气溶胶光学厚度、类型及廓线对CO2反演的敏感性分析

位于1.6和2.06 μm附近的短波红外波段可用于探测低层大气CO²信息,然而除大气分子(主要是CO²)吸收外,大气分子散射、气溶胶和云散射也是限制这些波段的卫星测量信号的主要因素,因此气溶胶光学参数及其垂直分布也必然制约着GOSAT(Greenhouse Gases Observing Satellite)CO²的反演精度。利用正演模式DISORT分析气溶胶光学厚度(AOD)、类型以及廓线对CO²反演精度的敏感性,旨在提高CO²反演精度。结果表明:①不同类型气溶胶AOD增大对CO²柱总量的影响各不相同,且CO²柱总量变化量的变化趋势也不相同,这取决于气溶胶的散射相函数与单次散射反照率的大小;②气溶胶类型变化会导致CO²柱总量变化,且这种变化随着AOD增大而增大;③对于满足指数分布的沙尘气溶胶,标高的低估会导致反演的CO²柱总量偏大,而气溶胶的集中分布导致反演的CO²柱总量偏小,且气溶胶层越高,反演的CO²柱总量越小。     

利用MODIS资料反演杭州市500米分辨率气溶胶光学厚度

反演城市/区域范围内高空间分辨率的气溶胶光学厚度时,如果气溶胶类型选取的不合理造成的反演误差会很大,甚至超过地表反射率确定误差导致的反演误差。针对这一问题,本文提出了一种结合MODIS L1B资料和AERONET(Aerosol Robotic Network)的气溶胶光学厚度产品,基于6S大气辐射传输模型的计算,确定杭州市在2008年12月16日的气溶胶类型的方法。利用得到的气溶胶类型,结合改进的暗像元法,反演了杭州市500m空间分辨率的气溶胶光学厚度。将气溶胶光学厚度反演结果与采用标准气溶胶类型时的反演结果进行比较,结果表明,本文确定的气溶胶类型更符合杭州市当天的情况,应用到气溶胶光学厚度反演中,精度也最好,相对误差的绝对值在20%以内。     

利用GOME-2卫星数据反演对流层臭氧

基于GOME-2level 1B数据利用最优估计反演算法获得了GOME-2臭氧廓线产品,分析了GOME-2对流层臭氧反演产品的误差和信息量等特征,并对比验证了紫外光谱仪GOME-2与热红外光谱仪TES反演的对流层臭氧柱总量及其敏感性。结果表明:GOME-2对流层臭氧柱总量反演随机误差在10%以内;GOME-2相对TES的对流层臭氧柱总量偏小5%~20%;晴空下GOME-2对流层臭氧反演的敏感性随高度增加而上升,接近TES的敏感性垂直分布;在有云条件下,GOME-2和TES的云下部分信号都被屏蔽,在云顶之上GOME-2臭氧反演敏感性明显高于热红外仪器TES。     

利用MODIS资料计算不同云天条件下的地表太阳辐射

利用MODIS气溶胶和云产品卫星数据与大气辐射传输模式RSTAR,进行了晴空和有云条件下地表太阳辐射计算,并与香河综合辐射站的地基辐射测量值相比较。分析表明,晴空下二者相关性较好,相关系数平方R~2值为0.95,均方根误差RMSE为38.8 W/m~2。有云条件下,计算结果较差于晴空条件下,R~2值为0.88,RMSE为88.2 W/m~2。观测显示,香河站云—气溶胶共存现象较多,而MODIS仅按单一层的云进行微物理参数反演,导致模式输入参数误差,给地表太阳辐射计算结果引入误差。为了分析云-气溶胶共存状态对计算地表太阳辐射的影响,利用RSTAR计算了不同光学厚度的云和气溶胶在特定波段卫星观测的辐亮度值,并对于特定波段卫星接收的辐亮度值,用不同垂直结构的云和气溶胶分别反演其光学和微物理参数,再利用反演的结果分别计算相应的地表太阳辐射。结果表明:相对于单一云层的反演结果,云下气溶胶光学厚度(AOD)为0.1时,由反演误差所导致的地表太阳辐射估算误差较小;而随着AOD增加影响明显增大,在AOD为1.2时,相对误差达17.79%~18.38%。对于污染较重的华北地区而言,分析云覆盖下的气溶胶对地表太阳辐射的影响,有助于提高有云条件下地表太阳辐射的计算精度。     

