高分辨率静止轨道遥感卫星可见光及近红外波段邻近效应建模及分析

结合高分辨率静止轨道遥感卫星的特点,通过对已有研究方法的适当改进,给出了基于大气辐射传输机理的高分辨率静止轨道遥感卫星可见光及近红外波段的点扩散函数(Point-spread Function,PSF)模型,并进行邻近效应分析预研究.文中对邻近像元到目标像元距离、邻近像元范围(区域)、观测天顶角、气溶胶光学厚度及其散射相函数的非对称因子等因素对邻近效应的影响进行了系统地实验,并对各因素的影响机制进行了一定分析.结果显示,邻近像元对目标像元入瞳处辐亮度的贡献最高可达2.3％左右.故在对该类型遥感卫星进行大气影响分析、成像模拟、大气校正时考虑邻近效应是必要的.     

舰船目标光学特性模型构建

为了给舰船光学特性研究和可探测性研究提供理论基础。为了建立舰船目标光学特性模型。采用BRDF理论分析和计算中的微面元分析法,利用3D MAX软件将舰船表面划分为许多可计算三角形微面。在计算每个三角形微面的散射特性时,选用双向分布函数中适合计算的Cook-Torrance模型。并通过坐标转换将太阳-目标-探测器统一到面元坐标系下以及利用面元几何可见性进行消隐简化了计算量。在计算入瞳处的辐亮度时,分析了大气中分子、分子和气溶胶粒子对可见光散射的影响。最后得到了大气通过率与波长的计算公式。通过分析每个三角形微面在入瞳处的辐亮度,得到了入瞳辐亮度与波长的关系。最后建立了舰船目标光学特性模型,并通过仿真,计算了不同波长下的大气透过率以及入瞳处辐亮度。     

HJ-1B卫星热红外通道在轨绝对辐射定标

利用青海湖水面辐射校正场对HJ-1B卫星热红外通道进行绝对辐射定标,由CE312热红外辐射计测量水面辐亮度,结合辐射传输模型MODTRAN4.0计算大气透过率和上行程辐射,同时进行CE312通道与HJ-1B卫星热红外通道光谱匹配,计算传感器入瞳处等效辐亮度值。通过2010年8月1日和5日两组传感器入瞳等效辐亮度值和卫星通道计数值回归得到该卫星通道绝对定标系数,并使用内蒙达里湖水面辐射校正场2010年6月29日实测数据对定标结果进行检验。     

山地TM遥感影像大气辐射校正模型改进及地表反射率反演

基于光学遥感辐射传输理论,着重阐述了地形对天空散射光相互作用及邻近像元的影响,提出了一种改进的山地大气辐射校正模型及地表反射率反演方法;基于IDL编程实现模型算法,选择贵州黎平县丘陵森林覆盖典型研究区,结合Landsat-5TM和1∶50000DEM数据进行了实例验证、评价与分析。研究结果表明,本研究方法能够同时有效消除TM数据的大气与地形影响,提高地表反射率反演精度与数据质量,将进一步推动山地光学遥感数据的定量分析与应用。     

基于多个稳定目标的吉林一号光谱02卫星多光谱成像仪的在轨绝对辐射定标

卫星在轨后精准的绝对辐射定标是对其观测数据进行定量化应用的基础。与传统的场地定标法、交叉定标法相比，基于稳定场景目标的定标方法具有成本低、频次高、可实现历史数据定标等优点。使用中分辨率成像光谱仪（MODIS）的MCD19A1产品、MCD43A1产品和MOD03(MYD03)产品模拟出MODIS band8在光谱02卫星观测条件下的方向反射率，再结合MCD43A1产品中MODIS band1～band5的方向反射率、MCD19A2产品中的气溶胶参数、水汽参数以及MOD07(MYD07)产品中的臭氧参数，对2021年10月光谱02卫星多光谱成像仪对多个稳定目标成像的入瞳辐亮度进行辐射传输模拟，实现对其在轨绝对辐射定标。对该定标系数的真实性检验结果表明：与发射前定标系数相比，基于重新标定系数进行大气校正的结果与哨兵2号反射率产品的差异明显减小；重新标定的观测辐亮度与包头地基自动辐射定标数据的平均相对差异为3.18%，说明定标结果具有较高的精度。研究结果可以为使用稳定目标对中高空间分辨率光学遥感卫星在轨绝对辐射定标提供方法支撑。     

森林覆盖区山地遥感地形校正的方法研究

基于山地遥感地形校正方法中的STS朗伯体模型和SCS模型,结合TM影像,提出了一种新的森林地形校正方法.该方法引入一个植被覆盖率参数用来估计亚像元中的各成分对辐亮度的影响,同时考虑了像元与像元之间的邻边效应影响.通过与其他现有的一些模型进行实地验证与检验,说明该方法能在一定的程度上解决不同覆盖程度的森林地形校正问题.     

