A Closed Algorithm to Create Detailed Animated Water Vapor Fields over the Oceans from Polar-orbiting Satellites' Data
Ermakov, D.M.1; Chernushich, A.P.1; Sharkov, E.A.2
1Institute of Radioengineering and Electronics of RAS, RUSSIAN FEDERATION; 2Space Research Institute of RAS, RUSSIAN FEDERATION

Obtaining animated fields of geophysical parameters of the atmosphere-ocean system with high spatiotemporal sampling is critically important for many remote sensing applications in at least two respects: for investigating of quick and energy-consuming processes in atmosphere like tropical storms and hurricanes, and for more accurate fusion of quasi-synchronous remote data from different space-borne, airborne and other sources. However, there exists a known trade-off between spatial and temporal resolution of the available satellite data: generally speaking, polar orbiters can provide much better spatial details in comparison to geostationary ones, but with a coarse time resolution (usually, twice per day).

Several interpolation techniques were suggested to increase temporal resolution of the polar-orbiting satellites' data while preserving their spatial resolution unchanged. A method of advective blending [1] can be mentioned as one of the most deeply developed and reaching the level of operational technology which allows both interpolating the retrieved fields of atmospheric total precipitable water (TPW) in the past with a time step of 1 hour and spatial resolution of 0.25°, and, to a certain extent, applying it in the aims of now-casting and forecasting. However, this method is significantly dependent on the ancillary data (the model or operationally retrieved winds in the lower troposphere) and is partially based on an empirically chosen dependence between TWP advection velocity and wind speeds at several heights. The latter can be the reason, in absence of significant retrieval errors, for some artifacts (sharp discontinuities) occasionally noticeable on the final product.

The present work discusses a new algorithm for animated TPW global fields' retrieval with spatial resolution of 0.2° and temporal resolution of 1.5 hour. The algorithm is closed in respect to microwave satellite data and uses minimum model assumptions, based on motion estimation/compensation approach well-known in machine vision and video processing domains. These minimum requirements make the algorithm widely applicable to various satellite data and, in the authors' opinion, help discriminating the processing artifacts from critical natural phenomena. The main attention in the report is drawn to a problem of constructing reference maps of TWP twice per day on the 0.2° x 0.2° net with good temporal consistency and global coverage (without gaps). The step of temporal interpolation is based on previous work [2] and is considered in less detail. The algorithm's overall performance is illustrated on example of a global animated (1.5 hour time step) TPW field constructed for the interval of August, 2000 (including the life time of hurricane Alberto in North Atlantic). In this example the SSM/I data from the DMSP satellites F13, F14, F15 were used. However, to improve temporal consistency and overall quality of the reference maps the authors are considering different approaches to integrate information from various instruments and missions, primarily from MetOp and POES, and also from Megha-Tropiques, Clouds and other missions.

References
1. Wimmers A.J., and Velden C.S. (2011). Seamless advective blending of total precipitable water retrievals from polar-orbiting satellites. J. Appl. Meteor. Climatol., 50(5), 10241036.
2. Ermakov D., Chernushich A., Sharkov E., Shramkov Ya. (2011). Stream Handler system: an experience of application to investigation of global tropical cyclogenesis. Proc. of 34th International Symposium on Remote Sensing of Environment, 10 15 April, 2011, Sydney, Australia. http://www.isprs.org/proceedings/2011/ISRSE-34/211104015Final00456.pdf