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Point Orthogonal Projection onto a Spatial Algebraic Curve

Taixia Cheng, Zhinan Wu, Xiaowu Li, Chan Wang
2020 Mathematics  
Greatly inspired by these works [2, 23, 25] , Wu et al. [26] proposed an improved curvature circle algorithm for orthogonal projection onto a planar algebraic curve.  ... 
doi:10.3390/math8030317 fatcat:yuv5zljnnfdh5ayrtq6pe4gpai

Laboratory Calibration of a Field Imaging Spectrometer System

Lifu Zhang, Changping Huang, Taixia Wu, Feizhou Zhang, Qingxi Tong
2011 Sensors  
A new Field Imaging Spectrometer System (FISS) based on a cooling area CCD was developed. This paper describes the imaging principle, structural design, and main parameters of the FISS sensor. The FISS was spectrally calibrated with a double grating monochromator to determine the center wavelength and FWHM of each band. Calibration results showed that the spectral range of the FISS system is 437-902 nm, the number of channels is 344 and the spectral resolution of each channel is better than 5
more » ... . An integrating sphere was used to achieve absolute radiometric calibration of the FISS with less than 5% calibration error for each band. There are 215 channels with signal to noise ratios (SNRs) greater than 500 (62.5% of the bands). The results demonstrated that the FISS has achieved high performance that assures the feasibility of its practical use in various fields.
doi:10.3390/s110302408 pmid:22163746 pmcid:PMC3231591 fatcat:zriuqp3vdfg23i4cow2cdyytmu

South China Tropical Forest Changes in Response to Economic Development and Protection Policies [chapter]

Shudong Wang, Taixia Wu
2018 Tropical Forests - New Edition  
The destruction of tropical forests continues to attract attention from the international community. China's National Forest Administration has adopted protective measures for tropical forests, and efforts have been developed to balance forest protection and economic development in Hainan Island, China. However, the response of natural tropical forest to local economic development and the effectiveness of forest management and protection policies remain unclear because of complexity of tropical
more » ... evergreen ecosystems. After comprehensive analysis of spectral characteristics, spatial distribution, patch shape, and other characteristics of main forests, we developed an information extraction method based on the decision tree method, combining digital elevation model (DEM) and forest planning maps, and established flowcharts and processes for sophisticated object-based information extraction. The accuracy of our method was 92%, and the method proved to be applicable and effective in the classification of complex surface features in a tropical evergreen ecosystem. Forces resulting in the change of these forests were explored by analyzing the relationships between economic development, protection policies, as well as environmental factors.
doi:10.5772/intechopen.73296 fatcat:nqhp5atbc5crbarq3pxt7qabga

Analysis of ancient painting by shortwave infrared imaging spectroscopy

Taixia Wu, Guanghua Li, Zehua Yang, Yong Lei
2018 Microscopy and Microanalysis  
doi:10.1017/s1431927618011303 fatcat:4lzf76ortna6vindv7qvzlkaje

Exploring the Potential of Spectral Classification in Estimation of Soil Contaminant Elements

Weichao Sun, Xia Zhang, Bin Zou, Taixia Wu
2017 Remote Sensing  
The spectral classification result is similar to the two categories identified by Wu and Wang [51] on studying soil spectral characteristics in southern China.  ...  Wu and Wang [51] analyzed reflectance spectral of four main soils in southern China, including latosol, red soil, yellow soil, and paddy soil, over range of 360-2500 nm and concluded that soil type and  ... 
doi:10.3390/rs9060632 fatcat:vi7omx7hrrfrpgyfj3m2kotc5e

Integrated Hybrid Second Order Algorithm for Orthogonal Projection onto a Planar Implicit Curve

Xiaowu Li, Feng Pan, Taixia Cheng, Zhinan Wu, Juan Liang, Linke Hou
2018 Symmetry  
The computation of the minimum distance between a point and a planar implicit curve is a very important problem in geometric modeling and graphics. An integrated hybrid second order algorithm to facilitate the computation is presented. The proofs indicate that the convergence of the algorithm is independent of the initial value and demonstrate that its convergence order is up to two. Some numerical examples further confirm that the algorithm is more robust and efficient than the existing methods.
doi:10.3390/sym10050164 fatcat:u3cc5t7lubfavi7wpozm2xnn6i

