[Modeling of CO2 fluxes at cropland by using SiB3 model].

The aim is to study the influence of different vegetation types on CO2 fluxes at the same site, taking farmland as the object by using the simple biosphere model (SiB3) , select different vegetation types in Suzhou Dongshan site as input parameters of model to simulate CO2 fluxes, and compare with the observational data in Suzhou Dongshan site during 2011-04-16 to 2011-06-30. Results show that using corn as the site vegetation type input model to simulate CO2 fluxes showed a very good diurnal variation agreement compared to the measured data, but selecting the ordinary crop type input model to simulate CO2 fluxes, CO2 fluxes during the daytime in April and May were undervalued, and CO2 fluxes in June were overvalued; when we select the tea type to input the model, the simulated results significantly overestimated CO2 fluxes during the daytime in May and June. In addition, when using SiB3 model to simulate the daily CO2 fluxes, all three vegetation types input model can effectively simulate daily CO2 fluxes, but not significantly. It shows that choosing the right type vegetation input SiB3 model can effectively simulate the diurnal variation of CO2 fluxes, but can not effectively improve the daily CO2 fluxes simulation.

[Study of the microwave emissivity characteristics over different land cover types].

The microwave emissivity over land is very important for describing the characteristics of the lands, and it is also a key factor for retrieving the parameters of land and atmosphere. Different land covers have their emission behavior as a function of structure, water content, and surface roughness. In the present study the global land surface emissivities were calculated using six month (June, 2003-August, 2003, Dec, 2003-Feb, 2004) AMSR-E L2A brightness temperature, MODIS land surface temperature and the layered atmosphere temperature, and humidity and pressure profiles data retrieved from MODIS/Aqua under clear sky conditions. With the information of IGBP land cover types, "pure" pixels were used, which are defined when the fraction cover of each land type is larger than 85%. Then, the emissivity of sixteen land covers at different frequencies, polarization and their seasonal variation were analyzed respectively. The results show that the emissivity of vegetation including forests, grasslands and croplands is higher than that over bare soil, and the polarization difference of vegetation is smaller than that of bare soil. In summer, the emissivity of vegetation is relatively stable because it is in bloom, therefore the authors can use it as its emissivity in our microwave emissivity database over different land cover types. Furthermore, snow cover can heavily impact the change in land cover emissivity, especially in winter.