Assessing Spatial and Temporal Patterns of Observed Ground-level Ozone in China.

Elevated ground-level ozone (O3), which is an important aspect of air quality related to public health, has been causing increasing concern. This study investigated the spatiotemporal distribution of ground-level O3 concentrations in China using a dataset from the Chinese national air quality monitoring network during 2013-2015. This research analyzed the diurnal, monthly and yearly variation of O3 concentrations in both sparsely and densely populated regions. In particular, 6 major Chinese cities were selected to allow a discussion of variations in O3 levels in detail, Beijing, Chengdu, Guangzhou, Lanzhou, Shanghai, and Urumchi, located on both sides of the Heihe-Tengchong line. Data showed that the nationwide 3-year MDA8 of ground-level O3 was 80.26 µg/m3. Ground-level O3 concentrations exhibited monthly variability peaking in summer and reaching the lowest levels in winter. The diurnal cycle reached a minimum in morning and peaked in the afternoon. Yearly average O3 MDA8 concentrations in Beijing, Chengdu, Lanzhou, and Shanghai in 2015 increased 12%, 25%, 34%, 22%, respectively, when compared with those in 2013. Compared with World Health Organization O3 guidelines, Beijing, Chengdu, Guangzhou, and Shanghai suffered O3 pollution in excess of the 8-hour O3 standard for more than 30% of the days in 2013 to 2015.

[In-Flight Radiometric Calibration for ZY-3 Satellite Multispectral Sensor by Modified Reflectance-Based Method].

Through integrating multi-spectral sensor characteristics of ZY-3 satellite, a modified reflectance-based method is proposed and used to achieve ZY-3 satellite multispectral sensor in-flight radiometric calibration. This method chooses level 1A image as data source and establishes geometric model to get an accurate observation geometric parameters at calibration site according to the information provided in image auxiliary documentation, which can reduce the influences on the calibration accuracy from image resampling and observation geometry errors. We use two-point and multi-points methods to calculate the absolute radiometric calibration coefficients of ZY-3 satellite multispectral sensor based on the large campaign at Dongying city, Shan Dong province. Compared with ZY-3 official calibration coefficients, multi-points method has higher accuracy than two-point method. Through analyzing the dispersion between each calibration point and the fitting line, we find that the residual error of water calibration site is larger than others, which of green band is approximately 67.39%. Treating water calibration site as an error, we filter it out using 95.4% confidence level as standard and recalculate the calibration coefficients with multi-points method. The final calibration coefficients show that the relative differences of the first three bands are less than 2% and the last band is less than 5%, which manifests that the proposed radiometric calibration method can obtain accurate and reliable calibration coefficients and is useful for other similar satellites in future.

[Evaluation of four dark object atmospheric correction methods based on ZY-3 CCD data].

The present paper performed the evaluation of four dark-object subtraction(DOS) atmospheric correction methods based on 2012 Inner Mongolia experimental data The authors analyzed the impacts of key parameters of four DOS methods when they were applied to ZY-3 CCD data The results showed that (1) All four DOS methods have significant atmospheric correction effect at band 1, 2 and 3. But as for band 4, the atmospheric correction effect of DOS4 is the best while DOS2 is the worst; both DOS1 and DOS3 has no obvious atmospheric correction effect. (2) The relative error (RE) of DOS1 atmospheric correction method is larger than 10% at four bands; The atmospheric correction effect of DOS2 works the best at band 1(AE (absolute error)=0.0019 and RE=4.32%) and the worst error appears at band 4(AE=0.0464 and RE=19.12%); The RE of DOS3 is about 10% for all bands. (3) The AE of atmospheric correction results for DOS4 method is less than 0. 02 and the RE is less than 10% for all bands. Therefore, the DOS4 method provides the best accuracy of atmospheric correction results for ZY-3 image.

[A review of atmospheric aerosol research by using polarization remote sensing].