太湖水体GF-1/WFV影像的6S逐像元大气校正

水体光谱信息微弱,常用的基于辐射传输模型的大气校正方法在水体中校正精度较差。基于覆盖太湖水体的2016年4月29日的高分一号宽幅相机影像（GF-1/WFV）和同步的实测光谱数据,对6S辐射传输模型的输入参数进行敏感性分析,逐像元计算观测几何,使用分区气溶胶类型、分区暗像元和Spline插值确定的气溶胶光学厚度（Aerosol Optical Depth,AOD）进行6S逐像元大气校正。实验结果表明:气溶胶模式对6S大气校正结果的影响最大,与FLAASH方法相比,逐像元计算观测几何和气溶胶参数的校正方法对大气校正精度有改进作用,4个波段的平均相对误差分别降低了1.84%、7.78%、4.79%和17%。结合精确大气参数输入的6S逐像元大气校正方法可以改进水体表面遥感反射率的大气校正精度。     

海岸带高光谱遥感与近海高光谱成像仪(HICO)

应海岸带监测需求,高光谱成像仪开始在海岸带监测中发挥重要作用。搭载于国际空间站上的HICO(Hyperspectral Imager for the Coastal Ocean)是第一颗针对近岸海洋遥感的高光谱成像仪,其波谱范围为360～1 080 nm,光谱分辨率为5 nm。介绍了HICO数据的基本情况,并与在轨星载高光谱成像仪EO-1 Hyperion和HJ-1A HSI基本参数做了对比。同时针对高浑浊水体,以黄河三角洲近岸3种典型地物为例,结合FLAASH大气校正模型,提取了辐亮度和地表反射率,初步对比分析了HICO和HSI的光谱性能。结果表明HICO能更好地反映近岸地物的光谱特征。     

珠海一号欧比特高光谱数据交叉辐射定标初探

搭载于“珠海一号”卫星星座的欧比特高光谱OHS（Orbit Hyper Spectral）传感器,以较高的光谱分辨率和空间分辨率,在近岸及内陆湖泊水色遥感应用方面具有很大潜力。然而OHS缺乏星上定标系统,目前在轨定标采用陆地定标场的资料,其定标结果在水体等低反射率地物误差较大。因此提出一种基于传感器入瞳总辐亮度的交叉辐射定标法,该方法结合QAA（Quasi-Analytical Algorithm）准分析算法和6SV2.1辐射传输模型,利用GOCI（Geostationary Ocean Color Imager）多光谱数据对OHS高光谱数据进行交叉辐射定标。研究结果表明：①GOCI和OHS传感器获取的地物辐射相关性好,在可见光波段范围内,R²均高于0.84;②重新定标后的数据能明显改善不同传感器之间的辐射差异,在可见光波段范围内,定标误差小于9%。实验为高光谱传感器的辐射定标提供了一种新的方法,对建立高光谱定量化、业务化水色遥感处理系统,特别对OHS数据在水域的各种应用具有重要意义。     

高分五号高光谱图像自动大气校正方法

高分五号是我国高分辨率对地观测系统重大专项中唯一的高光谱卫星，为有效提高其应用的效能和质量，首先必须对其图像数据进行大气校正。文章提出了一种基于MODTRAN辐射传输模型的高分五号高光谱图像大气校正方法。首先，通过MODTRAN辐射传输模型构建能见度查找表、水汽含量查找表和反射率查找表；其次，分别采用Version 5.2法和大气预处理微分吸收法逐像元反演得到图像能见度和水汽含量；之后，根据反射率查找表逐像元完成高分五号高光谱图像的大气校正，并与FLAASH校正结果进行对比。结果表明，能见度和水汽含量反演效果较好，校正后的光谱曲线与经FLAASH校正的光谱曲线相吻合，3种定量化指标均保持在较高水平，且该方法能够实现高分五号高光谱图像的自动化批量化大气校正，大气校正过程无需其他额外参数，具有一定的应用价值。     

