遥感影像空间分辨率及粒度变化对城市景观格局分析的影响

尺度是景观生态学和遥感领域的重要问题,已有研究主要考虑景观的粒度效应,很少涉及遥感影像空间分辨率对景观格局,尤其是对城市景观格局的影响.基于2000年和2002年分别由ETM 和IRS-PAN影像解译得到的土地利用图,从景观和类型两个层次分析了不同粒度下上海市一城市化样带的景观格局.结果表明,城市景观有明显的尺度效应,空间分辨率和粒度变化都会影响城市景观格局,而道路等线性廊道对尺度变化的敏感则是造成这一影响的主要原因.斑块密度、边界密度、平均斑块分维度、景观聚集度和最大斑块指数的粒度效应比较明显,而景观比例、Shannon多样性指数对粒度变化并不敏感.高分辨率影像适用于城市景观格局,尤其是破碎度的分析,其用于分析的合适粒度是5～10m.

Effects of varied remote sensor spatial resolution and grain size on urban landscape pattern analysis

Scale is an important issue both in landscape ecology and remote sensing. Although scale in landscape ecology involves both grain and extent, changing grain size is much more concerned by scientists. Choosing data of proper resolution has always been a big problem for landscape pattern analysis using satellite images. Many studies have been conducted trying to investigate the effects of remote sensor spatial resolution on landscape pattern analysis. However, the effects of remote sensor spatial resolution on urban landscape pattern analysis have rarely been reported.
Land use transects across urban center of Shanghai were clipped from the land use maps of 2000 and 2002, which were created by manual interpretation from ETM+ and IRS-PAN images, to produce Land use transect I and II (LUT-I and II). To study the impacts of road corridors on urban landscape pattern, road corridors and urban patches in LUT-II were merged to create Land use transect III (LUT-III). The three transects were then converted to ArcGrid formats at the grain size of 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 80, 100, 120, 140, 160, 180, 200, 250m using ArcView Spatial Analyst. Seven landscape indices were examined from both landscape and class-level including percent of coverage (PLAND), patch density (PD), edge density (ED), mean patch fractal dimension (MPFD), contagion (CONTAG), largest patch index (LPI) and Shannon diversity index (SHDI).
The results showed that scale effects of selected landscape indices were different in urban landscape. PD in LUT-II dropped as grain size increased from 5m to 10m, and increased as grain size reached 30m, and then decreased again with increasing grain size. Linear corridors such as roads were the major reasons leading to scale effects in urban landscape, because they are quite sensitive to varied remote sensor resolution and grain size.
PD, ED, MPFD, CONTAG and LPI were more sensitive to changing grain size comparing with PLAND and SHDI. Although PD, ED, MPFD and LPI could be used to quantify urban fragmentation, their behavior was different with changing grain size, highlighting the necessity of measuring urban fragmentation from different aspects.
The results also suggested that satellite images from IKONOS, SPOT or IRS-PAN with fine resolution were necessary for examining urban fragmentation, while data from TM/ETM+ with coarser resolution might be used to monitor urban sprawl. For data derived from IRS-PAN image, grain size about 5-10m is necessary to avoid scale effects in landscape pattern analysis, while the optimal grain size for data derived from TM/ETM+ images is 30-80m.