1、,遥 感 物 理,绪论 第一章 基本概念 第二章 植被遥感模型 第三章 土壤与冰雪遥感模型 第四章 海色遥感 第五章 大气效应及其纠正 第六章 热红外遥感 第七章 地表能量平衡遥感模型,第五章 大气效应及其纠正,前言Introduction 第一节 大气组成与大气的基本特性ATMOSPHERE CONTENT AND BASIC PROPERTIES 第二节 辐射与大气的相互作用INTERACTION OF RADIATION WITH ATMOSPHERE 第三节 大气效应纠正ATMOSHPHERIC EFFECT CORRECTION 第四节 大气的遥感探测 ATMOSHPHERIC RE
2、MOTE SOUNDING,第五章 大气效应及大气纠正,前 言（Introduction） 大气：是介于遥感传感器与地球表层之间的一层由多种气体及气溶胶等组成的介质层，当电磁波由地球表层传至遥感传感器时，大气是必经的通道； 大气对电磁波的作用：主要可以归纳为两种物理过程，即吸收与散射，对地表遥感来说，大气的吸收与散射作用均可使电磁波信息受到削弱； 遥感图像的大气纠正：如何依据遥感图像直接或间接获得的大气参数，消除大气对电磁波属性量的影响，恢复其在地球表层的“本来面目” ，就成为定量遥感不可回避的问题； 大气属性参数的遥感反演：无论是置于地面的传感器还是星载的传感器，当它接收到从大气作用后的电磁
3、波时，它必然带有大气的特征信息，因此我们可以设法从中反演出表征大气属性的参数，如大气气溶胶与大气水汽等。,第五章 大气效应及大气纠正,第一节 大气组成与大气的基本特性ATMOSPHERE CONTENT AND BASIC PROPERTIES 第二节 辐射与大气的相互作用INTERACTION OF RADIATION WITH ATMOSPHERE 第三节 大气效应纠正ATMOSHPHERIC EFFECT CORRECTION 第四节 大气的遥感探测ATMOSHPHERIC REMOTE SOUNDING,第一节 大气组成与大气的基本特性 Content and basic proper
4、ties5.1.1 大气成分5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线5.1.5 大气温度和湿度的垂直廓线5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环5.1.9 云与降水,5.1.1 大气成分 CompositionThe composition of the atmosphere is important in any understanding of the role which the atmosphere plays in remote sensing and in interactions with ele
5、ctromagnetic radiation.The atmosphere is largely a mixture of gases混合气体, some with fairly constant concentrations, others that are variable in space and time. In addition there are suspended particles 悬浮颗粒(e.g. aerosol, smoke, ash etc.) and hydrometeors (e.g. cloud droplets, raindrops, snow, ice cry
6、stals, etc). About 99% of the mass lies below an altitude of 30km. Table 1 below shows the composition of the atmosphere below 100km.,Table 1: Main constituents of the earths atmosphere * a concentration near the earths surface,Nitrogen氮, oxygen氧 and argon氩 account for about 99.99% of the permanent
7、gases.Of the variable constituents, carbon dioxide 二氧化碳can be somewhat variable in concentration on a localised basis at low levels. Water vapour 水汽content may vary from about 0 to 4%ozone臭氧 concentrations also vary markedly. In addition to these variable constituents there are also aerosols 气溶胶 and
8、 hydrometeors水颗粒 which can vary widely in space and time.,大气中的氧与臭氧（oxygen and Ozone ）氧气占地球大气质量的23%，除游离存在的氧气以外，氧还以硅酸盐、氧化物和水化物等形式存在，在高空中还有臭氧与原子氧。氧占包括海洋和大气在内的地壳质量的49.5%。光合作用： nCO2+nH2OCH2On+nO2水汽的光解作用：2H2O2H2+O2（太阳紫外辐射）氧的分解作用 ：O2+hO+O （短于0.24微米的紫外辐射）复合作用：O+ O +M O2+M OO2+ O +M O3+M 臭氧分解作用：O3+ h O2+O* （
9、臭氧分子吸收短于0.32微米的紫外辐射）O3+ O*2 O2 （太阳紫外辐射） 其中M是第三种分子（N2、O2或其它分子），吸收反应中释放的化学能。,臭氧（ Ozone ）The concentration of ozone is highly variable in space (latitude and altitude for example) and time. Most ozone is generated and destroyed by photochemical reactions in the layer between 20 km and 60 km. Ozone tend
10、s to accumulate in the lower stratosphere at altitudes between 15 and 25 km. Small amounts of ozone are also produced by electrical discharges and in photochemical smog over cities. At the surface, ozone is destroyed rapidly by reacting with plants and dissolving in water, whereas in the stratospher
11、e the lifetime is on the order of months.Ozone has characteristic pronounced absorption at UV, IR and microwave wavelengths. The absorption of UV radiation makes human life possible on the earths surface. Depletion of the earths ozone layer has become a very serious issue following detailed observat
12、ional and theoretical studies which have focused primarily on the Antarctic “ozone hole“.,二氧化碳（ Carbon Dioxide ）Carbon dioxide has a relatively constant mixing ratio with height in the atmosphere, that is, it is fairly evenly distributed on average. The main sources 源: burning of fossil fuels化石燃料, h