Polarization Remote Sensing for Land Observation [chapter]

Lei Yan, Taixia Wu, Xueqi Wang
2018 Understanding of Atmospheric Systems with Efficient Numerical Methods for Observation and Prediction [Working Title]  
Author details details Lei Yan 1 , Taixia Wu 2 * and Xueqi Wang 1 *Address all correspondence to: wutx@hhu.edu.cn 1 School of Earth and Space Sciences, Peking University, Beijing, China 2 School of Earth  ... 
doi:10.5772/intechopen.79937 fatcat:etza3wyxj5e2nc44nowa3kdccq

Evaluation of the Chinese Fine Spatial Resolution Hyperspectral Satellite TianGong-1 in Urban Land-Cover Classification

Xueke Li, Taixia Wu, Kai Liu, Yao Li, Lifu Zhang
2016 Remote Sensing  
Taixia Wu supervised all the work that has been done by the first author. Yao Li and Lifu Zhang revised the manuscript extensively.  ... 
doi:10.3390/rs8050438 fatcat:l2pnsmrkircstjvmwdy7fltjka

Temporal and Spatial Characteristics of the Global Skylight Polarization Vector Field

Lei Yan, Yanfei Li, Wei Chen, Yi Lin, Feizhou Zhang, Taixia Wu, Jouni Peltoniemi, Hongying Zhao, Siyuan Liu, Zihan Zhang
2022 Remote Sensing  
There are two widely recognized global fields in nature: the gravity field and the geomagnetic field. Universal gravitation and Earth rotation are important sources of the Earth's gravity and geomagnetic fields, which are well known to us. After years of long-term observation, global research, and analysis, it was discovered that we have neglected a direct incident energy of the universe on the Earth. Solar radiation, leading to energy exchange from the atmosphere 100 km above the land surface,
more » ... is the energy source of the Earth. Polarization is one of the four basic physical properties of solar radiation. After the solar radiation reaches the surface of these media, it reflects, scatters or refracts, and exhibits different degrees of polarization. The polarized solar light forms the Earth–sky polarization vector field. The polarized light dispersion is expected to become a new method for global analysis of the human environment. Polarization detection is the best way to accurately explore the atmospheric effects. Local polarized skylight distribution was found in different sites in the world; however, the global distribution of the polarized sunlight radiation has never been explored. In this paper, we investigate the Global Skylight Polarization Field. This study aimed at providing new insight into the laws of polarization over our Earth. We use a Rayleigh scattering model to obtain the simulation results of the sky polarization field. Rayleigh scattering occurs when the particle size is much smaller than the wavelength of the incident electromagnetic wave. We also use a polarized fisheye camera to collect the sky polarization image and calculate the distribution pattern of the DOLP (degree of linear polarization) and AOLP (azimuth of linear polarization) of the skylight. The stability and gradual change in the degree of polarization in the zenith direction are verified, and the distribution law and daily change law of the degree of polarization in the sky are obtained. With the increase in the solar altitude angle, the degree of polarization will decrease. We also observed the skylight polarization in different weather conditions. Our results demonstrate the physical basis, characteristics, and usability of the polarization field. They show an inevitable trend from optical remote sensing to polarization remote sensing.
doi:10.3390/rs14092193 fatcat:kv3wbzdomnezfmyqy2t4mnwooe

Evaluation of Multiple Spring Phenological Indicators of Yearly GPP and NEP at Three Canadian Forest Sites

Qian Wang, Lifu Zhang, Taixia Wu, Yi Cen, Changping Huang, Qingxi Tong
2014 Remote Sensing  
Author Contributions Qian Wang has done the research and written the whole paper; Taixia Wu, Yi Cen and Changping Huang have given some useful suggestions; Lifu Zhang and Qingxi Tong have supervised and  ...  [31] and Wu et al. [32] . This was reasonable due to the large footprints (>1.5 km) of all sites throughout the year reported by Chen et al. [33] .  ... 
doi:10.3390/rs6031991 fatcat:voxho4itlzgp5eputhc6woyjve

