福建省长汀县河田盆地区近35年来地表裸土变化的遥感时空分析

Spatiotemporal dynamics of the bare soil cover in the Hetian basinal area of County Changting,China,during the past 35 years

福建省长汀县河田盆地区是中国南方最典型的红壤水土流失区之一,当地人民和各级政府一直为治理该区的水土流失进行着不懈的努力。利用遥感技术对该区1976年以来地表裸土分布的时空变化进行了分析,基于所提出的双重遥感指数法对该区的裸土信息进行提取,查明了该区地表裸土分布的时空变化情况。研究表明,该区近35年的治理已大大减轻了地表的裸露程度,地表裸土面积从1976年的159.17 km2锐减到2010年的51.98 km2。在3个不同的观察时间段里,裸土面积的变化呈现逐次减少、减速加快的趋势,客观地反映了该区水土流失治理的3个重要历史时期和政策所产生的效应。

The Hetian basinal area in County Changting of Fujian province is one of the most typical soil loss areas in the reddish soil regions of southern China. Local people and governments have been struggling for the control of the soil loss for decades. This study used remote sensing technology to analyze spatiotemporal dynamics of the bare soil cover in the Hetian basinal area since 1976. The bare soil features were extracted from the Landsat images of 1976, 1988, 1999, 2004 and ：2010 using two thematic indices-normalized difference soil index （NDSI） and normalized difference impervious surface index （NDISI）. After converting the original digital number values of the images to at-satellite reflectance, the soil and impervious surface features were enhanced using the two indices, respectively. The soil features were then extracted from the soil-enhanced images. However, the extracted soil information was found to have been mixed with built-up land information due to the spectral confusion between the two categories. Therefore, the NDISI was further used to filter out the unwanted built-up land information from the soil images using a logical tree algorithm, as the NDISI is the index specially designed for highlight impervious surface features represented mainly by buih-up lands. Results showed that the nearly thirty-five years of fight for controlling soil loss have greatly reduced bare soil covers in the basinal area. The area of the bare soil cover has been greatly reduced from 159.17 km2 in 1976 to 51.98 km2 in 2010. In the three observed periods, 1976-1988, 1988--1999, and 1999--2010, the decrease in bare soil cover was in an accelerate speed, which was -2.45 km2 per year, -2.75 km2 per year, and -4.33 km2 per year for the three periods, respectively. This corresponds to themajor policies issued by the government for the soil loss treatment of the area. Government policies accompanied with effective actions have played a key role in the reducing of the bare soil cover in the Hetian basinal area.