The albedo is the light flow scattered in all directions by the illuminated part of the celestial body surfaceφAnd the optical flow incident on the surface of the celestial bodyφ0.
Planetary physicsThe physical quantity used to represent the reflection ability of celestial bodies, including plane albedoGeometric albedo、BondAlbedo, etc.The most valuable one is Bond albedo (i.e. spherical albedo).
Albedo is also called hemisphere in remote sensing applicationsreflectivity, defined as the ratio of reflected emittance and incidence of the target figure, that isTotal radiationThe ratio of energy (M) to the total incident radiation energy (E), usually α=M/E.
It is defined as the light flow scattered in all directions by all the illuminated parts on the surface of the celestial bodyφAnd the optical flow incident on the surface of the celestial bodyφRatio of 0:
A (Bond albedo)=φ/φ0，
It represents the share of solar energy reflected into space by the surface of the celestial body.The albedo of dark objects is lower than that of white objects.An object with an albedo of 1 can incident allLight reflectionGo out, the object is pure white;On the contrary, objects with zero albedo are pure black.It can be seen that the albedo of planets and satellites quantitatively indicates the properties of the material covering their surfaces.[1]
Surface albedo
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Surface albedo concept
The surface albedo is remote sensinginversionThe first important parameter in, conceptually, albedo（Albedo）Is the ratio of the total reflected radiation flux to the incident radiation flux for a surface.In general application, it refers to a broadband, such asSolar spectrumSection (0.3~4.0 μ m).yesMultiband remote sensingIs called spectral albedo.These are reflections pointing towards the entire hemisphere.The reflection of a band in a certain direction is calledreflectivity(Reflectance)。The surface albedo reflects the surface's influence on the sunShortwave radiationPhysical parameters of reflection characteristics;
Percentage of diffuse sunlight relative to various surface conditions
SurfaceSpecific emissivity(LandsurfaceEmissivity), LSE, also called surfaceEmissivity, is the characterization of the ability of ground objects to radiate electromagnetic waves.staySurface temperatureIt plays an important role in inversionThermal infrared remote sensingObtain the parameters necessary for surface temperature.It depends not only on the composition of surface objects, but also on the surface conditions of objects（Surface roughnessAnd physical properties（Dielectric constant, water content, temperature, etc.)Observation conditions(observation wavelength, observation angle, etc.)（Zhao YingshiEt al., 2003).Because of theRadiant emittanceIt is less than the radiant emittance of the black body at the same temperature, so the specific emissivity is defined as the radiant emittance of the object at the same temperature T and wavelength and the radiant emittance at the same temperature and wavelengthBlackbody radiationThe ratio of emittance.
The mouth is the wavelength, T is the object temperature, Ms (T, mouth) is the radiation emittance of the object at the temperature T, wavelength mouth, and the field MB (T, mouth) is the radiation emittance of the blackbody at the same temperature and wavelength.Specific emissivityIs aDimensionlessThe value of is between 0 and 1, which can generally be summarized as a function of ground object type, temperature and wavelength (Zha Shuping, 2004).At 8~14 μ mthermal infraredFor the land surface with rich soil and vegetation information, the specific emissivity varies from 0.90 to 0.99.staySurface temperatureinversionIn the process, if the specific emissivity has an error of 0.01, it will lead to an error of l~2 ℃ in the inverted surface temperature.Therefore, it is particularly important to accurately obtain the surface emissivity.There are three methods to obtain the surface emissivity: first, laboratory measurement;The second isField survey;The third is inversion using remote sensing data.The first two methods have high precision, but the specific measurement methods are very cumbersome and not easy to be applied in practice, and the "point" scaleSpecific emissivityIt is also difficult to transform to the spatial scale and establish the spatial distribution data set of surface emissivity.However, the remote sensing inversion method has great advantages in obtaining the spatially continuous surface emissivity information.[2]
spatial resolution
Provided by NOAA series satellitesAVHRRThe data is very highspatial resolution (~1km) is used to calculateSurface reflectance Ideal information for.This paper first describes some facts of surface observation of surface reflectance in the Qinghai Tibet Plateau, then discusses the principle and method of calculating surface reflectance using AVHRR data, and applies this method to calculate and analyze the two observations in the Qinghai Tibet Plateau on July 13, 1983 and August 22, 1984.The results show that the spatial variation of surface albedo in the Qinghai Tibet Plateau is very strong due to the complexity of underlying surface;In terms of regional average, previous estimates of surface albedo in most parts of the plateau are generally high.
For example, Venus has a higherreflectivity0.65；andMercuryThere is no atmosphere, only rock surface, and its albedo is only 0.11.The earth's albedo is 0.37.
Retrieval of surface albedo from multiple satellite remote sensing data
Existing products include China's products from 2000 to 2009, and products from Inner Mongolia Autonomous Region, Qinghai Province, and Tibet Autonomous Region for 8 days, month by month, and annual average in 2010. The resolution is 1km, 0.01 degrees, and the precision is good.
Model algorithm
Surface albedo characterizes the surface of the earthsolar radiationReflective ability, usingLiang ShunlinThe quality of spatial accuracy is good.
Surface albedo of Inner Mongolia Autonomous Region in December 2010
Surface albedo map
planetary albedo
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Due to the different characteristics of the material and structure of the planet surface, the ability of the planet surface to reflect solar radiation is also different, and the reflection ability is usually measured by albedo.American astronomer George Phillips Bond (1825-1865) used the ratio of the electron radiation reflected by the celestial body to the total electron radiation radiated to the celestial body to measure the reflection characteristics of the celestial body. Later, this coefficient was called Bond reflectivity, which was simply called albedo without causing confusion.aboutcelestial bodies In terms of albedo, it refers to the ratio of the electron radiation from the sun reflected by a celestial body to the total electron radiation radiated to the celestial body.Since the energy radiated from the sun is mainly concentrated in the visible light band, the Bond albedo of solar system objects mainly reflects the reflection performance of objects to the energy in the solar visible light band.The value range of Bond albedo is [0,1], which was initially applied to spherical objects and later extended to irregular surfaces.Another albedo that is often used is geometric albedo.Geometric albedo is the ratio of the true brightness in the direction of zero phase angle to the brightness of an ideal flat, total reflector on the same section.The geometric reflectivity of the same object is often higher than Bond reflectivity.
Geometric reflectance p and Bond reflectance A have the following relationship: A=p · q
Where,
The phase angle α is the included angle between the radiation source reflection target direction and the observation point reflection target direction.I (α) is the scattering flow in the phase angle direction, and I (0) is the scattering flow in the phase angle direction of 0 degrees.[3]
