Tangent Height Research Articles

Technical Note: Feasibility of CO<sub>2</sub> profile retrieval from limb viewing solar occultation made by the ACE-FTS instrument

Abstract. Major limitations of our present knowledge of the global distribution of CO2 in the atmosphere are the uncertainty in atmospheric transport mixing and the sparseness of in situ concentration measurements. Limb viewing space-borne sounders, observing the atmosphere along tangential optical paths, offer a vertical resolution of a few kilometers for profiles, which is much better than currently flying or planned nadir sounding instruments can achieve. In this paper, we analyse the feasibility of obtaining CO2 vertical profiles in the 5–25 km altitude range from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS, launched in August 2003), high spectral resolution solar occultation measurements. Two main difficulties must be overcome: (i) the accurate determination of the instrument pointing parameters (tangent heights) and pressure/temperature profiles independently from an a priori CO2 profile, and (ii) the potential impact of uncertainties in the temperature knowledge on the retrieved CO2 profile. The first difficulty has been solved using the N2 collision-induced continuum absorption near 4 μm to determine tangent heights, pressure and temperature from the ACE-FTS spectra. The second difficulty has been solved by a careful selection of CO2 spectral micro-windows. Retrievals using synthetic spectra made under realistic simulation conditions show a vertical resolution close to 2.5 km and accuracy of the order of 2 ppm after averaging over 25 profiles. These results open the way to promising studies of transport mechanisms and carbon fluxes from the ACE-FTS measurements. First CO2 vertical profiles retrieved from real ACE-FTS occultations shown in this paper confirm the robustness of the method and applicability to real measurements.

Measurements of polar mesospheric clouds in infrared emission by MIPAS/ENVISAT

We report on the infrared emission (10–13 μm) of polar mesospheric clouds (PMCs) as measured by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Environmental Satellite (MIPAS/ENVISAT) during 19–21 July 2005 in the summer Northern Hemisphere. The spectral distribution of MIPAS radiances is well described by that simulated for ice particle emission at low temperatures and hence provides further evidence of the water ice nature of the PMC particles. The vertical profiles of integrated radiance clearly show an emission peak at tangent heights of 81–83 km, as expected from PMC emission. Ice particles' volume density retrieved from MIPAS spectra shows a layer of ice particles extending from 80.5 to 87 km and from about 60°N to the North Pole, well confined within the region where temperature is below approximately 150 K. The upper part of the ice particle layer then extends to altitudes higher than that observed by UV/visible measurements, which confirms the current understanding that PMCs cover the entire polar mesopause region. The altitude of the layer peak changes from 82.5–83 km at 70°N–90°N to slightly higher altitudes (83–85 km) at lower latitudes (60°N–70°N). MIPAS ice particle altitude/latitude distribution suggests that they are formed mainly close to the pole and then are transported upward and to lower latitudes by the ascending branch of the meridional circulation, confirming previous modeling.

Ozone profile retrieval from GOMOS limb scattering measurements

We analyzed a set of Global Ozone Monitoring by Occultation of Stars (GOMOS) bright limb measurements with solar zenith angles less than 85° and within 150 km of Stratospheric Aerosol and Gas Experiment II (SAGE II) measurements. In order to perform any species retrieval, GOMOS measurements were first corrected for stray light contamination. GOMOS pointing was analyzed using scene‐based tangent height algorithms, and the best results were achieved using ∼350 nm (Rayleigh) pixels that were consistent with GOMOS known accurate pointing. In order to demonstrate GOMOS bright limb capabilities, ozone profile retrievals were performed using GOMOS measurements of limb‐scattered radiances with the Ozone Mapping and Profiler Suite limb profiler algorithm. The algorithm performs a simultaneous optimal estimation inversion of both Hartley‐Huggins and Chappuis band radiances. We restricted our GOMOS ozone retrievals to the range 25–53 km, a region of relatively constant measurement uncertainty. In this first look at GOMOS limb data, the retrieved ozone profiles agree with collocated SAGE II measurements on average to within 10–15% and with a standard deviation of 10%. Retrieval results were consistent for both upper and lower GOMOS detector bands.

