In recent decades, polarization imaging has garnered much interest and research focus, due to its wide range of applications in the fields of atmospheric remote sensing, astronomy, biomedical and target detection, etc. Linear division-of-focal plane (DoFP) polarimeters deploying metal wire grid micro-polarization array as the polarization state analyzer (PSA) possess the capacity to capture polarization properties of the scene target during a single snapshot and benefit from their rugged and compact designs. However, these systems acquire the polarization measurements through spatial modulation and inevitably lead to spatial resolution loss, which cause instantaneous field of view (IFOV) errors and degradation of polarimetric accuracy. In response to this challenge, various interpolation/demosaicking methods tailored to DoFP imaging to fill the missing polarization information have emerged in recent years. This survey aims to explore these methods and briefly describe their effectiveness in enhancing the image restoration performance, highlighting their advantages and disadvantages. Lastly, according to current progress, some suggestions are made for high accuracy polarimetric measurements, especially for polarization remote sensing applications at different scales.
Differential Absorption Lidar (DIAL) is an effective approach for measuring atmospheric ozone with high precision. To solve the problem of wavelength pair selection for DIAL, numerical simulation experiments of DIAL were carried out. Within the ultraviolet band of 220nm to 360nm, tests were conducted for each wavelength with an interval of 1nm, and wavelength combinations with differences of 5nm, 10nm, 20nm, 30nm, 40nm, and 50nm were tested. The feasibility and of different wavelength combinations in the band for ozone measurement were synthesisly evaluated. The experimental results show that for DIAL systems with wavelength differences of 5 nm, 10 nm, and 20 nm, the combined error of ozone measurements in the troposphere from 0 to 6 KM below 15% if the strong absorption wavelengths (λon) are selected in the range of 260 nm to 283 nm, and the synthesis error of ozone measurements in the stratosphere from 15 to 30 KM below 15% if λon are selected in the range of 305 nm to 315 nm. For DIAL systems with wavelength differences of 30nm and 40nm, the synthesis error of ozone measurements in the troposphere from 0 to 6 KM below 15% if λon are selected in the range of 254 nm to 270 nm, and the synthesis error of ozone measurements in the stratosphere from 15 to 30 KM below 15% if λon are selected in the range of 305nm to 312nm. For DIAL systems with a wavelength difference of 50nm, the synthesis error of ozone measurement in the troposphere at 0 to 6KM is higher than 15%, and the synthesis error of ozone measurements in the stratosphere from 15 to 30 KM below 15% if λon are selected in the range of 305nm to 311nm. This result serves as a reference for the selection of wavelength pairs for DIAL measurements of atmospheric ozone.
To satisfy a space patrol telescope system with high angular resolution, large space area and high stray light suppression, the stray light environmental characteristics at low earth orbit are summarized. In accordance with the parameters, which diameter is 1.5m, focal length is 20m, field of view is 1.1°×1°, and the optical and mechanical structure joint-design stray light suppression is compared and analyzed for on-axis cross type, off-axis back end type and off-axis sideway type. A method of optical and mechanical structure joint-design stray light suppression is proposed to reduce the stray light suppressing angle to enhance the efficiency of the observation time and sky patrol efficiency in orbit. The detailed stray light suppression design and optimization of off-axis sideway type is given. The simulation and analysis of total optical and mechanical periodic line is presented, and the major stray ray path is simulated and analyzed.Compared with the other two types, the off-axis sideway type presents the best performance of image quality and stray light suppression. The modulation transfer functions (MTF) approach the diffraction limit at all fields. When the evadable angle out of the field is 40°, the PST is less than 10-11 and the system can approach to the stray light suppression limitation.
The precisely extraction of construction areas in remote sensing images can play an important role in territorial planning, land use management, urban environments and disaster reduction. In this article, we propose a method for extracting construction areas using Gaofen-1 panchromatic remote sensing images by adopting the improved Pantex[1] (a procedure for the calculation of texture-derived built-up presence index) and unsupervised classification. First of all, texture cooccurrence measures of 10 different directions and displacements are calculated. In this step, we improve the built-up presence index that we use the windows size of 21*21 to calculate the GLCM contrast measure instead of 9*9 according to the spatial resolution of Gaofen-1 panchromatic image. Then we use the intersection operator “MIN” to combine the 10 different anisotropic GLCM contrast measure to generate the final built-up presence index result. At last, we use the unsupervised classification method to classify the Pantex result into two classes and the one with larger cluster center is the construction area class. Confusion matrix of Beijing-Tianjin-Hebei region experiment shows that this method can effectively and accurately extract the construction areas in Gaofen-1 panchromatic images with the overall accuracy of more than 92%.
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