Short-wave aerosol radiative efficiency over the global oceans derived from satellite data

Using 5 yr (December 2000–November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency ( E_τ ) of aerosols during the morning Terra satellite overpass time over the global oceans (60°N–60°S). We calculate E_τ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes. Over the 5 yr, the global mean instantaneous E_τ between the methods is remarkably consistent and within 5 W m⁻²τ⁻¹ with a mean value of –70 W m⁻²τ⁻¹. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of <3 W m⁻²τ⁻¹. These differences are largely due to assumptions in aerosol models and definition of clear sky backgrounds. Independent assessments of aerosol radiative effects from different satellite sensors and methods are extremely valuable and should be used to verify numerical modelling simulations.     

A synergic algorithm for retrieval of aerosol optical depth over land

In this paper, a novel algorithm for aerosol optical depth(AOD) retrieval with a 1 km spatial resolution over land is presented using the Advanced Along Track Scanning Radiometer (AATSR) dual-view capability at 0.55, 0.66 and 0.87 μm, in combination with the Bi-directional Reflectance Distribution Function (BRDF) model, a product of the Moderate Resolution Imaging Spectroradiometer (MODIS). The BRDF characteristics of the land surface, i.e. prior input parameters for this algorithm, are computed by extracti...     

从NOAA卫星AVHRR资料反演中国区域地表反照率

由NOAA卫星AVHRR短波通道1、2反射率反演地表反照率需要3个反演模式,分别是窄-宽波段反射率转换模式、大气顶双向反射模式、大气订正模式.基于模式和国家卫星气象中心接收处理的NOAA-18 AVHRR1B数据,处理了2006年1月至2010年12月的中国区域地表反照率,由于云的影响,15天合成技术用来形成周期为15天的地表反照率数据文件.2006年、2010年2年的处理结果与MODIS同类产品对比,RMS为0.028～0.074、相关系数为0.76～0.93,误差较大出现在冬季,原因是两者15天合成方法不同;5年的日平均地表反照率与21个中国地面气象一级辐射站的观测测值作对比,结果是：RMS为0.053、相关系数为0.88.反演模式系统误差以及云和气溶胶影响是卫星反演地表反照率的主要误差来源.     

利用AVHRR数据反演陆地气溶胶光学厚度

开发AVHRR可见光通道反演陆地气溶胶光学厚度 (AOD) 的算法对于研究长时间序列AOD的变化有重要意义。AVHRR由于缺少2.1 μm通道而不能采用MODIS的暗背景算法,该文利用背景合成算法进行陆地AOD反演。背景合成算法是指假设一段时间内地表反射率变化不大且会出现相对清洁大气, 采用最小值合成即可得到地表反射率,再通过辐射传输模式6S制作的查算表查算得到AOD的反演结果。将此算法应用到2009年AVHRR中国部分陆地区域 (15°~45°N,75°~135°E) 得到AOD的时空分布,将反演结果与同期Aqua/MODIS的MOD04 AOD产品进行对比分析表明,华北和华东地区的反演效果较好,西北地区结果较差。以长江三角洲地区为例可知,AVHRR AOD产品与MODIS AOD产品以及AERONET观测的AOD相比相关系数基本在0.6以上,从时间变化规律来看,AVHRR AOD和MODIS AOD产品年变化趋势具有很好的一致性。该文为建立长时间序列AVHRR AOD数据集提供了一个较为可行的方法。     

