MODIS卫星数据地表反照率反演的简化模式

以内蒙西部地区的MODIS遥感图像数据和地表野外同步观测的光谱数据为例,在野外数据量较少且有定标数据的条件下反演地表反照率。使用6S大气1辐射传输模型进行大气校正,并通过MODTRAN4.0模型获取各波段地表入射光通量和窄波段的地表反照率;在窄波段反照率与宽波段反照率之间存在线性关系的前提下,以各波段的入射光通量占总入射通量的比例作为反演参数,实现窄波段到宽波段的反演。反演结果证明此方法简便可行。     

FY-3C中分辨率成像光谱仪数据的窄波段地表反照率验证研究

地表反照率数据对地表能量平衡和全球变化研究具有重要意义。基于2014年FY-3C卫星250 m分辨率的反射率数据和角度数据,选取非洲及北美洲的4个区域作为研究区,采用RossThick-LiSparseR模型作为BRDF(Bidirectional Reflectance Distribution Function)核模型反演了地表窄波段反照率,得到250 m分辨率的4个窄波段黑空、白空反照率。将反演得到的FY-3C地表窄波反照率产品与MODIS反照率产品（MCD43A3）数据进行了交叉验证,结果表明：FY-3C窄波段反照率与对应MODIS窄波段反照率对比的均方根误差在0.01~0.04,平均偏差(MBIAS)为0.09,FY-3C窄波段反照率与对应的MODIS窄波段反照率在可见光波段、近红外波段有较好的一致性。本研究提升了国产风云极轨卫星的应用范围,可为FY-3C地表反照率业务化产品提供算法支撑。     

HJ-1A/B星地表反照率生成算法与检验

提出了适合环境与灾害监测预报小卫星-A、B星(简称HJ-1A/B星)CCD相机的大气订正算法,并基于不同地表特性和大气条件下的辐射传输模拟数据,建立HJ-1A/B星的窄波段向宽波段反照率转换的模型.利用多级灰阶靶标实测数据、敦煌检验场实测数据验证了大气订正算法以及转换模型的可靠性和精度,并将HJ-1A/B星影像数据计算的反照率产品与同时相的MODIS反照率产品进行对比分析.结果表明:文章提出的HJ-1A/B星CCD相机大气订正算法可有效校正大气影响;窄波段向宽波段反照率转换模型反演的反照率精度可靠;基于研究成果生成的HJ-1A/B星地表反照率与MODIS反照率产品一致性较好,满足后续遥感数据定量化模型研究的精度需要.     

HJ-1/CCD地表反照率估算及其与NDVI关系分析

参照TM地表反照率反演算法,建立了适用于HJ-1/CCD传感器估算地表反照率的算法。通过应用6S辐射传输模型建立查找表,对覆盖内蒙古自治区锡林浩特市的HJ-1/CCD数据进行大气校正,并根据反照率定义,回归分析得到可见光波段地表反照率;通过与地面实测数据进行对比分析,表明该算法估算得到的地表反照率精度较高,其最大相对误差为14.32%。同时,本文将估算结果与同时期NDVI进行拟合分析,得出地表反照率与NDVI存在较高的负相关关系。     

中国不同土地利用类型分光辐射地表反照率研究

选取2000～2015年遥感反演的地表反照率数据及2000和2015年两期土地利用数据,采用经典统计学方法分析不同土地利用类型分光辐射地表反照率的特征及其年际变化趋势。为了解土地利用类型的反照率特征、认知区域气候或陆面模式中能量模块的相关分光辐射变量的物理过程提供科学依据。结果表明:不同的土地利用类型具有差异明显的地表反照率特征,同种土地利用类型地表反照率的差异甚至超过了不同类别土地利用类型之间的差异,说明了地表反照率巨大的空间异质性;大部分土地利用类型在短波总辐射及分光辐射地表反照率满足:近红外短波可见光,说明短波地表反照率的上限值更大程度上取决于近红外波段的地表反照率;研究时段内,各土地利用类型在3个波段地表反照率分别呈现出了不同的变化趋势,但是大部分土地利用类型分光辐射地表反照率的年际变化速率较小,基本保持稳定。     

地表粗糙度的测量计算方法及其对微波辐射散射的影响分析

地表粗糙度反映了地表的微小起伏,是土壤水分微波遥感反演研究中重要的地表参数.以闪电河流域为研究区,首先利用针板法对不同地物下的地表粗糙度进行测量,然后对测量数据进行透视变换、数字化、倾斜校正及周期校正等一系列的处理,计算得到不同地表的粗糙度结果.研究表明:在使用针板法测量地表粗糙度时,为校正不同剖面测量姿态的影响需要进...     

