基于容差动态调整的旋转门(SDT)改进算法

提出了一种基于容差动态调整的旋转门(SDT)改进压缩算法,该算法通过在数据压缩过程中,根据相近两个压缩区间的标准差对容差进行动态调整,并记录在压缩区间内对压缩精度影响较大的原始数据点,实现了压缩率的提高,压缩误差的降低。应用结果表明,该算法与标准的SDT算法相比,压缩率可以提高0.10%,而压缩精度却提高了56.7%。     

Vegetation change detection using artificial neural networks with ancillary data in Xishuangbanna,Yunnan Province,China

Timely and accurate change detection of the Earth’s surface features provides the foundation for better planning, management and environmental studies. In this study ANN change detection was used to perform vegetation change detection, and was compared with post-classification method. Before the post-classification was performed the ANN classification was used to yield multitemporal vegetation maps. ANN were also used to perform a one-pass classification for the images in 2003 and 2004. DEM and slope were used as two extra channels. During the training stage, the training data was separated into 82 subclasses including 36 change subclasses and 46 no change subclasses. Moreover NDVI differencing methods were used to develop the change mask. The result showed that combining the NDVI differencing method with visual interpretation when identifying reference areas can produce more accurate change detection results for the ANN one pass change classification. Moreover, it is effective to use elevation and slope as extra channels together with PCA components, to perform ANN-based change detection in mountainous study areas. It is also important to separate the vegetation transition classes into subclasses based on spectral response patterns, especially for mountainous terrains. This processing can reduce the topographic effect and improve the change detection accuracy.

     

Rapid assessment and explanation of tree species abundance along the elevation gradient in Gaoligong Mountains,Yunnan, China

This article presents an analysis of tree species abundance and its association with climatic variables along elevation gradient in the Gaoligong Mountains in west Yunnan, China. Data from scientific papers and books in the Gaoligong Mountains area were collected and extrapolated to elucidate a mechanistic understanding of elevation patterns and the relationship between the elevation range and elevation mid-point of tree species along the gradient by examining climatic variables. Tree species abundance showed a unimodal pattern with a peak at mid-elevation (about 2000 m) and species with a narrow elevation range occurred at higher or lower elevation, while a wider elevation range was found at the middle of the gradient. Tree species abundance was the highest where both temperature and water availability were moderate. The relationship between the climatic variables affecting species appear to be due to both direct and indirect factors, and the effect of these effects varied at different gradients.

     

Key issues on watershed ecological security assessment

Based on analyses of key issues concerning watershed ecological security assessment including the subject, content, and methodology of assessment, this paper points out that ecological security should be assessed dynamically at different levels (e.g. watershed and ecosystem levels) with human being as the main assessment subject. Both the functional security and the structural security must be considered in watershed ecological security assessment. In order to reflect the overall and timely security status of the watershed, the PSR (pressure-state-response) method should be employed. Longitudinal Range-Gorge Region (LRGR) was researched as an example. An index system of watershed ecological security assessment has been proposed, which includes structural index, functional index, pressure and response index, and the state of ecological security is analyzed for LRGR in Yunnan Province.