Study of crop growth parameters using Airborne Imaging Spectrometer data

High-spectral-resolution data of the Airborne Imaging Spectrometer (AIS) developed by the Indian Space Research Organisation were analysed to check their potential for extraction of information concerning crop growth parameters. Reflectance spectra of wheat plots at different growth stages were generated to study the position of red edge. The shift of inflection wavelength towards longer wavelength was observed with increase in Leaf Area Index (LAI) and chlorophyll content. For the range of LAI from 0.08 to 3.16 and chlorophyll content from 2 to 39 (gm^-2), the shift of inflection wavelength was observed in the range of 713-723 nm. A linear relationship was observed between the inflection wavelength and LAI as well as chlorophyll content.     

机载成像光谱图象边缘辐射畸变校正

由于受大气效应、地物反射非朗伯特性、仪器－太阳－目标相对几何关系以及仪器系统本身特性等多种因素的影响,机载成像光谱数据中不可避免地将引入系统或非系统的辐射畸变,严重地影响了数据表达信息的可靠性和有效性。目前虽然已有一些机载遥感图像辐射畸变校正方法,但由于受各种应用条件的限制,所发展的这些方法普遍缺乏实用性和通用性。该文在对机载成像光谱图象边缘辐射畸变形机制进行理论分析和探讨的基础上,针对机载成像光     

Analysis of Airborne Visible/Infrared Imaging Spectrometer (AVTRIS) data of volcanic hot spots

Abstract

In July 1991, the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was flown over Mount Etna and Stromboli, Italy. At the time, magma-filled vents, of subpixel dimensions, occupied the summit craters of both volcanoes. For pixels located over these hot spots, thermal radiation dominates the sensor response between about 1-4 and 2-4 μm, the latter figure being the upper limit of spectral coverage. One thermal source within the Northeast Crater of Mount Etna is evident at wavelengths as short as I 0 μm despite this intensity, therc is no saturation of the AVIRIS sensors because of their wide dynamic range. A curve-fitting algorithm is used to match the thermal spectra with Planck radiation models, in order to derive information on temperature distributions at the subpixel scale. Difficulties arise because the sequential readout of detector elements during scanning leads to interband spatial misregistration. Although the standard preprocessing of AVIRIS data includes a linear interpolation of adjacent pairs of cross-track pixels to compensate for the readout delay, this procedure only complicates further the extraction of subpixel resolution thermal information. Only by reconfiguring AVIRIS, such that all spectral channels arc recorded simultaneously, could this problem be completely overcome. Nevertheless, by examining geometrically unprocessed spectra, and selecting from thcm thermal measurements in a few adjacent channels, meaningful radiometric calculations are possible in some cases. In this manner, we estimate that one of the hot spots on Stromboli was at ≈600°C and occupied ≈ 15 m₂ of ground. The methodologies proposed here are applicable to any hyperspectral record of thermal emission of volcanic or other origin     

机载成像光谱遥感器场地外定标规范的初步研究

根据作者近几年来的实际工作经验,在参照国内外场地外定标实验方法的基础上,从概念研究入手,概括总结机载成像光谱遥感器定标研究内容和总体实施方案,对机载成像光谱遥感器场地外定标规范进行了初步研究。     

High spatial resolution sea surface climatology from Landsat thermal infrared data

High spatial and temporal resolution maps of sea surface temperature (SST) have numerous applications in coastal and estuarine systems. A climatology map, tracking SST as a function of year-day, was produced at Southern New England using 53 Landsat TM and ETM+ thermal infrared data. A recursive curve-fitting algorithm was used to fit these data and eliminate cloud contamination, resulting in an average daily temperature at every 60-m pixel. The climatology was validated against long-term in situ records that were analyzed with the same techniques. The results show, as expected, that isolated and shallow water bodies undergo more extreme temperature variation (−2 to 25 °C) than deeper, well-connected embayments (1 to 21 °C) or the coastal ocean (4 to 18 °C). The coastal ocean is shown to lag insolation and shallow lakes by up to 44 days, with embayments showing a gradation between these extremes. Despite the subtle temperature range variation, there is rich detail in the spatial patterns which are relevant to the applied sciences of coastal and estuarine systems. The spatial pattern of the climatology reveals anomalous patterns, such as occur where anthropogenic forcing alters climatological patterns. The heat budget of Mount Hope Bay in northeast Narragansett Bay has anthropogenic thermal input from a large power plant, and this input is reflected in the climatology. From the results, it is seen that Narragansett Bay has, on average, a mean annual temperature of 11.86±0.41 °C, while the Mount Hope Bay system is consistently warmer at 12.30±0.21 °C and shows a delayed response to autumn cooling. The long history of Landsat data acquisition can be used to create a climatology of coastal and estuarine scale dynamics at an order of magnitude finer scale resolution than AVHRR climatologies.     