基于IDL的遥感影像大气与地形校正方法实现

介绍了利用交互式数据语言（Interactive Data Language,IDL）开发TM/ETM遥感影像大气与地形校正模型的详细过程,以2000年4月30日密云ETM影像为例,对大气与地形校正方法的有效性和实用性进行了验证。结果表明,该方法有效地消除了大气与地形影响,提高了地表反射率等地表参数的反演精度和数据质量,为进一步开展定量遥感研究提供了数据质量保障。     

一种基于物理机理的高光谱遥感图像真彩色校正模型

针对高光谱遥感影像由于各波段光谱范围窄,难以获得符合人们视觉效果的真彩色合成影像问题,提出一种基于物理机理的高光谱遥感图像真彩色校正模型。该模型充分利用高光谱影像在红、绿、蓝反射区的所有谱段信息,通过插补波段并进行波段加权积分重建真彩色合成图像,进而结合实测地物反射率光谱,利用辐射传输模拟的方式,构建具备普适性的真彩色校正模型。利用航空高光谱遥感影像进行色彩校正实验的结果表明,所构建的真彩色校正模型能够很好地应用于高光谱遥感影像真彩色校正。     

面向遥感叶面积指数产品的地形校正研究

地形校正是提高复杂地形区地表参数遥感定量化反演精度的重要手段。当前广泛应用的遥感叶面积指数产品（Leaf Area Index, LAI）多具有一定的地形误差,减少地形影响、提升其产品精度有着非常重要的意义。以我国江西省千烟洲地区为研究区域,利用地面实测LAI数据、LandsatTM数据和高程数据等,基于高程标准差和GLOBMAP LAI产品值的关系,建立面向叶面积指数产品的地形校正模型,利用这一模型对GLOBMAP LAI产品进行地形校正。结果表明：校正后的LAI与地面实测数据更为接近,LAI产品与地面测量值的RMSE由2.11下降到2.04;校正后LAI产品的标准差由2.08下降至1.69,LAI产品的地形误差得到了较好的改正。该方法较好地完成了LAI产品的地形校正,进一步提高了产品精度,具有一定的实用价值。     

卫星遥感影像数据的地形影响校正

地形影响校正是遥感影像辐射校正的主要内容，是获得地表真实反射率的必不可少的一步。本文提出的方法中，将6S大气校正模型与数字高程模型（DEM）结合起来，计算出水平地面上接收到的直接辐射与漫射辐射，并采用一个简单公式将其转化到地形坡面上，从而实现了对地面的辐射能量校正，同时，6S模型对卫片还进行了大气改正，可输出卫片在大气层底部的辐射亮度与反射率；然后将基于坡面的反射率换算到其在水平面上的对应值，即实现了对反射率的地形影响校正。在我们所实施的“滇金丝猴保护项目”的植被研究中，应用本方法对梅里雪山区域的ETM＋影像进行了校正，大大减小了地形对遥感数据的附加影响。     

Simulated reflectance technique for ATM image enhancement

The thermal band of the Airborne Thematic Mapper (ATM) has the same spatial resolution as that of the reflective spectral bands and therefore can be used together with other bands without degrading the resolution as happens with Landsat TM. Here we show that the total solar irradiance on the land surface can be simulated by a properly weighted summation of the thermal band and all the reflective spectral bands. The simulated reflectance as well as emittance can then be derived from the relation between irradiance, thermal emittance, spectral reflectance and albedo based on a simplified energy conservation model of solar radiation incident on a land surface. Compared with other methods for spectral enhancement and topography suppression, such as ratio and logarithmic residual, this method has the advantage of conserving surface albedo information and thus produces a reasonable simulation of reflectance.     

