遥感物理-大气2011-1.ppt

1、,遥感物理柳 钦 火工作单位： 中国科学院遥感应用研究所 遥感科学国家重点实验室联系电话：64849840（O）Email: 2011年11-12月,中国科学院研究生课程,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 第七章地表通量遥感模型,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 ATMOSPHERECONTENT AND BASIC PROPERTIES 第二节辐射与大气的相互作用 INTERACTION OF RADIATION WITH ATMO

2、SPHERE 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,前 言,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；

3、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,前言 Introduction 第一节大气组成与大气的基本特性 ATMOSPHERECONTENT 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 ATMOSHPHER

4、IC REMOTE SOUNDING,5.1.1 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,第一节 大气组成与大气的基本特性,The composition of the atmosphere is important in any understanding of the role which the atmosphere plays in remote sensing and in int

5、eractions with electromagnetic 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 水汽凝结体(e.g. cloud droplets,

6、raindrops, snow, ice crystals, etc). About 99% of the mass lies below an altitude of 30km. Table 1 below shows the composition of the atmosphere below 100km.,5.1.1 大气成分 Composition,Table 1: Main constituents of the earths atmosphere * a concentration near the earths surface,氮、氧、氩、二氧化碳、氖、氦、氪、氙、氢、甲烷、氧

7、化氮、一氧化碳 水汽、臭氧、氨、二氧化硫、二氧化氮、痕量气体、气溶胶、尘埃,Nitrogen氮, oxygen氧 and argon氩 account for about 99.99% of the permanent gases. Of the variable constituents, carbon dioxide 二氧化碳can be somewhat variable in concentration on a localized basis at low levels. Water vapor 水汽content may vary from about 0 to 4% ozone臭

8、氧 concentrations also vary markedly. In addition to these variable constituents there are also aerosols 气溶胶 and hydrometeors水颗粒 which can vary widely in space and time.,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

9、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 O2+ O +M O3+M 臭氧分解作用：O3+ h O2+O* （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。,大气中的氧与臭氧（oxygen and Ozone ）,The concentration of ozone is highly variable in space (latitude and altitude for example) and time. Most ozo

10、ne is generated and destroyed by photochemical reactions in the layer between 20 km and 60 km. Ozone tends 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 surfac

11、e, ozone is destroyed rapidly by reacting with plants and dissolving in water, whereas in the stratosphere 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 earth

12、s surface. Depletion of the earths ozone layer has become a very serious issue following detailed observational and theoretical studies which have focused primarily on the Antarctic ozone hole.,臭氧（ Ozone ）,Carbon dioxide has a relatively constant mixing ratio with height in the atmosphere, that is,

13、it is fairly evenly distributed on average. The main sources 源: burning of fossil fuels化石燃料, human 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 carbo

14、n dioxide, a greenhouse gas, is observed to be less than the generation (from fossil fuel burning) because the concentration of carbon dioxide in the atmosphere has been rising steadily since the early part of the last century. About 99% of the earths carbon dioxide is dissolved in the oceans. The s

15、olubility is temperature dependent. It is estimated that the annual amount of carbon dioxide entering or leaving the air by all mechanisms is about one tenth of the total carbon dioxide content of the atmosphere.,二氧化碳（ Carbon Dioxide ）,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

16、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,大气中的其他微量成分（trace gases）,Atmospheric gases critically 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 ea

17、rths surface is determined by atmospheric gases. For example harmful UV radiation is blocked by the ozone layer. Also, “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 fo

18、r remote sensing applications.,Figure 1: (a) Atmospheric absorption at ground level for diffuse terrestrial radiation 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 (19

19、85), Atmospheric absorption features are shown in Figure1 for ground level and at an altitude of 11 km. Regions of minimal absorption (windows) .,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 gase

20、s. After Valley (1965).,5.1.1 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,第一节 大气组成与大气的基本特性,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

21、，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。,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,湿度参量,5.1.1 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

22、.8 水圈与水文循环 5.1.9 云与降水,第一节 大气组成与大气的基本特性,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：,5.1.1 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

23、5.1.8 水圈与水文循环 5.1.9 云与降水,第一节 大气组成与大气的基本特性,Vertical structure of pressure and density Quantities such as pressure, density and mean free 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 variati

24、ons. Meteorologists therefore commonly make use of a standard atmosphere in which geophysical quantities have been averaged horizontally and in time, and which vary as a function of height only.,5.1.4 大气压力和密度的垂直廓线,Figure 3: Vertical variation of pressure in hPa, and density in g/m3, for the US exten

25、sion 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, observed values of atmospheric pressure and density are fairly close to the standard atmosphere values for the same level. The ICAO standard atmosphere i

26、s specified by : sea level pressure (p) 1013.2 hPa Sea level temperature (T) 15 deg C fixed 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

27、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028.9644kg/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 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

28、 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 factor 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 deri

29、ved for density as follows: (z) = (0) exp (-z/H) Note that density also decreases rapidly with height. It can be shown that half of the mass of the earths 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

30、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 hectoPascals 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 atmos

31、phere lies above that level.,5.1.1 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,第一节 大气组成与大气的基本特性,In 1962 the World Meteorological Organization adopted a description of the atmosphere in terms of four distinct layers called

