Alternative polarisation retrieval for SCIAMACHY in the ultraviolet

Tilstra, L. G.; Stammes, P.

doi:10.5194/acp-5-2099-2005

Cited by 13 publications

(7 citation statements)

References 9 publications

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“…Since late 1999 the degradation of the GOME UVpart in the spectra has become scan mirror angle dependent which means that the solar and the earthshine spectra ob-served in different scan angle directions degrade at different rates (Snel, 2001;Tanzi et al, 2001). For SCIAMACHY, the currently available processor version of level 1 spectral data has errors in the polarisation correction and radiometric calibration (Tilstra and Stammes, 2005). Generally, the DOAS method, at least for ozone retrievals has been proven to be relatively insensitive to radiometric calibration errors because of the polynomial subtraction in the DOAS approach (see e.g.…”

Section: Discussionmentioning

confidence: 99%

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS

Bracher¹,

Weber²,

Bramstedt³

et al. 2005

Preprint

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Abstract. Global stratospheric ozone columns measured by SCIAMACHY (Scanning Imaging Spectrometer for Atmospheric Chartography; data versions 5.01 and 5.04) aboard the recently launched Environmental Satellite (ENVISAT) from January to June 2003 were compared to collocated total ozone data from GOME (Global Ozone Monitoring Experiment on ERS-2) retrieved using the weighting function DOAS algorithm (WFDOAS; Version 1.0) in order to assess the level-2 data (trace gas data) retrieval accuracy from SCIAMACHY. The large number of collocated total ozone data from the two instruments which are flying in the same orbit were spatially binned into regular 2.5° and 2.5° grids and then compared. This binning method shows similar results than direct comparisons but is about thousand times faster. Results of these satellite comparisons show that SCIAMACHY O3 vertical columns (version 5.01/5.04) are on average 1% (±2%) lower than GOME WFDOAS and scatter increases at solar zenith angles above 85° and at low total ozone values. Results show dependencies on the seasonal cycle, latitudes, and total ozone amounts which are explained by the implementation of an old GOME algorithm based on GOME Data Processor (GDP) version 2.4 algorithm for the SCIAMACHY operational product. A reprocessing with an algorithm equivalent to GOME GDP version 4.0 and/or GOME WFDOAS V1.0 will improve significantly the quality of the SCIAMACHY ozone product. Since GOME lost its global coverage in July 2003 due to data rate limitation, continuation of the total ozone time series with SCIAMACHY is of highest importance for long-term trend monitoring.

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Section: Discussionmentioning

confidence: 99%

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS

Bracher¹,

Weber²,

Bramstedt³

et al. 2005

Preprint

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“…However, currently, the quality of the polarization parameters Q / I and U / I determined by SCIAMACHY is not up to the level required [ Tilstra and Stammes , 2005], which is why in this paper the SCIAMACHY reflectance is corrected for polarization based on the Q / I and U / I obtained from simulations. In other words, the operational SCIAMACHY polarization correction is bypassed using our own polarization correction.…”

Section: Reflectance Comparisonmentioning

confidence: 99%

Method for in‐flight satellite calibration in the ultraviolet using radiative transfer calculations, with application to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)

2005

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[1] We present a reflectance validation method, using a polarized radiative transfer model as a reference. The method involves calculating the complete radiative transfer in the ultraviolet for a carefully selected, natural, cloud-free Earth target. An extensive sensitivity study shows that in the ultraviolet, the ozone profile (mainly below 330 nm) and the surface albedo (mainly above 330 nm) are the important parameters that affect the reflectance and are therefore the major sources of error in the modeled reflectances. The accuracy with which the reflectance in the UV range of 240-400 nm can be calculated, because of uncertainty in input parameters, is 2-6%, depending on wavelength. The method is applied to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), using a cloud-free scene over the Sahara desert. The reflectance measured by SCIAMACHY turns out to show a scan-angle-independent calibration error of 10-25% for this particular Sahara target. The result is confirmed for ocean and vegetation targets.Citation: Tilstra, L. G., G. van Soest, and P. , Method for in-flight satellite calibration in the ultraviolet using radiative transfer calculations, with application to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography

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“…Such offsets cannot be explained by absolute calibration errors of the solar irradiance alone, suggesting also uncertainties with the absolute calibration of the earth radiance different from solar irradiance calibration errors. Reflectance comparisons have also revealed the presence of residual polarisation sensitivity structures in the spectra even after application of the polarisation correction (Tilstra and Stammes, 2005).…”

Section: Level 1 Productsmentioning

confidence: 99%

Overview of SCIAMACHY validation: 2002–2004

Piters¹,

Bramstedt²,

Lambert³

et al. 2005

Preprint

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Abstract. SCIAMACHY, on board Envisat, is now in operation for almost three years. This UV/visible/NIR spectrometer measures the solar irradiance, the earthshine radiance scattered at nadir and from the limb, and the attenuation of solar radiation by the atmosphere during sunrise and sunset, from 240 to 2380 nm and at moderate spectral resolution. Vertical columns and profiles of a variety of atmospheric constituents are inferred from the SCIAMACHY radiometric measurements by dedicated retrieval algorithms. With the support of ESA and several international partners, a methodical SCIAMACHY validation programme has been developed jointly by Germany, the Netherlands and Belgium (the three instrument providing countries) to face complex requirements in terms of measured species, altitude range, spatial and temporal scales, geophysical states and intended scientific applications. This summary paper describes the approach adopted to address those requirements. The actual validation of the operational SCIAMACHY processors established at DLR on behalf of ESA has been hampered by data distribution and processor problems. Since first data releases in summer 2002, operational processors were upgraded regularly and some data products – level-1b spectra, level-2 O3, NO2, BrO and clouds data – have improved significantly. Validation results summarised in this paper conclude that for limited periods and geographical domains they can already be used for atmospheric research. Nevertheless, remaining processor problems cause major errors preventing from scientific usability in other periods and domains. Untied to the constraints of operational processing, seven scientific institutes (BIRA-IASB, IFE, IUP-Heidelberg, KNMI, MPI, SAO and SRON) have developed their own retrieval algorithms and generated SCIAMACHY data products, together addressing nearly all targeted constituents. Most of the UV-visible data products (both columns and profiles) already have acceptable, if not excellent, quality. Several near-infrared column products are still in development but they have already demonstrated their potential for a variety of applications. In any case, scientific users are advised to read carefully validation reports before using the data. It is required and anticipated that SCIAMACHY validation will continue throughout instrument lifetime and beyond. The actual amount of work will obviously depend on funding considerations.

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Alternative polarisation retrieval for SCIAMACHY in the ultraviolet

Cited by 13 publications

References 9 publications

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS

Method for in‐flight satellite calibration in the ultraviolet using radiative transfer calculations, with application to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)

Overview of SCIAMACHY validation: 2002–2004

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Alternative polarisation retrieval for SCIAMACHY in the ultraviolet

Cited by 13 publications

References 9 publications

Global satellite validation of SCIAMACHY O&lt;sub&gt;3&lt;/sub&gt; columns with GOME WFDOAS

Global satellite validation of SCIAMACHY O&lt;sub&gt;3&lt;/sub&gt; columns with GOME WFDOAS

Method for in‐flight satellite calibration in the ultraviolet using radiative transfer calculations, with application to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)

Overview of SCIAMACHY validation: 2002–2004

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Resources

About

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS

Global satellite validation of SCIAMACHY O<sub>3</sub> columns with GOME WFDOAS