星载NO_(2)探测发展及对流层柱浓度产品精度分析北大核心CSCD

NO_(2)作为大气中重要的痕量气体之一,是衡量大气污染状况的重要风向标。与传统地基观测相比,星载传感器能够提供大范围、长时间序列的观测资料,利用遥感卫星数据反演获取对流层NO_(2)浓度已成为近些年研究的热点之一。首先介绍了国内外星载紫外高光谱传感器的发展。然后从原理方面对国际上通用的对流层NO_(2)垂直柱浓度反演算法进行阐述。之后介绍了各官方对流层NO_(2)柱浓度产品的反演流程及产品精度,并比较了各产品DOAS算法的区别。可见,由于传感器所获取数据的时间、空间、光谱分辨率越来越高,NO_(2)柱浓度产品的反演模型及算法的选择更加合理,因此NO_(2)产品精度也更高。     

大气光谱光学厚度测量方法研究

为满足辐射校正场同步观测的需要,寻求一种能以简便的操作、较高的精度测量大气光谱光学厚度的观测方法是必要的。在合肥用地物光谱辐射计VF921-256和太阳辐射计DTF-1进行了为期几天的同步测量,经分析比较,发现VF921-256与DTF-1的测量结果之间存在1%~4%的相对偏差。这一偏差不但取决于光谱辐射计的测量误差,而且与太阳辐射计的标定误差也有一定关系。从VF921-256数据的Langley Plot拟合结果来看,其标准偏差小于0.03。因此,应用光谱辐射计测量大气光谱光学厚度的辐照度基法,可以用于辐射校正中对大气光谱光学厚度的同步测量。此外,我们利用光学厚度信息反演了气溶胶谱分布、臭氧和水汽的柱总量。     

基于HJ-1卫星数据反演长江三角洲地区气溶胶光学厚度

探索利用我国HJ-1卫星CCD数据,运用深蓝算法开展长江三角洲地区气溶胶光学厚度反演的可行性,并将结果与其他气溶胶光学厚度产品进行比较。针对HJ-1A和HJ-1B数据,反演结果分别与MODIS气溶胶光学厚度产品以及AERONET地基观测数据进行对比验证。结果表明:深蓝算法得到A星、B星的反演结果与MODIS气溶胶产品呈显著相关,但在数值上普遍高于MODIS产品;反演结果与AERONET站点数据之间的误差介于0.008~0.364之间,研究时段内站点数据缺乏,未对误差进行严格的统计分析。基于深蓝算法的HJ-1卫星数据反演结果虽然在数值上与MODIS气溶胶光学厚度产品存在系统性偏差,但在空间上能够较好地反映长江三角洲地区大气气溶胶分布状况,且具有空间分辨率高的优势。     

基于通用地球系统模式的不同类型气溶胶直接辐射效应的数值模拟

气溶胶可以通过直接效应来影响地气系统的辐射平衡,然而目前气溶胶直接辐射效应的研究主要集中于总气溶胶,缺乏不同类型气溶胶直接辐射效应研究。利用通用地球系统模式(Community Earth System Model, CESM)模拟研究了晴空和有云条件下总气溶胶、硫酸盐气溶胶和含碳气溶胶在大气层顶和地表的直接辐射强迫,并利用多源数据对模拟结果进行验证。结果表明,CESM模拟总气溶胶光学厚度与气溶胶自动观测网(Aerosol Robotic Network, AERONET)有较好的相关性(R2=0.44),但模拟数值整体偏小;与MERRA-2(Modern-EraRetrospective Analysis for Research and Applications Version 2)对比发现,高估了含碳气溶胶光学厚度,低估了硫酸盐气溶胶光学厚度;CESM模拟的辐射通量与基线地表辐射观测网(Baseline Surface Radiation Network, BSRN)的模拟效果良好(R2=0.93)。在晴空条件下,CESM模拟的总气溶胶以及硫酸盐气溶胶、含碳气溶胶在大气层顶的直接...     

