Single-scan Radar Refractivity Retrieval (SR3): Theory and Simulations

A novel radar technique for retrieving refractivity near the earth's surface from ground clutter echoes is presented. The technique is different from the conventional approach in which a reference phase field and a reference refractivity field are needed for each retrieval process. The present technique is referred to as the single-scan radar refractivity retrieval (SR3), in which the absolute refractivity field is derived from a single measurement of the propagation phase of ground targets. By using numerical simulations to radar phase data, the practical limitations and potential of the SR3 technique will be demonstrated. In the past, we have explored the possibility of single-scan refractivity derivation but the effort failed given that the radar wavelengths are on the order of centimeters while the range distances are on the order of kilometers. With these constraints, single-scan retrieval was deemed excessively challenging and, thus, the effort was stopped. Recently, we revisited the topic and have found that, instead of the absolute propagation phase from the radar, only the unwrapped phase difference from a range gate to its adjacent gate was necessary for the absolute refractivity retrieval process. Given that the wavelength and the range gate spacing, which are, in practice, on the order of centimeters and hundreds of meters, respectively, one can imagine that the radar phase wraps thousands of times within each range gate, resulting in thousands of possible solutions. Only one of them, however, is valid near the earth's surface, which enables us to choose the unique solution. In this study, the usage of multiple frequencies was applied to derive one of the crucial components in the SR3 technique, i.e., the centroid spacing from one range gate to the next. For this presentation, different variables that affect the quality and limitations of the technique will be shown. These variables include the operating frequency (wavelength), frequency drift, range-gate centroid spacing and the spatial complexity of the refractivity field. The potential application of the SR3 technique on existing radar systems and future work will also be discussed.