Hourly evapotranspiration derived from NOAA-AVHRR visible and GOES-IMAGER thermal infrared data

In previous studies, remotely sensed values of evapotranspiration are generally computed using a simplified surface energy budget model that employs a semi-empirical coefficient with combinations of Sun-synchronous satellite data and ground-based data. This approach has two main limitations, however: Sun-synchronous satellites have low temporal resolution and the estimation is limited only to a local point around the meteorological station because the models require the aid of ground-base measurements, especially air temperature. This study reduced both limitations through the supplemental use of geostationary satellite (GOES-8) data and remotely sensed estimates of all necessary parameters, including net radiation, air temperature and surface temperature. In particular, air temperature, which is an important meteorological parameter in evapotranspiration estimation, was reproduced through third-order polynomial multiple regressions (R² = 0.88; root mean square (rms) error = 2.21 °C). The coefficient needed for the hourly estimate of evapotranspiration was represented through both a Gaussian model and a plane model. The models were constructed using surface roughness length and Sun hour angle, which replaced wind speed – a parameter that is difficult to estimate remotely over land. Assessments show that the models can depict the temporal distributions of empirical coefficients over various land-cover types. The standard error of this coefficient estimate was 0.002 mm h^?1 K^?1 for both time periods. A strong correlation (R² > 0.87; rms. error <0.17 mm h^?1) was found in comparisons between the selected potential and remotely sensed actual evapotranspiration for four land-cover classes.     

Surface-sediment dynamics in a dust source from spaceborne multispectral thermal infrared data

This study utilized spaceborne multispectral thermal infrared (TIR) data to document spatial relationships of surface sediments over time in a modern depositional environment associated with dust emissions, Soda Lake playa, Mojave Desert, United States. The approach employed here involved time-series TIR data acquired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and a linear spectral mixture analysis. An automated algorithm was applied to derive emissivity image endmembers. Evaluation of the chosen endmembers revealed that they can be categorized into five major spectra classes based on diagnostic absorption features. Each spectrum has been identified in relation to mineral abundance and soil arrangement that are common in playa settings: A, “clayey silt-rich crust”; B, “intermediate-salt crust”; C, “quartz-rich deposit”; D, “salt-rich rough crust”; E, “sulfate-rich crust”. Spectral classes A-B-C-D yielded the lowest RMS errors (0-0.025) over time in the iterative deconvolution algorithm between the measured and modeled spectra. The produced fractional abundance images show high areal concentrations for clayey silt-rich crust, salt-rich rough crust, and quartz-rich deposit, as the first surficial mapping of Soda Lake. Significant changes in the spatial relationships of the major surface sediments in Soda Lake were observed after a flooding event (2005) and a relatively dry period (2006). The approach utilized in this study can be advantageous for continuous monitoring of environments characterized by a small area and a complex surface, which may enable a better understanding of their responses to climate changes and potential for dust emissions.     