卫星红外高光谱反演大气水汽含量

利用高光谱大气红外探测仪AIRS模拟及观测数据,发展基于主成分分析技术的多层前馈神经网络反演算法,进行大气中水汽柱总量(IWV)的反演计算、模拟及实测验证。首先,基于全球晴空大气廓线训练样本SeeBorV4.0,利用快速辐射传输模式CRTM进行了辐射传输模拟计算,得到全球高光谱分辨率模拟辐亮度;其次,利用主成分分析技术对模式模拟和AIRS实测高光谱数据进行降维、去噪及去相关处理,并采用多层前向神经网络算法反演大气水汽柱总量;最后,利用数值试验、AIRS实测L1B数据及其水汽产品,对反演算法进行了验证。通过与AIRS官方大气产品的统计分析,本算法反演均方根误差为0.387 g/cm²,最大偏差为0.82 g/cm²,空间分辨率保留了AIRS像素原分辨率(比AIRS官方大气产品高3倍)。     

基于静止卫星GOCI数据的陆地上空气溶胶光学厚度遥感反演

以长江三角洲地区为研究区,基于2013年共72d的晴空GOCI数据,利用深蓝算法进行了研究区上空气溶胶光学厚度的遥感反演研究,并利用两个实测站点数据进行了验证。结果表明:GOCI数据可以用于陆地气溶胶的反演,两个站点均呈现较高的拟合精度,南京信息工程大学北辰楼站拟合度为0.659,AERONET太湖站拟合度为0.747,与MODIS气溶胶产品相比也表现出很好的一致性。同时,研究发现基于静止卫星GOCI数据的气溶胶产品具有监测气溶胶日内变化的能力,为气溶胶的动态扩散和气候效应研究等提供参考和借鉴。     

Seasonal variation of columnar aerosol optical properties over Athens, Greece, based on MODIS data

A long-term (2000–2005) data set of aerosol optical properties obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode particles (FM) are employed to evaluate the inter-annual and seasonal variability of the aerosol properties over Athens. Based on AOD₅₅₀ and FM values three specific aerosol types are discriminated corresponding to different aerosol load and optical properties. The aerosol types considered correspond to urban/industrial aerosols, coarse-mode particles and clean maritime conditions. This study focuses on the seasonal and year-to-year fluctuation of the number of occurrences as well as the AOD₅₅₀ and FM values of each aerosol type. The coarse-mode particles are observed mainly in the summer, while spring is the most favorable season for the occurrence of urban/industrial aerosols. On the other hand, clean maritime conditions occur mainly in the winter. The AOD₅₅₀ values for the coarse-mode particles are higher in spring, while the urban/industrial and clean maritime aerosols exhibit slightly higher values in the summer. The seasonal distribution of the aerosol properties is related to anthropogenic and dust emissions in the spring/summer period, but is modified by atmospheric dispersion and precipitation in late autumn/winter. The main conclusion of the study is that the coarse-mode particles exhibit much stronger inter-annual and seasonal variability compared to the urban/industrial aerosols. Finally, three cases corresponding to each aerosol type are analyzed with the aid of synoptic weather maps, air mass trajectories and MODIS data.     

Remote sensing of mineral dust over land with MSG infrared channels: A new Bitemporal Mineral Dust Index

A new Bitemporal Mineral Dust Index (BMDI) is derived from Meteosat Second Generation (MSG) infrared observations over land at two different time slots per day.This daily dust index is evaluated with AErosol RObotic NETwork (AERONET) surface observations, MODerate resolution Imaging Spectro-radiometer (MODIS) “Deep Blue” Aerosol Optical Depth (AOD) and Ozone Monitoring Instrument (OMI) Aerosol Index, showing a good capability of the BMDI for dust detection and dust load estimation over land and also over deserts. BMDI dust detection is shown to be limited in scenes with high atmospheric humidity as e.g. coastal regions. In particular the insensitivity of BMDI to biomass burning aerosol is shown, leading to the possibility of remote sensing of mineral dust also in regions with large contributions of biomass burning aerosol to the total column aerosol concentrations. Time series of mineral dust as inferred from BMDI for the year 2006 are presented for four regions over the Sahara. These time series show strong (and different) annual cycles of dust load for all four regions. Especially the strong episodic character of atmospheric dust in the main source regions can be inferred from BMDI observations.     

