Satellite infrared remote sensing observation of surface circulation of the northeast South China Sea in winter

I~IOX \The investigation of physical oceanography in the South China Sea dates from early in the17th century and was carried out by scientists from many countries, including the United StateS,the United Kingdoms, Japan, .Russia and so on, but the survey area was rather limited at thattime and the data which were collected were still fragmentary. Since the 20th century, the investigation on the sleuth China Sea has made great progreSS not only in the scale of survey, but alsoin the depth …     

Satellite observation of Brazil Current inshore thermal front in the SW South Atlantic: Space/time variability and sea surface temperatures

A data set of 199 sea surface temperature maps derived from the Advanced Very High Resolution Radiometer for the period 2000–2002 was processed to derive the position of the surface inshore thermal front of the Brazil Current (BCIF) in the SE Brazilian coastal and oceanic area. After the derivation of the position of the BC front for each image, the ensemble of digital frontal vectors was processed using the algorithm of frontal density (FD). For each 5′×5′ cell in the domain the calculated FD provided an index expressing the presence and persistence of the front in the area or the probability of finding the front in the region. In the paper we present the results of the FD analysis to get a better view of the space and time variability of the BC front in the region. The highest values of FD were in general observed close to or at the shelf break zone (between 200 and 1000 m isobaths). From 20°S to 23°S there is a tendency of BCIF to be positioned over the outer shelf, inshore of the 200 m isobaths. SE of Cape Sao Tome and S of Cape Frio it was observed a bimodal spatial distribution of highest FD caused by the presence of two semi-permanent frontal eddies. After moving offshore near Cape Frio, the BCIF tends to return to the shelf break zone south of 24°S probably due to a potential vorticity conservation mechanism. The position of the highest FD values calculated for different seasons confirms previous studies in that BCIF is closer to the coast during the summer and furthest offshore in the winter. Statistical analysis of the SST data gave for the BCIF an average SST gradient of 0.31°C km⁻¹ with a standard deviation of 0.15°C km⁻¹. A mean frontal width of 6 km was inferred from the average SST gradient and typical temperatures near the front at both sides, at outer shelf and in the BC itself. A Weibull probability density function can be fitted to describe the BCIF SST gradients with scale factor c=0.3460°C km⁻¹ and shape factor k=2.1737. The BCIF SST gradient showed a seasonal variability with the smallest gradients in summer (~0.24 °C km⁻¹) and the highest in autumn (~0.33 °C km⁻¹). Using a three harmonic Fourier fit for the SST field near the BCIF, at the outer shelf and at interior of BC, it was possible to derive an analytical model for the time variability of the SST gradient of BCIF.     

M变换在NOAA/AVHRR数据变化检测中的应用

将基于典型相关分析的正交变换的基础理论用于NOAA/AVHRR数据的多元变化检测 ,对具体实施步骤进行了深入的探讨 ,并对部分中间结果进行了分析。实验表明 ,该方法应用于NOAA/AVHRR数据的多元变化检测具有明显的优势 ,克服了传统方法存在的缺陷 ,具有良好的应用前景。     

Mesoscale Satellite Bioclimatology

This paper examines the strength of relationships between the Normalized Difference Vegetation Index (NDVI) and climatic data, when examined at the mesoscale. Mean monthly AVHRR NDVI data for 1988‐1996 for the months of April through October for State of Kansas, its nine climatic divisions (CDs), and dominant land cover types within each CD were used. Corresponding climatic and water budget data were obtained or derived from National Climatic Data Center data. Temperature, precipitation, and NDVI deviations from normal were determined. Statistical analysis revealed significant relationships between NDVI and climatic variables, although strengths of the associations were modest. The highest correlation coefficient (r) for the state as a whole was 0.53, between NDVI and estimated actual evapotranspiration. When examined by climatic division or major land cover type, relationships between NDVI and a drought index were statistically significant in most cases and ranged from 0.30 to 0.56.     

2004年秋季江苏省干旱遥感监测研究

2004年秋季,江苏省绝大多数地区降水明显比常年偏少,丘陵及高岗地区受旱严重。为了直观获得全省干旱空间分布情况,采用“表观热惯量指数”方法,结合2004年11月8日NOAA/AVHRR资料反演的地表反照率和昼夜地表温度,生成了江苏省“表观热惯量指数”空间分布图,获取了全省干旱空间分布情况,并在2004年11月9—14日全省出现2—6 d的降水过程后,利用2004年11月18日卫星资料,及时分析了全省旱情缓解情况,取的了很好的监测结果。     

A modified Becker’s split-window approach for retrieving land surface temperature from AVHRR and VIRR

In order to provide a long time-series,high spatial resolution,and high accuracy dataset of land surface temperature(LST) for climatic change research,a modified Becker and Li’s split-window approach is proposed in this paper to retrieve LST from the measurements of Advanced Very High Resolution Radiometer(AVHRR) onboard National Oceanic and Atmospheric Administration(NOAA)-7 to-18 and the Visible and InfraRed Radiometer(VIRR) onboard FY-3A.For this purpose,the Moderate Resolution Transmittance Model(MODTRAN) 4.1 was first employed to compute the spectral radiance at the top of atmosphere(TOA) under a variety of surface and atmosphere conditions.Then,a temperature dataset consists of boundary temperature T s(which is one of the input parameters to MODTRAN),and channels 4 and 5 brightness temperatures(T 4 and T 5) were constructed.Note that channels 4 and 5 brightness temperatures were simulated from the MODTRAN output spectral radiance by convolving them with the spectral response functions(SRFs) of channels 4 and 5 of AVHRRs and VIRR.The coefficients of modified Becker and Li’s split-window approach for various AVHRRs and VIRR were subsequently regressed based on this temperature dataset using the least square method.As an example of validation,one AVHRR satellite image over Beijing acquired at 0312 UTC 27 April 2008 by AVHRR onboard NOAA-17 was selected to retrieve the LST image using the modified Becker and Li’s approach.The comparison between this LST image and that from the MODIS level-2 LST product provided by the University of Tokyo in Japan indicates that the correlation coefficient is 0.88,the bias is 0.6 K,and the root mean square deviation(RMSD) is 2.1 K.Furthermore,about 70% and 37% pixels in the LST difference image,which is the result of retrieved LST image from AVHRR minus the corresponding MODIS LST image,have the values within ± 2 and ± 1 K,respectively.     