基于混合光谱分解的兰州城市热岛与下垫面空间关系分析

利用Landsat ETM+数据,采用混合像元线性光谱分解方法提取的城市植被覆盖度与不透水面表征城市下垫面,通过单窗算法反演地表真实温度,对兰州市中心城区的夏季城市热岛强度与城市下垫面的空间分布关系进行相关分析。结果显示,利用中等分辨率ETM+影像对兰州中心城区不透水面和植被盖度分布提取,其成本较低,精度令人满意;兰州城区植被覆盖、不透水面与热岛强度的分布呈空间正自相关,地表温度的空间依赖性极强,与植被盖度和不透水面在空间方向上的相关性差异较大。     

An Albedo Downscaling Method based on Stratified Linear Regression

In recent years,remote sensing technology has been widely used in the field of surface energy,thermal environment,and climate research in small and medium-sized regions.The demand for high resolution,high precision albedo products has increased.In view of this,a physical-based downscaling method is proposed for efficiently and accurately generating high-resolution albedo results.First,under the Lambert hypothesis,the primary albedo of Landsat 8 could be obtained based on Landsat 8 reflectance at 30m resolution.On the 500 m scale,it is found that after classification,the primary albedo of Landsat 8 has a better correlation with the broad-band albedo of MODIS MCD43A3 product.Therefore,a linear regression function based on surface classification is established to integrate the high-resolution primary albedo of Landsat 8 with high-precision MCD43A3 albedo to obtain downscaled albedo.Compared to MODIS albedo,the downscaled albedo provided more rich details.Verification experience based on SURFRAD observation data shows that Bias of the albedo downscaling is 0.01,and standard deviation is 0.012,which has good adaptability for different surface categories.It shows that the algorithm has great application value for producing high-resolution albedo products.     

Examining the effectiveness of weighted spectral mixture analysis (WSMA) in urban environments

Spectral mixture analysis (SMA) has been widely applied for estimating fractional land-cover types from remote sensing pixels. SMA typically assumes each spectral band has equal contribution to the unmixing results, which has attracted debates on whether a different weight should be given to each band. Subsequently, a number of weighted SMA (WSMA) approaches have been developed and applied to different research fields. The necessity and applicability of WSMA, however, have not been adequately addressed, especially when applied to urban environments. This paper, therefore, aims to answer two research questions, including 1) whether significantly different results would be generated through applying a WSMA, and 2) which WSMA approach performs better in an urban environment. Specifically, five existing schemes: Shannon Entropy-weighted method (Entropy), reflected energy fixed-weighted vector (REFWV), InStability Index-based weighting method (ISIb), combined weighting vector (WV), and within-class variance (V_W), and five potential schemes: between-class variance (V_B), total-class variance (V_T), inversed Optimum Index Factor (IOIF), mean (Mean), and standard deviation (SD), were employed to construct WSMAs. We tested each weighting scheme 100 times with different endmember classes’ spectra. Performance of each WSMA was evaluated using the mean absolute error (MAE). Paired-samples t-test was applied to indicate if there is a significant difference between the mean of MAEs. Results illustrated that only REFWV, ISIb, and WV in All samples (samples included vegetation, high albedo impervious surface area, and low albedo impervious surface area) outperformed the unweighted scheme significantly. Other weighting schemes, such as IOIF, V_B, V_T, and SD illustrated unstable performance in different study areas. The rest of weighting schemes weakened the performance compared to the unweighted scheme. We concluded that REFWV, ISIb, and WV in All samples can be applied in analysing urban environments with three-endmember (vegetation – high albedo impervious surface area – low albedo impervious surface area) model to improve the performance of SMA. The construction of future weighting schemes would be better to consider the class variance.     

Study on Surface Albedo of Spectral Radiation of Different Land Use Types in China

The change of surface albedo directly affects the radiation balance and surface heat budget,but it is limited by the lack of temporal and spatial discontinuity of remote sensing inversion data,the analysis of surface albedo on large-scale areas still faces many uncertainties.Moreover,the current researchesalways focus on short-wave albedo and few studies on surface albedo involving the visible and near-infrared bands.Select surface albedo data of 2000~2015 remote sensing inversion and land use data for 2000 and 2015,the classical statistical method was used to analyze the characteristics of surface albedo of different land use types and their inter-annual variation trend.Provide a scientific basis for understanding the albedo characteristics of land use types,the physical processes of the relevant spectral splitting variables of energy modules in cognitive regional climates or land surface models.The results show that different land use types have different surface albedo characteristics,and the difference in surface albedo of the same land use type even exceeds the difference between different types of land use types,indicating the spatial heterogeneity of the surface albedo sexuality.Most land use types meet the surface albedo of short-wave total radiation and spectral radiation： near-infrared>short-wave>visible,indicating that the upper limit of short-wave surface albedo depends more on the surface albedo in the near-infrared.During the period,the albedo of each land use type showed different trends in the three bands,but the annual inter-annual rate of surface albedo of most land use types was relatively small and remained basically stable.     