The NDVI-CV Method for Mapping Evergreen Trees in Complex Urban Areas Using Reconstructed Landsat 8 Time-Series Data

Yingying Yang, Taixia Wu, Shudong Wang, Jing Li, Farhan Muhanmmad
2019 Forests  
Evergreen trees play a significant role in urban ecological services, such as air purification, carbon and oxygen balance, and temperature and moisture regulation. Remote sensing represents an essential technology for obtaining spatiotemporal distribution data for evergreen trees in cities. However, highly developed subtropical cities, such as Nanjing, China, have serious land fragmentation problems, which greatly increase the difficulty of extracting evergreen trees information and reduce the
more » ... xtraction precision of remote-sensing methods. This paper introduces a normalized difference vegetation index coefficient of variation (NDVI-CV) method to extract evergreen trees from remote-sensing data by combining the annual minimum normalized difference vegetation index (NDVIann-min) with the CV of a Landsat 8 time-series NDVI. To obtain an intra-annual, high-resolution time-series dataset, Landsat 8 cloud-free and partially cloud-free images over a three-year period were collected and reconstructed for the study area. Considering that the characteristic growth of evergreen trees remained nearly unchanged during the phenology cycle, NDVIann-min is the optimal phenological node to separate this information from that of other vegetation types. Furthermore, the CV of time-series NDVI considers all of the phenologically critical phases; therefore, the NDVI-CV method had higher extraction accuracy. As such, the approach presented herein represents a more practical and promising method based on reasonable NDVIann-min and CV thresholds to obtain spatial distribution data for evergreen trees. The experimental verification results indicated a comparable performance since the extraction accuracy of the model was over 85%, which met the classification accuracy requirements. In a cross-validation comparison with other evergreen trees' extraction methods, the NDVI-CV method showed higher sensitivity and stability.
doi:10.3390/f10020139 fatcat:r6n473ivsfchjcjo7ffwc24yuq

Blood hyperviscosity identification with reflective spectroscopy of tongue tip based on principal component analysis combining artificial neural network

Ming Liu, Jing Zhao, XiaoZuo Lu, Gang Li, Taixia Wu, LiFu Zhang
2018 BioMedical Engineering OnLine  
Blood hyperviscosity influences severely on human health. According to the reports, there is a growing awareness of blood hyperviscosity as the leading cause of cardiovascular disease [1-3]. Antonova et al. report increasing blood viscosity leads to vascular obstruction, and induces thrombosis and atherosclerosis [4] . And chronic blood hyperviscosity is a serious threat factor for human life. Therefore, the blood hyperviscosity diagnosis is a very important element to prevent and control the
more » ... ronic vascular diseases. Currently, the diagnosis results of blood sample are provided by hemorheological instruments, and the relative procedure is still complex and time consuming. Furthermore, blood collection procedure may bring suffering to patients, and even lead to infection sometimes. So noninvasive and fast detection methods are required to be developed for hyperviscosity diagnosis. In the clinical environment, the integration of optical spectroscopy into disease
doi:10.1186/s12938-018-0495-3 pmid:29747693 pmcid:PMC5946417 fatcat:mzkqruiwwvhtpgih25h3llfpp4

An improved algorithm for retrieving the fine-mode fraction of aerosol optical thickness, part 1: Algorithm development

