Can spaceborne SAR interferometry be used to study the temporal evolution of PWV?

In this work we investigate the use of Synthetic Aperture Radar (SAR) interferometry (InSAR) to generate maps of temporal variations of the Precipitable Water Vapor (PWV) spatial distribution with a horizontal resolution as fine as 10 ÷ 20 m depending on the radar wavelength, and over a swath typically 100 km wide. We present the result of a time series of PWV maps obtained by processing a set of interferometric SAR images acquired by the ENVISAT-ASAR mission over the Lisbon region from November 2008 to November 2009. Maps are calibrated by means of GPS measurements of the PWV over the same area and covering the time interval between the first and last SAR acquisition. Current interferometric spaceborne missions, which can also be used to generate PWV maps, relies on SAR sensors working at different frequency bands: L (ALOS-PALSAR), C (ENVISAT-ASAR, RADARSAT) and X (TerraSAR-X, Cosmo-Sky-Med) and with a repetition cycle ranging from 11 (TerraSAR-X and Cosmo-Sky-Med) to 46 days (ALOS-PALSAR). The precision of these maps can be smaller than 1 mm depending on the radar wavelength and the spatial filtering. We also demonstrate that the merging of PWV maps obtained by processing time series of interferometric SAR images acquired from different tracks of the same satellite and/or different spaceborne missions gives information about the temporal evolution of the PWV spatial distribution with a sampling period of a few days, much shorter than the revisiting times of each SAR sensor. The availability of such PWV maps could increase the quality of quantitative precipitation forecasting and open interesting perspectives for nowcasting applications.

► PWV maps from SAR interferometry.
► 3DVAR and 4DVAR analysis.
► Nowcasting.