In the present paper, aerosol research by using polarization remote sensing in last two decades (1993-2013) was reviewed, including aerosol researches based on POLDER/PARASOL, APS(Aerosol Polarimetry Sensor), Polarized Airborne camera and Ground-based measurements. We emphasize the following three aspects: (1) The retrieval algorithms developed for land and marine aerosol by using POLDER/PARASOL; The validation and application of POLDER/PARASOL AOD, and cross-comparison with AOD of other satellites, such as MODIS AOD. (2) The retrieval algorithms developed for land and marine aerosol by using MICROPOL and RSP/APS. We also introduce the new progress in aerosol research based on The Directional Polarimetric Camera (DPC), which was produced by Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences (CAS). (3) The aerosol retrieval algorithms by using measurements from ground-based instruments, such as CE318-2 and CE318-DP. The retrieval results from spaceborne sensors, airborne camera and ground-based measurements include total AOD, fine-mode AOD, coarse-mode AOD, size distribution, particle shape, complex refractive indices, single scattering albedo, scattering phase function, polarization phase function and AOD above cloud. Finally, based on the research, the authors present the problems and prospects of atmospheric aerosol research by using polarization remote sensing, and provide a valuable reference for the future studies of atmospheric aerosol.

[Effects of aerosol optical thickness on the optical remote sensing imaging quality].

In recent years, due to changes in atmospheric environment, atmospheric aerosol affection on optical sensor imaging quality is increasingly considered by the load developed departments. Space-based remote sensing system imaging process, atmospheric aerosol makes optical sensor imaging quality deterioration. Atmospheric medium causing image degradation is mainly forward light scattering effect caused by the aerosol turbid medium. Based on the turbid medium radiation transfer equation, the point spread function models were derived contained aerosol optical properties of atmosphere in order to analyze and evaluate the atmospheric blurring effect on optical sensor imaging system. It was found that atmospheric aerosol medium have effect on not only energy decay of atmospheric transmittance, but also the degradation of image quality due to the scattering effect. Increase of atmospheric aerosol optical thickness makes aerosol scattering intensity enhanced, variation of aerosol optical thickness is also strongly influences the point spread function of the spatial distribution. it is because the degradation of aerosol in spatial domain, which reduces the quality of remote sensing image, in particularly reduction of the sharpness of image. Meanwhile, it would provide a method to optimize and improve simulation of atmospheric chain.

[Influence of measurement errors of radiation in NIR bands on water atmospheric correction].

For standard algorithm of atmospheric correction of water, the ratio of two near-infrared (NIR) channels is selected to determine an aerosol model, and then aerosol radiation at every wavelength is accordingly estimated by extrapolation. The uncertainty of radiation measurement in NIR bands will play important part in the accuracy of water-leaving reflectance. In the present research, erroneous expressions were derived mathematically in order to see the error propagation from NIR bands. The errors distribution of water-leaving reflectance was thoroughly studied. The results show that the bigger the errors of measurement are made, the bigger the errors of water-leaving reflectance are retrieved, with sometimes the NIR band errors canceling out. Moreover, the higher the values of aerosol optical depth or the more the component of small particles in aerosol, the bigger the errors that appear during retrieval.

[The research on remote sensing dust aerosol by using split window emissivity].

Dust aerosol can cause the change in the land surface emissivity in split window by radiative forcing (RF). Firstly, the present paper explained from the microscopic point of view the extinction properties of dust aerosols in the 11 and 12 microm channels, and their influence on the land surface emissivity. Secondly, on April 29, 2011, in the northern region of Inner Mongolia a strong sandstorm outbroke, and based on the analysis of the changes in land surface emissivity, this paper proposed a dust identification method by using the variation of emissivity. At last, the dust identification result was evaluated by the dust monitoring product provided by the National Satellite Meteorological Center. The result shows that under the assumption that the 12 microm emissivity equals to 1, using 11 microm relative emissivity could identify dust cover region effectively, and the 11 microm relative emissivity to a certain extent represented the intensity information of dust aerosol.

[The polarization characteristics distribution and correction method of the polarization coupling error in ocean remote sensing system].

With the development of the quantitative researches using ocean color remote sensing data sets, study on reducing the uncertainty of the response of the ocean color remote sensors to the polarization characteristics of the target has been attracting more and more attention recently. Taking MODIS as an example, the polarization distribution in the whole field of view was analyzed. For the atmosphere path radiance and the apparent radiance considering the coupling between ocean surface and atmosphere, the polarization distribution has a strong relation with the imaging geometry. Compared to the contribution of the polarization from the rough sea surface, the contribution from the atmosphere is dominated. Based on the polarization characteristics in the field of view, the influence of the polarization coupling error on the quality of the satellite data was studied with the assumption of different polarization sensitivities. It was found that errors due to polarization sensitivity in the field of view are lower than water leaving radiance only when the polarization sensitivity is less than 2%. And in this case it can meet the need of the retrieval of water leaving radiative products. The method of the compensation for the polarization coupling error due to the atmosphere is proposed, which proved to be effective to improve the utilization of satellite data and the accuracy of measured radiance by remote sensor.