Land surface emissivity retrieval from combined mid-infrared and thermal infrared data of MSG-SEVIRI

This work addressed the retrieval of Land Surface Emissivity (LSE) from combined mid-infrared and thermal infrared data of Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) onboard the geostationary satellite—Meteosat Second Generation (MSG). To correct for the atmospheric effects in satellite measurements, a new atmospheric correction scheme was developed for both Middle Infra-Red (MIR) and Thermal Infra-Red (TIR) channels. For the MIR channel, because it is less sensitive to the change of water vapor content, the clear-sky and time-nearest European Centre for Median-range Weather Forecast (ECMWF) atmospheric data were used for the images where no atmospheric data are available. For TIR channels, a modified model of Diurnal Temperature Cycle (DTC) used by Göttsche and Olesen [Göttsche, F. M., and Olesen, F. S. (2001). Modeling of diurnal cycles of brightness temperature extracted from METEOSAT data. Remote Sensing of Environment, 76, 337-348.] and Schädlich et al. [Schädlich, S., Göttsche, F. M., and Olesen, F. S. (2001). Influence of land surface parameters and atmosphere on METEOSAT brightness Temperatures and generation of land surface temperature maps by temporally and spatially interpolating atmospheric correction. Remote Sensing of Environment, 75, 39-46.] was adopted. The separation of Land Surface Temperature (LST) and LSE is based on the concept of the Temperature Independent Spectral Indices (TISI) [Becker, F., and Li, Z. L. (1990a). Temperature independent spectral indices in thermal infrared bands. Remote Sensing of Environment, 32, 17-33.] constructed with one channel in MIR and one channel in TIR. The results of two different combinations (combination of channels 4 and 9 and of channels 4 and 10) and two successive days at six specific locations over North Africa show that the retrievals are consistent. The range of emissivity in MSG-SEVIRI channel 4 goes from 0.5 for bare areas to 0.96 for densely vegetated areas, whereas the emissivities in MSG-SEVIRI channels 9 and 10 are usually from 0.9 to 0.95 for bare areas and from 0.95 to 1.0 for vegetated areas. For densely vegetated areas, the emissivities in MSG-SEVIRI channel 9 are larger than the ones in channel 10, whereas the opposite is observed over bare areas. The rms differences between two combinations over the whole studied region are 0.017 for emissivity in channel 4, 0.008 for emissivity in channel 9 and 0.007 for emissivity in channel 10.     

Bare surface soil moisture retrieval from the synergistic use of optical and thermal infrared data

Land surface soil moisture (SSM) is crucial to research and applications in hydrology, ecology, and meteorology. To develop a SSM retrieval model for bare soil, an elliptical relationship between diurnal cycles of land surface temperature (LST) and net surface shortwave radiation (NSSR) is described and further verified using data that were simulated with the Common Land Model (CoLM) simulation. In addition, with a stepwise linear regression, a multi-linear model is developed to retrieve daily average SSM in terms of the ellipse parameters x₀ (horizontal coordinate of the ellipse centre), y₀ (vertical coordinate of the ellipse centre), a (semi-major axis), and θ (rotation angle), which were acquired from the elliptical relationship. The retrieval model for daily average SSM proved to be independent of soil type for a given atmospheric condition. Compared with the simulated daily average SSM, the proposed model was found to be of higher accuracy. For eight cloud-free days, the root mean square error (RMSE) ranged from 0.003 to 0.031 m³ m^?3, while the coefficient of determination (R²) ranged from 0.852 to 0.999. Finally, comparison and validation were conducted using simulated and measured data, respectively. The results indicated that the proposed model showed better accuracy than a recently reported model using simulated data. A simple calibration decreased RMSE from 0.088 m³ m^?3 to 0.051 m³ m^?3 at Bondville Companion site, and from 0.126 m³ m^?3 to 0.071 m³ m^?3 at the Bondville site. Coefficients of determination R² = 0.548 and 0.445 were achieved between the estimated daily average SSM and the measured values at the two sites, respectively. This paper suggests a promising avenue for retrieving regional SSM using LST and NSSR derived from geostationary satellites in future developments.     

