Fluctuations of radio occultation signals in X/K band in the presence of anisotropic turbulence and differential transmission retrieval performance

Abstract

We investigated amplitude fluctuations and differential transmission errors for radio occultation (RO) measurements performed in X/K band for Low‐Earth Orbiter – Low‐Earth Orbiter (LEO–LEO) cross‐links. We performed a series of high‐resolution numerical simulations using a quasi‐realistic anisotropic turbulence model with European Centre for Medium‐Range Weather Forecast (ECMWF) ERA40 reanalyses as the background fields. Three test cases were simulated: high, middle, and low latitudes, with turbulence intensity profile being estimated based on high‐resolution radio sonde data. The numerical end‐to‐end simulations were based on the multiple phase screens technique (forward modeling) and the canonical transform amplitude ratioing method (differential transmission retrieval). The anisotropy coefficient was varied from 3 to 50. We found the dependences of the scintillation index on anisotropy in the area of weak fluctuations to be consistent with previous theoretical studies: scintillation index is approximately proportional to the square root of the anisotropy coefficient. For strong fluctuations this dependence becomes weaker. The type of dependence of differential transmission errors from anisotropy is more sensitive to the fluctuation strength. Generally, it increases with anisotropy, but the dependence saturates for stronger anisotropy and becomes flat or even slightly reverse. At all fluctuation levels, including the strongest ones, the differential transmission error is found smaller than 5% (smaller than 1–2.5% for all weak and moderately strong fluctuations) for ∼1 km height resolution, reinforcing the results of the previous studies that X/K band RO phase delay and transmission are a promising future source for accurate temperature and humidity profiling.