Retrieval of Vertical Distribution of Tropospheric Refractivity through Ground-Based GPS Observation
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ABSTRACT:In the present reported study, the vertical distributions of local atmospheric refractivity were retrieved from groundbased GPS observations at low elevation angles. An improved optimization method was implemented at altitudes of 0–10 km to search for a best-fit refractivity profile that resulted in atmospheric delays most similar to the delays calculated from the observations. A ray-tracing model was used to simulate neutral atmospheric delays corresponding to a given refractivity profile. We initially performed a “theoretical retrieval”, in which no observation data were involved, to verify the optimization method. A statistical relative error of this “theoretical retrieval” (−2% to 2%) indicated that such a retrieval is effective. In a practical retrieval, observations were obtained using a dual-frequency GPS receiver, and its initial value was provided by CIRA86aQ UoG data. The statistical relative errors of the practical retrieval range from −3% to 5% were compared with co-located radiosonde measurements. Results clearly revealed diurnal variations in local refractivity profiles. The results also suggest that the general vertical distribution of refractivity can be derived with a high temporal resolution. However, further study is needed to describe the vertical refractivity gradient clearly.
ABSTRACT:In the present reported study, the vertical distributions of local atmospheric refractivity were retrieved from groundbased GPS observations at low elevation angles. An improved optimization method was implemented at altitudes of 0–10 km to search for a best-fit refractivity profile that resulted in atmospheric delays most similar to the delays calculated from the observations. A ray-tracing model was used to simulate neutral atmospheric delays corresponding to a given refractivity profile. We initially performed a “theoretical retrieval”, in which no observation data were involved, to verify the optimization method. A statistical relative error of this “theoretical retrieval” (−2% to 2%) indicated that such a retrieval is effective. In a practical retrieval, observations were obtained using a dual-frequency GPS receiver, and its initial value was provided by CIRA86aQ UoG data. The statistical relative errors of the practical retrieval range from −3% to 5% were compared with co-located radiosonde measurements. Results clearly revealed diurnal variations in local refractivity profiles. The results also suggest that the general vertical distribution of refractivity can be derived with a high temporal resolution. However, further study is needed to describe the vertical refractivity gradient clearly.
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