Research On The Optical Polarized Radiation Characteristics Of Sea Targets

The polarization properties of the interaction between light and matter provide scientific basis for the application of optical polarization remote sensing technology.The characteristics and difference of polarized radiation produced by the reflection and scattering of ocean targets and background have contributed to the polarization observation of the ocean.In this paper,multi-angle polarization technology to obtain the polarized spectral characteristics of marine targets.The changing trend of the polarization characteristics of the sea water background and the typical marine targets are analyzed which provides the theoretical basis and experimental verification for the remote sensing of marine targets.First of all,from the principle of polarization detection,a portable BPDF(Bidirectional Polarized-reflectance Distribution Function)measurement system is designed and manufactured according to the time-sharing polarization detection method for the purpose of obtaining the polarized spectral characteristics of targets.The system comprises a BPDF measurement bracket and a spectropolarimeter.The radius of the zenith arc and azimuth circle of BPDF measurement bracket is 0.9m and it can be obtained a variety of field targets multi-angle polarized radiation information in the hemisphere space with spectropolarimeter.Secondly,the spectropolarimeter and polarized camera used in this study are tested for radiation and polarization calibration and the polarization measurement accuracy of them is better than 2%.Then,for the background water,the measurement experiment of the optical polarization characteristics is carried out with large scale BPDF measurement system and polarized camera.The polarization characteristics of the reflection of the calm water surface is analyzed by combining the Fresnel reflection law,and measure the multi-angle polarization characteristics of the calm water surface.The experimental results show that the view zenith angle has a great influence on the degree of polarization(DOP)of the water.The DOP increases with observing zenith angle increases and the maximum value of it is about 0.8.The polarization characteristics of the dynamic water were analyzed by using the Cox-Munk rough surface BPDF model and measured by polarized camera.The results show that the maximum value of DOP is 0.23 in backscattering region and is up to 1 in forward scattering.Finally,according to the typical marine target,ship and island targets are selected as the research objects.The measurements focus on the four kinds of ship material plates,ship's shrinkage models,vegetation,soil,gravel mixed land and so on.A large number of polarized spectral information and imaging information of targets is obtained.For radiation characteristics,the maximum reflectance is in the principal plane.Ship plates have apparent specular reflection because of the smooth surface;there are hot spot effect in vegetation target;soil has a strong backscattering characteristics and the mixture of sand and gravel shows a certain Lambert characteristic.For polarization characteristics,changes trend in the DOP of various targets are basically the same,but they have their own band characteristics and direction characteristics for different targets.The DOP of the material plates is not obvious with wavelength changing.However,it has apparent change with the observation angle.The DOP of vegetation,soil and gravel mixed land has obvious band characteristics.The maximum values are 0.25,0.07,0.15 which are obtained at 490nm and they are slightly higher than the values which are obtained at 550nm and 670nm.Therefore,it is necessary to choose the appropriate observation direction and band according to the different targets.