Abstract. The Global Ozone Monitoring Experiment-2 (GOME-2) flies on the Metop series of satellites, the space component of the EUMETSAT Polar System. In this paper we will provide an overview of the instrument design, the on-ground calibration and characterization activities, in-flight calibration, and level 0 to 1 data processing. The current status of the level 1 data is presented and points of specific relevance to users are highlighted. Long-term level 1 data consistency is also discussed and plans for future work are outlined. The information contained in this paper summarizes a large number of technical reports and related documents containing information that is not currently available in the published literature. These reports and documents are however made available on the EUMETSAT web pages and readers requiring more details than can be provided in this overview paper will find appropriate references at relevant points in the text.
Global data sets of total column precipitable water and cloud cover derived from the Global Ozone Monitoring Experiment (GOME) are analyzed with respect to anomalies induced by the strong El Niño 1997/1998. In contrast to other satellite observations of water vapor, the GOME nadir observations in the visible spectral range are of similar sensitivity over both land and ocean. In addition, they are sensitive in particular to the water vapor concentration close to the surface where a major fraction of the water vapor column is present. Information on the atmospheric cloud cover was derived from the observed broadband intensity as well as the oxygen (O 2 ) absorption. While the first quantity is mainly a measure of geometrical cloud fraction, the latter also yields information on the cloud altitude. We investigated the time series of monthly mean values as well as anomalies calculated for a 6‐month period during the El Niño 1997/1998. For all three quantities we found strong anomalies over large areas and for extended periods. Especially for the total column precipitable water, significant anomalies were found even in mid and high latitudes indicating substantial changes in the hydrological cycle and the global circulation patterns.
We have analyzed global trends of total column precipitable water from measurements of the Global Ozone Monitoring Experiment (GOME) on the European Research Satellite (ERS‐2) for the period January 1996 to June 2003. In contrast to other satellite retrieval methods of total column precipitable water, our analysis does not rely on a priori assumptions or additional information; thus it is particularly well suited to trend studies. The chosen wavelength range in the red spectral region ensures similar sensitivity for observations over land and ocean and thus a consistent global picture. To minimize the influence of clouds on the water vapor trends, we selected observations under mainly clear‐sky conditions. The temporal evolution of the monthly or yearly averaged total column precipitable water, especially in the tropics, is highly correlated to that of the near‐surface temperature, indicating that the global atmospheric humidity is mainly driven by Clausius‐Clapeyron's principle. The magnitude of the dependence on near‐surface temperature indicates a strong water vapor feedback. The spatial patterns of the water vapor trends show both positive and negative signs. Especially over the oceans, trend patterns very similar to those of near‐surface temperature are found. In contrast, over Northern Hemispheric continents the trend patterns are much less correlated, and even opposite trends for water vapor and the near‐surface temperatures are found. During the period 1996–2002 the globally and yearly averaged total column precipitable water increased by 2.8 ± 0.8% (excluding the ENSO period).
From the spectra of UV/vis satellite instruments the H2O VCD can be measured. Compared to other methods, the main advantages of our algorithm are similar sensitivity over land and oceans and for the whole atmospheric column. Also, it does not rely on a- priori assumptions or additional information. From the measured spectra also information on cloud properties can be derived. Besides the absolute radiance, also the absorptions of O2 and O4 and the strength of the Ring effect can be measured. Especially from the strong and narrow-band O2 absorption, cloud information can be analysed with high precision. Here we present global trends of the H2O VCD and the O2 cloud cover analysed from GOME observations for 1996-2003. During this period, both quantities show a substantial increase, mostly consistent with the trends of the near-surface temperatures. The time series from GOME-I can be continued with observations of its successors SCIAMACHY and GOME-II; the total time period can thus be extended to up to about 25 years. 1. INSTRUMENTS The GOME instrument aboard the European research satellite ERS-2 (1) measures sunlight reflected from the Earth's atmosphere and surface covering the wavelength range between 240 and 790 nm with moderate spectral resolution (0.2-0.4nm FWHM). The satellite operates in a nearly polar, sun-synchronous orbit at an altitude of 780 km with an equator crossing time of approximately 10:30 am local time. While the satellite orbits in an almost north-south direction, the GOME instrument scans the surface of earth in the perpendicular east-west direction. During one scan, three individual ground pixels are observed, each covering an area of 320 km east to west by 40 km north to south. The Earth's surface is entirely covered within 3 days, and poleward from about 70° latitude within 1 day. GOME-II is similar to GOME-I, but has a finer spatial resolution (40x80km²) and better global coverage (within one day) (2). 2. DATA ANALYSIS 2.1 H2O VCD (total column precipitable water) Several algorithms for the retrieval of the total column precipitable water in the red part of the spectrum from GOME were developed during recent years (3-13). In contrast to these other methods, our water vapor algorithm is directly based on the results of the spectral
Abstract. The Global Ozone Monitoring Experiment-2 (GOME-2) flies on the Metop series of satellites, the space component of the EUMETSAT Polar System. In this paper we will provide an overview of the instrument design, the on-ground calibration and characterisation activities, in-flight calibration, and level 0 to 1 data processing. The quality of the level 1 data is presented and points of specific relevance to users are highlighted. Long-term level 1 data consistency is also discussed and plans for future work are outlined. The information contained in this paper summarises a large number of technical reports and related documents containing information that is not currently available in the published literature. These reports and documents are however made available on the EUMETSAT web pages (http://www.eumetsat.int) and readers requiring more details than can be provided in this overview paper will find appropriate references at relevant points in the text.
