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雪的热辐射多角度偏振特性研究.docx

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雪的热辐射多角度偏振特性研究 Introduction Snowisoneofthemajorcomponentsoftheearth'scryosphere.Itcoversabout10%oftheearth'slandsurfaceandplaysanimportantroleintheearth'senergybalance.Thereflectionandabsorptionofsolarradiationbysnowsurfaceshaveamajorimpactontheearth'sclimate.Theradiationpropertiesofsnowareoftencharacterizedbyitsspectralalbedo.Inaddition,itsemissivityorradiativepropertiesatthermalwavelengthsarealsoimportant.Snowhasacomplexmicrostructurethatcanaffectitsradiativeproperties.Theobjectiveofthisstudyistoinvestigatethepolarizedradiativepropertiesofsnowatdifferentanglesofincidenceandemission. Background Theradiativepropertiesofsnowhavebeenstudiedformanydecades.Itiswell-knownthatsnowhasahighalbedo,reflectingabout80-90%oftheincomingsolarradiation.Thealbedoofsnowdependsonseveralfactorssuchassnowgrainsize,shape,density,andimpuritycontent.Thespectralalbedoofsnowdecreaseswithincreasingwavelengthduetotheabsorptionofsolarradiationbyiceparticlesandimpuritiesinthesnow. Theemissivityofsnowisanimportantparameterforunderstandingitsradiativepropertiesatthermalwavelengths.Theemissivityofsnowisusuallylessthan0.99duetoitsroughandporoussurface.Theemissivityofsnowdecreaseswithincreasingsurfacetemperatureduetothedecreaseinthethermalradiationemittedbysnow. PolarizedRadiativePropertiesofSnow Snowhasacomplexmicrostructurethatcanaffectitspolarizedradiativeproperties.Thepolarizationoflightcanoccurduetothereflection,refraction,andscatteringoflightbysnowparticles.Thepolarizationoflightdependsontheangleofincidenceandemission.Thepolarizedradiativepropertiesofsnowatdifferentanglesofincidenceandemissionhavebeenstudiedusingdifferenttechniquessuchaspolarimeters,spectrometers,andradiometers. Polarimetersareinstrumentsthatmeasurethepolarizationstateoflight.Theycanbeusedtomeasurethedegreeandangleofpolarizationoflightreflectedortransmittedbysnow.Spectrometerscanbeusedtomeasurethepolarizedreflectanceofsnowatdifferentwavelengths.Radiometerscanbeusedtomeasurethepolarizedradianceofsnowatdifferentanglesofemission.