不同时相的遥感热红外图像在研究城市热岛变化中的处理方法

卫星图像的热红外波段已被广泛地用来研究城市热岛效应。由于客观条件的限制,在城市热岛变化的比较研究中,很难获得不同年代的同时相图像,特别是在南方多云雨的地区。所以,这给城市热岛的变化研究带来了很大的困难。为此,采用了将不同时相的热红外图像进行正规化、分级,并制成差值影像图的方法,较好地减少了季相差异的影响,使得不同时相的热红外图像得以对比。为了定量地研究城市热岛(UHI)的变化,还创建了城市热岛比例指数(URI)。该指数通过热岛面积和城市建成区面积的比例关系并赋于不同的权重值来定量地评估热岛现象的变化情况。

An Image Processing Technique for the Study of Urban Heat Island Changes Using Different Seasonal Remote Sensing Data

Thermal remote sensing imagery has been widely used to reveal urban heat island (UHI) phenomenon since the last two decades. To study the UHI change through change detection technique, it is usually expected to use the thermal data of different years with the same date. However, this is generally difficult special for the cloudy and rainy areas and the data with different date may have to be used. This will make the comparison of such thermal image data more difficult due to seasonal difference. In order to work out this problem, this paper introduces a method which can reduce the seasonal difference if the images acquired on different date have to be used. The thermal infrared bands of different date were first processed respectively through several image enhancement technologies. This generated 3\|dimension\|view images and revealed heat characteristics and spatial distribution features of the UHI. To find out the change of the UHI between different dates, the two thermal images were normalized and scaled to several grades to reduce seasonal difference and then overlaid to produce a difference image by subtracting corresponding pixels. To quantitatively compare UHI, an index, Urban\|Heat\|Island Ratio Index (URI), was created. It can further reveal the intensity of the UHI within the urban area. The calculation of the index is based on the ratio of UHI area to urban area. The greater the index is, the more intense the UHI is. This makes it possible to quantitatively study the UHI changes within a period of time. The technique has been successfully applied in a case study on UHI change in Xiamen City of China.