共查询到20条相似文献，搜索用时 31 毫秒
1.
卫星遥感大气订正的参数化模式及其模拟应用 总被引：2，自引：0，他引：2
发展了一个用于卫星大气订正的参数化模式,包括一个新的程辐射亮度模式和一个参数化的朗伯地表一大气辐射耦合引起的亮度增量模式.应用最小二乘法,程辐射亮度被参数化为大气总光学厚度、一次散射反照率、太阳天顶角、视天顶角、方位角、大气不对称因子的函数.应用这一参数化的亮度模式进行大气订正应用的数值模拟,即进行卫星遥感地表光谱反照率的模拟试验.数值检验结果表明对于865 nm,670nm,550nm和412nm 4个MODIS通道,在0°-70°的太阳天顶角、0°-60°视观测角以及0.05-0.8的地表反照率条件下,参数化的向上辐射亮度的标准差小于4%,由该参数化亮度模式引起的地表反照率解的标准差小于0.03. 相似文献
2.
一个植被双向反射模式的反演控制试验 总被引：1，自引：0，他引：1
利用地面遥感观测数据,对一个浑浊介质假定下的植被双向反射模式,增加了对太阳漫射辐射因素处理,在可见光波段上,进行了系列模式反演试验。这些试验有助于完善植被双向反射模式中物理过程的描述,了解模式反演过程的控制和选择合适遥感观测数据进行模式反演。分析试验结果发现：（１） 对 Ｌ Ａ Ｉ进行初值预估有利于获得较好的植被双向反射模式反演结果。（２） 加入植被对太阳漫射辐射的反射过程描述,可以使植被双向反射模式的反演结果更加合理。（３） 使用在太阳天顶角不太大（ ＜ ４５°） 和太阳方位角偏离１８０°不多（ ＜ ４５°） 观测条件下得到的遥感数据,可以使植被双向反射模式的反演结果较好。（４） 在３１°—６１°的太阳天顶角范围和１３６°—２５８°的太阳方位角范围内,多角度观测使太阳天顶角和方位角因素对 Ｌ Ａ Ｉ反演结果的影响不显著。（５） 当太阳漫射辐射的份额不大时,对 Ｌ Ａ Ｉ反演结果的影响不显著。如果只针对 Ｌ Ａ Ｉ,那么对反演植被双向反射模式所应用的地面遥感数据可以不进行大气校正处理,这样的结果虽然是从对地面遥感数据的处理中获得的,仍然对卫星遥感的观测时段选择和卫星遥感数据的选取和分析有一定的价值。 相似文献
3.
D. Barman V. K. Sehgal R. N. Sahoo S. Nagarajan 《Journal of the Indian Society of Remote Sensing》2010,38(1):35-44
The algorithms for deriving vegetation biophysical parameters rely on the understanding of bi-directional interaction of radiation
and its subsequent linkages with canopy radiative transfer models and their inversion. In this study, an attempt has been
made to define the geometry of sensor and source position to best relate plant biophysical parameters with bidirectional reflectance
of wheat varieties varying in canopy architecture and to validate the performance of PROSAIL (PROSPECT+SAIL) canopy radiative
transfer model. A field experiment was conducted with two wheat cultivars varying in canopy geometry and phenology. The bidirectional
measurements between 400nm–1100nm at 5nm interval were recorded every week at six view azimuth and four view zenith positions
using spectro-radiometer. Canopy biophysical parameters were recorded synchronous to bi-directional reflectance measurements.
The broadband reflectances were used to compute the NDVIs which were subsequently related to leaf area index and biomass.
Results showed that the bidirectional reflectance increased with increase in view zenith from 200 to 600 irrespective of the sensor azimuth. For a given view zenith, the reflectance was observed to be maximum at 1500 azimuth where the difference between the sun and sensor azimuth was least. For sun azimuth of 1600 and zenith of 520, the view geometry defined by 1500 azimuth and 500 zenith corresponded to hotspot position. The measured bidirectional NDVI had significant logarithmic relationship with LAI
and linear relationship with biomass for both the varieties of wheat and maximum correlation of NDVI with LAI and with biomass
was obtained at the hotspot position. The PROSAIL validation results showed that the model simulated well the overall shape
of spectra for all combination of view zenith and azimuth position for both wheat varieties with overall RMSE less than 5
per cent. The hotspot and dark spot positions were also well simulated and hence model performance may be suitable for deriving
wheat biophysical parameters using satellite derived reflectances. 相似文献
4.