Estimating forest variables from top-of-atmosphere radiance satellite measurements using coupled radiative transfer models

Traditionally, it is necessary to pre-process remote sensing data to obtain top of canopy (TOC) reflectances before applying physically-based model inversion techniques to estimate forest variables. Corrections for atmospheric, adjacency, topography, and surface directional effects are applied sequentially and independently, accumulating errors into the TOC reflectance data, which are then further used in the inversion process. This paper presents a proof of concept for demonstrating the direct use of measured top-of-atmosphere (TOA) radiance data to estimate forest biophysical and biochemical variables, by using a coupled canopy-atmosphere radiative transfer model. Advantages of this approach are that no atmospheric correction is needed and that atmospheric, adjacency, topography, and surface directional effects can be directly and more accurately included in the forward modelling.In the case study, we applied both TOC and TOA approaches to three Norway spruce stands in Eastern Czech Republic. We used the SLC soil-leaf-canopy model and the MODTRAN4 atmosphere model. For the TOA approach, the physical coupling between canopy and atmosphere was performed using a generic method based on the 4-stream radiative transfer theory which enables full use of the directional reflectance components provided by SLC. The method uses three runs of the atmosphere model for Lambertian surfaces, and thus avoids running the atmosphere model for each new simulation. We used local sensitivity analysis and singular value decomposition to determine which variables could be estimated, namely: canopy cover, fraction of bark, needle chlorophyll, and dry matter content. TOC and TOA approaches resulted in different sets of estimates, but had comparable performance. The TOC approach, however, was at its best potential because of the flatness and homogeneity of the area. On the contrary, the capacities of the TOA approach would be better exploited in heterogeneous rugged areas. We conclude that, having similar performance, the TOA approach should be preferred in situations where minimizing the pre-processing is important, such as in data assimilation and multi-sensor studies.     

SIERRA: A new approach to atmospheric and topographic corrections for hyperspectral imagery

In mountainous areas, slope and altitude variations modulate the airborne sensed hyperspectral radiance image. A new algorithm, SIERRA, has been developed for atmospheric, relief and BRDF corrections in order to extract the surface reflectance in the form of bi-hemispherical albedo that does not depend on solar incidence and observation angles. The forward modeling efforts focus on the estimation of diffuse irradiance and upwelling diffuse radiance, and on the formulation of BRDF effects. The inversion scheme consists of four steps, that go deeper and deeper into the phenomena's complexity.To validate the model, reflectance images are assessed from radiance images simulated with different radiative transfer codes or forward models: MODTRAN4 in the case of homogeneous and flat ground, AMARTIS and SIERRA forward models for heterogeneous and mountainous cases. The surface reflectance is retrieved with a 5% relative error under standard acquisition conditions.SIERRA is applied to HyMap data acquired over the hilly landscape near Calanas, Spain. The hypercube reflectances are compared with those obtained using ATCOR4 and COCHISE. The benefit of relief correction is clearly demonstrated.     

Landsat8卫星影像大气校正及其植被指数与SEVI性能比较

遥感影像受大气的吸收散射以及地形起伏变化的影响,使得传感器接收到的辐射信号既包含了地物的信息,同时也包含了大气以及地形的信息。为了提高地表反射率的反演精度,需要去除遥感影像中大气和地形的影响。提出了一种基于查找表的Landsat8-OLI遥感影像的大气校正方法,该方法由6S辐射传输模型生成查找表,其中输入的参数包括大气水蒸汽含量、臭氧浓度和气溶胶光学厚度等MODIS大气参数产品。利用传统方法建立的大气参数查找表通常只考虑一部分因素,这对于以MODIS产品为输入参数的大气校正是不适用的。本文建立了一个包括大部分输入参数的高维大气校正查找表,对于Landsat-8 OLI传感器具有很高的通用性,通过进行光谱分析、与USGS地表反射率产品交叉验证等方式来验证模型的精度。验证结果表明该方法能有效地反演精确可靠的地表反射率。最后,采用目视解译、统计分析将校正结果与SEVI做对比分析,比较地形影响消减的效果。结果表明该模型与SEVI在地形消减的效果上作用相当。     

