3.6热红外遥感

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,热红外遥感,一、,概况,地表物体的温度一般在,+,40,-40,之间，平均环境温度为,27,(,相当于,300K),。根据维恩位移定律，地面物体,(,40,间,),的辐射峰值波长在,9.26,12.43,m,之间，其辐射峰顶值波长在,9.7,m,附近，正是在热红外谱段,8,14,m,的大气窗口内。,随温度升高发射辐射的峰值向短波方向移动。对于地表高温目标，如火燃等,:,其温度达,600K,，辐射峰值波长为,4.8m,，在热红外谱段,3,5m,的大气窗口内。所以，通常热红外遥感波段的选择总是在波长,8-14m,和,3,5 m,两个区间内,林火的发射波谱,8,14,m,热红外谱段的大气窗口，不仅集中了大多数地表特征的辐射峰值波长，而且在这个宽波段区间内，不同物体的发射率有较大的差异：同一物体的发射率则往往是不变的。进一步地研究还表明，在,8-14,m,谱段内，物质的发射率随着波长的变化仍有细微的变化。因此，在热红外遥感的应用中，往往又将此热红外谱段进一步分为,10.5,11.5,m,和,11.5,12.5,m,等不同的通道来分别感应物质发射特征的微弱差异。,热红外遥感的,8,14,m,谱段，主要用于调查地表一般物体的热辐射特性，探测常温下的温度分布、目标的温度场，进行热制图等。,美国陆地卫星,TM6 10.4,12.5,m,，热红外波段。中巴资源卫星,IRMSS,B9 10.40,12.50,m,热红外波段，,探测常温的热辐射差异。根据辐射响应的差异，可进行植物分析、土壤湿度研究、农业与森林区分、水体、岩石等地表特征识别以及监测与人类活动有关的热特征，进行热测定与热制图,热红外遥感中,3,5m,的短波红外谱段，对火灾、活火山等高温目标的识别敏感，常用于捕捉高温信息，进行各类火灾、活火山、火箭发射等高温目标的识别、监测。特别是对于森林火灾，它不仅可以清楚地显示火点、火线的形状、大小、位置，而且对小的隐火、残火，也有很强的识别能力。,二、热辐射原理,从理论上讲，自然界任何温度高于绝对温度,0,K(,或,273,C),的物体都不断地向外发射电磁波，即向外辐射具有一定能量和波谱分布位置的电磁波。其辐射能量的强度和辐射波谱分布位置是物质类型和温度的函数。正因为这种辐射依赖于温度，因而称“热辐射”,For any material, certain internal properties play important roles in governing the temperature of a body at equilibrium with its surroundings.,Heat Capacity,(C):,The measure of the increase in thermal energy content (Q) per degree of temperature rise. It denotes the capacity of a material to store heat. and we give it cgs units of calories per cubic cm. per degree Centigrade (recall from physics that a calorie cal is the quantity of heat needed to raise one gram of water by one degree Centigrade). We calculate heat capacity as the ratio of the amount of heat energy, in calories, required to raise a given volume of a material by one degree Centigrade (at a standard temperature of 15 Centigrade) to the amount needed to raise the same volume of water by one degree Centigrade. A related quantity,specific,heat,(c), is defined as C = c/ (units are calories per gram per degree Centigrade) where (rho) = density. This property associates Heat Capacity to the thermal energy required to raise a mass of one gram of water by one degree Centigrade.,三、影响因素,热容,:,是用以衡量物质所包含的热量的物理量，单位是,JK,-1,。,热容的定义是一定量的物质在一定条件下温度升高,1,度所需要的热,.,Thermal Conductivity,(K):,The rate at which heat passes through a specific thickness of a substance, measured as the calories delivered in one second across a one centimeter square area through a thickness of one cm at a temperature gradient of one degree Centigrade. (units: calories per centimeter per second per degree Centigrade),热容量,:,系统在某一过程中，温度升高（或降低）,1,所吸收（或放出）的热量,单位是,J/K,。,通常规定，系统吸收的热量为正值，而释放的热量为负值，故在系统吸收热量引起温度升高时，热容量为正值。也有的系统，如饱和水蒸汽，在温度升高时，释放热量，故其热容量为负值。,Thermal Inertia,(P):,The resistance of a material to temperature change, indicated by the time dependent variations in temperature during a full heating/cooling cycle (a 24-hour day for Earth); defined as P = (Kc )1/2 = c (k)1/2. (The term k, related to conductivity K, is known as,thermal,diffusivity, and has units of centimeters squared per second; this parameter governs the rate of temperature change within a material; it is a measure of a substances ability to transfer heat in and out of that portion that received solar heating during the day and cools at night). P is a measure of the heat transfer rate across a boundary between two materials. e.g., air/soil. Because materials with high P possess a strong inertial resistance to temperature fluctuations at a surface boundary, they show less temperature variation per heating/cooling cycle than those with lower thermal inertia.,热惯量：物体对温度变化的阻力。