Abstract. A new global albedo climatology for Oxygen A-band cloud retrievals is presented. The climatology is based on MEdium Resolution Imaging Spectrometer (MERIS) Albedomap data and its favourable impact on the derivation of cloud fraction is demonstrated for the FRESCO+ (Fast Retrieval Scheme for Clouds from the Oxygen A-band) algorithm. To date, a relatively coarse resolution (1° × 1°) surface reflectance dataset from GOME (Global Ozone Monitoring Experiment) Lambert-equivalent reflectivity (LER) is used in FRESCO+. The GOME LER climatology does not account for the usually higher spatial resolution of UV/VIS instruments designed for trace gas remote sensing which introduces several artefacts, e.g. in regions with sharp spectral contrasts like coastlines or over bright surface targets. Therefore, MERIS black-sky albedo (BSA) data from the period October 2002 to October 2006 were aggregated to a grid of 0.25° × 0.25° for each month of the year and for different spectral channels. In contrary to other available surface reflectivity datasets, MERIS includes channels at 754 nm and 775 nm which are located close to the spectral windows required for O2 A-band cloud retrievals. The MERIS BSA in the near infrared compares well to Moderate Resolution Imaging Spectroradiometer (MODIS) derived BSA with an average difference lower than 1% and a correlation coefficient of 0.98. However, when relating MERIS BSA to GOME LER a distinctly lower correlation (0.80) and enhanced scatter is found. Effective cloud fractions from two exemplary months (January and July 2006) of Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) data were subsequently derived with FRESCO+ and compared to those from the Heidelberg Iterative Cloud Retrieval Utilities (HICRU) algorithm. The MERIS climatology generally improves FRESCO+ effective cloud fractions. In particular small cloud fractions are in better agreement with HICRU. This is of importance for atmospheric trace gas retrieval which relies on accurate cloud information at small cloud fractions. In addition, overestimates along coastlines and underestimates in the Intertropical Convergence Zone introduced by the GOME LER were eliminated. While effective cloud fractions over the Saharan desert and the Arabian peninsula are successfully reduced in January, they are still too high in July relative to HICRU due to FRESCO+'s large sensitivity to albedo inaccuracies of highly reflecting targets and inappropriate aerosol information which hampers an accurate albedo retrieval. Apart from FRESCO+, the new MERIS albedo data base is applicable to any cloud retrieval algorithms using the O2 A-band or the O2-O2 absorption band around 477 nm. Moreover, the by-product of BSA at 442 nm can be used in NO2 remote sensing and the BSA at 620 nm, 665 nm, and 681 nm could be integrated in current H2O retrievals.
Abstract. A new method for the satellite remote sensing of different types of vegetation and ocean colour is presented. In contrast to existing algorithms relying on the strong change of the reflectivity in the red and near infrared spectral region, our method analyses weak narrow-band (few nm) reflectance structures (i.e. "fingerprint" structures) of vegetation in the red spectral range. It is based on differential optical absorption spectroscopy (DOAS), which is usually applied for the analysis of atmospheric trace gas absorptions. Since the spectra of atmospheric absorption and vegetation reflectance are simultaneously included in the analysis, the effects of atmospheric absorptions are automatically corrected (in contrast to other algorithms). The inclusion of the vegetation spectra also significantly improves the results of the trace gas retrieval. The global maps of the results illustrate the seasonal cycles of different vegetation types. In addition to the vegetation distribution on land, they also show patterns of biological activity in the oceans. Our results indicate that improved sets of vegetation spectra might lead to more accurate and more specific identification of vegetation type in the future.
