| Atmosphere, the most active composition of the earth system, with whichthe land and sea interacts, is very important to the life-beings on the earth.Long-term observation shows that the activities of human-beings are changingthe composition of the atmosphere, and thus cause the variety of the climate,human's health, ecosystem balance and the ability of atmosphere. Andbecause of the importance of the trace gas and the greenhouse gas, long-termand short-term observations of atmospheric chemical composition's changingtrend are always the problems of concern to atmospheric scientists. Theatmospheric observation system consists of ground-base observing, aerialobservation, satellite remote sensing and data assimilation system. Comparedwith the traditional ground-base observing and aerial observing, the satelliteremote sensing provides a global three-dimensional dynamic atmosphericozone profile and volume ozone measurement, and the atmosphere limbscattering technology can provide a measurement with better ground overlayand higher precision of atmospheric profile measurement. The Simulation onAtmospheric Volume Emission from Limb Scatting, which is one part of thenational '863 Project, aims at the retrieval of the atmospheric ozone profileusing the the atmospheric limb scattering data and better studying thetempo-space transformation of the ozone by means of the tomography technique in medical science and earthquake science. The Simulation on Atmospheric Volume Emission from Limb Scatting is the pre-research of this project, this paper mainly discusses the simulation on atmospheric volume emission and the analysis on the simulation result by analyzing the geometric features and the imaging mechanism of the atmospheric limb scattering technique, and provides the theoretical basis for the upper retrieval and can be used to test the retrieval algorithm and observation data.For the purpose of simulation of observation, three coordinate systems such as ascending node coordinate system, satellite coordinate system and instrument coordinate system with whose transformation were established from the analysis of relationship between satellite, earth and imager in the Limb mode. It provides spatial reference to the quantitative expression of attitude and position parameters of satellite and volume emission grid.Each measurement is made with a finite exposure time and the satellite changes its orientation and position during this time, a temporal resolution factor - NumTimes is required to discretize one observation to some instantaneous fields of view (IFOV). In order to process the continuous field of view, the observation set were firstly divided into sub-fields of view according to pixel array, and then made it discretization in single observation model, finally expresses it with observation direction vector set and corresponding sensitivity factor in the observation model. Similarly, for the sake of the numerical expression of the volume emission rate of the continuous atomspheric detective area above the earth surface, two-dimensional discrete emission grid was established, and the volume emission profile based on the grid and the atmospheric vertical volume emission profile was simulated.The brightness observation is the integration of volume emission rate, which is incumbent on the two-dimensional discrete emission grid, along the observation vector direction. The integration was discretized into cumulative sum along the observation direction, so each grid cell was regarded as one integral unit. The contribution to each cell acted on the whole observation brightness could be calculated when the length of visual line of each cell and volume emission rate were calculated. This paper describes how to calculate the intercept when the visual line pass through the grid cell based on the theory of direction vector and the difference between the adjacent intersection points. Two main input factors of simulation, volume emission grid and visual line intercept, are obtained, thus completes the model of the brightness observation.It implies that any further increase in resolution dose not result in a significant change (>0.01%) for the results by the comparison and analysis on different resolution. To be important, the analysis and interpretation about the image feature of intermediate result were presented; this deepeneds the understanding and knowledge of geometry and observation mechanism of Limb mode. Series of work in this paper will provide basic theory for the future ozone retrieval and data evaluation. |