基于ART模型的MODIS积雪反照率反演研究

积雪反照率是研究局地或全球的能量收支平衡和气候变化中的重要参数,遥感反演为积雪反照率的获取提供了便利的手段。积雪反照率大小主要取决于积雪的自身物理属性(雪粒径、形状和污染物等因子)以及天气状况,遥感反演反照率大多基于双向反射模型(BRDF),积雪BRDF模型常使用积雪辐射传输模型获得。采用考虑了雪粒径、粒子形状以及污染物影响的渐进辐射传输理论(ART)模型,建立了MODIS积雪反照率反演算法,得到了MODIS 8d合成积雪反照率产品。将此算法应用于具有均一积雪地表的格陵兰岛地区,并使用GC-Net实测数据进行了验证,反演的总均方根误差(RMSE)为0.018,相关系数(r)为0.83,结果表明考虑了积雪特性的ART模型能够较好地反演积雪反照率,而且反演需要的参数较少。     

Comparison of MODIS broadband albedo over an agricultural site with ground measurements and values derived from Earth observation data at a range of spatial scales

Land surface albedo is dependent on atmospheric state and hence is difficult to validate. Over the UK persistent cloud cover and land cover heterogeneity at moderate (km-scale) spatial resolution can also complicate comparison of field-measured albedo with that derived from instruments such as the Moderate Resolution Imaging Spectrometer (MODIS). A practical method of comparing moderate resolution satellite-derived albedo with ground-based measurements over an agricultural site in the UK is presented. Point measurements of albedo made on the ground are scaled up to the MODIS resolution (1 km) through reflectance data obtained at a range of spatial scales. The point measurements of albedo agreed in magnitude with MODIS values over the test site to within a few per cent, despite problems such as persistent cloud cover and the difficulties of comparing measurements made during different years. Albedo values derived from airborne and field-measured data were generally lower than the corresponding satellite-derived values. This is thought to be due to assumptions made regarding the ratio of direct to diffuse illumination used when calculating albedo from reflectance. Measurements of albedo calculated for specific times fitted closely to the trajectories of temporal albedo derived from both Systeme pour l'Observation de la Terre (SPOT) Vegetation (VGT) and MODIS instruments.     

Curved Mondrians: shading analysis of patterned objects1

Most shape-from-shading methods assume that surface reflectance is constant within large image regions. This assumption is violated in natural scenes with objects made from different materials. We present a more general method for recovering shape from shading, assuming that surfaces are smooth and albedo is piecewise constant, as would be the case if a Mondrian image was painted on a smooth curved surface. Our method is based on combining Brooks and Horn's method for shape recovery with the recovery of albedo using stochastic relaxation.     

基于地表参数真实性的GF-1和SPOT-7多光谱影像质量评价

目的 遥感影像中地表信息表达真实程度决定了影像信息提取和定量化应用水平,传统的从像素灰度和视觉特性角度的影像质量评价方法难以评价影像对地表信息表达能力,本文从地表反射率和NDVI（normalized difference vegetation index）两种地表参数真实性角度评价GF-1和SPOT-7多光谱影像质量。方法 提出了一种基于地表参数真实性的多光谱影像质量评价方法,完成GF-1和SPOT-7卫星对实验区同步成像,地面同步测量大气光学特性和典型地物样区光谱,获取同步观测数据并对多光谱影像进行辐射误差处理,计算地物样区在影像上的反射率和NDVI,通过与地面实测光谱数据比较分析了地表参数真实性,评价GF-1和SPOT-7多光谱影像质量。结果 人工靶标中GF-1影像在4个波段反射率误差均在5%内,精度优于SPOT-7;植被地物中SPOT-7影像在蓝绿红波段反射率误差在4%内,近红外波段误差在15%内,NDVI误差在16%内,反射率和NDVI精度均优于GF-1;硬地地物中GF-1影像在4个波段反射率误差在6%内,精度优于SPOT-7;评价结果表明SPOT-7多光谱影像对植被类地物光谱表达真实度更高,GF-1对硬地类地物光谱表达真实度更高。结论 提出的基于地表参数真实性的遥感影像质量评价方法,能够有效地从地物光谱信息表达精度的角度评价影像质量。