【作者】 项海兵；

【导师】 刘劲松；

【作者基本信息】 河北师范大学 ， 地图学与地理信息系统， 2011， 硕士

【摘要】 基于DVBS(Digital Video Broadcast by Satellite)系统转发的MODIS 1B影像,依托ENVI/IDL软件,集成了一套MODIS 1B数据的预处理技术流程,提出了合成晴空影像的新思路。详细论述了条带去除、几何校正、大气校正、标准晴空影像合成4个技术环节,为利用MODIS影像开展景观尺度土地覆被变化研究奠定了技术支撑体系。研究表明,MODIS 1B影像存在横向和纵向条带,横向条带可分为单行条带、宽条带和多行条带3种类型。尽管包括:频率域去噪法、空间域去噪法和统计量调整法等多种去除条带方法,但由于MODIS影像有36个波段,单独使用某种方法,都不能得到较为理想的条带去除效果。基于均衡化曲线补偿技术,提出了一种快速检测和去除条带的算法,给出了条带检测判定参数,即:如果A帧和B帧的10组传感器校正系数Ci值分别位于0的两侧,且ABS(Ci)>0.008,则存在宽条带;如果10组传感器的校正系数MAX(Ci)>0.05时,则存在单行条带。去除宽条带时,需以当前列为首列,从其后连续的100列影像中提取各传感器相对当前列的校正系数。试验表明,条带检测模型能有效识别单行条带和宽条带,多行条带需目视识别,单行条带和宽条带去除效果明显好于NASA网站公布数据,多行条带虽未彻底去除,但处理后的影像质量得到明显改善。基于ENVI/IDL软件,总结了一套针对HDF格式的MODIS 1B影像的几何校正和大气校正的技术处理方案。采用ENVI中的Georeference MODIS进行去“双眼皮”(bow-tie)和几何校正;采用FLAASH模块对几何校正的短波辐射亮度波段进行大气校正,用热红外大气校正模块(Thermal Atm Correction)对几何校正的长波发射率波段进行大气校正。预处理后的影像质量明显提高,为MODIS产品的反演计算创造了有利条件。研究表明,影像预处理流程应根据不同产品的反演算法来定。一般来讲,几何校正后的数据可用于反演大气产品,大气校正后的影像可用于开发陆地和海洋产品。在反演陆地和海洋产品时,如果指标或算法具有减小大气影响的特性,也可直接使用几何校正后的影像数据作为这些模型和算法的输入数据。将一七波段比值法合成的影像与NASA公布的8日合成的MOD09GA数据比较,得出一七波段比值法适用于提取晴空陆地像元的结论;将最大饱和度法合成的影像与NASA公布的8日合成的MOD09GA数据比较,得出最大饱和度合成法适用于水体像元的结论。结合一七波段比值法和最大饱和度法,将陆地表面B1/B7最小的像元定为晴空像元;将水体表面饱和度最大的像元定为晴空像元,提出适合华北地区的晴空影像合成方法。基于地表反射率影像合成晴空影像的过程中,逐像元建立了标准晴空的时间索引,生成了HC_time影像,以HC_time为合成影像索引,拓展合成了表观反射率、辐射亮度、发射率、地表发射率等系列晴空影像。利用本方法,面向不同时间跨度的数据集,可合成候晴空影像、旬晴空影像、月晴空影像。晴空合成算法改善了京津冀地区土地覆被变化时空演化规律研究的数据基础。更多还原

【Abstract】 Based on the MODIS 1B images transponded by the DVBS (Digital Video Broadcast by Satellite) system, relying on the ENVI / IDL software, integrate MODIS 1B image pre-processing technique flow, propose a new idea for clear sky image synthesis. Pre-processing includes three main components of destriping, geometric correction and atmospheric correction. In destriping, improve equalization curve compensation, obtain good results.There are two kinds of stripes in MODIS 1B images transponded by DVBS(Digital Video Broadcast by Satellite)system: horizontal and vertical stripes, and horizontal stripes have three types: single stripes, wide stripes and multi-line stripes. The destriping methods mainly include the frequency domain method, the spatial domain method and the statistic adjustment method. MODIS sensor has 36 spectral bands, using only one destriping method can not reach desired effect. Based on compensation and elimination of equalization curve method, this article proposes a new set of algorithm on rapidly detecting and removing stripes. Given a definite stripe detection judgment parameter,namely: the correction factor Ci of 10 groups of sensors,if the value Ci of A-frame and B-frame are separated by 0, moreover ABS (Ci)> 0.008, then there exists wide stripes; if the maximum of correction factor Ci ’ is greater than 0.05, then there exists single stripes. In the wide destriping model, the current column correction factor of each sensor can be extracted from the data that the current column as the first column to continuous 100 columns of image. The experimental results show that: the striping detection model can effectively identify the single stripes and the wide stripes, multi-line stripes need visual identification .The removal effect of single and wide stripes is better than NASA website’s data, although multi-line stripes are not completely removed, image quality is significantly improved after the treatment.Based on ENVI software, this article summarizes a set of pre-processing process for MODIS 1B image, including three main components of destriping, geometric correction and atmospheric correction. In this paper, Use Georeference MODIS module in ENVI to wipe off bow-tie and do geometric correction; Use FLAASH module to do atmospheric correction for VNIR radiation intensity bands that after geometric correction, use thermal infrared atmospheric correction module (Thermal Atm Correction) to do atmospheric correction for thermal infrared band emissivity that after geometric correction. Image quality is markedly improved after the pre-processing , advantage for retrieving the MODIS products. Image pre-processing procedures should be based on retrieval a?lgorithm of different products , in general, the data after geometric correction can be used to retrieve atmospheric products, image after atmospheric correction can be used to develop the land and ocean products. When retrieve the land and ocean products, if the indicator or algorithm has the characteristic that can reduce the atmosphere impact, then can directly use image data after geometric correction.Compared the images composed by b1/b7 ration method with MOD09GA released by NASA,the conclusion can be leaded to that this method is good at the land part clear image composition; by contrast, the max saturation method was sutible for the water part. Combined these two methods, the special method was proposed,which regarded the land piexl of the minimum value of b1/b7 in a certain days as the clear piexl;considered the water piexl of the maximum value of saturation as the clear piexl of the water. According to the index image, producted during the compound progress of the land surface reflectance, named as HC_time, the compound clear images of Apparent reflectance, radiance, emitivity or land suface emitivity could be producted. As the time span change, the 5 days clear image,10 days clear image and month clear image could be produced. This algrithm of compound clear image improved the data basis for the research of land-use spatio-temporal evolution rule around Beijing ,Tianjin and Hebei province.更多还原