| Passive Millimeter-wave(PMMW)radiation measurement has attracted attention of domestic and foreign researchers in recent years,which is widely used in close-range(relative to remote sensing)observation fields such as security detection,topographic mapping,and sea surface target detection.Since PMMW with a passive reception signal,the ability to penetrate clouds and strong,all-time and other advantages,it can be used as a complementary technology to detect active radar system,infrared,etc.,and therefore has a very high research value and pressing needs.At present,there are few studies on the marine radiation characteristics of PMMW,especially the ocean radiation data in the 3mm band is still incomplete.And the only ocean radiation models are pure theoretical models based on computational electromagnetic theory or semi-theoretical and semi-empirical models fitted from remote sensing data.The former has complex calculations,severe application conditions,and poor accuracy in practical applications;the latter is greatly affected by atmospheric transmission and needs to obtain a large number of atmospheric cross-sectional parameters during use,so it is subject to certain restrictions in practical applications.In addition,this type of model fits from remote sensing data.If directly transplanted to short-distance applications,there will be large errors.Based on this,this article will carry out theoretical and experimental research on the radiation characteristics of ocean millimeter wave.The main contents of this study are shown as follows:The paper first introduces the basic millimeter wave thermal radiation theory.According to the surface roughness of the medium,the millimeter wave emissivity theoretical models of the smooth surface and the rough surface are respectively given,and then the theoretical brightness temperature models of the two surfaces are given.Then,based on the theoretical model and the wave spectrum model,the influence of atmospheric scattering on the total received brightness temperature of the radiometer is analyzed,and then the scattering brightness temperature correction coefficient of the rough sea surface is defined to describe the degree of the influence.Considering the wind field on the sea surface,a semi-theoretical and semi-empirical model of millimeter wave emissivity on rough seas is established based on the influence of geometric characteristics,which is composed of three parts: calm sea emissivity,wind-induced emissivity and wind direction emissivity.Based on the above-mentioned scattering brightness temperature correction coefficient and emissivity model,the paper finally establishes a semi-theoretical and semi-empirical ocean millimeter wave brightness temperature model.Finally,the paper gives the measurement method of various parameters in the ocean millimeter wave brightness temperature model,and builds a measurement platform to carry out the ocean millimeter wave radiation characteristic measurement experiment.Through a large number of measured data analysis,the ocean millimeter wave brightness temperature model obtaines all parameters.Independent verification experiments show that the relative error of the predicted value of ocean millimeter wave brightness temperature calculated by this model is about 1%.The paper conducts theoretical and experimental research on the marine millimeter wave radiation characteristics.The established models and measured data can provide theoretical basis and data references for applications such as marine target detection and ocean parameter inversion. |
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