GPS radio occultation events observed between 24 July and 17 November 2008 by the IGOR occultation receiver aboard the TerraSAR-X satellite are processed and analyzed. The comparison of 16 262 refractivity profiles with collocated ECMWF data yield a mean bias of −0.60% to +0.02% at altitudes between 5 and 30 km. Standard deviations decrease from about 0.8% to 1.8% at 5 km to about 0.5% to 0.8% at about 10 km altitude. At low latitudes mean biases and standard deviations are larger, in particular in the lower troposphere. The results are consistent with 15 159 refractivity observations collected during the same time period by the BlackJack receiver aboard GRACE-A and processed by GFZ's operational processing system. The main difference between the two occultation instruments is the implementation of open-loop signal tracking in the IGOR (TerraSAR-X) receiver which improves the tropospheric penetration depth in terms of ray height by about 2 km compared to the conventional closed-loop data acquired by BlackJack (GRACE-A).

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Beyerle, G.; Grunwaldt, L.; Heise, S.; Köhler, W.; König, R.; Michalak, G.; Rothacher, M.; Schmidt, T.; Wickert, J.; Tapley, B. D.; Giesinger, B. (2011): First results from the GPS atmosphere sounding experiment TOR aboard the TerraSAR-X satellite. Atmospheric Chemistry and Physics, 11, 13, 6687-6699.