IOCAS-IR  > 海洋环流与波动重点实验室
泡沫覆盖海面微波辐射机理研究
刘淑波
学位类型博士
导师魏恩泊
2015-05-10
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理海洋
关键词海面泡沫层 微波辐射率 辐射亮温 海表面盐度 微波遥感
摘要海表微波辐射亮温和散射系数是海洋表层物理和几何参量的函数,海洋被动微波遥感主要依据测量的海面辐射亮温对海面物理参量进行反演,如海表温度、盐度、风速等。主动遥感采用海面微波后向散射系数与海面几何参数的关系,反演海面几何参数,如:波高、波面斜率、风速等。 然而,在高风速情况,由海浪破碎在海面产生的泡沫层能够改变海面的介电性质和海面的几何结构,进而影响其散射和辐射特性。本论文主要通过理论和实验研究海洋泡沫层的海面亮温增益机理,目的是在理论和经验模式中消除白冠的亮温影响,获得高精度的海面参数反演模式。 论文利用有效介质近似理论,将泡沫层视为是由带海水壳层结构的球形空气粒子随机分布于空气基质中构成的一层均匀介质。对该种复合介质,我们发展Rayleigh方法,解决了计算泡沫(含涂层)结构复合介质有效介电常数的问题,该方法充分考虑了高浓度随机分布杂质粒子的电场相互作用对复合物有效物性的影响。为方便计算,还利用帕德近似方法获得了1.4GHz泡沫层有效介电常数的简易求解公式,进一步获得了泡沫-海水双层介质波近似微波辐射率理论模式。通过瑞利方法计算结果与辐射率实验测量数据的比较,发现两者在低微波频率下能够取得很好的一致。该现象符合有效介质理论条件,即微波波长大于杂质颗粒尺度。 为了更好地探讨泡沫层微波辐射机理,论文对C波段及低温L波段泡沫覆盖海面的微波辐射率进行了实验研究。利用测量的泡沫覆盖海面亮温,经过分析得到了受泡沫参数影响的微波辐射率资料和辐射率增益结果。结合该观测辐射率资料和代价函数方法,确定了泡沫层微波辐射率理论模式,并且利用其讨论了泡沫各参量对辐射率的影响。实验和理论结果表明:泡沫辐射率对空气体积分数和泡沫层厚度敏感性较大,远大于对温盐的敏感性。通过L和C波段的微波辐射率增益结果,还估算了泡沫层引起的盐度和温度反演误差。在风速为10 m/s时,海面白冠覆盖约为1%,在较低海面温度(1.5 ),大约引起盐度误差(45入射角)0.7-1.0 psu,当海面温度在19 左右,盐度误差约为0.6 psu;常温下,泡沫层对温度反演的影响大约为3 。因此,在海表参量遥感反演研究中泡沫层的影响是今后考虑的重要因素。 论文在L波段主被动盐度遥感模式仿真研究中,利用模拟资料(模式值+高斯噪音)代替观测资料的方法,分析了遥感仪器设备精度、海表温盐、风速、风向以及入射角等因素对海表盐度和风速反演结果的影响。统计结果表明:1)盐度和风速反演误差随入射角的增大而减小;2)顺风(180 )和逆风(0 )情况的反演精度强于侧风(90 ,270 )情况;3)高温、高盐、低风速下,盐度反演误差较小;4)风速反演误差受风速影响很大,风速越大,反演误差越大;5)若要实现0.2psu的盐度反演精度,在月平均尺度上,需要设备亮温和散射系数高斯噪音标准差低于0.2K和0.1dB,而在季平均尺度上,需要亮温和散射系数噪音标准差低于0.3K和0.2dB。 实际上,真实海洋在高风速下其海表状态复杂多变,物理参量间相互制约,除了海表泡沫层的影响,海表粗糙度、表层流及海气温差等都可以改变海面的介电性质和辐射特性,这些要素对遥感探测的复杂影响需要结合实验或遥感数据进一步深入讨论。
其他摘要Generally, the sea surface microwave brightness temperature and scattering coefficient are the functions of sea surface physical and geometric parameters. The measurement principle for ocean passive remote sensing is based on the response of sea surface brightness temperature to sea surface physical parameters, such as sea surface temperature (SST), salinity (SSS) and wind speed. The active remote sensing measurements utilize the relationship of sea surface backscattering coefficient and sea surface geometric parameters to retrieve these parameters, such as significant wave height, the slope of wave surface and wind speed. However, the sea foam produced by waves breaking under high wind speed can change the dielectric and geometric properties of sea surface, and then influence scattering and emission characteristics of sea surface. This paper investigates the mechanism of sea surface brightness temperature increments induced by sea foam with theory and experiments, aiming to eliminate the brightness temperature influence of foam (whitecap) on theoretical and empirical models, and obtain the sea surface parameters retrieval models with high accuracy. With the effective medium approximation (EMA) theory, the foam layer is regarded as an isotropic dielectric medium, in which spherical air bubbles coated with sea water shell distributes randomly in the air background medium. Subsequently, the Rayleigh method, which exactly considers the influence of interactions between dense particles, is developed to calculate the effective dielectric constant of this kind of composite medium. Furthermore, in order to calculate conveniencely, a simple formula for foam effective dielectric constant at 1.4GHz is derived with Pade approximation method and Rayleigh results. Through the comparison of