GOME Level-1 Products were provided by DLR. The GOMETRAN radiative transfer model and the highresolution solar reference spectrum used in this study were supplied by J. Burrows (Univ. Bremen) and K. Chance (Harvard-Smithsonian Astrophysical Observatory), respectively.

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on-board the European ENVIronmental SATellite (ENVISAT) launched on 1 March 2002, is a middle infrared Fourier Transform spectrometer measuring the atmospheric emission spectrum in limb sounding geometry. The instrument is capable to retrieve the vertical distribution of temperature and trace gases, aiming at the study of climate and atmospheric chemistry and dynamics, and at applications to data assimilation and weather forecasting.Correspondence to: U. Cortesi (u.cortesi@ifac.cnr.it) MIPAS operated in its standard observation mode for approximately two years, from July 2002 to March 2004, with scans performed at nominal spectral resolution of 0.025 cm −1 and covering the altitude range from the mesosphere to the upper troposphere with relatively high vertical resolution (about 3 km in the stratosphere). Only reduced spectral resolution measurements have been performed subsequently. MIPAS data were re-processed by ESA using updated versions of the Instrument Processing Facility (IPF v4.61 and v4.62) (and, to a lesser extent, v4.62) O 3 VMR profiles and a comprehensive set of correlative data, including observations from ozone sondes, ground-based lidar, FTIR and microwave radiometers, remote-sensing and in situ instruments on-board stratospheric aircraft and balloons, concurrent satellite sensors and ozone fields assimilated by the European Center for Medium-range Weather Forecasting.A coordinated effort was carried out, using common criteria for the selection of individual validation data sets, and similar methods for the comparisons. This enabled merging the individual results from a variety of independent reference measurements of proven quality (i.e. well characterized error budget) into an overall evaluation of MIPAS O 3 data quality, having both statistical strength and the widest spatial and temporal coverage. Collocated measurements from ozone sondes and ground-based lidar and microwave radiometers of the Network for the Detection Atmospheric Composition Change (NDACC) were selected to carry out comparisons with time series of MIPAS O 3 partial columns and to identify groups of stations and time periods with a uniform pattern of ozone differences, that were subsequently used for a vertically resolved statistical analysis. The results of the comparison are classified according to synoptic and regional systems and to altitude intervals, showing a generally good agreement within the comparison error bars in the upper and middle stratosphere. Significant differences emerge in the lower stratosphere and are only partly explained by the larger contributions of horizontal and vertical smoothing differences and of collocation errors to the total uncertainty. Further results obtained from a purely statistical analysis of the same data set from NDACC ground-based lidar stations, as well as from additional ozone soundings at middle latitudes and from NDACC ground-based FTIR measurements, confirm the validity of MIPAS O 3 profil...

The advent of quantum cascade lasers has provided matured continuously tunable solid state laser sources emitting from mid-infrared to terahertz wavelengths. Such sources, used as local oscillators, offer the practical prospect of aircraft, high altitude platform, and satellite deployment of compact and shot noise limited heterodyne radiometers for Earth observation and astronomy. A ground-based prototype of a quantum cascade laser heterodyne radiometer operating in the mid-infrared has been developed and is presented. The instrument design and concepts are described, together with evaluation of the instrument in the laboratory and during field measurements of atmospheric ozone. In this study the best performance achieved by the prototype quantum cascade laser heterodyne radiometer was a signal-to-noise ratio of three times the theoretical shot-noise limit. The prototype has allowed the main sources of excess noise to be identified as residual optical feedback in the local oscillator optical path and a lack of mechanical and thermal stability in the local oscillator collimation system. Instrument improvements are currently being implemented and enhanced performance is expected in the near future.