Odin/OSIRIS observations of stratospheric NO<sub>3</sub> through sunrise and sunset

Abstract. The nitrate radical (NO3) has been detected in visible limb-scattered spectra measured by the Optical Spectrograph and InfraRed Imager System (OSIRIS) on-board the Odin satellite when observing at large solar zenith angles (91–97°). Apparent slant column densities of NO3 at tangent heights between 10 and 45 km are derived via spectral fitting in the 610–680 nm window. Using observations from multiple scans spanning solar zenith angles of 91–97°, the rapid evolution of NO3 through sunrise and sunset can be traced. Slant column densities are found to be generally consistent with those simulated using a radiative transfer model with coupled photochemistry. In addition, a strong dependence of NO3 with temperature is observed. These results indicate that our current knowledge of NO3 photochemistry is generally consistent with OSIRIS observations to within the limitations of the radiative transfer modeling. Furthermore, they reveal that OSIRIS possesses signal-to-noise sufficient to make useful measurements of scattered sunlight out to solar zenith angles of 91–97° and suggest the possibility of retrieving profile information for NO3 and other species at large solar zenith angles.

Aura MLS THz observations of global cirrus near the tropopause

The first global cirrus observation from spaceborne THz (terahertz) sensors is presented. The 2.5 THz channels of the Microwave Limb Sounder (MLS) instrument on NASA's Aura satellite, measuring atmospheric thermal emission at the limb, has sensitivity to cloud ice particle scattering above ∼15 km. The magnitude of cloud‐induced radiance (Tcir), as high as 40 K, is observed in the THz radiances at the lowermost tangent heights of limb viewing. A special algorithm is developed to extract the THz Tcir by averaging the data spectrally and vertically, removing systematic error in the radiances, and screening cloudy radiances from clear‐sky variability. The derived THz Tcir has typical precision of 1.5–1.7 K, and a threshold of −6 K is used to determine significant cloud measurements. Monthly maps show that morphologies of the THz Tcir are generally consistent with those of cloud IWC (ice water content) at 121 hPa retrieved simultaneously from the MLS 240 GHz channel. However, the spatial distribution of THz clouds often spreads more broadly in latitude than the GHz clouds, as expected for the better sensitivity of the THz channels to small ice particle scattering. The THz Tcir can be converted to a partial ice water path (pIWP) above ∼15 km, and the estimated 0.7 g/m2/K sensitivity for THz Tcir is consistent with the radiative transfer model calculation and MLS 240 GHz measurements.

Accounting for the effect of horizontal gradients in limb measurements of scattered sunlight

Abstract. Limb measurements provided by the SCanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite allow retrieving stratospheric profiles of various trace gases on a global scale, among them BrO for the first time. For limb observations in the UV/VIS spectral region the instrument measures scattered light with a complex distribution of light paths: the light is measured at different tangent heights and can be scattered or absorbed in the atmosphere or reflected by the ground. By means of spectroscopy and radiative transfer modelling these measurements can be inverted to retrieve the vertical distribution of stratospheric trace gases. The fully spherical 3-D Monte Carlo radiative transfer model "Tracy-II" is applied in this study. The Monte Carlo method benefits from conceptual simplicity and allows realizing the concept of full spherical geometry of the atmosphere and also its 3-D properties, which is important for a realistic description of the limb geometry. Furthermore it allows accounting for horizontal gradients in the distribution of trace gases. In this study the effect of horizontally inhomogeneous distributions of trace gases along flight/viewing direction on the retrieval of profiles is investigated. We introduce a tomographic method to correct for this effect by combining consecutive limb scanning sequences and utilizing the overlap in their measurement sensitivity regions. It is found that if horizontal inhomogenity is not properly accounted for, typical errors of 20% for NO2 and up to 50% for OClO around the altitude of the profile peak can arise for measurements close to the Arctic polar vortex boundary in boreal winter.

Validation of the Aura MLS cloud ice water content measurements

Retrieval and validation of upper tropospheric ice water content (IWC) measurements with the Aura Microwave Limb Sounder (MLS) are described. The MLS version 2.2 (V2.2) IWC, derived from 240‐GHz cloud‐induced radiances (Tcir) at high tangent heights, is scientifically useful at 215–83 hPa. The V2.2 IWC represents a bulk cloud property averaged over a ∼300 × 7 × 4 km3 volume near the pointing tangent height. Precision, accuracy, and spatial resolution of the V2.2 IWC are determined through model simulations and comparisons with CloudSat observations. Comparisons of MLS V2.2 and CloudSat R03 IWCs are made for the months of January and July in terms of normalized probability density function (PDF). The differences between MLS and CloudSat IWC PDFs are generally less than 50% over the IWC range where the MLS technique is valid. At pressures <177 hPa and extratropical latitudes, the MLS V2.2 IWC exhibits a slightly low bias compared to CloudSat, part of which can be attributed to systematic errors in the MLS retrieval. Cloud inhomogeneity and particle size distribution are the leading sources of uncertainties in the V2.2 IWC.