13、uman and animal respiration呼吸, the oceans and volcanic activity火山活动. The main sinks 汇: photosynthesis光合作用 and the production of carbonates (limestones) in the ocean/land system. The rate of removal of carbon dioxide, a greenhouse gas, is observed to be less than the generation (from fossil fuel burn
14、ing) because the concentration of carbon dioxide in the atmosphere has been rising steadily during and since the early part of this century.About 99% of the earths carbon dioxide is dissolved in the oceans. The solubility is temperature dependent. It is estimated that the annual amount of carbon dio
15、xide entering or leaving the air by all mechanisms is about one tenth of the total carbon dioxide content of the atmosphere.,大气中的其他微量成分（trace gases）硫化合物二氧化硫 SO2 + 硫化氢 H2S 占硫化合物总量的80-90%氮化合物氮气是大气中最丰富的气体，性质稳定，仅有极少量的N2能被微生物固定在海洋和土壤里，变成有机化合物。气体氮化合物主要有：氧化亚氮N2O, 一氧化氮NO,二氧化氮NO2 , 氨NH3,Atmospheric gases cri
16、tically affect the earths global energy balance 能量平衡 through absorption and re-emission and through the role they play in global geophysical cycles. Solar radiation太阳辐射 reaching the earths surface is determined by atmospheric gases. For example harmful UV radiation is blocked by the ozone layer. Als
17、o, “windows” 大气窗口 in which atmospheric effects are minimal allow ground-based measurements of celestial(天体) objects, and satellite-based measurements of the earths surface or clouds for remote sensing applications.,Figure 1: (a) Atmospheric absorption at ground level for diffuse terrestrial radiatio
18、n and for solar radiation, with a zenith angle of 50 degrees. (b) Same as in a but for the layer of atmosphere above 11km. After Wallace and Hobbs (1977), p332.,Table 2: From Smith (1985), Atmospheric absorption features are shown in Figure1 for ground level and at an altitude of 11 km. Regions of m
19、inimal absorption (windows) are the troughs in the curves.,Figure 2: Solar irradiance at the top and bottom of the earths atmosphere, for the sun at the zenith. Shaded areas indicate absorption by atmospheric gases. After Valley (1965).,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composi
20、tion5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical structure of pressure and density5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,气象要素：大气中的物理现象和物理变化过程，可以用气温、气压、湿度、能
21、见度、风向、风速、云量、日照、辐射强度等物理量来描述。其中气温、气压、湿度和能量等最为重要。气象台站的观测场通常设在空旷的平地上，并把温度表放入离地面1.5米的百页箱内，是温度不受阳光的直射，又能保持通风。地面气温通常指百页箱温度。物理表面单位面积所受的大气分子的压力称为大气压强或气压。空气可看成是混合气体，压强可写成：p=(2/3) *sum(n0iw)w=(3/2)*kT其中n为各气体成分的数密度，w为分子平均动能，k为波尔兹曼常数。气压与分子数密度及温度成正比。,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composi
22、tion5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical structure of pressure and density5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,空气可以看作是有多种化学成分的混合气体。理想气体的状态方程为：其中p
23、为总压强，V是容积，T为绝对温度，m为气体的总质量，R*为普适气体常数8.3143X*103J/kmol*K, 为平均mol质量。根据气体状态方程和道尔顿分压定律，可定义混合气体的平均mol质量为比气体常数为：干空气的状态方程可以写为：,湿度参量饱和水汽压混合比与比湿水汽压水汽密度（绝对湿度）相对湿度露点与霜点虚温,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composition5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical structure of pre
24、ssure and density5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,5.1.4 大气压力和密度的垂直廓线 Vertical structure of pressure and densityQuantities such as pressure, density and mean free
25、path vary dramatically with height in the atmosphere. The variation can be over many orders of magnitude and is very much larger than horizontal or temporal variations. Meteorologists therefore commonly make use of a “standard atmosphere“ in which geophysical quantities have been averaged horizontal