航空成像光谱仪的发展和在侦察中的应用

成像光谱仪在进行航空成像侦察时能够获得一个三维的数据立方体,其中,两维表示目标的空间信息,一维表示目标的光谱信息,因此,成像光谱仪在进行航空成像侦察时不仅能够对目标进行定位和判别,还可以利用自身可以获取目标光谱信息的能力更好地进行遮蔽和伪装目标的辨别。本文介绍了成像光谱仪的发展与现状,对成像光谱仪的成像原理进行了分析,比较了成像光谱仪不同成像原理的优缺点,并对成像光谱仪在航空成像侦察中的应用进行了讨论。     

Error sources on the land surface temperature retrieved from thermal infrared single channel remote sensing data

In this paper, a theoretical study complementary to others given in the literature about the errors committed on the land surface temperature retrieved from the radiative transfer equation in the thermal infrared region by remote sensing techniques has been analysed. For this purpose, the MODTRAN 3.5 code has been used in order to simulate different conditions and evaluate the influence of several parameters on the land surface temperature accuracy: atmospheric correction, noise of the sensor, land surface emissivity, aerosols and other gaseous absorbers, angular effects, wavelength uncertainty, full‐width half‐maximum of the sensor and band‐pass effects. The results show that the most important error source is due to atmospheric effects, which leads to an error on surface temperature between 0.2 K and 0.7 K, and land surface emissivity uncertainty, which leads to an error on surface temperature between 0.2 and 0.4 K. Hence, assuming typical uncertainties for remote sensing measurements, a total error for land surface temperature between 0.3 K and 0.8 K has been found, so it is difficult to achieve an accuracy lower than these values unless more accurate in situ values for emissivity and atmospheric parameters are available.     

Estimating surface temperatures from satellite thermal infrared data—A simple formulation for the atmospheric effect

In recent years the availability of high spatial resolution thermal infrared data from satellites has prompted the use of energy budget models relating satellite-derived surface temperatures to surface moisture, near-surface thermal inertia, energy exchange with the atmosphere, etc. However, correction of the high spatial resolution satellite data for atmospheric water vapor effects can represent a substantial computational burden unless simplifying assumptions are utilized. A simple formulation is developed and its applicability tested by application to standard meteorological soundings at a time near the overpass of an NOAA operational satellite. It appears that reasonable estimates of surface temperature (±2–3°C) are readily obtained for areas of order 100–300 km².     

全链路成像光谱仪信噪比仿真

研究成像光谱仪优化问题,由于光谱成像受到环境噪声影响,传感器精度达不到要求,传统信噪比优化仿真方法,通常只考虑传感器本身的特性,没有综合考虑地物的光谱特性、辐射传输对其影响,导致传感器信噪比很难满足要求。为消除噪声提出了全链路成像光谱仪信噪比仿真方法,以叶面积指数反演应用为背景,从地面植被反射率信号出发,考虑大气辐射传输和传感器能量转换过程,建立了全链路成像光谱仪信噪比仿真模型,并通过具体实例进行验证和分析。理论分析和仿真结果表明:方法是对成像光谱仪信噪比仿真的一种全新而有益的尝试,具有很好的扩展性,传感器的研制设计提高性能指标,并缩短研制周期,为设计提供了参考。     

Estimation of nuclear power plants influence on the Baltic Sea thermal state by using infrared thermal satellite data

The influence of the activity of nuclear power plants on the state of the environment attracts constant attention from environmental and scientific organizations. The great amount of heated water thrown off permanently into a water basin by nuclear power plants is one of the negative factors, one which seriously disturbs the thermal balance of water basins and leads to irreversible environmental changes. The degree of algae growth in a basin depends on the amount of inflowing biogenic substances, as well as the water temperature of a reservoir. The main aim of this research was to develop the remote method of monitoring the influence of nuclear power plants on the thermal state of water basins and to compare it with different natural inputs of heat. The objects of this research were the operating nuclear power plants of the Baltic Sea rim.     

Analysis of cloud type and cloud amount during GATE from SMS infrared data

Earth-located and edited infrared data from the Synchronous Meteorological Satellite-1 were used to analyze cloud amount and cloud type. A two-threshold weighted histogram model was developed for analysis of cloud amount. Five different cloud-type classes were identified from use of a maximum-likelihood classifier, in which the covariance matrix for each cloud-type class was approximated by the pooled within-groups dispersion matrix. The analysis techniques were developed and tested using satellite and ship data from three days during Phase 3 of the GARP Atlantic Tropical Experiment (GATE). Cloud observations from GATE ships within the A/B scale area were compared with the processed SMS-1 IR data. The cloud coverage derived from the IR data was in very good agreement with cloud amounts obtained from 599 daytime GATE ship observations. The results obtained with the cloud classification technique reflect known limitations of satellite data in specifying cloud systems, and also are limited by problems inherent in the derivation of cloud information from standard meteorological surface observations.     