表征了两个不同介质边界热交换的速率。,Question: Of the materials in this table, which will show the largest temperature fluctuation during a 24-hr heating/cooling cycle; which the smallest?,Water Sandy Soil Basalt stainless steel,Thermal Inertia,0.038 0.024 0.053 0.168,Answer: Soil will show the largest diurnal temperature variations; steel the smallest.,Other Factors,Number and distribution of different material classes in an instantaneous field of view,Variations in the angle of thermal insolation relative to sensor position,Dependency of thermal response on composition, density and texture of the materials,Emissivities of the surface materials,Contributions from geothermal (internal) heat flux; usually small and local,Topographic irregularities including elevation, slope angle, and aspect (surface direction relative to the Suns position),Rainfall history, soil-moisture content, and evaporative cooling effects near the surface,Vegetation canopy characteristics, including height, leaf geometry, and plant shape,Leaf temperatures as a function of evapotranspiration and plant stress,Near surface (1 to 3 meters) air temperature; relative humidity; and wind effects,Temperature history of the atmosphere above the surface zone,Cloud-cover history (during heating/cooling cycle),Absorption and re-emission of thermal radiation by aerosols, water vapor, and air gases,Question:,All of the above factors play a role but some are more influential in determining the radiant temperatures than others. List, in your opinion, the five most important of these.,Variations in Sun angle; dependency on composition, density, and texture; topographic irregularities; rainfall and moisture variations; near surface climatic conditions. Several others might make the top five under appropriate circumstances.,四、热作用与温度,热是物质的内部能量，这种能量是由组成物质的原子、分子运动引起的。物质内部的能量,(,分子运动热能,),可以转变为辐射能。热量的单位是卡。一卡指的是一克水温度升高,1,所需的热量。,热能有三种形式的热传递：传导、对流、辐射。,传导,通过组成物质的分子相互作用来传递热，如烹调食物：,对流,通过受热物质的物理运动来传递热，如水热循环：,辐射,以电磁波的形式传热，如太阳辐射。与前二者不同的是热辐射可以在真空中传递。,温度是物体相对冷暖的一种度量。常用的温度尺度有华氏一、摄氏一、开氏,K,。,它们可以相互转换，如,0,=,273K,1,、分子运动温度,(Kinetic),，又称为真实温度,(True),分子运动温度为动力学温度。它是物质内部分子的平均热能的表现。一般通过温度计直接放置在被测物体上或埋于被测物体中来获得。这种接触测温法，往往因测温感应元件接触物体表面而破坏了原表面的热状态。,2,辐射温度,(Radiant),，又称为表征温度,(Apparent),。,物体向外辐射的能量是物体能量状态的一种,“,外部,”,表现形式，可用热传感器来探测。辐射能量常被用来测量地表特征的辐射温度。大多数热红外遥感系统记录的是物体的辐射温度,(T,rad,),。,3,亮度温度,(Brightness),“,亮度温度”是指辐射出与观测物体相等的辐射能量的黑体的温度。由于自然界的物体不是完全的黑体，因而习惯用一个具有比该物体的真实温度低的等效黑体温度来表征物体的温度。它是衡量物体温度的一个指标，而不是物体的真实温度。在微波遥感中常用亮度温度，而在红外遥感中多用辐射温度,对于黑体而言，物体的辐射温度,(T,rad,),等于它的动力学温度,(T,kin,),，但对于真实物体而言，两者的关系为 ,T,rad,=,3/4,T,kin,(01),此式说明物质的辐射温度总小于它的分子运动温度；同时还说明，若物体的发射率是未知数，就无法估算物体的真实温度。,以上讨论的热辐射是把目标当作朗伯源考虑的。但事实上，自然界的物体非朗伯源，热辐射是具有方向性的。