26、ly and in time, and which vary as a function of height only.,Figure 3: Vertical variation of pressure in hPa, and density in g/m3, for the US extension to the ICAO(International Civil Aeronautics Organization国际民用航空组织) standard atmosphere. Adapted from Wallace and Hobbs (1977), p12.,Generally, observ
27、ed values of atmospheric pressure and density are fairly close to the “standard atmosphere“ values for the same level. The ICAO standard atmosphere is specified by :sea level pressure (p) 1013.2 hPa Sea level temperature (T) 15 deg Cfixed lapse rates for p and T dry,我国有关部门将此标准与我国60个台站的30公里以下部分的气球探空资
28、料进行比较后，认为与北纬45度的实际大气十分接近，低纬度地区有较大偏差。在建立我国自己的标准大气以前，可使用1976年美国标准大气，取其30公里以下部分作为国家标准。该模式假定大气是干燥的，在86公里以下是均匀混合物，可以作为理想气体处理，处于静力学平衡和水平成层分布。在给定温度-高度廓线及边界条件后，通过对静力学方程和气体状态方程求积分，就可以得到压力和密度数值。 海平面大气的部分特性如下：空气Mol质量 0 28.9644kg/kmol重力加速度 g0 9.80665 m/s 2压强 P0 101325Pa密度 0 1.2250kg/m3温度 T0 288.15K,The vertical
29、 variation of pressure (p) with height (z) may be derived as approximately (see Wallace and Hobbs, 1977 pp 12-13): p(z) = p(0) exp (-z/H) where p(z) is the pressure at height z above sea level, p(0) is the sea level pressure, and H is a constant called the scale height. Pressure decreases by a facto
30、r of e in passing upward through a layer of depth H. For the earths atmosphere, H is about 8.4 km.A similar approximate expression may be derived for density p as follows: p (z) = p (0) exp (-z/H) Note that density also decreases rapidly with height. It can be shown that half of the mass of the eart
31、hs atmosphere is below the 500 hPa level or an altitude at about 5.5 km. At an altitude of 50 km the pressure (ie mass of particles above unit area at that level) is about 1hPa so that only about 0.1 per cent of the mass of the atmosphere lies above that level.(Recall that 1 millibar = 100 hectoPasc
32、als and that 1 Pascal = 1 Newton/m2). Similarly because the pressure at 90 km is about 0.001 hPa, only about one millionth of the mass of the atmosphere lies above that level.,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composition5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical
33、 structure of pressure and density5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture,In 1962 the World Meteorological O
34、rganization adopted a description of the atmosphere in terms of four distinct layers called the troposphere（对流层）, stratosphere（平流层）, mesosphere（中性层） and thermosphere（热层）. The tops of these layers are called the tropopause, stratopause, mesopause and thermopause, respectively.The layers are character
35、ised by distinct mean variations of temperature with altitude, as defined in the ICAO Standard Atmosphere: In the lower part of the “standard“ or “average“ atmosphere, which is assumed to be dry, the temperature lapse rate is 6.5 deg C per km, up to 11km altitude. From there up to 20km altitude the
36、temperature lapse rate is 0 deg C per km, but from about 20km to 32km the lapse rate is -1.0 deg C per km, in which case the atmospheric temperature increases with altitude.,Figure 4: Vertical temperature profile for the Standard Atmosphere with the main atmospheric regions as indicated. Adapted fro
37、m Butler et al (1987), p111.,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composition5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical structure of pressure and density5.1.5 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere a
38、nd the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,Atmospheric aerosols are small airborne particles of widely differing chemical composition. They are important for a number of reasons including: scattering of aerosols will be used by a number of next-generation active remote sensing instrum