HJ-1A CCD与TM数据及其估算草地LAI和鲜生物量效果比较分析 总被引：2，自引：1，他引：1
基于地面实测和PROSAIL模型模拟数据,研究了新型传感器HJ-1ACCD与TM数据一致性问题,分析了传感器天顶角和光谱相应函数差异的影响,对比两种传感器数据估算草地LAI和鲜生物量的效果,得出以下结论:(1)HJ-1ACCD和TM反射率数据的拟合系数R2在0.7322和0.9205左右,在反射率较小时,两种传感器数据一致性较好;随着反射率增大,HJ-1ACCD数值逐渐高于TM。总体而言,在可见光和近红外波段,两种传感器较为接近,其中红波段最接近。(2)两种传感器的NDVI数据一致性非常高,且受传感器天顶角和光谱响应函数影响作用较小(相对误差约为0.34%—0.53%),而反射率的相对差别在3.34%—9.54%。(3)传感器天顶角较光谱响应函数对反射率影响更大。(4)基于HJ-1ACCD反射率数据估算草地LAI和鲜生物量效果较好,其中以CCD2传感器估算效果最好。 相似文献
5.
Abstract Bidirectional reflectance characteristics of a wheat and a rice canopy were studied using radiometric measurements over the two canopies with an Exotech Radiometer Model 100AX. For both rice and wheat, the measurements exhibited significant variations in reflectance amplitude for varying viewing zenith angles and their values decreased from backward to forward scattering direction. Reflectance obtained its maximum value in the backscatter direction for the viewing angle that corresponds approximately to the solar zenith angle at the time of measurements. Canopy background condition (irrigated or non‐irrigated) was an important determining factor of canopy reflectance particularly in the near‐infrared region of the solar spectrum. Furthermore, bidirectional response characteristics of a vegetation canopy were influenced by the amount of vegetation cover. 相似文献
6.
G.F. Epema 《国际地球制图》2013,28(4):33-39
In an area in southern Tunisia diurnal trends of bare soil surfaces have been investigated. The study area comprises two main parts: the footslopes and the playas. The diurnal variation of the bidirectional reflectance factor (BRF) in nadir direction on the footslopes is dominated by the effect of roughness. Maximum BRF is found with small solar zenith angles due to decrease in shadow related to surface roughness. For Landsat overpass it implies that the normal ground reflectance for a bare surface on the footslopes at identical surface conditions is up to 10% lower in December (solar zenith angle 63 degrees) than in June (28 degrees). Band ratios on the footslopes hardly change with variation of zenith angle. The diurnal variation in the playas is dominated by moisture. Asymmetric daily curves, with the lowest reflectance in the morning have been found. Four phenomena are reported which can be held responsible for this effect. This daily effect of moisture is weather dependent and may obscure long time changes of TM signal. In band ratios even with TM band 7 the diurnal moisture change can hardly be detected. 相似文献
7.
Rahul Tripathi Rabi N. Sahoo Vinay K. Sehgal R. K. Tomar Debashish Chakraborty S. Nagarajan 《Journal of the Indian Society of Remote Sensing》2012,40(1):19-28
The current development of satellite technology particularly in the sensors like POLDER and MISR, has emphasized more on directional
reflectance measurements (i.e. spectral reflectance of the target measured from different view zenith and azimuth angles)
of the earth surface features mainly the vegetation for retrieval of biophysical parameters at regional scale using radiative
transfer models. This approach being physical process based and uses directional reflectance measurement has been found to
better and more reliable compared to the conventional statistical approach used till date and takes care of anisotropic nature
(i.e. reflectance from the target is different if measured from different view angles) of the target. Keeping this in view
a field experiment was conducted in mustard crop to evaluate the radiative transfer model for biophysical parameter retrieval
through its inversion with the objectives set as (i) to relate canopy biophysical parameters and geometry to its bidirectional
reflectance, (ii) to evaluate a canopy reflectance model to best represent the radiative transfer within the canopy for its
inversion and (iii) to retrieve crop biophysical parameters through inversion of the model. Two varieties of the mustard crop
(Brassica juncea L) were grown with two nitrogen treatments. The bidirectional reflectance data obtained at 5 nm interval
for a range of 400–1100 nm were integrated to IRS LISS–II sensor’s four band values using Newton Cotes Integration technique.
