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Bending Angle and Temperature Profiles from GOMOS in Comparison to Champ and Ecmwf Analysis Data

Christian Retscher(1), Gottfried Kirchengast(2) and Andreas Gobiet(2)

(1) ESA/ESRIN, Via Galileo Galilei CP. 64 , 00044 Frascati, Italy
(2) Wegener Center, University of Graz, Leechgasse 25, 8010 Graz, Austria

Abstract

The Envisat platform, in orbit since March 2002, carries several instruments important for monitoring Earth's atmosphere, oceans, land, and ice. Amongst those the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument is dedicated to perform high-accuracy altitude-resolved global ozone monitoring as well as measurements of other atmospheric trace gases and of temperature. Depending on the selected star, measurements are carried out within an altitude range of about 15 km to more than 100 km.

We present results of GOMOS bending angles and retrieved temperature profiles compared to CHAMP and ECMWF analysis data. GOMOS temperatures are gained by exploiting pointing data of the Steering Front Assembly (SFA) and the Star Acquisition and Tracking Unit (SATU), which provide information on the refraction of the star light in the atmosphere and thus allow to derive refractive bending angle profiles. The bending angle profiles are then converted via refractivity and pressure profiles to temperature profiles. According to the SFA sampling rate and retrieval algorithm requirements we performed the retrieval at 10 Hz including down-sampled SATU data from 100 Hz. Bending angles were assumed to have errors of approx. 4 microrad. Statistical optimization of observed bending angles with model bending angles was used to provide adequate data quality for the Abel transform from the stratopause region upwards, which led to a significant gain in temperature retrieval accuracy up to 40 km height due to suppressed downward propagation of errors induced by Abel transform and hydrostatic integral.

A comparison to co-located sets of CHAMP GPS occultation profiles and analysis profiles of the European Centre for Medium-range Weather Forecasts (ECMWF) will be discussed. For temperature profiles we find global mean errors below 2 K from 23 km up to about 35 km. In a future add-on to the present analysis, SFA/SATU temperature data will also be compared to newly processed high resolution temperature profiles (HRTP) from GOMOS fast photometer data.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry