Pieter Valks

Ten years of GOME/ERS-2 total ozone data- : The new GOME data processor (GDP) version 4: 1. Algorithm description

The Global Ozone Monitoring Instrument (GOME) was launched on European Space Agencys ERS-2 platform in April 1995. The GOME data processor (GDP) operational retrieval algorithm has generated total ozone columns since July 1995. In 2004 the GDP system was given a major upgrade to version 4.0, a new validation was performed, and the 10-year GOME level 1 data record was reprocessed. In two papers, we describe the GDP 4.0 retrieval algorithm and present an error budget and sensitivity analysis (paper 1) and validation of the GDP total ozone product and the overall accuracy of the entire GOME ozone record (paper 2). GDP 4.0 uses an optimized differential optical absorption spectroscopy (DOAS) algorithm, with air mass factor (AMF) conversions calculated using the radiative transfer code linearized discrete ordinate radiative transfer (LIDORT). AMF computation is based on the TOMS version 8 ozone profile climatology, classified by total column, and AMFs are adjusted iteratively to reflect the DOAS slant column result. GDP 4.0 has improved wavelength calibration and reference spectra and includes a new molecular Ring correction to deal with distortion of ozone absorption features due to inelastic rotational Raman scattering effects. Preprocessing for cloud parameter estimation in GDP 4.0 is done using two new cloud correction algorithms: OCRA and ROCINN. For clear and cloudy scenes the precision of the ozone column product is better than 2.4 and 3.3%, respectively, for solar zenith angles up to 80°. Comparisons with ground-based data are generally at the 1-1.5% level or better for all regions outside the poles.

The GOME‐2 total column ozone product: Retrieval algorithm and ground‐based validation

The Global Ozone Monitoring Instrument (GOME-2) was launched on EUMESATs MetOp-A satellite in October 2006. This paper is concerned with the retrieval algorithm GOME Data Processor (GDP) version 4.4 used by the EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M-SAF) for the operational generation of GOME-2 total ozone products. GDP 4.4 is the latest version of the GDP 4.0 algorithm, which is employed for the generation of official Level 2 total ozone and other trace gas products from GOME and SCIAMACHY. Here we focus on enhancements introduced in GDP 4.4: improved cloud retrieval algorithms including detection of Sun glint effects, a correction for intracloud ozone, better treatment of snow and ice conditions, accurate radiative transfer modeling for large viewing angles, and elimination of scan angle dependencies inherited from Level 1 radiances. Furthermore, the first global validation results for 3 years (2007–2009) of GOME-2/MetOp-A total ozone measurements using Brewer and Dobson measurements as references are presented. The GOME-2/MetOp-A total ozone data obtained with GDP 4.4 slightly underestimates ground-based ozone by about 0.5% to 1% over the middle latitudes of the Northern Hemisphere and slightly overestimates by around 0.5% over the middle latitudes in the Southern Hemisphere. Over high latitudes in the Northern Hemisphere, GOME-2 total ozone has almost no offset relative to Dobson readings, while over high latitudes in the Southern Hemisphere GOME-2 exhibits a small negative bias below 1%. For tropical latitudes, GOME-2 measures on average lower ozone by 0% to 2% compared to Dobson measurements.

Satellite Monitoring of Volcanic Sulfur Dioxide Emissions for Early Warning of Volcanic Hazards

Satellite-based remote sensing measurements of volcanic sulfur dioxide (SO2) provide critical information for reducing volcanic hazards. This paper describes the use of SO2 measurements from the thermal infrared sounder IASI and the UV-VIS instrument GOME-2 in services related to aviation hazard and early warning of volcanic unrest. The high sensitivity of both instruments to SO2 allows the detection and global tracking of volcanic eruption plumes and makes them a valuable tool for volcanic aviation hazard mitigation. The GOME-2 and IASI SO2 data are produced in near-real time and distributed to the Volcanic Ash Advisory Centers (VAACS) to assist them in issuing alerts to airlines and air traffic control organizations. Examples of recent eruptions affecting air traffic are presented including Jebel al Tair (Yemen, September 2007), Mount Okmok (Alaska, July 2008), and Mount Kasatochi (Alaska, August 2008). In addition, GOME-2 can detect changes in the SO2 emissions from passively degassing volcanoes and, therefore, provide critical information for hazard assessment. The monitoring of pre-eruptive degassing by GOME-2 is used in early warning of volcanic activity by a mobile volcano fast response system in combination with numerous other parameters, such as seismicity, deformation, and thermal anomalies.

