Horizontal and vertical gradient refractivity joint estimation from weather radar phase measurements

Refractivity variations can be easily obtained from radar phase measurements using based-ground clutter returns under certain basic assumptions such as flat terrain and zero vertical gradient of the refractivity. However, in more realistic conditions, phase measurements can be significantly affected by the vertical gradient variations of the refractivity and the height variations between the different based-ground targets. This paper focuses on retrieving jointly the average horizontal atmospheric refractivity and its vertical gradient variations over hilly terrain using triple targets located at different heights in order to obtain a higher spatial resolution. A linear decrease of the refractivity with the height is assumed. Refractivity measurements were obtained with an S-Band coherent radar during the International H₂O Project (IHOP_2002) held in the Southern Great Plains of Oklahoma (United States). Radar results have been compared with in situ measurements obtained from different weather based-ground stations located inside the influence area of the radar. A good correlation between both observations has been found.