,Kimes,观测到作物表面的亮度温度，从天顶角,0,一,80,可以相差,13,。这种差异是由作物的几何结构及真实温度的垂直分布造成的。,地表真实温度的反演,从热红外遥感数据反演地表真实温度是相当复杂的，只有同时获得亮度温度、比辐射率和环境辐照度三个基本要素，方可进行,在,反演,过程中，往往要进行热红外遥感与地面同步的测量或地面同步定标。建立起两者数据间的定量关系。最后，还需对所得的地面真实温度进行区域校正等，即运用到非遥感获得的微气象、植物生理生态、土壤物理等参数，方能得到具有实际应用价值的地表温度,五、典型地物的热特性,一般地物白天受太阳辐射影响，温度较高、呈暖色调；夜间物质散热，温度较低，呈冷色调。土壤、岩石尤为明显。,Diurnal Heating Effects,Central Atlanta,，,during the day (left) and then just before dawn (right),But in the dawn image, differences in temperature have decreased sharply (no shadows), although a part of that image is brighter, representing a local heat island effect. Also, in the dawn image, many streets are evident because, being asphalt paved, they absorb more heat and remain warmer through the night.,In the day thermal image, contrasts between heated buildings and streets and areas in shadow create a scene that resembles an aerial photo.,Changes in radiant temperatures of five surface-cover types during a 24-hour thermal cycle,不同土地覆盖类型的相对辐射温度变化曲线,从曲线看，黎明前各条温度曲线坡度较小，近于均衡状态，温度相对恒定；黎明后，这种均衡状态被打破，沙、草、林、水均变暖，往往在午后达到峰值，景物间的最大温差也往往出现于此时，以后景物又转为变凉。各条曲线均在黎明,(,日出,),后和黄昏,(,日落,),前温度变化最快，尤其是沙地,(,土壤岩石的代表类别,),曲线。而温度峰值及温度变化速率均能提供一些关于物质类型和条件的有用信息。,水的温度曲线表明一方面它的温度变化范围相比土壤岩石曲线十分小，另方面它到达最大温度的时间较沙、草、林等物质要滞后,l,2,小时，因而白天水温比周围地面温度低，而晚上，水温较周围地面温度高。仅在黎明后和日出附近，位于各曲线交叉点时，水和其它物质间辐射温度无差异。,一般说来，黎明前,(,约在午夜,2,3,时,),多反映一天中的最低温度；而午间,2,点左右，多反映一天中的最高温度，因而多采用这两个时段热红外成像的温度数据，构成日温差最大值，可以估算物体的热惯量，进行热制图。,水体具有比热大，热惯性大，对红外几乎全吸收，自身辐射发射率高，以及水体内部以热对流方式传递温度等特点，使水体表面温度较为均一，昼夜温度变化慢而小。因而白天水热容量大，升温慢，比周围土壤岩石温度低，呈冷色调,(,暗色调,),；,夜晚，水的贮热能力强，热量不易很快散失，比周围土壤、岩石温度高，呈暖色调,(,浅色调,),。这一现象主要是水体周围地面物体的温度变化大，而水本身温度变化小。,Question:,Letting the gray levels in a thermal image vary with temperature, predict the relative gray tones you would expect for a desert surface (rock and soil) and standing water at 4:00 AM and 2 PM.,At 4 AM, the water would be moderately warmer than the land; at 2 PM, the land would have bright gray tones and water moderate to dark tones.,4 thermal images taken by an airborne Daedalus thermal scanner that show a land area next to the Delaware River, on the New Jersey side.,The top three images were taken on December 28, 1979. The first on top was acquired during a pass at 06:00 hours when the air temperature was -9 C; the water relative to land was notably warmer (above freezing). The second image was obtained at 08:00 with the water still warmer than the land; the bright streak near the lands upper left point is hot effluent from a power plant. At 14:00 hours (3rd strip), the air temperature had climbed to -2 C and thermal contrast between land and water is near minimal; note the detail evident in the power plant; the effluent is now pointing downstream as ebb tide occurs. The power plant detail persists in the bottom image, taken on December 29th at 11:00 when the air temperature was -4: C. and the tide was near high. The scenes taken at different times and dates show the temperature variations that occur in the river water, and to a lesser extent on the land,湿地，昼夜均较干燥地面冷；这是因为水分蒸发时的冷却效应。,绿色林地,(,树,),辐射温度较高，夜间图像具暖标记，而白天虽受阳光照射，但因水分蒸腾作用降低叶的温度，升温不甚明显，使植被较周围土壤温度低。