Tang Shihao

Principle and application of three-band gradient difference vegetation index

Vegetation index is a simple, effective and experiential measurement of terrestrial vegetation activity, and plays a very important role in qualitative and quantitative remote sensing. Aiming at shortages of current vegetation indices, and starting from the analysis of vegetation spectral characteristics, we put forward a new vegetation index, the three-band gradient difference vegetation index (TGDVI), and established algorithms to inverse crown cover fraction and leaf area index (LAI) from it. Theoretical analysis and model simulation show that TGDVI has high saturation point and the ability to remove the influence of background to some degree, and the explicit functional relation with crown cover fraction and LAI can be established. Moreover, study shows that TGDVI also has the ability to partly remove the influence of thin cloud. Experiment in the Shunyi District, Beijing, China shows that reasonable result can be reached using the vegetation index to retrieve LAI. We also theoretically analyzed the reason why the normalized difference vegetation index (NDVI) owns the low saturation point, and show that it is determined by the definition of NDVI and the characteristic of vegetation spectra, and is unavoidable to some degree. Meanwhile, through model simulation, we also indicate that the relationship between simple ratio vegetation index (SR) and LAI closes to a piecewise linear one instead of a linear one, which is mainly caused by the influence of background and different change rates of reflectance in red and infrared bands with LAI increasing.

An improved TES algorithm based on the corrected ALPHA difference spectrum

Different from visible signals, thermal infrared radiances depend on both temperature and emissivity. It is a key problem for us to separate temperature and emissivity in thermal infrared remote sensing research. Another difficulty encountered in the retrieval of surface temperature is the correction of downwelling sky irradiance, because it is closely related to surface emissivity. When emissivity is unknown, the downwelling sky irradiance is difficult to be removed. In this paper, we introduce a correction term of downwelling sky irradiance developed by Li and Becker into Wien’s approximation, to derive an improved ALPHA difference spectrum which is independent of temperature, and furthermore develop a correction term to remove the error of Wien’s approximation. Under the support of the above work, attractive features of Alpha derived emissivity method and ASTER TES algorithm are combined together to acquire a new Improved TES algorithm based on Corrected ALPHA Difference Spectrum (ICADS TES). Because a multi-band inversion technique is applied, and the operations of band ratios and differences are included in the algorithm, it can partly remove the influence of atmosphere and noises. Numerical simulation experiments show that for various combinations of atmosphere, land covers and surface temperatures, the algorithm is applicable and stable. Its accuracy for temperature is 0–1.5 K, and that for emissivity is 0–0.015. Compared with current TES algorithms, our method has clear physical meaning, is easy to be implemented, and is applicable for a wide temperature range and surface types. The results are not influenced by the directional characteristic of emissivity. Because ICADS TES does not need the support of a priori information of surface types, it is also not influenced by the accuracy of classification and the problem of mixture pixels. Compared with our former TES algorithm based on corrected Alpha difference spectra (CADS TES), the new algorithm takes the effect of downwelling atmospheric radiation into account. When the quantity of atmosphere radiation can be estimated precisely, the performance of ICADS TES is much better.

A TES algorithm based on corrected Alpha difference spectra

In this study, we start from WIENs approximation to define and derive Alpha difference spectrum, which is independent of temperature. Then, we present a correction term to remove the influence of WIENs approximation on Alpha difference spectrum. On these bases, a new temperature and emissivity separation algorithm is advanced, which combines attractive features of Alpha derived emissivity method and ASTER TES algorithm. Compared with current TES algorithm, the new algorithm is fast, simple and precise. It can be used for wide temperature and surface type ranges

Study of relation between thermal distribution and the underground medium in urban area

The study utilizes remote sensing as the main monitoring means. With different spatial high-resolution, multi-channel ASTER remote sensing image as the main information in Beijing city zone; with regional border and statistical data as auxiliary factor, a study between the thermal space distribution character and the underground medium is analyzed based on the GIS logical algorithm and synthetic analysis technology. Results show thermal forming mechanism and the rule of distribution is mainly related to the underground medium and the change of the city distribution. Different underground medium has different degree and intensity influence on the thermal space distribution. Furthermore, urban greenbelt and water areas can reduce the thermal effect and large-scale greenbelt creates green island effect. In addition, Road net, residential area, population density, heat resources and so on have some positive effect on the thermal distribution, which increase the local temperature and intensity on the other hand. It is important to study the thermal distribution and its related factors, which contributes to the plan, construction and development of the city.

