The bidirectional reflectance distribution function (BRDF) is a physical quantity that represents the change of surface reflection with the Sun and the direction of observation, which is of great significance to the study of surface anisotropic reflection characteristics. In this paper, based on MODIS (Moderate Resolution Imaging Spectroradiometer) BRDF model parameters products (MCD43A1), we utilize the Ross-Li model to simulate the surface reflectance of the four land surface types in North China: vegetation, bare soil, cropland, and urban, and comparatively analyze the seasonal variation of their surface anisotropic reflection characteristics. Therefore, this study can provide reliable scientific basis for improving land surface process model, promoting surface-atmosphere interaction and global climate change research. The results show that: (1) The backscattering of the four land surface types is greater than the forward scattering, and the larger the scattering angle is, the larger the bidirectional reflectance will be. The distribution trend of bidirectional reflectance of different surface types is quite different in different bands and seasons. (2) The bidirectional reflectance of the four land surface types varies with the wavelength roughly the same in spring, summer, and autumn. In winter, due to snow covering the ground, the bidirectional reflectance of vegetation, cropland, and urban is higher in visible and near-infrared bands. Due to the fixed simulation angle, the distribution trend of the bidirectional reflectance of bare soil in four seasons is multipeak in the multi-band range.
For general power system, the thermal exhaust at the exit of funnel has obvious infrared radiation characteristics. In this paper, funnel exhaust plume about the dynamic system is modeled and analyzed. The 3D flow field of exhaust plumes is calculated based on CFD methods. A calculation method of high temperature exhaust plume's infrared radiation is obtained by spectral band model and calibration with C-G two parameters. And the effect of the detecting azimuth angle on the flow field and the infrared radiation of ship exhaust plumes is analyzed. It can be concluded that with the detection angles’ increasing, the space distribution of the exhaust plume shows a tendency to increase progressively. The difference of the radiation intensity of different detection angles can be up to 32.6%.
Using the meteorological statistics from NCEP reanalysis data, the detection distances of point source targets at sea in medium and long waves are calculated. The difference of detection distance between different locations in two infrared bands is analyzed. And the detection distance difference of the same location in different months of the year. The results show that the influence of season on detection distance is greater in long wave than in medium wave. There is little difference in detection distance between different locations and months of medium wave. The detection distance of long wave varies greatly with location and month. Of the three sites surveyed, the largest difference was 20%.
Detection distance is an important index of infrared imaging system, and meteorological parameters are one of the main factors affecting the detection distance. The calculation model based on the detection distance of infrared detector point source is calculated by using MODTRAN software. Peel off the factors associated with the environment. Selecting typical weather conditions to calculate the detection distance of infrared detector's point source target. The detection distance under different atmospheric parameters is obtained, and the sensitivity analysis is carried out between the detection distance of infrared detector and the parameters of the meteorological environment. The results show that the detection distance is influenced by the parameters such as temperature, humidity, pressure, visibility, wind speed and so on, and is linearly related to these meteorological parameters.
Cloud is a common natural phenomenon in the sky, and has an irregular and arbitrary appearance. Cloud has serious interference with optical sensors, so it is meaningful to research the optical characteristic of cloud. In this paper, lidar was used to measure the vertical atmosphere, and the atmospheric extinction characteristic data were obtained by retrieving the measured data. During the measurement period, clouds appeared in the sky, and it information was recorded. The extinction characteristics of cloud, the height of cloud bottom and the height of cloud top were given, and the transmittance and optical thickness of the cloud were further analyzed.
Cloud is an important natural phenomenon, and its radiation causes serious interference to infrared detector. Based on fractal and statistical data, a method is proposed to realize cloud background simulation, and cloud infrared radiation data field is assigned using satellite radiation data of cloud. A cloud infrared radiation simulation model is established using matlab, and it can generate cloud background infrared images for different cloud types (low cloud, middle cloud, and high cloud) in different months, bands and sensor zenith angles.
Typical natural backgrounds include land, sea, desert, sky and so on, and experimental measurement is an effective means to obtain background radiation data. Because the background infrared radiation is affected by season, weather and the angle of solar radiation, it is necessary to collect environmental parameters at the same time during testing. The screening and collection of major environmental parameters is crucial for subsequent radiation data processing. In view of this problem, first of all, the influence of environmental reference on background infrared radiation was theoretically calculated by MODTRAN software, and the main parameters were screened out. A test program for radiation measurement of natural background is formed, which is used as a reference for the design of background infrared radiation measurement.
Lidar is used to measure atmospheric aerosol, and horizontal visibility is retrieved based on lidar measurement data. In the process of visibility retrieval, it’s manually ascertaining linear region that existed in the curve of data, which is difficult for computer. An algorithm is presented to ascertain the linear region and gives out the horizontal visibility automatically. A group of lidar measurement data is processed by the algorithm, and the results show its practicability.