Rainfall over oceans: Remote sensing from satellite microwave radiometers

Summary Microwave radiometer brightness temperature (T _b) measurements obtained from satellites over the oceans in dual polarization, at frequencies ranging from 6.6 to 85 GHz, reveal information about the rain and precipitation sized ice. These multifrequency measurements are composited from observations made by the Scanning Multichannel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I). TheT _b measurements at 37 GHz, having a field of view (fov) of about 30 km, show relatively strong emissions due to rain, reaching values as large as 260 K over the tropical and mid-latitude rainbelts. Only marginal effects due to scattering by ice above the rain clouds are revealed. At frequencies below 37 GHz, where the fov is much larger than 30 km and the extinction is weaker,T _b is significantly smaller than 260 K. Additional information content about rain, at these low frequencies, is not appreciable. On the other hand, at 85 GHz (fov 15 km), where the extinction is very strong, the sea surface below the clouds is often masked and scattering due to ice above the rain clouds is vividly noticed. However, these high frequency measurements do not yield direct information about rain below the clouds.Recognizing the above merits inherent in the 37 GHz observations the SMMR and SSM/I data at this frequency are utilized to develop and empirical method to retrieve rain rate over oceans. In this method it is assumed that over an oceanic area, the statistics of the observedT _b must be derivable from the statistics of the corresponding rain rates. Furthermore, the underestimation of rain rate, arising from the inability of the radiometer to respond sensitively to rain above a given threshold is empirically rectified with the help of two parameters that depend on the total water vapor content in the atmosphere. Rain rates deduced over the oceans around Japan using the SSM/I data, when compared with those measured by radars that are calibrated against rain gauges, show a good correlation; there is, however, a systematic overestimation. Seasonal mean maps of the rainfall over the global oceans based on SMMR data compare favorably with climatological rain maps over the Atlantic and Pacific Oceans developed by Dorman and Bourke (1979, 1981).With 16 Figures     

AVHRR分裂窗算法反演高山草甸地表温度精度评估

利用理塘县高山草甸地表温度实测数据,分析6种常用AVHRR分裂窗算法的精度,为青藏高原地区地表温度的卫星反演提供技术支持.结果表明：6种常用AVHRR分裂窗算法反演地表温度与实测值之间有很好的线性正相关关系,反演温度与实测温度最大偏差3.36K,最大平均绝对误差2.25k,最小平均绝对误差0.77K.给出了反演高山草甸地表温度的AVHRR分裂窗算法建议.     

An operational MODIS aerosol retrieval algorithm at high spatial resolution,and its application over a complex urban region

Aerosol retrieval algorithms for the MODerate Resolution Imaging Spectroradiometer (MODIS) have been developed to estimate aerosol and microphysical properties of the atmosphere, which help to address aerosol climatic issues at global scale. However, higher spatial resolution aerosol products for urban areas have not been well-researched mainly due to the difficulty of differentiating aerosols from bright surfaces in urban areas. Here, an aerosol retrieval algorithm using the MODIS 500-m resolution bands is described, to retrieve aerosol properties over Hong Kong and the Pearl River Delta region. The rationale of our technique is to first estimate the aerosol reflectances by decomposing the top-of-atmosphere reflectances from surface reflectances and Rayleigh path reflectances. For the determination of surface reflectances, a Minimum Reflectance Technique (MRT) is used, and MRT images are computed for different seasons. For conversion of aerosol reflectance to aerosol optical thickness (AOT), comprehensive Look Up Tables specific to the local region are constructed, which consider aerosol properties and sun-viewing geometry in the radiative transfer calculations. Four local aerosol types, namely coastal urban, polluted urban, dust, and heavy pollution, were derived using cluster analysis on 3 years of AERONET measurements in Hong Kong. The resulting 500 m AOT images were found to be highly correlated with ground measurements from the AERONET (r² = 0.767) and Microtops II sunphotometers (r² = 0.760) in Hong Kong. This study further demonstrates the application of the fine resolution AOT images for monitoring inter-urban and intra-urban aerosol distributions and the influence of trans-boundary flows. These applications include characterization of spatial patterns of AOT within the city, and detection of regional biomass burning sources.     

Retrievals of rain-rate over oceans from ssm/ i data using som model

1.IntroductionOverthepasttwentyyears,anumberoftheoreticalandexperimentalworkhasbeencarriedoutontheretrievalsofrain--ratefromthespace--bornemicrowaveradiometers.Inrecentyears,manyalgorithmshavebeendevelopedtoretrieverain--ratefromtheSSM/Idata(Barrettetal.,1994;Ebertetal.,1996;Ferraroetal.,1995andsoon).However,becauseofthecomplicatednonlinearrelationshipbetweenbrightnesstemperatures(BTs)andrain--ratewhichiscausedbyvariousphysicalprocesses,theretrievalresultsbystatisticallychasedalgorithmsare…     