computed results with Rayleigh method and experimental measured emissivity, we find that the agreement is better at lower frequency. This phenomenon owes to the EMA theory which requires microwave wavelength larger than particle size. To investigate the microwave radiation mechanism of foam layer, we perform emissivity experiments at C-band and L-band (low SST) with a completely foam-covered surface. The data of microwave emissivity and emissivity increments are derived from the measured brightness temperature of foam-covered sea surface. Based on these measured data and cost function method, a microwave emissivity model of foam layer is determined to analyze the influence of foam parameters on microwave emissivity. Experimental and theoretical results indicate that the effects of air volume fraction and foam thickness on foam emissivity are stronger than those of SSS and SST. Besides, we estimate the SSS and SST retrieval error induced by foam layer with measured emissivity increments. When wind speed is 10.0 m/s, the foam coverage fraction on the sea surface is about 1% , the SSS retrieval errors (incidence angle 45 ) for SST= 1.5 and 19 are about 0.7-1.0 psu and 0.6 psu, respectively; the induced SST retrieval error is about 3 for SST =22 . The effect of foam layer on emissivity should be considered on retrieving sea surface parameters. Besides, with the method of simulated data (model results+Gaussian noise) replacing measured data, L band passive and active SSS retrieving model is simulated to analyze the influence of equipment accuracy, SST, SSS, wind field and incidence angle on retrieval results of salinity and wind speed. Statistical results show that: 1) Salinity and wind speed retrieval errors decrease with the increase of incidence angle; 2) The retrieval accuracy at downwind (180 ) and upwind (0 ) is higher than that at crosswind (90 , 270 ); 3) Salinity retrieval error is smaller for high SST, SSS and low wind speed; 4) Wind speed retrieval error is strongly affected by wind speed, the higher the speed is, the bigger the retrieval error will be; 5) the equipment noise standard deviation of brightness temperature and scattering coefficient need be less than 0.2K and 0.1db for monthly average, and less than 0.3K and 0.1dB for quarterly average, so that the salinity retrieval accuracy reaches to 0.2psu. Actually, the real sea surface state is complex and fast-changing under high wind speeds, and the physical parameters of sea surface have interactions. Except foam layer, there are many factors can change dielectric properties and emission characteristics of sea surface, such as surface roughness, surface current and sea-air temperature difference. These complicated influences on remote sensing measurements need to be further studied by combining experiments and remote sensing data.
学科领域海洋环流与波动
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/22733
专题海洋环流与波动重点实验室
作者单位1.中国科学院海洋研究所
2.中国科学院大学
推荐引用方式
GB/T 7714
刘淑波. 泡沫覆盖海面微波辐射机理研究[D]. 北京. 中国科学院大学,2015.
条目包含的文件
文件名称/大小 文献类型 版本类型 开放类型 使用许可
毕业论文—刘淑波(终稿).pdf(6726KB)学位论文 限制开放ODC PDDL浏览
个性服务
推荐该条目
保存到收藏夹
查看访问统计
导出为Endnote文件
谷歌学术
谷歌学术中相似的文章
[刘淑波]的文章
百度学术
百度学术中相似的文章
[刘淑波]的文章
必应学术
必应学术中相似的文章
[刘淑波]的文章
相关权益政策
暂无数据
收藏/分享
文件名: 毕业论文—刘淑波(终稿).pdf
格式: Adobe PDF
所有评论 (0)
暂无评论
 

除非特别说明,本系统中所有内容都受版权保护,并保留所有权利。