Abstract: The limitations of the sliding spectral （SS）method are the restriction of the resolution of bending angle profiles due to  the noise in the moist lower tropos phere. It has been  validated by simulations of atmospheric propagation using multiple phase screens technique under multipath conditions. A modified sliding spectral （MSS）method was developed to reduce these limitations. It demonstrates that MSS method can reasonably identify and decrease noise which may introduce retrieval errors in classical SS method, as well as further improve the resolution in the moist tropos pheric regions. About 4500 COSMIC （Constellation Observing System for Meteorology, Ionosphere and Climate）were analyzed using the SS method and MSS method respectively. Statistical comparisons of the retrieval refractivity profiles with that from ECMWF (European Centre for Medium range Weather Forecasts) analysis show that MSS method contains smaller systematic biases than SS method. Biases of the MSS method are close to that of  full spectrum inversion （FSI）method at all latitudes.

Key words: Radio occultation, Sliding spectral method, Open-loop mode, Multiple phase screens technique, Satellite navigation