Evaluation of apparent surface reflectance estimation methodologies

The estimation of apparent surface reflectance values from imaging spectroscopy data requires a correction for the efTects of the intervening atmosphere. Four methods of estimating apparent surface reflectance have been evaluated, the empirical line method and three methods of radiative transfer modelling. To compare the results of these correction methodologies two high albedo targets, of identified composition, were selected. The empirical line method was found to be sensitive to errors in locating and spectral variations within the ground survey targets and also target height differences. The radiative transfer modelling techniques gave relatively similar results, reasonably close to the library spectra. This study indicates that radiative transfer modelling using only atmospheric information derived from the imaging spectroscopy data, while still not as sensitive as correction methods using additional ground and atmospheric information, can satisfactorily correct the atmospheric elfects involved in estimating apparent surface reflectance, allowing the identification of the major diagnostic absorption features.     

Simulation of hyperspectral and directional radiance images using coupled biophysical and atmospheric radiative transfer models

Future remote sensing satellite missions exploring the earth will feature advanced hyperspectral and directional optical imaging instruments. Given the complex nature of the data to be expected from these missions, a thorough preparation for them is essential and this can be accomplished by realistic simulation of the imagery data, years before the actual launch. Based on given spectral and directional capabilities of the instrument, and in combination with biophysical land surface properties obtained from existing imagery, the spectral and directional responses of several types of vegetation and bare soil have been simulated pixel by pixel using the radiative transfer models PROSPECT (for hyperspectral leaf reflectance and transmittance), GeoSAIL (for two-layer canopy bidirectional spectral reflectance), and MODTRAN4 (for atmospheric hyperspectral and directional effects). In this way, one obtains realistically simulated hyperspectral and directional top-of-atmosphere spectral radiance images, with all major effects included, such as heterogeneity of the landscape, non-Lambertian reflectance of the land surface, the atmospheric adjacency effect, and the limited spatial resolution of the instrument. The output of the image simulations can be used to demonstrate the capabilities of future earth observation missions. In addition, instrument specifications and image acquisition strategies might be optimized on the basis of simulated image analysis results, and new advanced data assimilation procedures could be validated with realistic inputs under controlled circumstances. This paper describes the applied methodology, the study area with the input images, the set-up of the actual image simulations, and discusses the final results obtained.     

Geo-atmospheric processing of airborne imaging spectrometry data. Part 2: Atmospheric/topographic correction

A method for the radiometric correction of wide field-of-view airborne imagery has been developed that accounts for the angular dependence of the path radiance and atmospheric transmittance functions to remove atmospheric and topographic effects. The first part of processing is the parametric geocoding of the scene to obtain a geocoded, orthorectified image and the view geometry (scan and azimuth angles) for each pixel as described in part 1 of this jointly submitted paper. The second part of the processing performs the combined atmospheric/ topographic correction. It uses a database of look-up tables of the atmospheric correction functions (path radiance, atmospheric transmittance, direct and diffuse solar flux) calculated with a radiative transfer code. Additionally, the terrain shape obtained from a digital elevation model is taken into account. The issues of the database size and accuracy requirements are critically discussed. The method supports all common types of imaging airborne optical instruments: panchromatic, multispectral and hyperspectral, including fore/aft tilt sensors covering the wavelength range 0.35-2.55 w m and 8-14 w m. The processor is designed and optimized for imaging spectrometer data. Examples of processing of hyperspectral imagery in flat and rugged terrain are presented. A comparison of ground reflectance measurements with surface reflectance spectra derived from airborne imagery demonstrates that an accuracy of 1-3% reflectance units can be achieved.     

Assessment of biases in MODIS surface reflectance due to Lambertian approximation

Using MODIS data and the AERONET-based Surface Reflectance Validation Network (ASRVN), this work studies errors of MODIS atmospheric correction caused by the Lambertian approximation. On one hand, this approximation greatly simplifies the radiative transfer model, reduces the size of the look-up tables, and makes operational algorithm faster. On the other hand, uncompensated atmospheric scattering caused by Lambertian model systematically biases the results. For example, for a typical bowl-shaped bidirectional reflectance distribution function (BRDF), the derived reflectance is underestimated at high solar or view zenith angles, where BRDF is high, and is overestimated at low zenith angles where BRDF is low. The magnitude of biases grows with the amount of scattering in the atmosphere, i.e., at shorter wavelengths and at higher aerosol concentration. The slope of regression of Lambertian surface reflectance vs. ASRVN bidirectional reflectance factor (BRF) is about 0.85 in the red and 0.6 in the green bands. This error propagates into the MODIS BRDF/albedo algorithm, slightly reducing the magnitude of overall reflectance and anisotropy of BRDF. This results in a small negative bias of spectral surface albedo. An assessment for the GSFC (Greenbelt, USA) validation site shows the albedo reduction by 0.004 in the near infrared, 0.005 in the red, and 0.008 in the green MODIS bands.     