Biophysical parameters like leaf area index, leaf chlorophyll content, leaf length, plant height and average leaf inclination
angle, biomass etc were estimated synchronizing with the bi-directional reflectance measurements. Radiative transfer model PROSAIL model was
validated and its inversion was done to retrieve LAI and ALA. Look Up Table (LUT) of Bidirectional reflectance distribution
function (BRDF) was prepared simulating through PROSAIL model varying only LAI (0.2 interval from 1.2 to 5.4 ) and ALA (5°
interval from 40° to 55°) parameters and inversion was done using a merit function and numerical optimization technique given
by Press et al. (1986). The derived LAI and ALA values from inversion were well matched with observed one with RMSE 0.521
and 5.57, respectively. 相似文献
8.
Because of the pointing capability of the Hyperion/Earth Observing-One (EO-1) to improve the revisit time of the scene, temporal series of narrowband vegetation indices (VIs) can be generated to study the phenology of the Amazonian tropical forests. In this study, 10 selected narrowband VIs calculated from Hyperion nadir and off-nadir data and from different view directions (forward scattering and backscattering) were analyzed for their sensitivity to view-illumination effects along the dry season on the Seasonal Semi-deciduous Forest. Data analysis was also supported by PROSAIL modeling to simulate the spectral response of this forest type in both directions. Hyperion and PROSAIL results showed that the Enhanced Vegetation Index (EVI) and Photochemical Reflectance Index (PRI) were the two more anisotropic VIs, whereas the Normalized Difference Vegetation Index (NDVI), Structure Insensitive Pigment Index (SIPI) and the Vogelmann Red Edge Index (VOG) were comparatively less sensitive to view-illumination effects. When compared to the other VIs and because of the greater dependence on the near-infrared (NIR) reflectance, EVI showed a different spectral behavior. EVI increased from forward scattering to backscattering and with decreasing solar zenith angle (SZA) towards the end of the local dry season, due to reduction in shading and enhancement of the illumination effects. On the other hand, PRI was higher with increasing shading in the forward scattering direction, as deduced from the PROSAIL simulation. Results emphasized the importance of taking into account bidirectional effects when analyzing temporal series of VIs collected over tropical forests by imaging spectrometers with pointing capability or even by multispectral sensors with large field-of-view (FOV). 相似文献
9.
高分一号卫星(GF-1)WFV相机是中国新型高分辨率传感器,为了更好地进行定量应用,需完成高精度大气校正,但需要解决数量大,辅助数据不足等关键问题。针对WFV相机构建了快速大气校正模型,(1)采用交叉定标方法借助Landsat 8数据完成辐射定标;(2)从WFV相机的辅助数据出发,计算得到太阳天顶角、观测天顶角等辅助信息;(3)考虑不同海拔大气分子散射的不同,完成基于海拔数据的分子散射校正;(4)采用深蓝算法,从第一波段(蓝光)反演得到气溶胶信息;(5)计算每个像元的大气校正参数,进而获取地表反射率,完成大气校正。在此基础上,利用IDL语言建立相应的大气校正模块,以过境华北地区的3景WFV数据为例进行大气校正实验。结果表明,模型能够快速完成大气校正,并能较好的去除大气分子与气溶胶影响,较好地还原植被、裸土等典型地表类型的光谱反射曲线,校正后的NDVI更好地反映了各地物的特征。 相似文献
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11.
