Vladimir V. Rozanov

SCIAMACHY: Mission Objectives and Measurement Modes

Abstract SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) is a spectrometer designed to measure sunlight transmitted, reflected, and scattered by the earth’s atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) at moderate spectral resolution (0.2–1.5 nm, λ/Δλ ≈ 1000–10 000). SCIAMACHY will measure the earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere observed in occultation. The extraterrestrial solar irradiance and lunar radiance will be determined from observations of the sun and the moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the earth’s surface is determined from comparison of earthshine radiance and solar irradiance. Inversion of the ratio of earthshine radiance and solar irradiance yields information about the amounts and distribution of important atmospheric constituents and the spectral reflecta...

The Global Ozone Monitoring Experiment (GOME): Mission Concept and First Scientific Results

The Global Ozone Monitoring Experiment (GOME) is a new instrument aboard the European Space Agencys (ESA) Second European Remote Sensing Satellite(ERS-2), which was launched in April 1995. The main scientific objective of the GOME mission is to determine the global distribution of ozone and several other trace gases, which play an important role in the ozone chemistry of the earths stratosphere and troposphere. GOME measures the sunlight scattered from the earths atmosphere and/or reflected by the surface in nadir viewing mode in the spectral region 240-790 nm at a moderate spectral resolution of between 0.2 and 0.4 nm. Using the maximum 960-km across-track swath width, the spatial resolution of a GOME ground pixel is 40 3 320 km2 for the majority of the orbit and global coverage is achieved in three days after 43 orbits. Operational data products of GOME as generated by DLR-DFD, the German Data Processing and Archiving Facility (D-PAF) for GOME, comprise absolute radiometrically calibrated earthshine radiance and solar irradiance spectra (level 1 products) and global distributions of total column amounts of ozone and NO 2 (level 2 products), which are derived using the DOAS approach (Differential Optical Absorption Spectroscopy). (Under certain conditions and some restrictions, the operational data products are publically available from the European Space Agency via the ERS Helpdesk.) In addition to the operational data products, GOME has delivered important information about other minor trace gases such as OClO, volcanic SO2 ,H 2CO from biomass burning, and tropospheric BrO. Using an iterative optimal estimation retrieval scheme, ozone vertical profiles can be derived from the inversion of the UV/VIS spectra. This paper reports on the GOME instrument, its operation mode, and the retrieval techniques, the latter with particular emphasis on DOAS (total column retrieval) and advanced optimal estimation (ozone profile retrieval). Observation of ozone depletion in the recent polar spring seasons in both hemispheres are presented. OClO observed by GOME under twilight conditions provides valuable information on the chlorine activation inside the polar vortex, which is believed to be responsible for the rapid catalytic destruction of ozone. Episodes of enhanced BrO in the Arctic, most likely contained in the marine boundary layer, were observed in early and late spring. Excess tropospheric nitrogen dioxide and ozone have been observed during the recent Indonesian fire in fall 1997. Formaldehyde could also clearly be identified by GOME and is known to be a by-product resulting from biomass burning.

Ring effect: impact of rotational Raman scattering on radiative transfer in Earth's atmosphere.

Abstract One significant limitation to the accuracy of the remote sensing of trace gas constituents in the atmosphere, using UV-visible spectroscopy and scattered sunlight, has often been a reliable knowledge of the so-called Ring effect. In this study it is demonstrated that the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect. A radiative transfer model has been adapted to include RRS and carefully validated by comparison with Ring effect data by other models and from ground-based and satellite data. The analysis of the principle components of the simulated Ring spectra enabled the Fraunhofer and gas absorption filling-in to be separated. This yields a simple, and therefore computational fast, parameterization of the Ring effect suitable for trace gas retrievals. This approach was tested for the retrieval of NO 2 which is considered to be a worst case with respect to absorption feature filling-in for a trace gas retrieved from scattered light. Analysis of the errors in the vertical column of NO 2 derived using differential optical absorption spectroscopy (DOAS) technique indicate that they are dependent on the amount of NO 2 present in the atmosphere when regarding the experimental Ring spectra. This implies that calculated Ring spectra may be superior for DOAS retrievals, compared to the experimentally determined Ring spectra.

GOMETRAN : A radiative transfer model for the satellite project GOME, the plane-parallel version

The Global Ozone Monitoring Experiment (GOME) is a new, nadir-viewing instrument on the European Space Agency satellite ERS 2 which was launched in April 1995. With diode-array detector technology, spectra of the upwelling radiance are measured simultaneously at thousands of wavelengths in the UV, visible, and near-IR regions. Inversion of these measurements by appropriate algorithms allows the retrieval of the distribution of gaseous and particulate constituents, which modulate the radiance by absorption, emission, or scattering processes. Such a retrieval algorithm requires an accurate radiative transfer model to describe the propagation of light through the atmosphere. The model GOMETRAN has been specially designed to fulfill the needs of GOME, but it applies generally to other downward looking space instrumentation in the UV, visible, or near-IR. In this paper the model is described in the plane-parallel version, and the optimization of computational parameters and comparisons with other radiative transfer models is presented.