A new vegetation index and its principle and application

Aiming at shortages of current vegetation indices, we put forward Three-band Gradient Difference Vegetation In- dex(TGDVI), and established algorithms to inverse crown cover fraction and Leaf Area Index(LAI) from it. Theoretical analysis and model simulation show that TGDVI has high saturation point and the ability to remove the influence of background, and explicit functional relation with crown cover fraction and LAI can be established. We also theoretically analyzed why NDVI has low saturation point and indicate that relationship between Sim- ple Ratio Vegetation Index(SR) and LAI closes to piecewise linear instead of linear.

Validation of an improved TES algorithm based on corrected ALPHA difference spectra

On IGARSS’04 conference, we introduced a new TES algorithm we developed basing on corrected ALPHA difference spectra. Although that algorithm can separate temperature and emissivity successfully, it didn’t take downwelling sky irradiance into account.That means it can only be applied in very special circumstances where downwelling sky irradiance can be neglected. In fact, the surface thermal infrared radiance can be expressed as:Lj=εjBj(Ts)+(1-εj)Latj↓. According to that equation, we must take the influence of downwelling sky irradiance into account in most cases to separate temperature and emissivity correctly. In this paper, we developed an improved TES algorithm which takes downwelling sky irradiance into account on the basis of our old algorithm. The new algorithm is applicable in most cases. To validate our algorithm, we compare it with ASTER TES algorithm and found that they agree quite well, especially for the inverted temperatures.

Validation of scale effect based on computer simulation model

With the developing of satellite technology, more and more sensors, based on various resolutions and functions, are launched to the sky to perform their missions. Enormous data are sent back to the Earth stations. In deriving surface parameters using these remotely sensed data, the transportability of algorithms from one resolution to another often cause the scale effect because of the surface heterogeneity on the Earth which can induce the change of reflectance. The problem, that the change of reflectance data affected by discontinuity as part of surface heterogeneity impacts the retrieval of vegetation leaf area index (LAI), is addressed in This work. Two cases, inducing the scaling issue in deriving surface parameters of interest, are considered here. One is the discontinuity between contrasting cover types within a mixed scene, the other is the nonlinear relationship of NDVI and LAI. Therefore, it is necessary to apply the correction based on NDVI-LAI relationships to modify scaling problem. In the processing, considering the field of wheat, firstly a series of 3D scenes with wheat and soil mixed are made based on the field measurement; secondly, computer simulation model

A large scale LAI inversion algorithm

the method of radiosity, which can calculate the balance of light energy in the simulated scenes, is used to model BRF (bi-directional reflectance factor) of these scenes. If the NDVI-LAI relationship from homogeneous scenes can be taken as standard, the relationship from heterogeneous scenes will be modified according to contextural parameter. Some conclusions are drawn from the investigation: (1) different distributional contextures of vegetation even with the same LAI affect the reflectance heavily; (2) we compare the reflectance simulated by the method of radiosity with the mean reflectance calculated using the area-weighted linear relationship of reflectance from components, and find that the accuracy of the mean reflectance can be accepted so that the linear equation to calculate the reflectance of mixed pixels is reasonable to relate images with high and low resolution; (3) using contextural parameter for quantifying the scale effect can get promising results.

The design and realization of web-based remote sensing model library

In this paper, a new LAI retrieval method is developed. The algorithm borrows ideas from the principles and methods of ground LAI measurements, and adopts a new frame which differs from traditional remote sensing LAI inversion methods. The ground data acquired from two field experiments are used to validate the algorithm. In order to resolve the scale exchange problem between high resolution ground observation and low resolution remote sensing data, two high resolution remote sensing images almost having the same resolutions with ground measurements are used as transitions

Technological Progress and Sustainable Development of Remote Sensing for Uranium Geology since the Beginning of the 21st Century

In this paper, we proposed the construction of a spectral knowledge library, which is composed of observed data library, image library, prior knowledge library and remote sensing model library. We stated the status and functions of remote sensing model library in the whole library, and discussed its structure, system architecture and development technique under network environment We also discussed remote sensing model librarys driving mechanism under the support of spectral knowledge library and meta data.