Study On Atmospheric Motion Signal Extraction For Clear Region From FY-2E Infrared Window Imagery——Time Difference Technique

The technique for atmospheric motion vectors(AMVs) derivation from satellite infrared images for cloud-free regions is to detect the radiance and brightness temperature(TB)difference for cloud-free regions measured by sequential geostationary satellite IR imagery and extract the possible water vapor or dust aerosol tracers from it, so that AMVs in cloud-free regions can be obtained. A new tracer selection and tracking procedure based on atmospheric radiative transfer theory, which we call time difference algorithm in this paper, is demonstrated here for the estimation of AMVs for cloud-free regions from FengYun-2E (FY-2E) infrared (IR) window imagery. It will be a great supplement to cloud-free regions.The total decrease in brightness temperature (TB) in FY-2E IR window imagery corresponding to a10%increase in water vapor density over half an hour, which happens quite frequently in air at middle and low latitudes and has been computed with the MODTRAN4radiative transfer model, and the contributions to the total decrease from each of the10layers has been analyzed under4typical conditions:tropical, mid-latitude summer, U.S. standard, and mid-latitude winter atmospheres. Besides, the contribution of a50%and30%increase in aerosol extinction coefficient in half an hour to the total decrease in brightness temperature (TB) from each of the5layers under the U.S. standard atmosphere is calculated by using the MODTRAN radiative transfer model. The height assigned to the derived AMVs is the level at which the layered decrease in TB caused by an increase in water vapor density or aerosol extinction coefficient is absolutely maximal compared with the TB values of other levels.Examples of low-level winds for cloud-free regions near typhoon or arid and semi-arid derived from FY-2E IR images using the time difference algorithm have been conducted. It shows that the present technique is able to produce the quality-controlled wind vectors from the FY-2E IR imagery. Case studies have been presented to verify the simulation analysis, and the results show that by tracking the movement of dust aerosol or water vapor as tracers in cloud-free regions using the time difference algorithm, AMVs rather than traditional CMWs have been obtained. The results of the statistical comparison between FY-2E IR AMVs for cloud-free regions and NCEP wind observations are in good agreement.