利用NOAA-AVHRR遥感资料反演长江三角洲地表反照率的试验

利用NOAA－AVHRR的CH1和CH2资料，反演了长江三角洲地区地表反照率瞬时值，与前人给出的不同地面覆盖物反照率进行对比，表明对该地区的反演是可行的。还提出一种由单一时刻反照率推算一天中其他任意时刻反照率的方法，发现方法可靠。最后比较了太阳天顶角和地表状况对地表反照率的影响大小，发现二者量级相当，说明在短时、超短时数值模式中，必须同时考虑二者的作用。     

A new method for estimation of near surface specific humidity over global oceans

Summary A new methodology for deriving daily averages of near surface specific humidity (Q _a ) is developed. Remotely sensed parameters, total water vapor (W), boundary-layer water vapor (W _b ), and sea-surface temperature (SST) are used to derive Q _a . Genetic algorithm (GA) is used to find the empirical function relating the input (W, W _b , and SST) and output (Q _a ) parameters. The input data consist of 2 years (1999–2000) of daily W, W _b , from SSM/I (Special Sensor Microwave Imager), and SST data from AVHRR (Advanced Very High Resolution Radiometer). COADS (Comprehensive Ocean Atmospheric Data Set) observations of Q _a are used to develop and evaluate the new methodology. The performance of the algorithm is measured with COADS observations, which are not used in the development phase. The global mean rms error for daily averages Q _a is 1.5 ± 0.40 g/kg. Slightly higher discrepancies between Q _a derived from the new method and COADS observations are found over the Northwestern Pacific, North Atlantic oceans and Arabian Sea. This method improves upon the humidity retrieval of Liu (1986), Schulz et al (1993), and Chou et al (1997).     

基于FastICA算法和MODIS数据的水稻面积提取

以苏、皖、赣三省为研究区域,采用FastICA算法从MODIS数据中提取2010年水稻种植面积,并验证该算法在混合像元分解中的有效性。在对2010年46景8 d合成地表反射率产品数据进行预处理的基础上,结合MODIS土地利用产品和平滑滤波算法,构建耕地类型像元的I_LSW和I_NDV时相变化曲线。依据I_LSW和I_NDV曲线在水稻移栽期前后的变化规律,并根据由各地区水稻I_NDV时相曲线计算得到水稻相似性指数,从MODIS影像中提取水稻像元。采用FastICA算法对潜在水稻像元水稻生长期内的I_NDV时相曲线进行分解,计算每个像元的水稻丰度,绘制水稻丰度图,获取研究区各省水稻分布和种植面积。利用统计年鉴数据和样方资料对FastICA算法提取的水稻面积进行了验证。结果显示:采用水稻相似性曲线有利于提高稻田识别效率,所获取的水稻分布与实际情况吻合;FastICA算法能够分解不同地区水稻I_NDV时相曲线;与统计资料比较,江苏、安徽、江西三省水稻面积的提取精度分别为86.4%、87.9%、51.5%。江西水稻面积提取误差主要出现在地形起伏较大的山区。     

An analytical method for the determination of the roughness parameters over complex regions

The values of roughness length for momentum z ₀and zero-plane displacement d ₀over a hilly rough complex region with vegetation were evaluated without any assumption concerning z ₀and d ₀.It was found that for widely scattered profile data, the method of least squares will not give a reasonable result in determining the roughness parameters. For this purpose, the method of maximum correlation was introduced instead. This method gave a fair result for captive balloon observations conducted in hilly terrain mainly covered with forest in the northwestern part of the Kanto Plain, Japan.     

An aerosol climatology of Samoa

An atmospheric monitoring station is operated at Cape Matatula, American Samoa, by the Geophysical Monitoring for Climatic Change program under the National Oceanic and Atmospheric Administration. A nearly continuous record of condensation nucleus (CN) concentration and multiwavelength aerosol scattering extinction coefficient (_sp) is available from mid-1977 to the present. This report presents the 1977–1983 data. The long-term mean of CN concentration is 274 cm^-3 the long-term mean of _sp (550 nm) is 1.54×10^-5, and no significant long-term, annual, or diurnal trend is apparent in either data record.     

