Thermal Infrared Radiance Modeling Of Land Surface Background And Imaging Simulation

The modeling of land surface thermal radiance scene and the simulation of the remote sensing imaging procedure play an important role in the studies of thermal remote sensing fields. Recently, with active renewals for remote sensors, the application fields meet more actuate observation precision for the Earth land. In this situation, the sensor designers need to develop various thermal imaging systems to meet the different and complex land radiance conditions, and the plentiful early demonstrations of the new remote sensing system are desired. The definitions of the sensors'parameters depend on various evaluations for the land surface radiance and imaging characteristics in different natural conditions, which require lots of field experiments. An economic and effective way is computer modeling and simulation. Meanwhile, with the correct understanding of the origin, reactive, and atmospheric transfer of surface energy flux senses, and the systematic analysis of the factors affecting the final thermal imagery, it is useful to improve the accuracy of land surface temperatures retrieval from thermal remotely sensed imageries.This research is made around the whole link of the thermal remote sense imaging system, and the main purpose of this paper is to investigate the thermal radiant characteristics of the typical land surface and to analyze the main factors for thermal remote sense imaging procedures. The main line of this paper is the origin and transfer of the land surface energy flux, where the focal points are the modeling and analyzing of the dynamic thermal radiance scenes.Assuming that the land surface background is composed by 5 typical components, including the vegetation canopy, the bare soil, the water body, the asphalt pavement and the concrete surface. Land surface temperatures for different land covers are the key parameters for land thermal radiance scenes modeling. Firstly, the temperature daily variations for four typical solid surfaces are modeled and analyzed, which are the vegetation canopy, the bare soil, the asphalt pavement and the concrete surface. The harmonic model is built to simulate the daily change of the temperature for bare soil, asphalt pavement and concrete surface, and a model of SVAT (soil-vegetation-atmosphere transfer), CUPID, is employed to simulate the vegetation canopy temperature. The biological and thermal proprieties of the foresaid four kinds of land surface are measured or evaluated, which are then used as inputs of the temperature models respectively, and 24-hour observations of the surface temperatures are carried to calibrate the modeled results. The sensitive analysis for the harmonic and CUPID model is made to exhibit the main impact factors for surface temperature.Based on the radiation heat exchange equation over surfaces and the linear-energy-mixed theory, the thermal radiance of land scenes with 5m/10 m spatial resolutions are modeled. The main inputs of the model are surface temperature, emissivity and spatial distribution of the components. The fractal-based method is applied to simulate the 3-Dimentional natural terrain; the proportion of each component is evaluated or extracted from multi/hyper-spectral optical remote sensing imageries. Daily variation of the directional brightness temperatures (DBT) for a 5 m resolution scene is simulated, and the influence of downwelling atmospheric radiant to the scene DBT is analyzed.The thermal reflectance for bare surface is not negligible during the scene radiance modeling, since the thermal radiance that emitted and reflected synchronously at each component are at the similar levels.. The concept of configuration factor is applied, and the multiple scattering effects between heterogeneous non-isothermal surfaces are described rigorously, based on which a directional thermal radiance model named Multi-Scattering Model (MSM) is built, and the numerical calculation of the MSM is discussed. The MSM is applied to modeling the DBT of row crops, and the results are compared with measured DBTs. The MSM is also used to describe the effective emissivity over non-isothermal targets, and a simulation of the remotely sensed pixels with "V" structure is performed, respectively.The atmospheric attenuation of land surface thermal radiation is simulated with 3 ways according to the abundance of the meteorological data, which is the radiative transfer method, the empirical method and the lookup table (LUT) method. The atmospheric effects simulations are carried out with a Gaussian-Triangular filter as the sensor channel response function, which takes the radiation wavelength range of 10.5μm-12.5μm. The degeneration of the land surface radiance by the atmospheric turbulence is simulated using very short exposure atmospheric modulate transfer function (MTF), and then the land scene thermal radiance at the top of the atmosphere is obtained. The physical procedure of the at-sensor radiance transfer in the thermal remote sensing camera system is analyzed briefly, and the halo and diffractive effects caused by the optical imaging system, and the image movement that is brought by the dither of the remote sensor platform are simulated. The stochastic noise of imaging system is indicated by the noise equivalent temperature difference (NETD) and the SiTF. The NETD is modeled and calculated according to the parameters of a remote sensor, and then the system noise is injected to the digital image. Finally, the