遙感物理-大氣2011-1.ppt

1、,遙感物理柳 欽 火工作單位： 中國科學(xué)院遙感應(yīng)用研究所 遙感科學(xué)國家重點(diǎn)實(shí)驗(yàn)室聯(lián)系電話：64849840（O）Email: 2011年11-12月,中國科學(xué)院研究生課程,遙 感 物 理,緒論 第一章基本概念 第二章植被遙感模型 第三章土壤與冰雪遙感模型 第四章海色遙感 第五章大氣效應(yīng)及其糾正 第六章熱紅外遙感 第七章地表通量遙感模型,第五章大氣效應(yīng)及其糾正,前言 Introduction 第一節(jié)大氣組成與大氣的基本特性 ATMOSPHERECONTENT AND BASIC PROPERTIES 第二節(jié)輻射與大氣的相互作用 INTERACTION OF RADIATION WITH ATMO

2、SPHERE 第三節(jié)大氣效應(yīng)糾正 ATMOSHPHERIC EFFECT CORRECTION 第四節(jié)大氣的遙感探測(cè) ATMOSHPHERIC REMOTE SOUNDING,前 言,大氣：是介于遙感傳感器與地球表層之間的一層由多種氣體及氣溶膠等組成的介質(zhì)層，當(dāng)電磁波由地球表層傳至遙感傳感器時(shí)，大氣是必經(jīng)的通道； 大氣對(duì)電磁波的作用：主要可以歸納為兩種物理過程，即吸收與散射，對(duì)地表遙感來說，大氣的吸收與散射作用均可使電磁波信息受到削弱； 遙感圖像的大氣糾正：如何依據(jù)遙感圖像直接或間接獲得的大氣參數(shù)，消除大氣對(duì)電磁波屬性量的影響，恢復(fù)其在地球表層的“本來面目” ，就成為定量遙感不可回避的問題；

3、大氣屬性參數(shù)的遙感反演：無論是置于地面的傳感器還是星載的傳感器，當(dāng)它接收到從大氣作用后的電磁波時(shí)，它必然帶有大氣的特征信息，因此我們可以設(shè)法從中反演出表征大氣屬性的參數(shù)，如大氣氣溶膠與大氣水汽等。,第五章大氣效應(yīng)及大氣糾正,前言 Introduction 第一節(jié)大氣組成與大氣的基本特性 ATMOSPHERECONTENT AND BASIC PROPERTIES 第二節(jié)輻射與大氣的相互作用 INTERACTION OF RADIATION WITH ATMOSPHERE 第三節(jié)大氣效應(yīng)糾正 ATMOSHPHERIC EFFECT CORRECTION 第四節(jié)大氣的遙感探測(cè) ATMOSHPHER

4、IC REMOTE SOUNDING,5.1.1 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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混合氣體, some with fairly constant concentrations, others that are variable in space and time. In addition there are suspended particles 懸浮顆粒(e.g. aerosol, smoke, ash etc.) and hydrometeors 水汽凝結(jié)體(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 大氣成分 Composition,Table 1: Main constituents of the earths atmosphere * a concentration near the earths surface,氮、氧、氬、二氧化碳、氖、氦、氪、氙、氫、甲烷、氧

7、化氮、一氧化碳 水汽、臭氧、氨、二氧化硫、二氧化氮、痕量氣體、氣溶膠、塵埃,Nitrogen氮, oxygen氧 and argon氬 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 氣溶膠 and hydrometeors水顆粒 which can vary widely in space and time.,氧氣占地球大氣質(zhì)量的23%，除游離存在的氧氣以外，氧還以硅酸鹽、氧化物和水化物等形式存在，在高空中還有臭氧與原子氧。氧占包括海洋和大氣在內(nèi)的地殼質(zhì)量的49.5%。 光合作用： nCO2+nH2OCH2On+nO2 水汽的光解作用：2H2O2H2+O2（太陽紫外輻

9、射） 氧的分解作用 ：O2+hO+O （短于0.24微米的紫外輻射） 復(fù)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微米的紫外輻射） O3+ O*2 O2 （太陽紫外輻射） 其中M是第三種分子（N2、O2或其它分子），吸收反應(yīng)中釋放的化學(xué)能。,大氣中的氧與臭氧（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火山活動(dòng). The main sinks 匯: 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 + 硫化氫 H2S 占硫化合物總量的80-90% 氮化合物 氮?dú)馐谴髿庵凶钬S富的氣體，性質(zhì)穩(wěn)定，僅有

