| 用MODIS反演北京城市地区地表反照率精度以及算法改进 |
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| 引用本文： | 王开存,王建凯,王普才,等.用MODIS反演北京城市地区地表反照率精度以及算法改进[J].大气科学,2008,32(1):67-74. |
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| 作者姓名： | 王开存 王建凯 王普才 等 |
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| 作者单位： | 中国科学院大气物理研究所中层大气与全球环境探测开放实验室,北京, 100029 |
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| 基金项目： | 国家自然科学基金资助项目40520120071、40675017，中国科学院海外杰出青年学者基金项目2003-2-9，遥感科学国家重点实验室开放基金SK050012 |
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| 摘 要： | MODIS(MODerate-resolution Imaging Spectroradiometer)地表反照率的精度在乡村地区已经得到了检验，但是至今没有在城市地区的有关研究。地表反照率的精度在很大程度上取决于大气订正的精度，作者利用2002年以来的北京AERONET(国际气溶胶检测网络)站点Cimel气溶胶观测资料对反射率进行大气订正，通过对比来评价MODIS地表反照率算法中大气订正的精度。结果发现，MODIS大气订正在蓝光波段具有明显的过度订正现象，MODIS大气订正后地表反射率平均偏低0.03。MODIS地表反照率在冬季有约75%的缺测，这是因为冬季严重的空气污染使得MODIS云检测得到晴空观测较少。MODIS使用三参数双向反射率函数（BRDF）要求16天以内至少有3次以上的晴空观测（MODIS算法中要求7次）。通过分析MODIS反演得到的三参数，发现虽然它们的绝对值具有明显的季节变化，但是它们的比值是十分稳定的，这样使BRDF函数降低到只需要一个参数，有效降低了对晴空观测次数的要求，这一思想可以应用到热带等晴空日数较少的地区。
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| 关 键 词： | 地表反照率 城市地区 气溶胶 双向反射率函数 北京 |
| 文章编号： | 1006-9895（2008）01-0067-08 |
| 收稿时间： | 2006-07-17 |
| 修稿时间： | 2006-11-27 |
The Accuracy of MODIS Albedo over Beijing Urban Area and Its Algorithm Improvement |
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| WANG Kai-Cun,WANG Jian-Kai,WANG Pu-Cai and et al.The Accuracy of MODIS Albedo over Beijing Urban Area and Its Algorithm Improvement[J].Chinese Journal of Atmospheric Sciences,2008,32(1):67-74. |
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| Authors: | WANG Kai-Cun WANG Jian-Kai WANG Pu-Cai and |
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| Abstract: | Although many studies on rural areas have been published,there is no validation of Moderate Resolution Imaging Spectroradiometer(MODIS) albedo over urban areas available.The accuracy of albedo retrievals depends on the atmospheric correction.This paper evaluates the accuracy of MODIS atmospheric correction by comparing with the atmospheric correction using Beijing Aerosol Robotic Network(AERONET) Cimel aerosol and water vapor measurements.The results show that the reflectance in MODIS blue band is over-corrected and MODIS surface blue reflectance is 0.03 less than that corrected by AERONET Cimel aerosol information.The heavy aerosol loading makes less clear sky in winter,which results in 75% albedo retrievals missed in winter.MODIS surface albedo retrieval uses three-parameter semiempirical Bidirectional Reflectance Distribution Function(BRDF),which means that at least three clear-day measurements during the 16-day period are needed to perform the retrieval.It is found that the ratios of the three parameters are stable throughout a year though their absolute values demonstrate distinctively seasonal variation.Based on this result,the authors propose to use one parameter BRDF to retrieve albedo when the number of clear-sky measurement days is less than 3 during the 16-day period.This method can be used in the area where clear sky measurements are small. |
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| Keywords: | albedo urban area aerosol BRDF Beijing |
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