response and degenerate of the radiance scene by the thermal remote sensor is simulated.With the modeling, simulation and analysis of the thermal radiance scene and the imaging procedure, some of results and conclusions can be drawn as follows: (1) The daily variation of the land surface temperatures are fluctuated by the solar radiance and the near surface metrological conditions. Meanwhile, they are restricted by the surface thermal/biological properties.The analytical temperature model with second harmonic terms presented in this paper can be used to predict the daily bare ground surface temperature variation with sufficient accuracy, and the result is restricted by the measurement or estimation veracity of the ground thermal properties. The solar radiance is the basic reason that makes the ground temperatures changing temporally. For bare surfaces, the daily diversity of the temperatures increases with the rise of the thermal conductivity, while the time that the peak value of the daily temperatures occursclose to midday as the convective heat transfer coefficient decreased.In addition, for vegetation canopies, the temperature in daytime is also affected by the leaf area indexes (LAI). There is a high correlation between surface and the air temperature, and a good correlation between temperatures and the relative humidity. In daily scale, the fluctuation of surface temperature is smoothly for vegetation canopy and water body, and rough for bare and dry surfaces; the minimized differs of all kinds of ground surface occurs at a short period of time before sunrise or after sundown. (2) The land radiance scene dynamically changed with the distribution of surface temperature, land cover and the observation directions.Base on the fractal terrain simulation and proportion information extraction of surface components, the land radiance scene and the DBT variation of it can be modeled easily and effectively, which the texture details of the land radiance distribution is remained. The multi-scattering effects over components of pixels can be completely described by the MSM model, with which the accuracy for effective radiance modeling of mixed pixels is enhanced. The effective emissivity for non-isothermal targets can also be defined by the usage of MSM. The results of thermal scene modeling show that both the detailed grade of the scene texture and the DBT characteristic of the whole scene are changing with solar-time, especially in a time period after sunrise. The more acuteness of the thermal diversity over pixels, the more details of the scene radiant textures and the variations of the scene DBTs. The effective radiance of land surface takes directional property, which is correlated with the temperatures, emissivity, spatial structure and subdivision extent of the components in each pixel. The effective radiance is aggrandized because of the multi-scattering effects, whereas the change range of DBT is smoothed. At the same time; the effective radiance is also enhanced by the downward atmospheric irradiation, which makes the brightness temperature close to the surface temperature, while the influence of the atmosphere for the scene directional brightness character can be neglected. The effective emissivity is magnified by the multi-scattering effects; the distinctness of the directional effective emissivity for non-isothermal pixel increases with the rise of the diversion for the components temperatures, the isomerous and subdivide state of the substructure, and decreases with the emissivity of components. (3) The land radiance scene is fainted by the atmospheric effects.The dynamic range of the thermal radiance scene is reduced by atmospheric extinction and radiation. The surface radiance transfer path is shuddered by the turbulent diffusion of atmosphere, and then the image that is projected to the infrared focal plane assembling (FPA) of sensor is shortly moved, which blurs the detected scene. The blurring effect drought by the atmospheric turbulence is increased with the rise of the spatial resolution for land scene and the atmospheric refractive index turbulent structure constant. The contribution of the atmospheric effects for ground radiance at TOA is positive at night while negative in daytime. Some parameters should be regarded during the simulation of atmospheric effects, which are the total water vapor contents, the observation angle, the setting of the response channels and the ground surface emissivity. (4) The land radiance scene image is deteriorated further after the response, transmission, processing of the signals by the sensor system.With the increase of the aperture size of the infrared camera, the energy focused to the FPA increases accordingly, and the image blurring brought by diffraction of the optical system is reduced consequently. The radiance response of the sensor is disturbed by detector integral time and vibration of the platform, and the remotely sensed imagery is deteriorated. The noise originated from the entire process of the land radiance imaging can be characterized by the NETD for highly integrated thermal infrared remote sensing system. With the simulation of the main steps of the sensor imaging procedures, the results show that image drift by the movement of platform is the key reason for which the image is blurred by sensor; the system noise is influenced by the ground radiant levels and the atmospheric transmittance, therefore the noise has significant effect on the image quality for night thermal scene.