3.6热红外遥感

热红外遥感中3—5μm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”
Question: Of the materials in this table, which will show the largest temperature fluctuation during a 24-hr heating/cooling cycle; which the smallest?
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.
三、影响因素
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/ρ (units are calories per gram per degree Centigrade) where ρ (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.
热红外遥感的8—14μm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—12.5μm，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
林 火 的 发 射 波 谱
8—14μm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8-14μm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—11.5μm和11.5—12.5μm等 不同的通道来分别感应物质发射特征的微弱差 异。
热容:是用以衡量物质所包含的热量的物理量，单位是J· -1。 K
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 = (Kcρ )1/2 = cρ (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 substance's 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。
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— 12.43μm之间，其辐射峰顶值波长在 9.7μm附近，正是在热红外谱段8—14μm 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4.8μm， 在热红Байду номын сангаас谱段3—5μm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8-14μm和3—5μ m两个区间内．
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 Sun's 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