[Retrieval of dust fraction of atmospheric aerosols based on spectra characteristics of refractive indices obtained from remote sensing measurements].

Mineral dust is an important chemical component of aerosol, which has a significant impact on the climate and environmental changes. The spectral behavior of aerosol refractive indices at four wavelengths from 440 to 1 020 nm was analyzed based on one year observation obtained from Beijing AERONET site. The real parts of refractive index (n) in each band did not differ greatly, however the imaginary parts (k) showed a significant difference due to the absorption of mineral dust in aerosol. From 440 to 670 nm k decreased rapidly, while from 670 to 1 020 nm featured a lower, constant value. Accordingly, k(440 nm) could be considered separately with other three bands. Hence, we added mineral dust into the currently used three-component aerosol chemical model to form a new four-component model (i. e. BC, AS, dust and water) which is more suitable to represent the aerosol chemical composition. Then we presented a method to retrieve dust content in aerosols using this four-component model and refractive indices obtained from the sunphotometer measurements. Finally the dust content in aerosol was investigated under different weather conditions, i. e. clear, haze and dust in Beijing. The results showed that volume fractions of the dust component were 88%, 37% and 48% for clear, hazy and dusty day respectively, which was consistent with the coarse mode proportion in aerosols calculated from aerosol size distributions.

[Spatial resolution standardization of payload on board of remote sensing satellite based on application requirements].

Remote sensing application requirements are the starting point for design of payload on board earth observation satellite. The generalization, standardization and serialization of payload are the future development trend for payload design. In the present paper, based on the analysis of remote sensing application requirements, the spatial resolution standardization of satellite remote sensing payload, which is the main concerned indicator, was investigated. The design standards of national payload spatial resolution of earth observation satellite are presented, which are important to the promotion of satellite payload production and saving in design cost.

[Research on calibration methods of ground-based thermal-infrared radiometer CE312].

The accuracy of the calibration coefficients of the ground-based thermal-infrared radiometer CE312 is one of the most important factors affecting the calibration of the thermal-infrared remote sensors. The theory of two calibration methods which calculate the bandpass radiance and spectral radiance respectively is introduced. The calibration of the CE312-1b is conducted with the blackbody in the laboratory, the accuracy and influence factors of the results are conducted by the MODIS data combined with in situ measurements data at Qinghai Lake in Aug 2010. The results show that calibration coefficients of thermal-infrared field radiometer CE312 calculated by the bandpass radiance method has better performance in the accuracy and applicability than the spectral radiance method.

[Stereoscopic remote sensing used in monitoring Enteromorpha Prolifra disaster in Chinese Yellow Sea].

In the summer 2008, Enteromorpha Prolifra broke out in Yellow Sea and East Sea on a large scale for the first time, and became a marine disaster. The authors constructed a stereoscopic monitoring system which monitored the disaster continuously, dynamically and in real time. The present paper introduced the construction of the stereoscopic monitoring system; through analyzing the spectral characteristics of Enteromorpha Prolifra and ocean water which were acquired in a field experiment, confirmed Enteromorpha Prolifra retrieval models based on multi-platform multi-sensor and multi-spectral remote sensing data, contrasted the different scale monitoring results, and analyzed the evolvement rules with time-series analysis. This system was applied to the Enteromorpha Prolifra emergency monitoring in the 29th Olympic sailing area. It was proved feasible and valuable for the Olympic safeguard.

[Simulation and analysis of polarization characteristics for real sea surface sunglint].

The sea surface sunglint is caused by specular reflectance. Water is a kind of dark target with a very low reflectance, so sunglint becomes a big noise in the aerial or aerospace remote sensing images; sunglint is strongly polarized, and can be a natural standard light source for polarized sensor in-flight calibration; sunglint also can be utilized to retrieve gaseous constituents and aerosol properties. For both de-noising and being standard light source, the radiative physic parameters should be calculated accurately. First, A 3-D sea surface model was constituted according to the Cox & Munk model; Second, the polarized radiative model of sunglint was deduced based on the 3-D sea surface model and polarized Fresnel reflectance law; Third, the sensitivities of solar-viewing relative azimuth, zenith, wind speed and wind direction were analyzed utilizing the polarized radiative model. The polarization characteristics analysis of sunglint provides a theoretical basis for the quantitative remote sensing retrievals which uses sunglint.