Xing Yan, Zhanqing Li, Wenzhong Shi, Nana Luo, Taixia Wu, Wenji Zhao
2017 Remote Sensing of Environment  
The fine-mode fraction (FMF) can be a useful tool to separate natural aerosols from man-made aerosols and to assist in estimating surface concentrations of particulate matter with a diameter b 2.5 μm. A LookUp Table- based Spectral Deconvolution Algorithm (LUT-SDA) was developed here for satellite-based applications using data such as MODerate resolution Imaging Spectroradiometer (MODIS) measurements. This method was validated against ground-based FMF retrievals from the Aerosol Robotic Network
more » ... (AERONET). The LUT-SDA was then applied to two MODIS-retrieved aerosol optical thickness (AOT) products for the period of December 2013 to July 2015: the MODIS Collection 6 (C6) Dark Target (DT) AOT product and the simplified high-resolution MODIS Aerosol Retrieval Algorithm (SARA) AOT product. In comparison with the MODIS C6 FMF product in three study areas (Beijing, Hong Kong, and Osaka), FMFs estimated by the LUT-SDA agreed more closely with those retrieved from the AERONET with a very low bias. Eighty percent of the FMF values fell within the expected error range of ±0.4. The root mean square error (RMSE) was 0.168 with few anomalous values, whereas the RMSE for the MODIS FMF was 0.340 with more anomalous values. The LUT-SDA FMF estimated using SARA AOT data conveys more detailed information on urban pollution than that from MODIS C6 DT AOT data. As a demonstration, the seasonally-averaged spatial distribution of the FMF in Beijing was obtained from the LUT-SDA applied to SARA AOT data and compared with that of the AERONET-retrieved FMF. Their seasonal trends agreed well.
doi:10.1016/j.rse.2017.02.005 fatcat:vc54n2crv5ddrgcsb2mebv6uei

An Analysis of Shadow Effects on Spectral Vegetation Indexes Using a Ground-Based Imaging Spectrometer

Lifu Zhang, Xuejian Sun, Taixia Wu, Hongming Zhang
2015 IEEE Geoscience and Remote Sensing Letters  
(Corresponding author: Taixia Wu.)  ...  An Analysis of Shadow Effects on Spectral Vegetation Indexes Using a Ground-Based Imaging Spectrometer Lifu Zhang, Senior Member, IEEE, Xuejian Sun, Taixia Wu, and Hongming Zhang Abstract-Sunlit vegetation  ... 
doi:10.1109/lgrs.2015.2450218 fatcat:d7gruvi3mzd73fbmglzwlp742e

An Adaptive-Parameter Pixel Unmixing Method for Mapping Evergreen Forest Fractions Based on Time-Series NDVI: A Case Study of Southern China

Yingying Yang, Taixia Wu, Yuhui Zeng, Shudong Wang
2021 Remote Sensing  
Spectral unmixing remains the most popular method for estimating the composition of mixed pixels. However, the spectral-based unmixing method cannot easily distinguish vegetation with similar spectral characteristics (e.g., different forest tree species). Furthermore, in large areas with significant heterogeneity, extracting a large number of pure endmember samples is challenging. Here, we implement a fractional evergreen forest cover-self-adaptive parameter (FEVC-SAP) approach to measure FEVC
more » ... t the regional scale from continuous intra-year time-series normalized difference vegetation index (NDVI) values derived from moderate resolution imaging spectroradiometer (MODIS) imagery acquired over southern China, an area with a complex mixture of temperate, subtropical, and tropical climates containing evergreen and deciduous forests. Considering the cover of evergreen forest as a fraction of total forest (evergreen forest plus non-evergreen forest), the dimidiate pixel model combined with an index of evergreen forest phenological characteristics (NDVIann-min: intra-annual minimum NDVI value) was used to distinguish between evergreen and non-evergreen forests within a pixel. Due to spatial heterogeneity, the optimal model parameters differ among regions. By dividing the study area into grids, our method converts image spectral information into gray level information and uses the Otsu threshold segmentation method to simulate the appropriate parameters for each grid for adaptive acquisition of FEVC parameters. Mapping accuracy was assessed at the pixel and sub-pixel scales. At the pixel scale, a confusion matrix was constructed with higher overall accuracy (87.5%) of evergreen forest classification than existing land cover products, including GLC 30 and MOD12. At the sub-pixel scale, a strong linear correlation was found between the cover fraction predicted by our method and the reference cover fraction obtained from GF-1 images (R2 = 0.86). Compared to other methods, the FEVC-SAP had a lower estimation deviation (root mean square error = 8.6%). Moreover, the proposed method had greater estimation accuracy in densely than sparsely forested areas. Our results highlight the utility of the adaptive-parameter linear unmixing model for quantitative evaluation of the coverage of evergreen forest and other vegetation types at large scales.
doi:10.3390/rs13224678 fatcat:fq7plqjf35b5njb333u4cvsm6y
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