Evaluation of PARASOL aerosol retrieval over North East Asia

The third POLDER (POLarization and Directionality of the Earth Reflectance) instrument, PARASOL (Polarization & Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) was launched in December 2004 and started its operational life at the early beginning of March 2005. This study is devoted to the regional validation of PARASOL aerosol retrieval scheme over land surfaces against independent automatic sun-photometers located in the northeast part of China at the Beijing and Xianghe sites both included in AERONET (Aerosol Robotic Network). PARASOL Level 2 Aerosol Optical Thickness (AOT) is shown, thanks to the high quality sun-photometer dataset, to be quite consistent with the AERONET AOT of the fine fractional part of the size distribution (radius ≤ 0.3 μm). In other words, PARASOL retrieval over land is mainly sensitive to the anthropogenic aerosols which are known for influencing the climate, environment as well as human health. Moreover, analysis of polarization in the 490 nm band (Level 1 data) shows the possibility of dust type aerosol identification thus yielding to a potential algorithm improvement in the future.     

边界层气溶胶垂直分布阶梯遥感

利用地面接收的太阳直射能量光谱可以提取整层大气气溶胶粒度谱分布信息。本文把这种思想予以延伸,在不同高度测量太阳直射光谱,则可以获得各高度层区间气溶胶粒度谱分布结构。文中以北京气象塔为试验场,利用地面实测资料,结合数值实验,指出了这种阶梯遥感方法在边界层气溶胶垂直廓线探测中的应用前景,并分析讨论了观测精度和垂直分辨率间的关系。     

Remote sensing of aerosols optical thickness over various sites using SeaWiFS or VEGETATION and ground measurements

A key problem in aerosol retrieval is to distinguish between surface and atmospheric contributions to the variability in the satellite signal. A major contribution in the surface-related variability is caused by the non-Lambertian nature of the Earth surface reflectance and the fact that the illumination/observation geometry varies considerably between successive observations of the same area (with a polar orbiting sensor). In principle, if the surface boundary condition can be specified with sufficient accuracy by means of a bidirectional reflectance distribution function (BRDF), the two contributions can be unfolded and aerosol information retrieved. This approach has been tested using combined datasets made of satellite measured “top of atmosphere” (TOA) radiance and corresponding ground estimation of the aerosol optical thickness. Studying a time series of data, taking into account geometrical conditions and assuming the ground BRDF to be constant during the time period, a coupled surface/atmosphere model was used to investigate the retrieval of aerosol optical thickness (AOT) over several sites. By fitting a subset of satellite observations associated with ground photometer data, a best fit of BRDF model parameters could be determined. This surface characterization is then used to reduce the model unknowns to AOT only and thereby to permit its retrieval from the satellite data alone, by means of a simple inversion process. The study was conducted on three European AERONET sites and using satellite data from both the VEGETATION and Sea viewing Wide Field of view (SeaWiFS) sensors. In all cases, the AOT retrieved from satellite was in good agreement with the measurements.     

An evaluation of satellite aerosol products against sunphotometer measurements

Because atmospheric aerosols scatter sunlight back to space, reflectance measurements from spaceborne radiometers can be used to estimate the aerosol load and its optical properties. Several aerosol products have been generated in a systematic way, and are available for further studies. In this paper, we evaluate the accuracy of such aerosol products derived from the measurements of POLDER, MODIS, MERIS, SEVIRI and CALIOP, through a statistical comparison with Aerosol Optical Depth (AOD) measurements from the AERONET sunphotometer network. Although this method is commonly used, this study is, to our knowledge, among the most extensive of its type since it compares the performance of the products from 5 different sensors using up to five years of data for each of them at global scale. The choice of these satellite aerosol datasets was based on their availability at the ICARE Data and Service Centre (www.icare.univ-lille1.fr).We distinguish between retrievals over land and ocean and between estimates of total and fine mode AOD. Over the oceans, POLDER and MODIS retrievals are of similar quality, with RMS difference lower than 0.1 and a correlation with AERONET of around 0.9. The POLDER estimates suffer from a small positive bias for clean atmospheres, which weakens its statistics. The other aerosol products are of lesser quality, although the SEVIRI products may be of interest for some applications that require a high temporal resolution. The MERIS product shows a very high bias. Over land, only the MODIS product offers a reliable estimate of the total AOD. On the other hand, the polarization-based retrieval using POLDER data allows a better fine mode estimate than that from MODIS. These results suggest the need for a product combining POLDER and MODIS products over land.The paper also analyses how the statistics change with the spatial and temporal thresholds that are used. Spatio-temporal averaging improves the statistics only slightly, which indicates that random errors are not dominant in the error budget. The paper includes various statistical indicators at global scale, and detailed results at individual ground stations can be obtained on request from the authors.     

