The radiation response of three-dimensional structure of ground objects is different from the reflection characteristics of their surface material at the pixel scale, which makes it difficult to extract and recognize the objects′ imaging features. Combined with the field experiment of the zero sight distance measurment of three-dimensional (3D) geometry, the influence of geometric structure on the composite reflectance of image pixels is analyzed. Based on the linear mixed model, some correction factors such as directional reflection characteristics, light shadow and end-member distribution are introduced into the model to improve its function. The results show that compared with the widely used linear mixed model, the accuracy of the improved model is increased to a certain extent for calculating the composite reflectance of the mixed pixel, and the relative error is reduced from 13.08% to 8.79%. In view of the complexity of the synthetic radiation effects of the 3D heterostructure mixed pixels, the completeness and universality of the improved model need to be further studied and verified.

In order to explore the response mechanism of PM2.5 concentration in ecotourism cities under the change of tourism activity intensity, the multifractal characteristics of PM2.5 and tourist population in Zhangjiajie City, China are analyzed respetively by using multifractal detrended fluctuation analysis method. The results show that the evolution of PM2.5 and tourist population has nonlinear and complex multifractal characteristics, and the multifractal characteristics of PM2.5 was stronger than that of tourists population. Furthermore, the cross-correlation between PM2.5 and tourism population is studied by using multifractal detrended cross-correlation analysis method. Itprimes found that not only there are multifractal characteristics with long-term sustainability between them, but also the multifractal characteristics of their correlation are obviously affected by the intensity of tourism activities, which shows that the multifractal characteristics in tourism peak season is stronger than that in slack tourism season. Finally, the backward trajectory model is used to analyze the spatial source of PM2.5 pollutants in Zhangjiajie during peak and slack tourism seasons. The results show that the PM2.5 pollutants in Zhangjiajie are mainly due to the local emissions, which indicates that tourism activity is the main influencing factors of PM2.5 in Zhangjiajie City.

By monitoring and analysis the ozone and meteorological observation data of the Yangtze River Delta, China, urban agglomeration in 2018, the temporal and spatial distribution characteristics of ozone and its correlation with meteorological elements in the region are studied.The results show that: (1) The ozone pollution in the Yangtze River Delta region shows the seasonal variation characteristics of high in spring and summer, and low in autumn and winter, and the ozone pollution in inland cities is more serious than that in coastal cities. (2) In the Yangtze River Delta region, inland cities mainly suffer from excessive pollution in summer, while coastal cities mainly in spring, and the number of daysof excessive ozone in inland cities is higher than that in coastal cities. (3) The daily variation of ozone is positively correlated with visibility, wind speed,and temperature, while negatively correlated with relative humidity. When the temperature is higher than 20°c, the relative humidity is between 20% and 60%, and the wind speed reaches 1.2 m·s－1 to 3.6 m·s－1, high-concentration ozone pollution is prone to occur. The research results have guiding significance for ozone joint prevention and control in the Yangtze River Delta.

The trend of total ozone column amount in China from 2005 to 2020 is studied with OMI daily Level-3 ozone column data products. By constructing the relevant database, the correlation between Chinarimes regional total ozone column density and latitude and longitude is analyzed based on data searching and data mining methods. The results show that the total ozone column amount over China increases with the increase of latitude from 2005 to 2020, and its relationship with longitude is affected by latitude. When the latitude is greater than a certain threshold, the total ozone column amount increases with the increase of longitude, and when the latitude is less than this value, the total ozone column amount basically remains stable from West China to East China. The results are of great significance to reveal the variation of total ozone column amount in China and to further analyze the change trend of global ozone.

Black carbon (BC) and brown carbon (BrC) are important light absorbers in the atmosphere. Recently, the contribution of atmospheric brown carbon to light absorption has become one of the research hotspots at home and abroad. During the 2014 Nanjing Youth Olympic Games, a real-time atmospheric observation was carried out using three-wavelength photoacoustic soot photometer (PASS-3), thermal denuder (TD), aerosol particle mass analyzer (APM), scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) at Nanjing Meteorological Bureau (32.06° N, 118.70° E) on Jiangxin Island of Nanjing, China. Based on Mie model and AAE method, the average light absorption coefficients of BrC at 405 and 532 nm were calculated to be (8.5±4.5) Mm－1 and (3.2±2.1) Mm－1, respectively, and the corresponding average light absorption contributions were (22.7±12.0)% and (13.6±9.2)%, indicating that the light absorptioncapacity of BrC is wavelength dependent. Furthermore, the sensitivity analysis of αBC with the change of refractive index in the core-shell model and external model was conducted. It is shown that in both models, αBC is the most sensitive to the imaginary part of the refractive index of BC core, followed by the real part of the refractive of BC core. While the difference is that in the external mixing model, the change of the real part of the refractive index of the non-light-absorption material does not affect the αBC.

