Simulation study on temperature retrieval deviations induced by occultationreceiver errors

KeyWord:Occultation receiver, EGOPS software, Errors, Simulation.

Abstract:

      In order to evaluate the influences of occultation receiver errors on the radio occultation sounding accuracy, we employ the EGOPS simulation software to evaluate the influences of Doppler biases and drifts, clock stability/single-differencing, receiver thermal noises and local multi-path on the retrievals of temperature, refractivity, density and pressure profiles. The METOP and GPS constellation are selected as the LEO satellite and transmit system respectively, and GRAS antenna is setting in the simulation process. From the 567 simulated occultation events, one rising and one setting occultation events are tested in the simulation. The results show that the maximum temperature deviation is about 2K due to the influence of Doppler bias, 0.3K due to the influence of Doppler shift, less than 1.5K due to the influence of local multi-path, 3K due to the influence of Clock stability/single-differencing, and over 4K due to the influence of receiver thermal noises, respectively. It can be seen that the worst situations for temperature retrieval occur near the stratopause. The major error sources are receiver thermal noises, Clock stability/single differencing and POD-induced Doppler biases. For the purpose of statistical analysis, thirty occultation events are randomly selected, and their temperature retrievals are compared with corresponding ECMWF data. We find that the average deviation of retrieved temperature errors reaches its maximum, 1K, at 45Km height, and the standard deviation its maximum, 5K, at the stratopause.