便携式成像光谱仪的软件设计与实现

成像光谱技术的迅速发展,使得出现了多种多样的成像光谱仪硬件设备,近几年,基于液晶可调谐滤波器(Liquid Crystal Tunable Filter,LCTF)的便携式成像光谱仪系统不断出现,使得成像光谱技术更加丰富。而与之配套的成像光谱仪软件尚没有过多的研究与方案提出,为了加强成像光谱仪软件的开发生态,针对成像光谱仪的功能需求,利用Qt界面开发框架,首先提出了一种高扩展性、高可读性的软件方案。按照面向对象与模块化设计的编程思想,将该软件分为图像控制接收模块、处理模块、显示窗口模块与光谱分析模块,然后根据各个模块的开发思路,介绍了其内部设计细节与模块间的通信方式。最后,测试表明该软件能够满足成像光谱仪的基本功能需求,具有较好的稳定性与鲁棒性。     

SEBASS hyperspectral thermal infrared data: surface emissivity measurement and mineral mapping

This study focuses on mapping surface minerals using a new hyperspectral thermal infrared (TIR) sensor: the spatially enhanced broadband array spectrograph system (SEBASS). SEBASS measures radiance in 128 contiguous spectral channels in the 7.5- to 13.5-μm region with a ground spatial resolution of 2 m. In September 1999, three SEBASS flight lines were acquired over Virginia City and Steamboat Springs, Nevada. At-sensor data were corrected for atmospheric effects using an empirical method that derives the atmospheric characteristics from the scene itself, rather than relying on a predicted model. The apparent surface radiance data were reduced to surface emissivity using an emissivity normalization technique to remove the effects of temperature. Mineral maps were created with a pixel classification routine based on matching instrument- and laboratory-measured emissivity spectra, similar to methods used for other hyperspectral data sets (e.g. AVIRIS). Linear mixtures of library spectra match SEBASS spectra reasonably well, and silicate and sulfate minerals mapped remotely, agree with the dominant minerals identified with laboratory X-ray powder diffraction and spectroscopic analyses of field samples. Though improvements in instrument calibration, atmospheric correction, and information extraction would improve the ability to map more pixels, these hyperspectral TIR data nevertheless show significant advancement over multispectral thermal imaging by mapping surface materials and lithologic units with subtle spectral differences in mineralogy.     

Observing air quality over the city of Nantes by means of Landsat thermal infrared data

This article investigates the potentials of satellite-made observations for the mapping of air quality parameters. Ground measurements of black particulates, sulphur dioxide and other pollutants have been measured in the city of Nantes and are compared with coincident Landsat TM6 data. It is found that the amount in black particulates is highly correlated to the apparent temperature observed by satellite. Some of the possible mechanisms for this correlation are investigated. The influence of the pixel size on this correlation is discussed in view of previous studies. Preliminary explanations are given. The mapping of the spatial distribution of the black particulates is possible from remotely sensed data. It is not very accurate and possible improvements are discussed. Finally, it is shown that pollution level should be taken into account in any use of satellite data for urban area classification purposes.     

Offner成像光谱仪的设计与航拍实验

介绍一种Offner结构高分辨率推扫式成像光谱仪的设计,包括光学结构设计、数据获取与存储系统配置、基于数据库的光谱图像拼接软件设计以及成像光谱仪波长标定和辐射标定方法.其次介绍成像光谱仪在青藏高原陆面敏感因子航空遥感实验中的使用情况,包括实验概况、成像光谱仪及其采集系统在机舱内的安装调试、光谱仪的航拍参数以及航带光谱图像的拼接处理,最终获取到高分辨率的高光谱图像立方体.仪器的首次航拍飞行实验取得预期成果.