ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-7-1615-2007 Characterization of MIPAS elevation pointing Kiefer M. 1 von Clarmann T. 1 Grabowski U. 1 De Laurentis M. 2 Mantovani R. 3 Milz M. 1 Ridolfi M. 4 Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany Operational MIPAS mission planner for ESA, Rhea System SA, Louvain-La-Neuve, Belgium Responsible for operational MIPAS mission calibration for ESA from 2002 to 2005 – Vitrociset S.p.A., Rome, Italy Dip.to di Chimica Fisica e Inorganica, Universitá di Bologna, Italy 26 03 2007 7 6 1615 1628 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/7/1615/2007/acp-7-1615-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/1615/2007/acp-7-1615-2007.pdf

Sufficient knowledge of the pointing is essential for analyses of limb emission measurements. The scientific retrieval processor for MIPAS on ENVISAT operated at IMK allows the retrieval of pointing information in terms of tangent altitudes along with temperature. The retrieved tangent altitudes are independent of systematic offsets in the engineering Line-Of-Sight (LOS) information delivered with the ESA Level 1b product. The difference of pointing retrieved from the reprocessed high resolution MIPAS spectra and the engineering pointing information was examined with respect to spatial/temporal behaviour. Among others the following characteristics of MIPAS pointing could be identified: Generally the engineering tangent altitudes are too high by 0–1.8 km with conspicuous variations in this range over time. Prior to December of 2003 there was a drift of about 50–100 m/h, which was due to a slow change in the satellite attitude. A correction of this attitude is done twice a day, which leads to discontinuities in the order of 1–1.5 km in the tangent altitudes. Occasionally discontinuities up to 2.5 km are found, as already reported from MIPAS and SCIAMACHY observations. After an update of the orbit position software in December 2003 values of drift and jumps are much reduced. There is a systematic difference in the mispointing between the poles which amounts to 1.5–2 km, i.e. there is a conspicuous orbit-periodic feature. The analysis of the correlation between the instrument's viewing angle azimuth and differential mispointing supports the hypotheses that a major part of this latter phenomenon can be attributed to an error in the roll angle of the satellite/instrument system of approximately 42 mdeg. One conclusion is that ESA level 2 data should be compared to other data exclusively on tangent pressure levels. Complementary to IMK data, ESA operational LOS calibration results were used to characterize MIPAS pointing. For this purpose MIPAS is used as a radiometer while the passage of infrared bright stars through the instrument's field of view is recorded. Deviation from expected time of passage gives information about mispointing. Results are: a pronounced seasonal variation of the LOS is seen before a correction of on-board software took place in December of 2003. Further a pitch bias of 26 mdeg with respect to the platform attitude information is found, which corresponds to 1.45 km tangent altitude offset towards low altitudes.

 References Bertaux, J L., Hauchecorne, A., Dalaudier, F., Cot, C., Kyrölä, E., Fussen, D., Tamminen, J., Leppelmeier, G W., Sofieva, V., Hassinen, S., Fanton d'Andon, O., Barrot, G., Mangin, A., Théodore, B., Guirlet, M., Korablev, O., Snoeij, P., Koopman, R., and Fraisse, R.: First results on GOMOS/ENVISAT, Adv. Space Res., 33, 1029–1035, 2004. Bovensmann, H., Burrows, J P., Buchwitz, M., Frerick, J., No\"el, S., Rozanov, V V., Chance, K V., and Goede, A. P H.: SCIAMACHY: Mission objectives and measurement modes, J. Atmos. Sci., 56, 127–150, 1999. Endemann, M.: MIPAS Instrument Concept and Performance, in Proceedings of European Symposium on Atmospheric Measurements from Space, Noordwijk, Netherlands, 18–22 January, vol. WPP-161, pp. 29–43, European Space Agency, ESTEC, Noordwijk, The Netherlands, 1999. Fischer, H., Blom, C., Oelhaf, H., Carli, B., Carlotti, M., Delbouille, L., Ehhalt, D., Flaud, J.-M., Isaksen, I., López-Puertas, M., McElroy, C T., and Zander, R.: Envisat-MIPAS, an instrument for atmospheric chemistry and climate research, European Space Agency-Report SP-1229, C. Readings and R. A. Harris (eds.), ESA Publications Division, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands, 2000. Kaiser, J W., von Savigny, C., Eichmann, K.-U., No\"el, S., Bovensmann, H., and Burrows, J P.: Satellite-pointing retrieval from atmospheric limb-scattering of solar UV-B radiation, Can. J. Phys., 82, 1041–1052, 2004 Kleinert, A., Aubertin, G., Perron, G., Birk, M., Wagner, G., Hase, F., Nett, H., and Poulin, R.: MIPAS Level 1B algorithms overview: operational processing and characterization, Atmos. Chem. Phys., 7, 1395–1406, 2007 Kyrölä, E., Tamminen, J., Leppelmeier, G W., Sofieva, V., Hassinen, S., Bertaux, J L., Hauchecorne, A., Dalaudier, F., Cot, C., Korablev, O., Fanton d'Andon, O., Barrot, G., Mangin, A., Théodore, B., Guirlet, M., Etanchaud, F., Snoeij, P., Koopman, R., Saavedra, L., Fraisse, R., Fussen, D., and Vanhellemont, F.: GOMOS on Envisat: an overview, Adv. Space Res., 33, 1020–1028, 2004. Pellegrini, A.: Envisat-1 Products Specifications, Volume 12 of MIPAS Products Specifications, PO-RS-MDA-GS-2009, ESA, 2003 Ridolfi, M., Carli, B., Carlotti, M., von Clarmann, T., Dinelli, B., Dudhia, A., Flaud, J.-M., Höpfner, M., Morris, P E., Raspollini, P., Stiller, G., and Wells, R J.: Optimized Forward and Retrieval Scheme for MIPAS Near-Real-Time Data Processing, Appl. Opt., 39, 1323–1340, 2000. Rodgers, C D.: Inverse Methods for Atmospheric Sounding: Theory and Practice, vol 2 of Series on Atmospheric, Oceanic and Planetary Physics, edited by: Taylor, F. W., World Scientific, 2000. Saavedra, L., Mantovani, R., and Dehn, A.: ENVISAT Restituted Pitch Assessment, Technical Note ENVI-SPPA-EOPG-TN-05-0011, ESA, 2005. von Clarmann, T., Glatthor, N., Grabowski, U., Höpfner, M., Kellmann, S., Kiefer, M., Linden, A., Mengistu Tsidu, G., Milz, M., Steck, T., Stiller, G P., Wang, D Y., Fischer, H., Funke, B., Gil-López, S., and López-Puertas, M.: Retrieval of temperature and tangent altitude pointing from limb emission spectra recorded from space by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), J. Geophys. Res., 108, 4736, 2003. von Savigny, C., Kaiser, J W., Bovensmann, H., Burrows, J P., McDonald, I S., and Leblanc, T.: Spatial and temporal characterization of SCIAMACHY limb pointing errors during the first three years of the misson, Atmos. Chem. Phys., 5, 2593–2602, 2005.