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Beijing, China

Chen Z.-W.,Tsinghua University | Chen Z.-W.,Ship Institute of NAA | Zhang L.-J.,Ship Institute of NAA | Wang H.-B.,Ship Institute of NAA | And 2 more authors.
Harbin Gongcheng Daxue Xuebao/Journal of Harbin Engineering University

The sea's color and optical properties often vary hugely with changing sea zones. Remote spectral sea images captured by satellites need to be analyzed by hand because current optical analysis instruments can't accurately evaluate features of the sea from the image's appearance. To resolve this, an eight-channel spectral imaging instrument was made, based on the narrow band multichannel imaging principle. It has eight optical channels, each capturing a spectral slice of each image. Multispectral imaging software to collect, manipulate and analyse data was then developed to complement the hardware. The software used the comparative color measurement method and the cubic spline spectral reconstruction method. In the southern part of the East China Sea, the sea color and spectral reflectivity were measured with this instrument and software. The measurement results fill a void in optical ocean research. While physically small and light weight, the instrument accurately measures the sea's color, spectral reflectivity and other image features, and can do so for large areas, and with a wide angle of view. The results showed maximum chromatic aberration of 14.89 between measured sea zones. Although these sea zones lie in one area, differences in sea color and spectral reflectivity between zones were significant. Source

Chen Z.-W.,Tsinghua University | Chen Z.-W.,Ship Institute of NAA | Liang X.-G.,Tsinghua University | Zhang L.-J.,Ship Institute of NAA | And 2 more authors.
Hongwai Yu Haomibo Xuebao/Journal of Infrared and Millimeter Waves

In order to improve the infrared stealth of water surface object, the attenuation character of water spray on infrared radiation was numerically investigated. The infrared attenuation and temperature response of the composite test board were measured before and after the water sprayed. The numerical and experimental results show that water spray with a certain concentration can decrease infrared transmission efficiently and change the infrared radiation feature of the test board quickly. According to the detective model of infrared system, the detective distance and image distance were analyzed with and without water spray between infrared imager and water surface object. The analysis result demonstrates that the detective distance of water surface object decreases about 25% and image distance decreases about 19% after water spray system was turned on, which tells that water spray is an effective method for infrared stealth and it can be widely used in the infrared stealth of water surface object. Source

Chen Z.,Tsinghua University | Chen Z.,Ship Institute of NAA | Liang X.,Tsinghua University | Xu X.,Tsinghua University | Zhang L.,Ship Institute of NAA
Qinghua Daxue Xuebao/Journal of Tsinghua University

Upper limit lognormal (LN) distribution and Rosin-Rammler (R-R) distribution functions are often used to simultaneously describe the droplet diameter distribution of the same water spray. This paper investigates the equivalence, approximation and conversion conditions of the two functions for the choice and application of these functions and the data transformation between the two functions in the data analysis and calculation. The Euclidean space distance was used to evaluate the optimum approximation of the two functions based on the derivation of LN's cumulative volume percent and volume diameter distribution. The results show that the LN distribution upper diameter limit dominates the cumulative volume curve shape and that an approximate conversion exists between the two functions with the two not being exactly equivalent. The results also show that the best approximation appears at the diameter at which the R-R distribution volume cumulative ratio is 94%. Source

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