Rama Rao Nidamanuri Bernd Zbell 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):683-691
Recent developments in hyperspectral remote sensing technologies enable acquisition of image with high spectral resolution, which is typical to the laboratory or in situ reflectance measurements. There has been an increasing interest in the utilization of in situ reference reflectance spectra for rapid and repeated mapping of various surface features. Here we examined the prospect of classifying airborne hyperspectral image using field reflectance spectra as the training data for crop mapping. Canopy level field reflectance measurements of some important agricultural crops, i.e. alfalfa, winter barley, winter rape, winter rye, and winter wheat collected during four consecutive growing seasons are used for the classification of a HyMAP image acquired for a separate location by (1) mixture tuned matched filtering (MTMF), (2) spectral feature fitting (SFF), and (3) spectral angle mapper (SAM) methods. In order to answer a general research question “what is the prospect of using independent reference reflectance spectra for image classification”, while focussing on the crop classification, the results indicate distinct aspects. On the one hand, field reflectance spectra of winter rape and alfalfa demonstrate excellent crop discrimination and spectral matching with the image across the growing seasons. On the other hand, significant spectral confusion detected among the winter barley, winter rye, and winter wheat rule out the possibility of existence of a meaningful spectral matching between field reflectance spectra and image. While supporting the current notion of “non-existence of characteristic reflectance spectral signatures for vegetation”, results indicate that there exist some crops whose spectral signatures are similar to characteristic spectral signatures with possibility of using them in image classification. 相似文献
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A time series of leaf area index (LAI) of a managed birch forest in Germany (near Dresden) has been developed based on 16-day normalized difference vegetation index (NDVI) data from the Landsat ETM+ sensor at 30 m resolution. The Landsat ETM+ LAI was retrieved using a modified physical radiative transfer (RTM) model which establishes a relationship between LAI, fractional vegetation cover (fC), and given patterns of surface reflectance, view-illumination conditions and optical properties of vegetation. In situ measurements of photosynthetically active radiation (PAR) and vegetation structure parameters using hemispherical photography (HSP) served for calibration of model parameters, while data from litter collection at the study site provided the ground-based estimates of LAI for validation of modelling results. Influence of view-illumination conditions on optical properties of canopy was simulated by a view angle geometry model incorporating the solar zenith angle and the sensor viewing angle. Effects of intra-annual and inter-annual variability of structural properties of the canopy on the light extinction coefficient were simulated by implementing variability of the leaf inclination angle (LIA), which was confirmed in the study site. The results revealed good compatibility of the produced Landsat ETM+ LAI data set with the litter-estimated LAI. The results also showed high sensitivity of the LAI retrieval algorithm to variability of structural properties of the canopy: the implementation of LIA dynamics into the LAI retrieval algorithm significantly improved the model accuracy. 相似文献
15.
Pavel Propastin Stefan Erasmi 《International Journal of Applied Earth Observation and Geoinformation》2010
A time series of leaf area index (LAI) has been developed based on 16-day normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) at 250 m resolution (MOD250_LAI). The MOD250_LAI product uses a physical radiative transfer model which establishes a relationship between LAI, fraction of vegetation cover (FVC) and given patterns of surface reflectance, view-illumination conditions and optical properties of vegetation. In situ measurements of LAI and FVC made at 166 plots using hemispherical photography served for calibration of model parameters and validation of modelling results. Optical properties of vegetation cover, summarized by the light extinction coefficient, were computed at the local (pixel) level based on empirical models between ground-measured tree crown architecture at 85 sampling plots and spectral values in Landsat ETM+ bands. Influence of view-illumination conditions on optical properties of canopy was simulated by a view angle geometry model incorporating the solar zenith angle and the sensor viewing angle. The results revealed high compatibility of the produced MOD250_LAI data set with ground truth information and the 30 m resolution Landsat ETM+ LAI estimated using the similar algorithm. The produced MOD250_LAI was also compared with the global MODIS 1000-m LAI product (MOD15A2 LAI). Results show good consistency of the spatial distribution and temporal dynamics between the two LAI products. However, the results also showed that the annual LAI amplitude by the MOD15A2 product is significantly higher than by the MOD250_LAI. This higher amplitude is caused by a considerable underestimation of the tropical rainforest LAI by the MOD15A2 during the seasonal phases of low leaf production. 相似文献
16.