Ozone profiles from GOME satellite data: Algorithm description and first validation

In April 1995 the Global Ozone Monitoring Experiment (GOME) was launched aboard the European Space Agencys second European Remote Sensing (ERS-2) satellite. GOME is a nadir-viewing spectrometer measuring solar radiation backscattered by the system Earth-atmosphere in the ultraviolet and visible spectral range. For the retrieval of ozone vertical distributions from GOME measurements the Full Retrieval Method (FURM) has been developed. It is based on the optimal estimation approach and on results from information theory. The joint retrieval of the ozone profile and several additional parameters (e.g., surface albedo) enables the ozone profile retrieval to be extended below the ozone number density maximum. A first validation of the GOME profiles is performed by a comparison with approximately 200 coincident ozonesonde measurements from five European stations. The RMS difference between ozone subcolumn amounts in 10 km layers as measured by GOME and by the sondes is approximately 7-8 % in the middle stratosphere and 15-20 % in the lower stratosphere. Furthermore, it is demonstrated that information about the ozone content in the troposphere can be retrieved from the GOME measurements.

A near-infrared optimized DOAS method for the fast global retrieval of atmospheric CH4, CO, CO2, H2O, and N2O total column amounts from SCIAMACHY Envisat-1 nadir radiances

A new method for the fast and accurate retrieval of atmospheric trace gas total column amounts from near-infrared nadir radiances, to be measured by the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) spectrometer on board the European Space Agency Envisat-1 satellite, has been investigated. It can be characterized as a weighting function modified differential optical absorption spectroscopy approach (WFM-DOAS). The reference spectra of the linear fit include the trace gas total column weighting functions, a weighting function for a temperature profile shift, and a low-order polynomial. Systematic errors due to uncertainties in atmospheric and surface parameters which cannot be retrieved, such as the trace gas vertical profile shapes, pressure and temperature profiles, aerosols, and the surface reflectivity, are quantified. The total column precisions of all trace gases to be retrieved from the SCIAMACHY near-infrared channels 7 (1940–2040 nm) and 8 (2265–2385 nm) have been estimated to be better than 1% for H2O, CO2, and CH4, and better than 10% for N2O and CO. The potential of SCIAMACHY to measure regional CO2 and CH4 emission fluxes has been investigated. Both are important greenhouse gases to be monitored and reduced according to the Kyoto Protocol of the U.N. Framework Convention on Climate Change.

A numerical radiative transfer model for a spherical planetary atmosphere: combined differential–integral approach involving the Picard iterative approximation

Abstract A new radiative transfer model suitable to calculate the radiation field in a spherical planetary atmosphere has been developed. The suggested approach involves the Picard iterative approximation to solve the radiative transfer equation in its integral form. The radiation field calculated by solving the integro-differential radiative transfer equation in a pseudo-spherical atmosphere is used as an initial guess for the iterative scheme. The approach has the same advantages as the Monte-Carlo method, but is much more computationally efficient. The comparisons between the spherical model presented in this paper and a Monte-Carlo radiative transfer model for radiances at the top of the atmosphere show differences less than 1% for most situations. The accuracy of the recently developed CDI approach, which was intended to perform fast and accurate radiance computations for non-limb viewing geometry, has been estimated for limb viewing geometry.

Retrieval of atmospheric constituents in the uv-visible: a new quasi-analytical approach for the calculation of weighting functions

Abstract Novel mathematical procedures for the efficient calculation of weighting functions inside finite differencing radiative transfer models are presented. Linearization of the radiative transfer equation allows to compute the weighting functions directly without the use of numerical perturbation schemes. The methods developed have been implemented in the finite-differencing model GOMETRAN. Validation of the quasi-analytical computations of the weighting functions has been achieved by comparison with results using numerical perturbation methods from finite-differencing and doubling-adding. An interpretation of the weighting functions is presented and outlines their relationship with air mass factors. Finally, the weighting function technique is applied to the retrieval of ozone and temperature vertical profiles from satellite measurements.

Sciatran - a new radiative transfer model for geophysical applications in the 240–2400 NM spectral region: the pseudo-spherical version

Abstract A radiative transfer model, SCIATRAN, has been developed mainly for the retrieval of atmospheric constituents from global nadir radiance measurements of the SCIAMACHY satellite spectrometer. This is a further development of the successful GOMETRAN. SCIATRAN solves the radiative transfer equation using the Finite Difference Method for a plane-parallel vertically inhomogeneous atmosphere taking into account multiple scattering. The present program version utilizes the pseudo-spherical approach, including refraction, appropriate for solar zenith angles up to about 92°. SCIATRAN comprises, amongst others, the following features: (i) quasi-analytical calculation of weighting functions of atmospheric and surface parameters, (ii) DOAS airmass factor calculations, (iii) height resolved radiation fluxes, including actinic fluxes for photolysis rate calculations, (iv) inelastic rotational Raman scattering by N 2 and O 2 molecules, (v) parameterization schemes for aerosols and clouds, (vi) a line-by-line and a correlated-k distribution mode for line absorption, and (vii) thermal emission. This paper presents an overview of the SCIATRAN model, focusing on the pseudo-spherical approach developed to consider the sphericity of the Earth. SCIATRAN will be made available via the world wide web for non-commercial scientific applications.

The Ozone Hole Breakup in September 2002 as Seen by SCIAMACHY on ENVISAT

An unprecedented stratospheric warming in the Southern Hemisphere in September 2002 led to the breakup of the Antarctic ozone hole into two parts. The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on the European Environmental Satellite (ENVISAT ) performed continuous observations of limb-scattered solar radiance spectra throughout the stratospheric warming. Thereby, global measurements of vertical profiles of several important minor constituents are provided with a vertical resolution of about 3 km. In this study, stratospheric profiles of O3 ,N O 2, and BrO retrieved from SCIAMACHY limb-scattering observations together with polar stratospheric cloud (PSC) observations for selected days prior to (12 September), during (27 September), and after (2 October) the ozone hole split are employed to provide a picture of the temporal evolution of the Antarctic stratosphere’s three-dimensional structure.