39、ents in derivation of geophysical parameters; many aerosols act as cloud condensation nuclei and are therefore important in the formation of clouds and precipitation; aerosol content affects the earths albedo and therefore the global energy balance and climate.,5.1.6 大气气溶胶,(a) Composition Most aeros
40、ol particles originate from blowing soil, smoke, volcanoes, and the oceans. Particles made of sodium chloride氯化钠 or magnesium chloride氯化镁 are hygroscopic 吸湿的and therefore act as good sites for the condensation of water to form cloud droplets. (b) Concentrations These vary considerably but are typica
41、lly of order 103 cm-3 over oceans, 104 cm-3 over rural land and 105 over cities. The concentrations generally decrease with altitude. (c) Size spectrum Aerosol particles are often classified by size as: Aitken nuclei (about 5x10-3 to 0.2 microns); large nuclei (about 0.2 to 1.0 microns); giant nucle
42、i (larger than 1.0 microns). The concentrations of nuclei fall off very sharply with increasing size e.g. the values are typically 103 to 105 cm-3 for Aitken nuclei, 100 cm-3 for large nuclei and 1 or less cm-3 for giant nuclei.,(d) Effect on solar, terrestrial and microwave radiation The scattering
43、 due to aerosols depends on a number of factors including the nature of the particles, their diameters and the wavelength of incident radiation. This is discussed in more detail later, but for the present it is noted that:at visible wavelengths, scattering of sunlight by aerosols can be significant
44、and is dominated by large particles 0.2 to 2 microns; at infrared wavelengths (around 10 microns), scattering although present, is very small compared to that at visible wavelengths; in the microwave, scattering by aerosols is negligible, as the particle size is very small compared to the wavelength
45、. This has very important consequences for remote sensing.,Although aerosols absorb and scatter only a small fraction of incoming solar radiation compared to clouds and gases, variations in global aerosol concentration could alter the earths energy budget. There are competing effects in that absorpt
46、ion of radiation would raise air temperatures, but aerosols tend to decrease temperatures by scattering solar radiation back into space.,第一节 大气组成与大气的基本特性 Content and basic properties5.1.1 大气成分 Composition5.1.2 描述大气状态的基本参量5.1.3 大气静力学方程5.1.4 大气压力和密度的垂直廓线 Vertical structure of pressure and density5.1.5
47、 大气温度和湿度的垂直廓线Vertical structure of temperature moisture 5.1.6 大气气溶胶5.1.7 大气水汽5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle5.1.9 云与降水Clouds and Precipitation,5.1.7 大气水汽（Water vapour） Water vapour is extremely important in radiative absorption and emission processes in the atmosphere. Its con
48、centration is highly variable. Although always present, in some localities it is difficult to measure, but in the tropics its concentration can be as high as 3 or 4 per cent by volume. Water vapour content of air is a strong function of air temperature. For example air at 40 deg C can hold up to 49.
49、8 grams of water per kg of dry air, while at 5 deg C this reduces to 5.5 grams per kg of dry air. The release of latent heat from condensation of water in the atmosphere is significant in the global energy budget and climate. Relatively small amounts of water vapour can produce great variations in w
50、eather. This is largely due to changes in its concentration and in latent heat release, particularly below about 6 km where a high proportion of moisture lies. The major sources of water vapour are evaporation and transpiration from plant life. The main sink is condensation in clouds with resulting precipitation over oceans and land. On average the concentration of atmospheric water vapour decreases with altitude, although this distribution may be reversed from time to time.,