Desertification is a severe stage of land degradation, manifested by “desert-like” conditions in dryland areas. Climatic conditions together with geomorphologic processes help to mould desert-like soil surface features in arid zones. The identification of these soil features serves as a useful input for understanding the desertification process and land degradation as a whole. In the present study, imaging spectrometer data were used to detect and map desert-like surface features. Absorption feature parameters in the spectral region between 0.4 and 2.5 μm wavelengths were analysed and correlated with soil properties, such as soil colour, soil salinity, gypsum content, etc. Soil groupings were made based on their similarities and their spectral reflectance curves were studied. Distinct differences in the reflectance curves throughout the spectrum were exhibited between groups. Although the samples belonging to the same group shared common properties, the curves still showed differences within the same group.Characteristic reflectance curves of soil surface features were derived from spectral measurements both in the field and in the laboratory, and mean reflectance values derived from image pixels representing known features. Linear unmixing and spectral angle matching techniques were applied to assess their suitability in mapping surface features for land degradation studies. The study showed that linear unmixing provided more realistic results for mapping “desert-like” surface features than the spectral angle matching technique. 相似文献
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Biodiversity mapping in extensive tropical forest areas poses a major challenge for the interpretation of Landsat images, because floristically clearly distinct forest types may show little difference in reflectance. In such cases, the effects of the bidirectional reflection distribution function (BRDF) can be sufficiently strong to cause erroneous image interpretation and classification. Since the opening of the Landsat archive in 2008, several BRDF normalization methods for Landsat have been developed. The simplest of these consist of an empirical view angle normalization, whereas more complex approaches apply the semi-empirical Ross–Li BRDF model and the MODIS MCD43-series of products to normalize directional Landsat reflectance to standard view and solar angles. Here we quantify the effect of surface anisotropy on Landsat TM/ETM+ images over old-growth Amazonian forests, and evaluate five angular normalization approaches. Even for the narrow swath of the Landsat sensors, we observed directional effects in all spectral bands. Those normalization methods that are based on removing the surface reflectance gradient as observed in each image were adequate to normalize TM/ETM+ imagery to nadir viewing, but were less suitable for multitemporal analysis when the solar vector varied strongly among images. Approaches based on the MODIS BRDF model parameters successfully reduced directional effects in the visible bands, but removed only half of the systematic errors in the infrared bands. The best results were obtained when the semi-empirical BRDF model was calibrated using pairs of Landsat observation. This method produces a single set of BRDF parameters, which can then be used to operationally normalize Landsat TM/ETM+ imagery over Amazonian forests to nadir viewing and a standard solar configuration. 相似文献
19.
S. Pradhan K. K. Bandyopadhyay R. N. Sahoo V. K. Sehgal R. Singh V. K. Gupta D. K. Joshi 《Journal of the Indian Society of Remote Sensing》2014,42(4):711-718
Field experiment was conducted in a sandy loam soil of Indian Agricultural Research Institute, New Delhi during the year 2011–13 to see the effect of irrigation, mulch and nitrogen on canopy spectral reflectance indices and their use in predicting the grain and biomass yield of wheat. The canopy reflectances were measured using a hand held ASD FieldSpec Spectroradiometer at booting stage of wheat. Four spectral reflectance indices (SRIs) viz. RNDVI (Red Normalized Difference Vegetation Index), GNDVI (Green Normalized Difference Vegetation Index), SR (Simple Ratio) and WI (Water Index) were computed using the spectral reflectance data. Out of these four indices, RNDVI, GNDVI and SR were significantly and positively related with the grain and biomass yield of wheat whereas WI was significantly and negatively related with the grain and biomass yield of wheat. Calibration with the second year data showed that among the SRIs, WI could account for respectively, 85 % and 86 % variation in grain and biomass yield of wheat with least RMSE (395 kg ha?1 (15 %) for grain yield and 1609 kg ha?1 (20 %) for biomass yield) and highest d index (0.95 for grain yield and 0.91 for biomass yield). Therefore it can be concluded that WI measured at booting stage can be successfully used for prediction of grain and biomass yield of wheat. 相似文献
20.
ABSTRACTThe Moon, Earth’s only natural satellite, is a potential new platform for Earth observation. Moreover, with the wide applicability of the angular information from remote sensing data, it has been attracting increasingly more attention. Accordingly, this study focuses on the angular characteristics of Moon-based Earth observations. Using ephemeris DE430 and Earth orientation parameters, the position and attitude of the Sun, Earth, and Moon were obtained and their coordinates normalized to a single framework using coordinate transformations between the related reference systems. Then, an angular geometric model of Moon-based Earth observations was constructed, and the corresponding angular algorithms were presented. The results revealed the angular range and distribution characteristics of Moon-based Earth observations. For every point on the surface of the Earth, the view and solar zenith angles all vary widely, which decreases with increasing latitude. The view and solar zenith angles all vary widely with the largest range of values in the equatorial and polar regions and a smaller range of values in mid-latitudes. Furthermore, the range of solar angles of Moon-based Earth observations is the same as that of all-time solar angles, indicating the potential for monitoring and understanding large-scale geoscientific phenomena using Moon-based Earth observations. 相似文献