SCIAMACHY limb measurements of NO 2, BrO and OClO. Retrieval of vertical profiles: Algorithm, first results, sensitivity and comparison studies

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) measures scattered sun light also in limb viewing mode (i.e. tangential to Earth’s surface and its atmosphere), which allows determining vertical profiles of atmospheric trace gases. First results on the retrieval of NO 2, BrO and OClO profiles from the SCIAMACHY Limb measurements are presented and compared to independent satellite and balloon borne observations. For the profile retrieval we use a two step approach: First, Slant Column Densities (SCDs) of the respective absorber are determined in the UV/VIS spectral range by Differential Optical Absorption Spectroscopy (DOAS). Second, inversion of the retrieved SCDs (as function of tangent height) yields vertical profiles of the trace gas concentration (as function of altitude). For that purpose, we either apply an optimal estimation method (constraining the inversion by a priori information) or invert the measurements by a least squares approach (independently from a priori). For both approaches box air mass factors calculated by the 3D full spherical radiative transfer model TRACY-II are utilized as weighting functions. The agreement of the retrieved profiles with balloon validation measurements as well as with other space borne measurements of stratospheric trace gas profiles (e.g. by SMR on Odin) is investigated. For OClO, case studies on the sensitivity of the retrieved SCDs on fitting parameters (e.g. wavelength range, polarisation correction) and the impact of the a priori on the retrieved profiles are performed. Also, the significance of the obtained dataset of concentration profiles of NO 2, BrO and OClO for studies on stratospheric chemistry is discussed.

Tangent height registration method for the Version 14 data retrieval algorithm of the solar occultation sensor ILAS-II

The Improved Limb Atmospheric Spectrometer-II (ILAS-II) is a satellite-borne solar occultation sensor onboard the Advanced Earth Observing Satellite-II (ADEOS-II). The ILAS-II succeeded the ILAS. The ILAS-II used four grating spectrometers to observe vertical profiles of gas volume mixing ratios of trace constituents and was also equipped with a Sun-edge sensor to determine tangent heights geometrically with high precision. The accuracy of gas volume mixing ratios depends on the accuracy of the tangent height determination. The combination method is a tangent height registration method that was developed to give appropriate tangent heights for the ILAS-II Version 1.4 data retrieval algorithm. This study describes the method used in the ILAS-II Version 1.4 retrieval algorithm to register tangent heights. The root-sum-square total random error is estimated to be 30 m, and the total systematic error is 180 m at an altitude of 30 km. The influence of the tangent height errors on the vertical profiles of gas volume mixing ratios in ILAS-II Version 1.4 is estimated by using the relative difference. The relative difference for each species is within 7% (20%) for an altitude shift of +/-100 m(+/-300 m).

Observations of middle ultraviolet emissions in the middle and lower thermosphere: NO, O2, O, and Mg+

[1] We present an analysis of day and night limb spectra obtained from the Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) satellite instrument in the middle ultraviolet spectral region between 260 and 300 nm. Tangent heights above the Earth's surface range from 81 to 200 km. These spectra contain signatures of daytime fluorescent scattering by nitric oxide in the γ bands, emission by atomic oxygen at 297.2 nm, and fluorescent scattering by ionized magnesium. The night spectra are dominated by the Herzberg bands of molecular oxygen. Our analysis includes retrievals for vertical profile densities of NO and slant column densities of O and Mg+ in the lower thermosphere. We show how these quantities are related to variable inputs of solar soft X-ray and extreme ultraviolet radiation. The Herzberg band emission is used to constrain the ratio of Herzberg I to Herzberg II band emission and to determine the nighttime vibrational distribution of the excited A3Σu+ state of molecular oxygen.

