The Orbita hyperspectral satellite (OHS) is the first commercial hyperspectral satellite in China that completed launching and networking. It can collect world-class hyperspectral data and obtain aerial hyperspectral imagery with 32 bands covering the spectrum range from 400 to 1000 nm at a 10-m resolution, which are of great significance for the quantitative analyses of remote sensing and refined recognitions of land covers. We explore the potentiality of the OHS image in land cover classification (LCC). Taking the Pearl River Delta region as the study area, we selected five feature indices from OHS data, i.e., original bands (OBs), vegetation indices (VIs), water indices (WIs), red edge indices (REIs), and gray-level co-occurrence matrix (GLCM) textures for the LCC. Then, data combination schemes were intended to analyze and compare the performance of different feature indices on the accuracies of the LCC. Last, feature optimization was performed on all input variables to determine the optimal variables combination to increase the accuracy and efficiency of the LCC. The random forest classifier was adopted in the above schemes, and the method of mean decrease in accuracy was used to determine the importance of the variables. The results show that (1) refined accuracy of LCC was obtained using only OBs; in addition, REIs can further improve the classification accuracy significantly. (2) The optimal variables combination achieves the highest classification accuracy (OA = 93.21 % and kappa coefficient = 0.91), and the user’s and producer’s accuracies exceeded 90% for most land cover categories. (3) Variable importance analyses show that the importance of both red-edge bands and REIs were greater than those of near-infrared bands and VIs for the LCC. The importance ranking of different indices from high to low was REIs > OBs > GLCM > WIs > VIs. This research demonstrates the potentialities and values of the OHS image for the application of LCC.
The generation of 3D models for indoor objects and scenes is an attractive tool for digital city, virtual reality and SLAM purposes. Panoramic images are becoming increasingly more common in such applications due to their advantages to capture the complete environment in one single image with large field of view. The extraction and matching of image feature points are important and difficult steps in three-dimensional reconstruction, and ASIFT is a state-of-the-art algorithm to implement these functions. Compared with the SIFT algorithm, more feature points can be generated and the matching accuracy of ASIFT algorithm is higher, even for the panoramic images with obvious distortions. However, the algorithm is really time-consuming because of complex operations and performs not very well for some indoor scenes under poor light or without rich textures. To solve this problem, this paper proposes an improved ASIFT algorithm for indoor panoramic images: firstly, the panoramic images are projected into multiple normal perspective images. Secondly, the original ASIFT algorithm is simplified from the affine transformation of tilt and rotation with the images to the only tilt affine transformation. Finally, the results are re-projected to the panoramic image space. Experiments in different environments show that this method can not only ensure the precision of feature points extraction and matching, but also greatly reduce the computing time.
In this study, the extended morphological attribute profiles (EAPs) and independent component analysis (ICA) were combined for feature extraction of high-resolution multispectral satellite remote sensing images and the regularized least squares (RLS) approach with the radial basis function (RBF) kernel was further applied for the classification. Based on the major two independent components, the geometrical features were extracted using the EAPs method. In this study, three morphological attributes were calculated and extracted for each independent component, including area, standard deviation, and moment of inertia. The extracted geometrical features classified results using RLS approach and the commonly used LIB-SVM library of support vector machines method. The Worldview-3 and Chinese GF-2 multispectral images were tested, and the results showed that the features extracted by EAPs and ICA can effectively improve the accuracy of the high-resolution multispectral image classification, ~2% larger than EAPs and principal component analysis (PCA) method, and ~6% larger than APs and original high-resolution multispectral data. Moreover, it is also suggested that both the GURLS and LIB-SVM libraries are well suited for the multispectral remote sensing image classification. The GURLS library is easy to be used with automatic parameter selection but its computation time may be larger than the LIB-SVM library. This study would be helpful for the classification application of high-resolution multispectral satellite remote sensing images.
In this study, the optical depth of vegetation is worked out with Microwave Polarization Difference Index (MPDI)
focusing on the drought that hit Yunnan in early 2010 and using AMSR-E data of the first three months of 2010 in
Yunnan Province. Inversion of soil moisture is conducted by using Microwave radiative transfer model and Dielectric
constant model, and thereupon drought grading is made, so that the drought grades of the first three months of 2010 in
most of the regions in Yunnan Province are obtained. By verifying the retrieval results by means of the soil moisture
data collected from ground-based measurements, the conclusion of this study is drawn: with the research method by
which soil moisture is retrieved from AMSR-E data, and thereupon the drought grading is made, the drought in
Yunnan Province can be effectively monitored.
The backscattering and emission measured respectively by scatterometer and radiometer show promise for the estimation of surface soil moisture and vegetation characteristics. In this paper, the 13.4GHz scatterometer of QuikSCAT and the 6.9GHz radiometer of AMSR-E are simultaneously used for the estimation of the near-surface soil moisture and vegetation water content. An algorithm using synthetic passive and active microwave data is proposed to estimation land surface parameters. At last, the retrieval algorithm was applied on AMSR and QUIKSCAT observations which have been carried out for the SMEX02 (Soil Moisture Experiment 2002) region in Ames, Iowa for the time period June 25 to July 13, 2002. The result shows a consistent performance.
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