[1] Comparisons of the latest High Resolution Dynamics Limb Sounder (HIRDLS) ozone retrievals (v2.04.09) are made with ozonesondes, ground-based lidars, airborne lidar measurements made during the Intercontinental Chemical Transport Experiment-B, and satellite observations. A large visual obstruction blocking over 80% of the HIRDLS field of view presents significant challenges to the data analysis methods and implementation, to the extent that the radiative properties of the obstruction must be accurately characterized in order to adequately correct measured radiances. The radiance correction algorithms updated as of August 2007 are used in the HIRDLS v2.04.09 data presented here. Comparisons indicate that HIRDLS ozone is recoverable between 1 and 100 hPa at middle and high latitudes and between 1 and 50 hPa at low latitudes. Accuracy of better than 10% is indicated between 1 and 30 hPa (HIRDLS generally low) by the majority of the comparisons with coincident measurements, and 5% is indicated between 2 and 10 hPa when compared with some lidars. Between 50 and 100 hPa, at middle and high latitudes, accuracy is 10-20%. The ozone precision is estimated to be generally 5-10% between 1 and 50 hPa. Comparisons with ozonesondes and lidars give strong indication that HIRDLS is capable of resolving fine vertical ozone features (1-2 km) in the region between 1 and 50 hPa. Development is continuing on the radiance correction and the cloud detection and filtering algorithms, and it is hoped that it will be possible to achieve a further reduction in the systematic bias and an increase in the measurement range downward to lower heights (at pressures greater than 50-100 hPa).

The retrieval and validation of the infrared measurements of the stratospheric aerosol layer derived from the improved stratospheric and mesospheric sounder (ISAMS) on board the Upper Atmsophere Research Satellite (UARS) are discussed in detail. The retrieval method is presented and an error analysis and sensitivity study are used to provide an error budget. The validation involves internal consistency checks, comparisons with coincident aerosol observations from other satellite-based instruments (cryogenic limb array etalon spectrometer (CLAES) and Stratospheric Aerosol and Gas Experiment II (SAGE II)) and in situ particle counters. The internal comparisons show that the precision of the 6.20-/•m retrievals are better than 30% for the data on the 32-hPa and 22-hPa pressure surfaces and that the 12.11-/•m retrievals are better than 20% and 25% for the data on pressure surfaces at 46 hPa and 32 hPa, respectively. Comparison of the ISAMS aerosol extinctions with the simultaneous CLAES measurements show systematic biases for both the 6-tim and the 12-tim retrievals with ISAMS generally measuring lower extinction values than CLAES. The comparison with calculated extinctions from balloon dustsonde data at 41 øN shows that the aerosol extinctions are systematically too high for pressures less than 40 hPa. Ballard et al. [1996]. The middle atmosphere contains a ubiquitous layer of particulate matter in the lower stratosphere which consists mainly of sulphuric acid-water drops [Turco et al., 1982]. This layer originates from the transport of background sulphurous gases, mainly OCS, from the troposphere and from the direct injection of SO2 by volcanic eruptions. Major volcanic explosions such as E1 Chich6n (1982) and Mount Pinatubo (1991) inject tens of megatonnes of SO2 into the stratosphere. The SO2 gas is converted over a period of months into sulphuric acid-water droplets [Bluth et al., 1992; Read et al., 1993], but the removal of the resulting submicron-size aerosol particles from the stratosphere by the process of sedimentation takes several years [Holmann, 1990]. The aerosol layer affects the radiative, chemical, and dynamical properties of the stratosphere. Evidence is increasing for the view that heterogeneous reactions on the background and volcanic sulphate aerosols can cause global changes in reactive nitrogen species, activation of chlorine reservoirs, and lead to ozone depletion [Holmann and Solomon, 1989; Granier and Brasseur, 1992; Grant et al., 1994; Hanson et al. , 1994; Holmann et al. , 1994; Rinsland et al., 1994a]. The interaction of aerosols with the solar and the Earth's radiation field can produce substantial dynamical changes in the lower stratosphere which affect transport of trace species [Kinne et al., 1992; Lacis et al., 1992]. The particle size distribution and chemical composition of aerosols are important factors in determining their radiative properties [Bohren and Huffman, 1983]. A wide variety of techniques are used to measure aerosol microphysical properties and abundances with height [...