Simulation and interpretation of the noise in the radar refractivity retrieval

Radar refractivity retrieval algorithm from S-band radar phase measurements of ground targets can provide high resolution near-surface moisture estimates in time and space. The reliability of the retrieval depends on phase variation due to both the fluctuation caused by the spatial variability of the refractive index along the ray-path and the uncertainty of the illuminated target heights by the ray over complex terrains associated with the gradient of the refractive index. Since the algorithm to retrieve refractivity assumes the phase variation caused only by the path integrated refractivity along the path, it would be worthwhile to quantify the role of factors listed above. With this purpose, we built a simple phase simulator using statistically distributed targets and generated with digital elevation model data and ground echo intensity. For selected atmospheric propagation conditions from the low-level profiles of soundings, the simulated phase variation and its local variability fields were evaluated with the same fields obtained from radar measurements.