Research Review of Remote Sensing for Atmospheric Aerosol Retrieval

Air aerosol pollution has become increasingly serious and become the focus of atmospheric research with the development of urban industrialization.Remote sensing technology is widely used in atmospheric research as a means of scientific,rapid and large-scale monitoring.The main content of remote sensing for atmospheric aerosol retrieval including Aerosol Optical Depth (AOD) of aerosol,aerosol concentration aerosol particle size distribution and air pollution are analyzed based on the atmospheric radiation transmission theory.Main progress around of the world in areas of atmospheric aerosol research by remote sensing techniques are introduced,especially the advantages and disadvantages of the different aerosol retrieval algorithms.At last,some existing problems and the trend of remote sensing for atmospheric aerosol retrieval are discussed.     

Algorithm for retrieval of aerosol optical properties over the ocean from the Geostationary Ocean Color Imager

An aerosol retrieval algorithm for the first Geostationary Ocean Color Imager (GOCI) to be launched in March 2010 onboard the Communication, Ocean, and Meteorological Satellite (COMS) is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF), and aerosol type in 500 m × 500 m resolution. All the products are retrieved over clear water which is defined by surface reflectance ratio between 640 nm and 860 nm (SRR) less or equal to 2.5, while only AOD is retrieved over turbid water (SRR > 2.5) due to high surface reflectance. To develop optimized algorithm for the target area of GOCI, optical properties of aerosol are analyzed from extensive observation of AERONET sunphotometers to generate lookup table. Surface reflectance of turbid water is determined from 30-day composite of Rayleigh- and gas corrected reflectance. By applying the present algorithm to MODIS top-of-the atmosphere reflectance, three different aerosol cases dominated by anthropogenic aerosol contains black carbon (BC), dust, and non-absorbing aerosol are analyzed to test the algorithm. The algorithm retrieves AOD, and size information together with aerosol type which are consistent with results inferred by RGB image in a qualitative way. The comparison of the retrieved AOD with those of MODIS collection 5 and AERONET sunphotometer observations shows reliable results. Especially, the application of turbid water algorithm significantly increases the accuracy in retrieving AOD at Anmyon station. The sensitivity study between MODIS and GOCI instruments in terms of relative sensitivity and scattering angle shows promising applicability of the present algorithm to future GOCI measurements.     

Exploration of the potential for using Spark-I observations to derive atmospheric parameters

As part of a low-cost nanosatellite constellation, Spark-I, a hyperspectral resolution instrument with 149 channels covering blue to near-infrared, has been successfully launched on 22 December 2016. In this study, we try to explore its potential to derive atmospheric parameters according to optimal estimation theory. From simulated measurements, we estimated the information content described as degrees of freedom for signal (DFS) and error reduction of typical aerosols, including dust, soot, sea salt, and sulphate, as well as water vapour (H₂O), nitrogen dioxide (NO₂), surface pressure, and Sun-induced fluorescence (SIF). Based on the results, only the H₂O column, aerosol optical depth (AOD), and surface albedo could be derived with error reduction of 20%, 40%, and near 100%, respectively. The retrieval of aerosol was strongly correlated with surface albedo, especially dust, with a DFS of 0.3–0.9 due to surface variations. After investigating the impact of the oxygen and H₂O absorption bands on the aerosol information content, we recommend retrieving aerosol characteristics using full channels, rather than sub-band channels. The more fraction one type of aerosol is, the larger information about it we can get. Different AOD results in 0.3–0.8 aerosol DFS change and solar zenith angle influences less. The information of atmospheric gases was sensitive to both signal-to-noise ratio (SNR) and spectral resolution due to their particular absorption patterns. However, improving only the SNR by double or more could allow for the derivation of SIF emissions, assuming the a priori estimation is accurate.