presented as an accuracy index for DEM evaluation at a global level. A promising method of surface modelling based on the theorem of surfaces (SMTS) has been developed. A numerical test and a real-world example are employed to comparatively analyze the simulation accuracy of SMTS and the classical interpolation methods, including IDW, SPLINE and KRIGING performed in ARCGIS 9.1 in terms of sampling and interpolation errors and of total DEM error. The numerical test shows that SMTS is much more accurate than the classical interpolation methods and ETR has a worse influence on the accuracy of SMTS than those of the classical interpolation methods. In a real-world example, DEMs are constructed with SMTS as well as the three classical interpolation methods. The results indicate that, although SMTS is more accurate than the classical interpolation methods, a real-world test indicates that there is a large accuracy loss. Total DEM error composed of, not only sampling and interpolation errors, but also ETRs can be considered as a good accuracy measure for DEM evaluation at a global level. SMTS is an alternative method for DEM construction.

Surface Modeling: High Accuracy and High Speed Methods

Although GIS provides powerful functionality for spatial analysis, data overlay and storage, these spatially oriented systems lack the ability to represent temporal dynamics, which is a major impediment to its use in surface modeling. However, rapid development of computing technology in recent years has made real-time spatial analysis and real-time data visualization become realizable. Based on newly developed methods, Surface Modeling: High Accuracy and High Speed Methods explores solutions to big-error and slow-efficiency problems, two critical challenges that have long plagued those working in with geographical information system (GIS) and computer-aided design (CAD). By developing high accuracy and high speed methods for surface modeling, the book builds a bridge between the mathematical-oriented theory of surface modeling and the user-oriented application where the user is actually able to retrieve information on the method itself. The author examines a novel method of high accuracy surface modeling (HASM) in terms of the fundamental theorem of surfaces. He then analyzes the coefficient matrix and develops an adaptive method of HASM (HASM-AM), a multi-grade method of HASM (HASM-MG), and an adjustment method of HASM (HASM-AD). He uses numerical tests and real world studies to demonstrate that HASM-AM, HASM-MG, and HASM-AD have highly accelerated computational speed, especially for simulations with huge computational work. Building on this, the book discusses a HASM-based method for dynamic simulation (HASM-FDS), and then applies HASM methods to simulate terrains, climate change, ecosystem change, land cover, and soil properties. It demonstrates HASMs potential for simulating population distribution, human carrying capacity, ecosystem services, ecological diversity, change detection, and wind velocity. The book concludes with a discussion of the problems that exist in surface modeling on a global level and evaluates possible solutions to these problems.

Numerical Simulation of Population Distribution in China

A model for simulating population distribution (MSPD) of China is developed based on the grid generation method and the Control of MapObjects of geographical information system. Elevation, net primary productivity, land use and land cover, city sizes and their spatial distribution, and spatial distribution of transport infrastructures are taken into full account in the MSPD. The result from the MSPD shows that in 2000, 90.8% of the total population of China distributed on the southeastern side of the Heihe-Tengchong line. The ratio of population on the northwestern side to total population of China has been increasing since 1935. The yearly growth rate was 0.8% from 1935 to 1990 and 6.1% from 1990 to 2000. One important advantage of the MSPD is that when scenarios of land cover, spatial distributions of transport infrastructures and cities are available, scenarios of spatial population distribution can be developed on the basis of total population forecast.

Changes of Holdridge life zone diversity in all of China over half a century

The research results show that diversity at the scale of Holdridge life zone observation has had a decreasing trend since the 1950s, and the ecological environment has become considerably unstable in China. The phenomena of unstable environment include continuous expansion of calamity areas since the 1950s, the seldom-seen flood that occurred in the summer of 1998 and the seldom-seen sand and dust weather that occurred in the spring of 2000. Both human activities and climate change are driving forces of the decrease in diversity and increasingly unstable environment in China.

A patch connectivity index and its change in relation to new wetland at the Yellow River Delta

In this paper, we introduce a patch connectivity index and analyse its changes in relation to ecotope diversity and human impact intensity. Land-use maps of the newly born wetland at the Yellow River Delta of 1984, 1991 and 1996 were produced by applying an unsupervised and a supervised classification algorithm to the corresponding three scenes of Landsat Thematic Mapper (TM) images. A model for calculating the patch connectivity index was proposed and applied to the classified images. Our results show that patch connectivity has a negative relationship with ecotope diversity and human impact intensity. This indicates that an important measure for conserving the benign succession of the newly born wetland is to prevent it from disturbance of industrial activities in order to maintain ecotope diversity and natural patch connectivity.

Adjustment computation of HASM: a high-accuracy and high-speed method

We developed a method for high-accuracy surface modeling (HASM) in terms of the fundamental theorem of surfaces, which has theoretically found a solution for error problems. However, the computing speed of HASM was too slow to be widely applied in practice. Thus, adjustment computation of HASM (HASM-AC) is developed in this article. For comparatively testing HASM-AC accuracy, a mathematical surface is first selected so that the true value is able to be predetermined to avoid uncontrollable data errors. The numerical test indicates that HASM-AC has the highest accuracy and its accuracy is 20.67, 15.67, and 14.67 times higher than the inverse distance weighting (IDW), kriging, and spline, respectively. Then, a 0.4 km × 0.5 km rectangular area is used to test the effects of different spatial resolutions and sampling intervals on accuracy. This real-world test demonstrates that HASM-AC accuracy increases at a much better and stable pace as the spatial resolution becomes finer and sampling intervals get shorter, compared to the classic methods. Finally, the computing speed is tested in an area with 6000 × 6000 grid cells where Qinghai, Gansu, and Sichuan provinces meet. The computing speed of HASM-AC is 11, 8, and 563 times faster than IDW, spline, and kriging, respectively, which makes HASM-AC able to process data in a huge size and make real-time visualization realizable. In short, HASM-AC performs best in both the numerical and real-world tests.

An Adaptive Method of High Accuracy Surface Modeling and Its Application to Simulating Elevation Surfaces

An adaptive method is employed to speed up computation of high accuracy surface modeling (HASM), for which an error indicator and an error estimator are developed. Root mean-square error (RMSE) is used as the error estimator that is formulated as a function of gully density and grid cell size. The error indicator is developed on the basis of error surfaces for different spatial resolutions, which are interpolated in terms of the absolute errors calculated at sampled points while paying attention to the landform characteristics. The error surfaces indicate the magnitude and distribution of errors in each step of adaptive refinement and make spatial changes to the errors in the simulation process visualized. The adaptive method of high accuracy surface modeling (HASM-AM) is applied to simulating elevation surface of the Dong-Zhi tableland with 27.24 million pixels at a spatial resolution of 10 m 10 m. Test results show that HASM-AM has greatly speeded up computation by avoiding unnecessary calculations and saving memory. In addition, HASM-AM improves simulation accuracy.

A curve-theorem based approach for change detection and its application to Yellow River Delta

A curve-theorem based approach is proposed and is used to handle NDVI data. The curve-theorem based approach includes a general index CD and two nonlinear transformations SAV and CAV . It is applied to Landsat MSS images of the Yellow River Delta, taken on 1 December, 1976 and 3 December, 1988. Results show that CD can describe the general situation of vegetation cover change in the Yellow River Delta and SAV is sensitive to environmental change in rivers and sea, while CAV is sensitive to environmental change in industrial and urban areas.