Evidence for N2O ν3 4.5 μm non‐local thermodynamic equilibrium emission in the atmosphere

We present a clear evidence for N2O 4.5 μm non‐local thermodynamic equilibrium (non‐LTE) emissions in the daylight stratosphere and mesosphere from measurements by the MIPAS experiment on board Envisat. We have used non‐LTE radiative transfer models in order to quantify the magnitude and extent of the non‐LTE deviation of N2O(001) in the Earth's atmosphere. The departure from LTE in N2O during daytime commences at altitudes around 40–50 km, but have significant effects (10%) on daytime limb radiance down to tangent heights of 20 km. The enhancement increases rapidly with altitude, being 20–80% at 50 km, and reaching factors of 2–8 in the lower mesosphere. This study shows that the enhancement is mainly produced by absorption of solar radiation by N2O at 4.5 μm and by V‐V collisions with N2(1). Non‐LTE effects are also significant at nighttime, where LTE calculations overpredict N2O radiances by 10–20% at 40–55 km tangent heights.

Linearization of a radiative transfer model in spherical geometry

For the interpretation of satellite limb observations we investigate the linearization capability of spherical radiative transfer in the ultraviolet and visible part of the solar spectrum, where multiple scattering of light complicates the model simulations. From plane‐parallel radiative transfer it is known that the forward‐adjoint perturbation theory provides a powerful linearization tool. Its application to limb measurement simulations is the subject of this paper. First, we solve the scalar radiative transfer problem in spherical geometry in its forward and adjoint formulation. Subsequently, we apply the perturbation theory approach in the calculation of the derivatives of the intensity at the top of the atmosphere with respect to the absorption properties of a trace gas species in the case of a limb‐viewing satellite instrument. The calculated derivatives are validated with a reference method, and the agreement in the upper atmosphere is very good, whereas deviations occur below the tangent height. Here the determination of the derivatives is clearly sensitive to the discretization of the problem. Finally, we perform an analysis for different viewing scenarios to characterize the capability of the described linearization approach.

A fast radiative‐transfer model for the assimilation of MIPAS limb radiances: Accounting for horizontal gradients

AbstractWe investigate the influence of horizontal structure in the atmosphere on the simulation of emitted infrared limb radiances from the Envisat‐MIPAS instrument, and examine a pragmatic extension of the regression‐based RTMIPAS fast radiative‐transfer model to deal with horizontal atmospheric structure. The extension of RTMIPAS takes into account the horizontal structure at the ray‐tracing step which is used to determine scene temperatures, path lengths, and other conditions along the ray. But the transmittance parametrization used in the extension is based on regression models previously derived from a set of horizontally homogeneous atmospheres. This reduces the computational effort required for the derivation of the regression models. The effects of horizontal gradients in the atmosphere on MIPAS radiances are examined by comparing radiance spectra simulated with RTMIPAS to line‐by‐line equivalents and to real MIPAS observations.It is shown that neglecting horizontal structure in the atmosphere can introduce errors in the radiance simulation that exceed by far the instrument noise, particularly for lower tangent heights and for strongly absorbing spectral regions. The extension of the fast radiative‐transfer model can substantially reduce this error, and for tangent pressures less than 350 hPa (tangent heights greater than about 8 km) almost all error due to horizontal gradients is eliminated. In agreement with this, fast‐model radiances simulated from cross‐sections of the European Centre for Medium‐Range Weather Forecasts model compare significantly better to observed MIPAS limb radiances than radiances simulated under the assumption of horizontal homogeneity. This further confirms a considerable reduction in forward‐model error when horizontal atmospheric structure is taken into account. Copyright © 2006 Royal Meteorological Society

Forward modeling and radiative transfer for the NASA EOS‐Aura High Resolution Dynamics Limb Sounder (HIRDLS) instrument

We describe the radiative transfer modeling developed for the High Resolution Dynamics Limb Sounder (HIRDLS) instrument on board the NASA EOS‐Aura satellite. HIRDLS is a 21‐channel broadband radiometer operating in the spectral region between 6 and 18 microns. It is designed to rapidly measure limb emission at tangent heights from the upper troposphere into the mesosphere on a global basis. Science products will include profiles of temperature and chemical constituents, aerosol estimates, the location of polar stratospheric clouds, and geopotential height gradients. We present the HIRDLS fast forward model, which must accurately and quickly estimate transmittances and channel radiances for use in the operational retrievals. The forward model uses a physically based approach that combines transmittance estimates from Curtis‐Godson and Emissivity‐Growth approximations with a statistical regression. Channel‐dependent radiance accuracies for an eleven‐member test ensemble are 0.5–1.0% or better, compared to a line‐by‐line reference, and satisfy the forward model design requirements. We also discuss the forward model hierarchy developed for HIRDLS which underlies the fast model and provides benchmark calculations, detailed spectroscopy, and access to the physics of the radiative transfer process for development work. Collectively, this framework provides an effective solution to the requirement for fast and accurate radiative transfer modeling for operational use.