32、 the troposphere（对流层）, stratosphere（平流层、同温层）, 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 characterised by distinct mean variations of temperature with altitude, as defined in the ICAO

33、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 temperature lapse rate is 0 deg C per km, but from about 20km to 32km the lapse rate is -1

34、.0 deg C per km, in which case the atmospheric temperature increases with altitude.,5.1.5 大气温度和湿度的垂直廓线,Figure 4: Vertical temperature profile for the Standard Atmosphere with the main atmospheric regions as indicated. Adapted from Butler et al (1987), p111.,5.1.1 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

35、 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,第一节 大气组成与大气的基本特性,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

36、 next-generation active remote sensing instruments 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 c

37、limate.,5.1.6 大气气溶胶,(a) Composition Most aerosol 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) Concent

38、rations These vary considerably but are typically 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

39、nuclei (about 0.2 to 1.0 microns); giant nuclei (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, terr

40、estrial and microwave radiation The scattering 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, scatter

41、ing of sunlight by aerosols can be significant 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 particl

42、e size is very small compared to the wavelength. 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 budg

43、et. There are competing effects in that absorption of radiation would raise air temperatures, but aerosols tend to decrease temperatures by scattering solar radiation back into space.,5.1.1 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

44、环 5.1.9 云与降水,第一节 大气组成与大气的基本特性,Water vapour is extremely important in radiative absorption and emission processes in the atmosphere. Its concentration 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 o

45、r 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 49.8 grams of water per kg of dry air, while at 5 deg C this reduces to 5.5 grams per kg of dry air.,5.1.7 大气水汽（Water vapour）,The release of latent heat from conden

46、sation 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 weather. This is largely due to changes in its concentration and in latent heat release, particularly below about 6 km where a high propo

47、rtion 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 dist

48、ribution may be reversed from time to time.,5.1.7 大气水汽（Water vapour）,5.1.1 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,第一节 大气组成与大气的基本特性,Atmospheric water vapour currently accounts for only a small fraction (0.001%) of the

49、 mass of water in the hydrosphere. The main components, by mass, are the oceans (97%), ice (2.4%), ground water (0.6%), and lakes and rivers (0.02%). The total mass of the hydrosphere is about 1.4 x 1021 kg or about 1400 million cubic kilometres of liquid water. Although only 0.001% of the total mas

50、s is in the atmosphere, this represents about 13000 cubic kilometres of water. The evaporation amounts to 250 cubic kilometres per day.,5.1.8 水圈与水文循环 The hydrosphere and the hydrologic cycle,Table 3: The earths water balance (from Murphy et al (1987), p10.),There are a number of atmospheric processe

51、s which are important in the hydrologic cycle. These include the following: evaporation; precipitation; scattering, absorption and emission of energy in the form of solar radiation which maintains the cycle, and infrared radiation from the atmosphere, clouds and the earths surface; atmospheric circu

52、lation which results from a heat source (i.e. solar energy) combined with the effects of earth rotation. The circulation distributes heat energy over the globe; the effect of local changes in temperature, pressure, wind, water vapour content etc induced by the movement and development of meteorologi

53、cal systems.,Both evaporation and precipitation affect the transfer of energy over the earths surface and throughout the atmosphere. About 65% of the moisture in precipitation arises from oceanic evaporation, the rest from evaporation and transpiration over land. The hydrologic cycle is relevant to

54、many branches of science but from a meteorological or hydrological perspective it reinforces the concept that the atmosphere, oceans and land form a closely coupled physical system.,5.1.1 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

55、5.1.9 云与降水,第一节 大气组成与大气的基本特性,Clouds are composed of tiny water droplets or ice crystals which form on cloud condensation nuclei. Only a small fraction of aerosol particles are cloud condensation nuclei: about 1% over land, about 10 to 20% over oceans. Typical concentrations of cloud droplets are of o

56、rder 100 droplets/cm3. On average, droplets of continental clouds have typical radii ranging from 2 to 10 microns, whereas maritime cloud droplets may be larger and range from 3 to 22 microns. The relatively rare giant condensation nuclei may produce drops in the 20 to 30 micron range or larger. An

57、arbitrary division between cloud droplets and raindrops is made at a radius of 100 microns. Beyond this radius the drops have terminal velocities above about 1m/s which exceeds updrafts or vertical motion in typical clouds.,5.1.9 云与降水 Clouds and Precipitation,Clouds scatter visible radiation conside

58、rably. They emit IR and microwave radiation. They are fairly opaque at IR wavelengths but are virtually transparent to microwave radiation. This can be seen in Table 4. Table 4: Cloud Transmission (after Smith 1972),The growth of cloud droplets can proceed initially via condensation. However, this p

59、rocess in itself does not result in droplet radii larger than about 30 microns. In warm clouds (which lie completely below the 0 deg C isotherm and in which only water droplets can form) raindrops form by the collision and coalescence of cloud droplets, the efficiency of which increases markedly for droplets above about 18 micron radii. In cold clouds, which may contain supercooled water droplets, collision and coalescence is also an important process. However many