Abstract
Rugged karst terrain relief that creates shadows in satellite imagery, combined with high karst landscape heterogeneity stand in the way of fractional cover retrieval on karst rocky desertification (KRD) monitoring. In this study, we explored the feasibility of applying multispectral high spatial resolution Advanced Land Observing Satellite (ALOS) imagery for the fractional cover extraction of rocky outcrops. Dimidiate pixel model (DPM) and spectral mixture analysis (SMA) approaches (including simple endmember spectral mixture analysis and multiple endmember spectral mixture analysis) were selected to explore their feasibility for KRD monitoring through accuracy improvement for fraction estimation. Results showed fractional cover retrievals at the sub-pixel scale is essential in highly heterogeneous karst landscapes. Indeed, mixed pixels accounted for 93.7% of the study area in southwest China. Multiple endmember spectral mixture analysis achieved high overall accuracy (80.5%) in monitoring the percentage of rocky outcrop land cover. Furthermore, the predicted exposed bedrock coverage via spectral mixture analysis were similar in sunlit and shadow areas for the same surface types. This reflected that SMA methods could effectively reduce topographic effects of satellite imagery to improve the accuracy of fractional cover extraction at sub-pixel level in heterogeneous and rugged landscapes.
Highlights
MethodsThe topography is rugged with elevations between 230 and 1050 m
The results of our study showed that estimated rocky outcrop coverage from Simple endmember liner spectral mixture analysis (SESMA) and multi-endmember spectral mixture analysis (MESMA) was similar in sunlit and shadow areas, largely because the shade fraction, as an independent component, was extracted by least squares in the spectral mixture analysis (SMA) model and removed through shade normalization[43]
With the objective of overcoming obstacles to monitoring heterogeneous, rugged terrain on rocky deserts using remote sensing, our study applied high spatial resolution Advanced Land Observing Satellite (ALOS) images and compared Dimidiate pixel model (DPM), SESMA and MESMA to extract the key indicators of karst rocky desertification (KRD) at a sub-pixel scale
Summary
The topography is rugged with elevations between 230 and 1050 m Typical landforms in this region are tower karsts and depressions. The climatic vegetation climax community in this area is subtropical evergreen forest, dominant vegetation communities are grass and shrub because of severe human disturbance (Fig. 4). This area has a relatively high population density (52 people per km[2] in 2005) and a >1000-year history of agricultural development. By the 1990s, 60% to 70% of the forested area in the karst regions was cleared, and most existing forests were early seral, secondary vegetation[45] (Fig. 5). The coexistence of rocky outcrops and vegetation cover at a fine scale is common in the karst region
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