卫星反演积雪信息的研究进展

综合分析了积雪信息反演的主要遥感信息源和提取方法。在光学遥感方面,应用较广的主要是改进型甚高分辨率扫描辐射仪（AVHRR）资料和中分辨率成像光谱仪（MODIS）资料;提取积雪信息大多是根据积雪在可见光波段的高反射率和近红外波段的低反射率,并通过建立回归模型反演积雪面积和深度。由于传感器的改进,MODIS卫星资料在空间分辨率、积雪反演算法等方面明显优于AVHRR资料。光学仪器受云层和大气的影响很大,由于云和积雪在可见光和近红外波段上都具有高反射率。并且由于云层的遮挡。云下的地表信息不能被光学遥感仪器所接收到。微波遥感方面,被动微波遥感仪如微波辐射计成像仪（SSM／I）、高级微波扫描辐射计（AMSR—E）等可以全天候穿过云层进行监测,具有光学仪器所没有的优势,并通过提取地表的亮温差,建立雪深反演模型得到积雪深度。被动微波传感器存在分辨率低。无法监测浅雪区信息等问题。另外影响地表微波亮温的因素很多,这些都在一定程度上影响了反演结果的精确度。主动微波遥感仪如合成孔径雷达、微波散射计等利用积雪与其它地物的后向散射系数的不同来识别积雪,但也同样存在分辨率低等问题。最后探讨了卫星反演积雪信息中仍然存在的问题和进一步发展的方向。     

用神经网络方法对NOAA-AVHRR资料进行云客观分类

利用NOAA AVHRR 5个通道资料建立了 6种云类以及陆地和水体的样本数据库 ,其中包括 8× 8象素样本和单象素样本。AVHRR的 5个探测通道都位于大气窗区 ,吸收物质少 ,比较透明 ,可以比较准确地反映探测表面的性质。理论分析和试验结果表明 :除了不同性质的云在 5个通道中有不同的表现外 ,通道之间的差别也可用于云分类。在理论分析和试验的基础上 ,对 8× 8象素样本库提取了包括光谱特征、灰度特征、通道差特征、灰度统计量和灰度直方图统计量特征在内的 80个特征 ,并利用逐步判别分析方法进行特征筛选 ,共选出 2 0个特征 ,用神经网络方法对 8种类型云和地表样本数据库分类 ,选择网络结构为 2 0 - 4 0 - 15 - 4的B P网络 ,利用 30 0 0多个样本进行神经网络训练 ,并用其余的 3万多个独立样本数据进行检验 ,测试正确率达 79%。类似地 ,对单象素样本数据 ,提取了包括光谱特征、灰度特征、通道差特征在内的 2 0个特征 ,用神经网络方法对 8种类型云和地表分类 ,选择网络结构为 2 0 - 4 0 - 15 - 4的 4层B P网络 ,利用 2 0 0 0多个样本进行神经网络训练 ,并用其余的 2万多个独立样本数据进行检验 ,测试正确率达 78%。设计并编写了实际云图客观云分类系统和软件 ,该系统输入为 5个通道的AVHRR数据 ,可自动获取已     

利用高程数据修正NOAA AVHRR轨道定位信息

在没有考虑高程数据的预处理方法得到的NOAA AVHRR资料中, 每条扫描线数据中的51点经纬度定位信息常常有误差, 尤其是在海拔较高、距卫星星下点较远的定位点, 其定位信息与实际差别很大。针对这种情况, 该文描述了一种引入高程数据并结合51点定位信息对2048个扫描点定位进行快速、简易的订正方法, 可有效地修正AVHRR资料预处理未考虑高程信息引起的经纬度定位偏差, 以便于对分辨率和定位精度要求不高的用户更好地使用AVHRR数据。     

西藏中部"一江两河"地区地表通量的卫星遥感估算

西藏中部一江两河地区(包括雅鲁藏布江中游和拉萨河、年楚河中下游地区)是西藏主要的农业区,藏中农业区地表特征参数(地表反照率、地表温度和植被指数)的变化和地表通量的遥感估算对农作物长势监测、农作物估产、灾害监测以及理解农业区内部乃至其与周边地区的能量水循环研究具有重要的意义.选取2003年4月14日和10月16日影像作为春季和秋季代表,利用两种相同空间分辨率的卫星资料———AVHRR和MODIS反演研究区地表特征参数和地表通量.在反演得到地表特征参数的基础上,结合研究区9个台站的地面气象观测资料,利用SEBS模式对该地区地表通量进行了遥感估算.结果表明,研究区地表能量平衡各分量具有明显的空间分布和时间变化特征.同一天中AVHRR和MODIS估算结果空间分布态势保持一致,但由于过境时间的差异,MODIS通量结果均大于AVHRR.