16、極少量的N2能被微生物固定在海洋和土壤里，變成有機(jī)化合物。氣體氮化合物主要有： 氧化亞氮N2O, 一氧化氮NO,二氧化氮NO2 , 氨NH3,大氣中的其他微量成分（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太陽輻射 reaching the ea

17、rths surface is determined by atmospheric gases. For example harmful UV radiation is blocked by the ozone layer. Also, “windows” 大氣窗口 in which atmospheric effects are minimal allow ground-based measurements of celestial(天體) 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 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,氣象要素：大氣中的物理現(xiàn)象和物理變化過程，可以用氣溫、氣壓、濕度、能見度、風(fēng)向、風(fēng)速、云量、日照、輻射強(qiáng)度等物理量來描述。其中氣溫、氣壓、濕度和能量等最為重要。 氣象臺(tái)站的觀測(cè)場(chǎng)通常設(shè)在空曠的平地上，并把溫度表放入離地面1.5米的百頁箱內(nèi)，是溫度不受陽光的直射

21、，又能保持通風(fēng)。地面氣溫通常指百頁箱溫度。 物理表面單位面積所受的大氣分子的壓力稱為大氣壓強(qiáng)或氣壓?？諝饪煽闯墒腔旌蠚怏w，壓強(qiáng)可寫成： p=(2/3) *sum(n0iw) w=(3/2)*kT 其中n為各氣體成分的數(shù)密度，w為分子平均動(dòng)能，k為波爾茲曼常數(shù)。氣壓與分子數(shù)密度及溫度成正比。,飽和水汽壓 混合比與比濕 水汽壓 水汽密度（絕對(duì)濕度） 相對(duì)濕度 露點(diǎn)與霜點(diǎn) 虛溫,濕度參量,5.1.1 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1

22、.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,空氣可以看作是有多種化學(xué)成分的混合氣體。理想氣體的狀態(tài)方程為： 其中p為總壓強(qiáng)，V是容積，T為絕對(duì)溫度，m為氣體的總質(zhì)量，R*為普適氣體常數(shù)8.3143X*103J/kmol*K, 為平均mol質(zhì)量。 根據(jù)氣體狀態(tài)方程和道爾頓分壓定律，可定義混合氣體的平均mol質(zhì)量為 比氣體常數(shù)為： 干空氣的狀態(tài)方程可以寫為：,5.1.1 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽

23、5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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 大氣壓力和密度的垂直廓線,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國際民用航空組織) 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,我國有關(guān)部門將此標(biāo)準(zhǔn)與我國60個(gè)臺(tái)站的30公里以下部分的氣球探空資料進(jìn)行比較后，認(rèn)為與北緯45度的實(shí)際大氣十分接近，低緯度地區(qū)有較大偏差。 在建立我國自己的標(biāo)準(zhǔn)大氣以前，可使用1976年美國標(biāo)準(zhǔn)大氣，取其30公里以下部分作為國家標(biāo)準(zhǔn)。該模式假定大氣是干燥的，在86公里以下是均勻混合物，可以作為理想氣體處理，處于靜力學(xué)平衡和水平成層分布。在給定溫度-高度廓線及

27、邊界條件后，通過對(duì)靜力學(xué)方程和氣體狀態(tài)方程求積分，就可以得到壓力和密度數(shù)值。 海平面大氣的部分特性如下： 空氣Mol質(zhì)量028.9644kg/kmol 重力加速度 g0 9.80665 m/s 2 壓強(qiáng) P0 101325Pa 密度 0 1.2250kg/m3 溫度 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 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,In 1962 the World Meteorological Organization adopted a description of the atmosphere in terms of four distinct layers called

32、 the troposphere（對(duì)流層）, stratosphere（平流層、同溫層）, mesosphere（中性層） and thermosphere（熱層）. 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 大氣溫度和濕度的垂直廓線,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 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程

35、 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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 大氣氣溶膠,(a) Composition Most aerosol particles originate from blowing soil, smoke, volcanoes, and the oceans. Particles made of sodium chloride氯化鈉 or magnesium chloride氯化鎂 are hygroscopic 吸濕的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 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循

44、環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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 大氣水汽（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 大氣水汽（Water vapour）,5.1.1 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán) 5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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 水圈與水文循環(huán) 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 大氣成分 5.1.2 描述大氣狀態(tài)的基本參量 5.1.3 大氣靜力學(xué)方程 5.1.4 大氣壓力和密度的垂直廓線 5.1.5 大氣溫度和濕度的垂直廓線 5.1.6 大氣氣溶膠 5.1.7 大氣水汽 5.1.8 水圈與水文循環(huán)

55、5.1.9 云與降水,第一節(jié) 大氣組成與大氣的基本特性,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 云與降水 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