[Simulation of polarization SAR imaging of ocean surface].

The polarization synthetic aperture radar (SAR) imaging simulation is of great significance to ocean surface scattering. According to the theory of wind-wave spectrum, rough ocean surface was modeled in the present paper using the two-scale-model. This treatment takes both the large scale and small scale surface into account. By using the velocity bunching (VB) theory, Bragg scattering model and the small perturbation model (SPM), the polarization SAR system can simulate the ocean surface with various parameters and ocean states. The effects of the parameters of ocean waves and the parameters of SAR system were analyzed. Finally, some useful conclusions were drawn, which are helpful for extracting the information of ocean surface. The method is an effective way in the ocean SAR design and the ocean surface research.

[Atmospheric correction method for HJ-1 CCD imagery over waters based on radiative transfer model].

Atmospheric correction is a bottleneck in quantitative application of Chinese satellites HJ-1 data to remote sensing of water color. According to the characteristics of CCD sensors, the present paper made use of air-water coupled radiative transfer model to work out the look-up table (LUT) of atmospheric corrected parameters, and thereafter developed pixel-by-pixel atmospheric correction method over waters accomplishing the water-leaving remote sensing reflectance with accessorial meteorological input. The paper validates the HJ-1 CCD retrievals with MODIS and in-situ results. It was found that the accuracy in blue and green bands is good. However, the accuracy in red or NIR bands is much worse than blue or green ones. It was also demonstrated that the aerosol model is a sensitive factor to the atmospheric correction accuracy.

[HJ1A/HSI radiometric calibration and spectrum response function sensitivity analysis].

Hyper spectrum imager (HSI) loaded on HJ-1A satellite is Chinese first spaceborne hyperspectrum sensor. Since the HSI has no spectrum response function of all channels, the usually used calibration method-reflectance based method has been modified, and a new calibration method is proposed, in which the spectrum response function is neglected. Based on the calibration experiment data of Dunhuang in Aug., 2009, the HSI sensor was calibrated on orbit. The different kinds of spectrum response were constructed based on the formula, and the errors of calibration results with different spectrum response function were analyzed. The results show, expecting for the channels of water vapor and oxygen absorption channel, the influence of spectrum response function in other channel is less than 3%, and the calibration result based on new calibration method can satisfy the application requirement.

[Error analysis of the land surface temperature retrieval using HJ-1B thermal infrared remote sensing data].

Error analysis is playing an important role in the application of the remote sensing data and model. A theoretical analysis of error sensitivities in land surface temperature (LST) retrieval using radiance transfer model (RT) is introduced, which was applied to a new thermal infrared remote sensing data of HJ-1B satellite(IRS4). The modification of the RT model with MODTRAN 4 for IRS4 data is mentioned. Error sensitivities of the model are exhibited by analyzing the derivatives of parameters. It is shown that the greater the water vapor content and smaller the emissivity and temperature, the greater the LST retrieval error. The main error origin is from equivalent noise, uncertainty of water vapor content and emissivity, which lead to an error of 0.7, 0.6 and 0.5 K on LST in typical condition, respectively. Hence, a total error of 1 K for LST has been found. It is confirmed that the LST retrieved from HJ-1B data is incredible when application requirement is more than 1K, unless more accurate in situ measurements for atmospheric parameters and emissivity are applied.

[Mid-infrared atmosphere radiation transfer analytic model and remote sensing images simulation].

In order to establish a complete set of simulation system for high-resolution mid-infrared remote sensing and provide a powerful reference for spacecraft design and related works, the importance of atmospheric radiative transfer simulation in this system was considered, and a reasonable and high precision imaging numerical simulation method was expected. Taking into account the characteristics of MIR, including scattering and thermal emission, terms of atmospheric radiative transfer were decomposed based on radiative transfer principle, and images of top of atmosphere (TOA) were simulated according to MODTRAN4 and look-up table method. Besides, adjacency effect caused by atmospheric scattering of neighboring pixels radiation was considered, and an extended point spread function in mid-infrared was coupled with analytical model of atmospheric radiative transfer to simulate TOA images. Finally, a preliminary test and simulation results show that the simulation model has better accuracy. If parameters of observation geometry and atmosphere were given and the land surface temperature/emissivity was determined, the calculation of pixel-level atmospheric radiative transfer was to be achieved.