Effectiveness Near Boundaries of Fibre Reinforcement in Concrete

Materials testing of relatively small specimens can lead to biases due to disturbances in fibre reinforcement near external surfaces. This paper presents a complete methodological framework for investigating reinforcement characteristics in bulk and in boundary zones. The developed model assumes actual fibre dispersion a mixture of 3D, 2D and 1D portions. Mostly, the 1D component is small, so that a partially planar fibre composite is resulting. Separate expressions for 2D and 3D portions are obtained for the average projected fibre length (tangent height) that governs fibre characteristics in sections (for image analysis purposes), and for the average embedment characteristics that are at the basis of the stress transfer capability. Crack opening in concrete is assumed counteracted by friction between fibres and matrix pockets. However, additional mechanisms can easily be incorporated. Plain cylindrical steel fibres, eventually curved, were envisaged, but anchoring facilities and arbitrary cross sections could be dealt with, as well. Expressions are given for stress transfer capability (strength) in bulk and in boundary zones. Most of the boundary effects are restricted to a zone half the fibre length in width. Magnitude of strength reduction in this zone is of the order of 10%.

Characteristics and performance of the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) on board the ADEOS‐II satellite

The Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) monitored components associated with Polar ozone depletion. ILAS‐II was on board the Advanced Earth Observing Satellite‐II (ADEOS‐II, “Midori‐II”), which was successfully launched on 14 December 2002 from the Tanegashima Space Center of the Japan Aerospace Exploration Agency (JAXA). ILAS‐II used a solar occultation technique to measure vertical profiles of ozone (O3), nitric acid (HNO3), nitrogen dioxide (NO2), nitrous oxide (N2O), methane (CH4), water vapor (H2O), chlorine nitrate (ClONO2), dinitrogen pentoxide (N2O5), CFC‐11, CFC‐12 and aerosol extinction coefficients at high latitudes in both the Northern and Southern hemispheres. ILAS‐II included Sun‐tracking optics and four spectrometers, a Sun‐edge sensor, and electronics. The four spectrometers measured in the infrared (channel 1) between 6.21 and 11.76 μm, in the midinfrared (channel 2) between 3.0 and 5.7 μm, at high resolution in the infrared (channel 3) between 12.78 and 12.85 μm, and in the visible (channel 4) between 753 and 784 nm. The vertical height of the entrance slit was 1 km at the tangent point. A Sun‐edge sensor accurately registered tangent height. After an initial check of the instruments, ILAS‐II recorded routine measurements for about 7 months, from 2 April 2003 to 24 October 2003, a period that included the formation and collapse of an Antarctic ozone hole in 2003 that was one of the largest in history. All of the ILAS‐II data were processed using the version 1.4 data‐processing algorithm. Validation analyses show promising results for some ILAS‐II measurement species, which can be used to elucidate mechanisms of Polar ozone depletion. Studies are ongoing on ozone depletion, on the formation mechanisms of Polar stratospheric clouds, on denitrification, and on air mass descent. A state‐of‐the‐art data retrieval algorithm that is currently being developed will yield more sophisticated data sets from the ILAS‐II data in the near future.

