基于地表温度-植被指数关系的地表温度降尺度方法研究
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北京师范大学,北京师范大学

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国家863计划项目(2006AA12Z142,2006AA120108)


Downscaling land surface temperature based on relationship between surface temperature and vegetation index
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Beijing Normal University,Beijing Normal University

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    摘要:

    地表温度(Land Surface Temperature, LST)在空间上和时间上均存在很大的差异性。而通过卫星遥感技术来监测地表温度存在着空间分辨率和时间分辨率上的矛盾:空间分辨率高的卫星时间分辨率低,反之亦然。为了解决这个矛盾,首先利用TsHARP (An algorithm for sharpening thermal imagery)温度降尺度方法将LSTMODIS,1km(1km MODIS(Moderate-resolution Imaging Spectroradiometer)地表温度)图像(2004年9月9日上午)降尺度为LSTMODIS,500m(500m MODIS地表温度)图像。为了对降尺度LSTMODIS,500m图像进行验证,对研究区内同一天(2004年9月9日上午)的ETM图像的第6波段的辐亮度值升尺度到500m后,再利用Sobrino ETM(Enhanced Thematic Mapper)温度反演方法反演得到LSTETM,500m(500m ETM地表温度)图像,将LSTETM,500m图像作为当日地表温度的实测值,对降尺度LSTMODIS,500m图像的降尺度效果进行验证。对比结果表明降尺度LSTMODIS,500m图像更加精细刻画LSTMODIS,1km图像在空间上的分布格局;定量对比3种降尺度LSTMODIS,500mLSTETM,500m的RMSE分别为0.786、1.002,0.754℃,降尺度结果达到预期效果。

    Abstract:

    Land surface temperature (LST) plays a very important role in obtaining the thermal information of land surface. LST has been widely used to detect the agricultural drought, monitor evapotranspiration, and estimate net radiation, sensible and latent heat flux, surface urban heat island intensity, precipitable water, urban-induced surface moisture and surface runoff. However, due to technical constraints of remotely sensed LST data, there is a trade-off between spatial and temporal resolution: a high temporal resolution is associated with a low spatial resolution and vice versa. Improvement in the spatial resolution of LST image will be greatly important when the revisit time of satellite remains the same. To solve this disadvantage, the aims of this study include the following aspects: firstly, to improve the original low spatial resolution of the Moderate Resolution Imaging Spectroradiometer (MODIS) LST image data (1km) to 500m resolution by applying three relationships between NDVI and LST in TsHARP (An algorithm for sharpening thermal imagery) method; secondly, to assess the accuracy of each downscaling model based on qualitative and quantitative analysis with synchronous Enhanced Thematic Mapper (ETM) LST data; thirdly, to examine whether the TsHARP downscaling method is applicable and valid in special and particular land cover types in China. The northwest of Shandong province and south of Hebei province in China were selected as the research area. Then we utilized the TsHARP method to downscale original 1km LST image (taken on 9th, September 2004, provided by MODIS sensor) to 500m LST image, given that MODIS can offer very high temporal resolution image. In order to validate the simulated 500m LST image, we compared the simulated LSTMODIS,500m image with the synchronous 500m ETM LST image generated from 500m ETM band 6 radiance by Sobrino technique, and the 500m ETM band 6 radiance image was upscaled from the original 120m ETM band 6 radiance image. Qualitative comparison results show that LSTMODIS,500m images visually capture more spatial details than LSTMODIS,1km and resemble more that of LSTETM,500m. In the downscaled 500m MODIS LST image, boundaries between different land covers are highlighted. When compared to 500m ETM LST, statistical results indicate that the Mean Absolute Error (MAE) in 500m MODIS LST generated by the downscaling techniques ranged from 0.536℃ to 0.752℃. Quantitative comparisons of the three downscaled LSTMODIS,500m images and LSTETM,500m image show that Root Mean Square Error (RMSE) are 0.786℃, 1.002℃ and 0.754℃, respectively, with method 3 (i.e. vegetation fraction is linearly correlated to 4th power of LST) corresponding to both the lowest MAE (0.536℃) and RMSE (0.754℃). The variance (S2) of method 2 (i. e. vegetation fraction is linearly correlated to LST) is the highest, which shows that method 2 captures more spatial details of LSTETM,500m. Considering the mean values of different methods, the mean of method 2 is also the most consistent one to the mean of the LSTETM,500m. As for the LST accuracy, an RMSE of 0.754℃ or 1.002℃ is regarded as reasonable and acceptable, given the change in the spatial resolution of the MODIS LST and the potential sources of error due to different sensor properties. Above all, all of the three methods were found to substantially achieve good performance and produce 500m LST results with the high accuracy and improve the spatial pattern of the 1km MODIS LST. The downscaling techniques were proved effective and applicable in our study area.

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聂建亮,武建军,杨曦,刘明,张洁,周磊.基于地表温度-植被指数关系的地表温度降尺度方法研究.生态学报,2011,31(17):4961~4969

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