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41.
遥感图像在生成、传输和转化过程中往往受到各种噪声的干扰,影响了图像本身的清晰度,降低了视觉效果,不利于真实信息的提取.研究目的是对高分辨率遥感图像进行预处理,以提高信息识别精度.研究方法是噪声检测结合混合滤波的方法,该方法基于均值滤波和中值滤波的互补性,首先对图像每一个像素点进行噪声检测,把受高斯噪声污染和受椒盐噪声污染的像素点区分开,然后分别对受高斯噪声污染和受椒盐噪声污染的像素点进行处理.与其他滤波算法进行比较的结果表明,噪声检测结合混合滤波方法能够有效去除椒盐噪声和高斯噪声,保留图像的纹理信息,提高图像的清晰度. 相似文献
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Large area tree maps, important for environmental monitoring and natural resource management, are often based on medium resolution satellite imagery. These data have difficulty in detecting trees in fragmented woodlands, and have significant omission errors in modified agricultural areas. High resolution imagery can better detect these trees, however, as most high resolution imagery is not normalised it is difficult to automate a tree classification method over large areas. The method developed here used an existing medium resolution map derived from either Landsat or SPOT5 satellite imagery to guide the classification of the high resolution imagery. It selected a spatially-variable threshold on the green band, calculated based on the spatially-variable percentage of trees in the existing map of tree cover. The green band proved more consistent at classifying trees across different images than several common band combinations. The method was tested on 0.5 m resolution imagery from airborne digital sensor (ADS) imagery across New South Wales (NSW), Australia using both Landsat and SPOT5 derived tree maps to guide the threshold selection. Accuracy was assessed across 6 large image mosaics revealing a more accurate result when the more accurate tree map from SPOT5 imagery was used. The resulting maps achieved an overall accuracy with 95% confidence intervals of 93% (90–95%), while the overall accuracy of the previous SPOT5 tree map was 87% (86–89%). The method reduced omission errors by mapping more scattered trees, although it did increase commission errors caused by dark pixels from water, building shadows, topographic shadows, and some soils and crops. The method allows trees to be automatically mapped at 5 m resolution from high resolution imagery, provided a medium resolution tree map already exists. 相似文献
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Land degradation is believed to be one of the most severe and widespread environmental problems. In South Africa, large areas of land have been identified as degraded, as shown by the lower vegetation cover. One of the major causes of grassland degradation is change in plant species composition that leads to presence of unpalatable grass species. Some grass species have been successfully used as indicators of different levels of grassland degradation in the country. This paper, therefore explores the possibility of mapping grassland degradation in Cathedral Peak, South Africa, using indicators of grass species and edaphic factors. Multispectral SPOT 5 data were used to produce a grassland degradation map based on the spatial distribution of decreaser (Themeda triandra) and increaser (Hyparrhenia hirta) species. To improve mapping accuracy, soil samples were collected from each species site and analysed for nutrient content. A t-test and machine learning random forest classification algorithm were applied for variable selection and classification using SPOT 5 data and edaphic variables. Results indicated that the decreaser and increaser grass species can be mapped with modest accuracy using SPOT 5 data (overall accuracy of 75.30%, quantity disagreement = 2 and allocation disagreement = 23). The classification accuracy was improved to 88.60%, 1 and 11 for overall accuracy, quantity and allocation disagreements, respectively, when SPOT 5 bands and edaphic factors were combined. The study demonstrated that an approach based on the integration of multispectral data and edaphic variables, which increased the overall classification accuracy by about 13%, is a suitable when adopting remote sensing to monitor grassland degradation. 相似文献
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中国东北耕地物候期对气候变化的响应(英文) 总被引:9,自引:3,他引:6
We investigated the responses of cropland phenophases to changes of agricultural thermal conditions in Northeast China using the SPOT-VGT Normalized Difference Vegetation Index (NDVI) ten-day-composed time-series data, observed crop phenophases and the climate data collected from 1990 to 2010. First, the phenological parameters, such as the dates of onset-of-growth, peak-of-growth and end-of-growth as well as the length of the growing season, were extracted from the smoothed NVDI time-series dataset and showed an obvious correlation with the observed crop phenophases, including the stages of seedling, heading, maturity and the length of the growth period. Secondly, the spatio-temporal trends of the major thermal conditions (the first date of ≥10℃, the first frost date, the length of the temperature-allowing growth period and the accumulated temperature (AT) of ≥10℃) in Northeast China were illustrated and analyzed over the past 20 years. Thirdly, we focused on the responses of cropland phenophases to the thermal conditions changes. The results showed that the onset-of-growth date had an obvious positive correlation with the first date of ≥10℃ (P < 0.01), especially in the northern part of the Songnen Plain, the eastern part of the Sanjiang Plain and the middle and eastern parts of Jilin Province. For the extracted length of growing season and the observed growth period, notable correlations were found in almost same regions (P < 0.05). However, there was no obvious correlation between the end-of-growth date and the first frost date in the study area. Opposite correlations were observed between the length of the growing season and the AT of ≥10℃. In the northern part of the Songnen Plain, the eastern part of the Sanjiang Plain and the middle part of Jilin and Liaoning Provinces, the positive correlation coefficients were higher than the critical value of 0.05, whereas the negative correlation coefficients reached a level of 0.55 (P < 0.05) in the middle and southern parts of Heilongjiang Province and some parts of the Sanjiang Plain. This finding indicated that the crop growth periods were shortened because of the elevated temperature; in contrast, the extended growth period usually meant a crop transformation from early- or middle-maturing varieties into middle or late ones. 相似文献
46.
卫星影像在1:5万地形图生产中的应用 总被引:1,自引:0,他引:1
本文从影像获取的效率、经济性、精度三个方面讨论了用SPOT立体影像生产1:5万地形图的问题,为1:5万地形图的生产提供参考。 相似文献
47.
基于多尺度分析的遥感影像融合研究 总被引:1,自引:0,他引:1
本文对SPOT5的多光谱波段和全色波段在像素级的融合层次上运用多尺度分析的方法进行了融合试验,主要用了小波变换和Curvelet变换的方法,这两种变换方法都能把图像分解为低频的近似图像和高频的细节图像,采用一定的融合规则对分解后的图像进行融合,并进行反变换得到融合后的图像,并把基于多尺度分析的融合结果与传统的融合方法进行了对比分析。结果表明,基于多尺度分析的融合方法比传统的PCA、Brovey融合方法效果要好;而Curvelet变换融合在光谱保持度及空间信息提高方面都比小波变换融合有所提高。 相似文献
48.
用模糊区/清晰区平均反射率匹配法对SPOT 5卫星影像进行去模糊处理.首先,结合SPOT 5各波段的统计特征,从影像上识别出模糊区;然后,对影像进行非监督分类,对同一分类区内像元在模糊区和清晰区的辐射值进行比较,计算出气溶胶空间分布;最后,将气溶胶分布输入MODTRAN模型中,对影像进行大气校正.研究中将反演的气溶胶浓度分布重采样到全色波段的分辨率,用MODTRAN对全色波段进行大气校正,也取得了较好效果.研究得出模糊区/清晰区平均反射率匹配法是一种有效的去模糊处理方法,且可将处理后的影像转换得出反射率,便于不同时相遥感影像进行对比. 相似文献
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