An algorithm for remote sensing of water color from space

The ocean color algorithm proposed in this paper takes into account the effects of Rayleigh and aerosol scattering. The inherent reflectance and the diffuse transmittance of the Rayleigh atmosphere are expressed as functions of optical thickness and satellite measurement geometry with the aid of simple and accurate formulas. In the case of a turbid atmosphere, from which the aerosol optical thickness is unknown, the aerosol contribution is estimated with the aid of a measurement in a channel where the ocean is a blackbody (in the red or near infrared). If the relationship between the ocean color and the chlorophyll-like pigment concentration is assumed to be known at sea level, it is shown that the chlorophyll-like pigment concentration at an open ocean site can be determined from space to within a factor of 1.5 to 3 (uncertainty equal to 0.2 to 0.5 log interval), depending on the atmospheric turbidity.     

中国及周边海域对流云团的水平和垂直尺度

利用2007年1月-2010年12月CloudSat-CALIPSO二级云产品2B-CLDCLASS-LIDAR,统计中国及其周边海域对流云的发生频率,根据对流云发生频率的分布特征将中国及周边海域划分为青藏高原（TP）、东部陆地（EC）、南部海域（SO）和西北太平洋（WP）4个子区域,并研究了4个子区域积云团和深对流云团的水平尺度和垂直尺度。统计结果表明,海洋积云团的水平尺度约为2 km,陆地积云团的水平尺度约为1 km,海洋下垫面热力性质均匀,积云团尺度更大;陆地下垫面非均匀性强,积云团分布更为零散。深对流云团的水平尺度为10-50 km,东部陆地最大,约为45 km,西北太平洋最小,约为30 km。陆地深对流云团水平尺度较海洋上大,且多尺度特征显著,应该与深对流云发生的复杂天气背景有关。积云团的垂直尺度范围为0.24-2 km,4个区域无明显差异。垂直尺度海洋深对流云团大于陆地云团,其中在南部海域地区最大,约为15 km,青藏高原最小,约为10 km。与陆地云团相比,海洋深对流云团表现为水平尺度更小、垂直尺度更大的中尺度对流体特征。      

Psychrometric apparatus for Bowen-ratio determination over forests

The psychrometric apparatus design for Bowen ratio determination reported previously by Sargeant and Tanner was modified and a new apparatus built. Modification of the intake design improved the symmetry and rigidity of the sensor mounting. Wet- and dry-bulb differences were measured with an error less than 0.01 °C over a vertical distance of 1 m. Continuous measurements of the Bowen ratio over a 7.8-m Douglas fir forest were made for 6 weeks. An example of the energy balance for the forest for one day using this equipment is reported.     

The simulation of aerosol transport over East Asia region

This study was carried out to understand the contribution of PM10 from China emission to Seoul Metropolitan Area (SMA) during high concentration period in January, 2007. The hourly PM10 concentration in Seoul Metropolitan Area had reached up to over 150 μg/m³ on 17th and 23rd of January in 2007. The aerosol transports from China along the Northwestern wind becomes the background concentrations in Korea and the assessment of the amount of contribution from China is very important in managing the air quality improvement plan in SMA.The U.S. EPA's Models-3/CMAQ (Community Multiscale Air Quality) was used to simulate PM10 concentration. The CMAQ performance was evaluated by comparing with the measurements in SMA for the episode period. The predictions were relatively in a good agreement with the measurements.The results show that the PM10 transport from China to Korea is significant and its contribution reaches up to 80% in the episode period. In order to assess more extensively the aerosol transport in East Asia region, the study to run the model in full year with speciated PM component measurements in super site is underway.     

中国西南地区气溶胶光学厚度的时空特征

采用MODIS卫星遥感产品研究西南地区气溶胶季节变化,并对成都和香格里拉两站2008年的太阳光度计观测资料进行分析。结果表明西南地区气溶胶光学厚度(AOD Aerosol Optical Depth)全年呈西低东高的地理分布特征,但东西部季节变化特征不同:西南地区东部AOD有春季最大,秋冬次之,夏季最小的演变特征,并且在四川盆地,黔、渝、湘交界和广西中部有三个明显的AOD高值区。西南地区西部AOD有春季最大,夏秋次之,冬季最小的演变特征,无明显高值区。太阳光度计资料分析表明,成都地区AOD日变化呈准双峰型,香格里拉AOD日变化呈上升趋势。