EOS MLS forward model polarized radiative transfer for Zeeman-split oxygen lines

This work supplements the Earth Observing System (EOS) Microwave Limb Sounder (MLS) clear-sky unpolarized forward model with algorithms for modeling polarized emission from the Zeeman-split 118.75-GHz O/sub 2/ spectral line. The model accounts for polarization-dependent emission and for correlation between polarizations with complex, 2/spl times/2 intensity and absorption matrices. The oxygen line is split into three Zeeman components by the interaction of oxygen's electronic spin with an external magnetic field, and the splitting is of order /spl plusmn/0.5 MHz in a typical geomagnetic field. Zeeman splitting is only significant at pressures low enough that collisional broadening (/spl sim/1.6 MHz/hPa) is not very large by comparison. The polarized forward model becomes significant for MLS temperature retrievals at pressure below 1.0 hPa and is crucial at pressures below /spl sim/0.03 hPa. Interaction of the O/sub 2/ molecule with the radiation field depends upon the relative orientation of the radiation polarization mode and the geomagnetic field direction. The model provides both limb radiances and the derivatives of these radiances with respect to atmospheric temperature and composition, as required by MLS temperature retrievals. EOS MLS views the atmospheric limb at 118.75 GHz with a pair of linear-cross-polarized, 100-kHz-resolution, 10-MHz-wide spectrometers. The antennas of the associated receivers are scanned to view rays with tangent heights from the Earth's surface to 0.001 hPa. Comparisons of the modeled MLS radiances with measurements show generally good agreement in line positions and strengths, however residuals in the line centers at the highest tangent heights are larger than desired and still under investigation.

Description and sensitivity analysis of a limb scattering ozone retrieval algorithm

We present the theoretical basis for an algorithm that retrieves vertical profiles of ozone concentration using measurements of light scattered from the limb of the atmosphere. Simulated radiances at wavelengths between 300 and 675 nm are inverted using the optimal estimation technique, producing a retrieved ozone number density profile between 10 and 55 km. A detailed sensitivity analysis of this ozone retrieval algorithm follows. The largest source of ozone retrieval error is tangent height misregistration (i.e., instrument pointing error), which is relevant throughout the altitude range of interest and produces retrieval errors on the order of 10–20% due to a tangent height registration error of 0.5 km. The retrieved profile is shifted in altitude relative to the true profile, with very little distortion of the profile shape. Sensitivity to stratospheric aerosol is also a significant source of error, with errors of 5–8% for altitudes less than 40 km under background aerosol conditions when an aerosol‐free atmosphere is assumed by the algorithm. Using an incorrect a priori ozone estimate can produce errors up to 15% at altitudes near 10 km, but the a priori profile has little influence above that level. Addressing these error sources (e.g., with better instrument pointing knowledge, introduction of reliable aerosol information, and better instrument signal‐to‐noise to reduce the importance of the a priori ozone estimate, respectively) is the key to significantly improving the retrieval accuracy. Further improvement would then be limited by several secondary error sources that produce retrieval errors at the 5% level.

Spatial and temporal characterization of SCIAMACHY limb pointing errors during the first three years of the mission

Abstract. Limb scattering retrievals of atmospheric minor constituent profiles require highly accurate knowledge of the tangent heights during the measurements. The limb scattering measurements of the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) on Envisat are affected by tangent height errors of up to 2 km. This contribution provides a summary of the temporal and spatial variation of the SCIAMACHY limb pointing errors during the first three years of the SCIAMACHY mission. The tangent height errors are retrieved from the limb measurements in the UV-B spectral range. A seasonal modulation of the monthly mean tangent height offsets is identified with amplitudes of 800m (220m) before (after) the improvement of the Envisat orbit propagator model in December 2003. Even after the December 2003 orbit model improvement a constant offset component of about 1km is present. Furthermore, pointing discontinuities are identified that coincide with the daily updates of the on-board orbit propagator model. In order to reduce the errors in ozone profile retrievals caused by pointing errors to less than 5%, the tangent heights have to be known to within 250m.

Solar occultation with SCIAMACHY: algorithm description and first validation

Abstract. This presentation concentrates on solar occultation measurements with the spaceborne spectrometer SCIAMACHY in the UV-Vis wavelength range. Solar occultation measurements provide unique information about the vertical distribution of atmospheric constituents. For retrieval of vertical trace gas concentration profiles, an algorithm has been developed based on the optimal estimation method. The forward model is capable of simulating the extinction signals of different species as they occur in atmospheric transmission spectra obtained from occultation measurements. Furthermore, correction algorithms have been implemented to address shortcomings of the tangent height pre-processing and inhomogeneities of measured solar spectra. First results of O3 and NO2 vertical profile retrievals have been validated with data from ozone sondes and satellite based occultation instruments. The validation shows very promising results for SCIAMACHY O3 and NO2 values between 15 to 35km with errors of the order of 10% and 15%, respectively.