An O2-A Band Atmospheric Correction Algorithm for Tower-based Platform based on Look-up Table

Tower-based spectral observation is an important connecting bridge between flux sites and satellite remote sensing data，and the effect of atmospheric absorption and scattering between horizontal surface and tower-based platform on the atmospheric absorption band such as O2-A is difficult to ignore.Firstly，the influence of atmospheric radiation transfer on the up-welling radiance and down-welling irradiance of the tower-based platform is analyzed，and the atmospheric correction method of based on upward and downward transmittance is established，that is，the influence of the upwelling radiance and down-welling irradiance is corrected by the direct transmittance and the total transmittance.Secondly，using the simulation data of MODTRAN model，the influence of AOD550 and radiative transfer path length on atmospheric transmittance is quantitatively analyzed，and the LUT of AOD550 is established based on the ratio of down-welling irradiance of near-infrared and red bands and solar zenith angle，as well as the upward and downward atmospheric transmittance LUT based on the AOD550 and the radiative transfer path length.Finally，using the canopy spectral data of different growth stages observed by the tower-based platform，the difference of the apparent reflectance between the inside and outside of the O₂-A band absorption line before and after atmospheric correction was analyzed.The results show that the atmospheric correction method based on LUT of AOD550 and radiative transfer path length proposed in this paper can better correct the influence of upwelling radiance and down-welling on the O₂-A absorption band of the tower-based platform，and provides important method support for applications such as SIF observation on the tower platform.     

Landsat8卫星影像大气校正及其植被指数与SEVI性能比较

遥感影像受大气的吸收散射以及地形起伏变化的影响，使得传感器接收到的辐射信号既包含了地物的信息，同时也包含了大气以及地形的信息。为了提高地表反射率的反演精度，需要去除遥感影像中大气和地形的影响。提出了一种基于查找表的Landsat8-OLI遥感影像的大气校正方法，该方法由6S辐射传输模型生成查找表，其中输入的参数包括大气水蒸汽含量、臭氧浓度和气溶胶光学厚度等MODIS大气参数产品。利用传统方法建立的大气参数查找表通常只考虑一部分因素，这对于以MODIS产品为输入参数的大气校正是不适用的。本文建立了一个包括大部分输入参数的高维大气校正查找表，对于Landsat-8 OLI传感器具有很高的通用性，通过进行光谱分析、与USGS地表反射率产品交叉验证等方式来验证模型的精度。验证结果表明该方法能有效地反演精确可靠的地表反射率。最后，采用目视解译、统计分析将校正结果与SEVI做对比分析，比较地形影响消减的效果。结果表明该模型与SEVI在地形消减的效果上作用相当。     

Parametrized BRDF for atmospheric and topographic correction and albedo estimation in Jiangxi rugged terrain,China

A method is presented for bi‐directional reflectance distribution function (BRDF) parametrization for topographic correction and surface reflectance estimation from Landsat Thematic Mapper (TM) over rugged terrain. Following this reflectance, albedo is calculated accurately. BRDF is parametrized using a land‐cover map and Landsat TM to build a BRDF factor to remove the variation of relative solar incident angle and relative sensor viewing angle per pixel. Based on the BRDF factor and radiative transfer model, solar direct radiance correction, sky diffuse radiance and adjacent terrain reflected radiance correction were introduced into the atmospheric‐topographic correction method. Solar direct radiance, sky diffuse radiance and adjacent terrain reflected radiance, as well as atmospheric transmittance and path radiance, are analysed in detail and calculated per pixel using a look‐up table (LUT) with a digital elevation model (DEM). The method is applied to Landsat TM imagery that covers a rugged area in Jiangxi province, China. Results show that atmospheric and topographic correction based on BRDF gives better surface reflectance compared with sole atmospheric correction and two other useful atmospheric‐topographic correction methods. Finally, surface albedo is calculated based on this topography‐corrected reflectance and shows a reasonable accuracy in albedo estimation.