Accurate remote sensing monitoring of cyanobacteria blooms in lakes can provide scientific basis for prevention and control of lake pollution. Based on Landsat8 multispectral data, Chaohu Lake, China, was taken as research objects, and normalized difference vegetation index (NDVI) model and floating algae index (FAI) model were used to extract the cyanobacteria blooms, then the intensity of cyanobacteria blooms extracted was divided into three levels.Furthermore, the two extraction methods were compared, and the distribution of cyanobacteria blooms in Chaohu Lake were analyzed. The research results show that: (1) the thresholds and grading thresholds determined for NDVI method and FAI method in this workcan effectively extract the cyanobacteria blooms in Chaohu Lake, (2) compared with NDVI method, FAI method can reduce the influence of clouds on the extraction accuracy, (3) the eutrophication in the western half of Chaohu Lake and its coastal waters has been serious, and the eutrophication in the eastern half of the Chaohu Lake is becoming serious. The extraction thresholds and classification thresholds of cyanobacteria blooms determined in this paper not only provide method support for the treatmentand early warning of cyanobacteria blooms in Chaohu Lake, but also provide reference for remote sensing monitoring of cyanobacteria blooms in other lakes.

Using MODIS L1B021KM data to obtain daily AOD data of Chengdu area, China, in 2018 firstly, then combined with PM2.5 ground monitoring data and meteorological data, a geographically weighted regression (GWR) model is constructed to obtain the monthly PM2.5 concentration of Chengdu. The results show that: (1) Compared with the multiple linear regression model, GWR model has higher credibility in the inversion of PM2.5 concentration in Chengdu area in 2018, which is specifically reflected in that R2, ERMS and EMA are 0.884, 7.8704 μg·m－3 and 6.1566 μg·m－3, respectively for GWR model in the inversion of PM2.5 concentration, which are better than 0.808, 9.7098 μg·m－3 and 7.6081 μg·m－3 of multiple linear regression. (2) On a monthly scale, PM2.5 concentration in Chengdu shows a characteristic of first decreasing and then increasing. The highest concentration reaches 67.38 μg·m－3 in February, and the lowest reaches 28.31 μg·m－3 in July. The seasonal variation of PM2.5 concentration is characterized by increasing in summer, autumn, spring and winter. (3) The spatial distribution of PM2.5 concentration in Chengdu generally presents a characteristics of “high in the middle and low on both sides”. The western region is a low-value PM2.5 concentration area, the central region is a high-valuearea, and Jianyang City and Jintang County in the east are the second-highest PM2.5 concentration areas.

To meet the technical requirement of on-orbit ground calibration of laser altimeter in the high precision stereo mapping satellite system in China, a laser pulse detector system is developed. The system adopts high-speed PIN detection unit and high-speed data acquisition circuit to realize quantitative acquisition of ns laser pulse, and realizes remote transmission of pulse detector data through radio frequency module. In order to ensure the field application performance of the pulse detector, the energy density test, energy response consistency and stability test, the field of view(FOV) measurement have been carried out for the system. The test results show that the energy acquisition in the range of 1-120 nJ·cm－2 can be accomplished by pulse detector, with the consistency of energy response better than 5% and the stability better than 1.5%, and ±12° FOV can be realized. Finally, the detector has been successfully applied tothe on-orbit calibration of the GF-7 satellite laser altimeter, and the effective laser trigger data of the detector array has been obtained, which provides effective data support for the on-orbit calibration test of the laser altimeter.

In order to achieve high-precision ground detection of time sequential signals of aerospace equipment, a special ground test system based on field programmable gate array (FPGA) is designed, and time-to-digital converers (TDC) is the key component of the system. The circuit adopts digital interpolation technology, where high-frequency clock is used to directly count for “coarse” measurement to ensure the measuring system range, and “fine” measurement is achieved by latching the phase shift clock level at the edge of the signal to be measured to improve the measurement accuracy. The sources of measurement errors is analyzed and the corresponding solutions are put forward. Through experimental verification, it is shown that the measurement resolution of the circuit meets the design value of 0.2 ns, and the measurement uncertainty caused by the repeatability is less than 0.1 ns. The circuit has high measurement accuracy, good flexibility and convenient design, and can meet the application requirements of related detection systems.