基于空间小波变换的生态地理界线识别与定位

为了提高生态地理分界线识别和定位的客观性,探讨了通过空间小波变换获取多尺度模极大值定位过渡带的方法.以NDVI和降水作为小波多尺度分解的对象,应用db3小波核函数分别对49条样带的模极大值进行了多尺度检测,并在GIS中确定其地理坐标.研究结果表明:识别半干旱半湿润生态地理分界线的最佳空间尺度为20～40 km,小于这一尺度定位过程容易受到局部地表覆被因素如城市区域或地形的影响,大于这一尺度由于要素被过度平滑,造成定位不准;从定位点的聚集度分析,NDVI的定位效果好于降水,特别是在较大空间尺度上.而与综合自然地理区划方案中的半干旱半湿润分界线比较,从定位点的方向性、平均最短距离以及均衡度三项指标综合判断,小波变换对于降水过渡带的定位优于对NDVI的定位.研究证实,空间小变换与GIS结合是提高生态地理分界线识别与定位科学性的重要途径,是对专家系统划分界线方法的有力补充和完善.

Identifying eco-geographical boundary using spatial wavelet transform

This paper attempts to use spatial wavelet transformation derived multi-scale module maximum as a geographical locator to objectively identify eco-geographical transition zone and its boundary. Employing the spatial patterns of NDVI and precipitation, we decomposed 49 transects with wavelet transformation of db3 kernel function. The geographical coordinates of all singularity points were located and marked in GIS. The results show that optimal spatial scale for identifying eco-geographical boundary of semiarid-subhumid transition zone is about 20-40 km. When the scale is less than this threshold value, the locating process is likely influenced by local scale ground structure such as built-up areas or fine scale landforms. On contrary, when the scale is larger than 20-40 km, the accuracy of locating points will drop sharply owing to over- smoothing treatment. In spite of the higher concentration degree of NDVI derived locating points than that of precipitation derived, the comprehensive locating accuracy for precipitation transition zone is superior to that of NDVI spatial pattern in terms of long axis direction coherence, mean minimum distance and point balance degree indicates. Our results suggest that the combination of spatial wavelet transformation and GIS is a powerful complement approach to expert based eco-geographical transition zone identification and locating.