不过针叶林有些例外，这是因为其树冠针叶丛束的合成发射率高,对农作物覆盖区，传感器感应的是土壤上作物的辐射温度，而不是裸土本身。由于干燥作物隔开了地面，使之保持热量，从而造成农作区夜间也呈暖色，与裸露土壤的冷色调相对照。,人工铺设区如街道、停车场，白天比周围区域加热得温度更高，而夜里因散热较慢,，仍保持比周围温度高些。,六、热扫描图像的特点,1,，热红外图像记录了地物的热辐射特性,一种人眼看不见的性质。它依赖于地物的昼夜辐射能量而成像，因而它不受日照条件的限制，可以在白天、夜间成像，提供其它波段所无法提供的信息。,热图像可以简单地被认为是地物辐射温度分布的记录图像，它用黑,白色调的变化来描述地面景物的热反差，图像色调深浅与温度分布是对应的色调与色差是温度与温差的显示与反映。由于不同物体间温度或辐射特征的差异，可以根据图像上的色差所反映的温差来识别物体。一般说来，热图像,(,正片,),上的浅色调代表强辐射体，表明其表面温度高或辐射率高：深色调代表弱辐射体，表明其表面温度低,热红外图像经过温度定标，用灰阶来确定地物的温度（辐射温度）范围。,2,由于热扩散作用的影响，热红外图像中反映目标的信息往往偏大，且边界不十分清晰,。,3,热红外扫描图像具有所有扫描图像所固有的几何畸变，如扫描镜旋转速度变化，使像点间隔不恒定；飞行姿态的滚动、倾斜，使图像弯曲变形或比例尺变化等。,4,热红外扫描图像具有不规则性，这种不规则性可以是由多种因素引起的。比如：天气条件的干扰，云将降低热反差，雨将产生平行纹理，风将产生污迹或条纹图示，冷气流将引起不同形状的冷异常等；电子噪声的影响，无线电干扰将产生电子噪声带和波状云纹的干扰图式；后处理的影响，包括曝光，显影将产生显影剂条纹，胶片质量、受潮等将引起不规则污迹。这一切均可以使图像出现一些,“,热,”,假象。在图像解译中，必须注意识别图像上的各种假异常、排除它的干扰。,七、热图像的解译,在许多热红外扫描图像的应用中，如地质、土壤热制图等，一般仅需要定性地研究地面景物间辐射温度的相对差异，而不产生真正的定量信息，往往可通过对热图像进行密度分割、彩色编码等增强处理，以便解译。,另外，在一些热红外遥感应用中，还需要严格的定量数据分析以测定绝对温度,物体的真实温度。如，环境保护和监测部门作为执法工具的定量指标，来监测发电厂排出的热废水的表面温度再如，地表能量交换、植物蒸散作用的研究均需要地表真实温度这一参数,热图像已被成功地应用于许多领域,区域地质、水文地质、地热调查：由于岩石粒度、密度、粗糙度、孔隙度、含水性、颜色等直接影响其辐射率，而地质体的热惯量大小，主要控制其表面温度。可以根据其表面状态与热学性质来区分岩性、构造、找放射性矿、煤、油气、热泉等。,环境污染鉴别：烟尘，使地面蒙上“薄纱”，影响探测器记录，而形成冷异常；油污染，因油膜辐射率低于水而呈冷异常；热污染，包括工业热流、热管道及建筑物的热泄漏、污水等均呈热异常；城市热岛效应监测,灾害调查：森林火灾监测，热图像可清晰地显示出林区、山脉、河流、公路、迹地以及火点、火线的位置形状，火情的范围等；地下煤层自燃，即地下煤层受阳光照射后，氧化发射，聚热增温，最后达到自燃。这种自燃现象在我国北部煤田较为普遍。自燃区往往温度高出正常区,12,250,，地表也出现热异常区。此外，煤层上面岩石在高温中烘烤，而呈现紫红色系列的烧变岩，一般可以采用热红外图像及彩红外像片结合的遥感方法进行调查。此外，火山活化、地震临震前的热异常等灾害监测。,a series of Band 14 ASTER images of a continuing flow from the Kilauea volcanic rift on the Island of Hawaii, obtained between May 13, 2000 and January 1, 2001.,海洋调查：包括，海流、渔情、海冰、滩涂等。,Thermography; Night Vision Systems,Thermal imaging, as well as use of specialized thermal detectors, has grown into an important technology that is applied directly by users on the ground or from low-flying aircraft. The field is commonly called thermography. Using thermal sensors coupled with optical systems, one is able to see in the dark by detecting varying temperatures from different objects in the scene. Typical users include hunters and law enforcement officials; there are a number of military uses. Another frequent application is to check for heat loss from buildings or thermal contamination in streams.,This now widely used technology, called,Thermography,depends on scanners and cameras with detectors sensitive to emitted thermal radiation. In the 3-5 m region, Indium-Antimony (InSb) and Platinum silicide materials are sensitive to radiation in that spectral interval, with thermal photons knocking off electrons to create the varying signals that indicate temperature differences. In the 8-14 m region, Mercury-Cadmium-Telluride detectors are used.,Camera, which has a platinum silicide detector sensing radiation between 1.2 and 5.9 m.,Here is a set of Night Goggles which can be worn by a person directly over the eyes. It has proved invaluable to police raiding a building, firefighters, and hunters, as well as military personnel in combat.,the heat distribution within this pipe fitting,the appearance of a tank and a supply truck,