Space-based measurements of air quality during the World Expo 2010 in Shanghai

During the World Exposition 2010 (Expo, from May to October), emission control measures were implemented in Shanghai and surrounding areas to improve the air quality. To evaluate the effect of these measures, we use the tropospheric NO2 column, aerosol optical thickness (AOT) and CO concentration observations from the satellite instruments GOME-2, MODIS and MOPITT, respectively. The analysis shows about 8% and 14% reductions of tropospheric NO2 columns and AOT respectively over Shanghai during the Expo period, compared to the past three years. A 12% reduction of CO concentration at 700 hPa over Shanghai and surrounding areas is found during the Expo period. On the other hand, the satellite measurements show increases of NO2 by 20% and AOT by 23% over Shanghai urban areas after the Expo (November 2010–April 2011), when the short-term emission control measures were lifted. Our study indicates that the air quality measures were effective in Shanghai and surrounding provinces during the Expo period.

Operational Integration of Spaceborne Measurements of Lava Discharge Rates and Sulfur Dioxide Concentrations for Global Volcano Monitoring

We present the rationale and the main initial achievements of the operational prototype of the first multi-method system for the real-time, unsupervised, quantitative monitoring of erupted masses simultaneously at all active volcanoes in Europe, Africa, the Eastern Antilles and the ocean islands. The system is structured as a multi-pole, geographically distributed system, where raw datasets from space payloads SEVIRI, MODIS, GOME-2, IASI and OMI are acquired at four downlink stations, distributed to, and automatically processed at six locations in four European nations, then returned to a central post-processor for real-time alert and Wide Area Network display. This architecture is aimed at optimizing quality and timeliness of the advanced methods run within it, and to let the inherent technical knowledge remain with inventors without concern for individual intellectual property. Before entering operations early in 2012, the system underwent extensive testing in 2011 during the major eruptions of Nabro (Eritrea) and Nyamulagira (DR Congo), which are presented here.

Operational Monitoring of the Antarctic Ozone Hole: Transition from GOME and SCIAMACHY to GOME-2

The European satellite-borne atmospheric sensors global ozone monitoring experiment (GOME), scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) and GOME-2 provide an important global ozone data record covering an expected time span of over 25 years. Accurate measurements of total ozone and other trace gas species have been gathered by GOME (since July 1995) and SCIAMACHY (since June 2002). This record has recently been extended with observations from the first GOME-2 sensor (fromMarch 2007). Two other identical GOME-2 sensors have been built and their future deployment in the next decade will provide global ozone and trace gas data for the next 14 years. The main goal of this chapter is to present results from the monitoring of the Antarctic ozone hole from 1995 to 2007 with these three instruments. Additionally, the algorithms currently used for total ozone retrieval and data assimilation are outlined, together with validation results and perspectives for future developments.

An Improved Total and Tropospheric NO 2 Column Retrieval for GOME-2

This paper focuses on an improved algorithm for theretrieval of total and tropospheric No2 columns fromthe Global Ozone Monitoring Experiment-2 (GOME-2). A larger 425-497 nm wavelength fitting windowwith correction for GOME-2 slit function variations isused to determine the No2 slant column density. TheSTRatospheric Estimation Algorithm from Mainz(STREAM) is applied to determine the stratosphericcolumn density of No2. A new surface Lambertianequivalent reflectance (LER) climatology based onGOME-2 observations is used for the calculation of theair mass factor (AMF). Examples of the retrievedGOME-2 total and tropospheric No2 columns areshown for Europe and Asia.

Investigating the GOME2/MetopA Total Sulphur Dioxide Load with the Aid of Chemical Transport Modelling over the Balkan Region

The current discerning capability of nadir viewing satellite instruments is mainly providing information on large volcanic events, such as the Kasatochi 2008 and the Eyjafjoll 2010 eruptions, and areas with high anthropogenic SO2 sources such as Peruvian smeltering regions. Consequently, there exists a constant need to improve the algorithms in order to provide satellite information on the megacities’ SO2 levels for air quality purposes. In the current study, we aim to assess the observational capability of the GOME2/MetopA instrument by analysing the total SO2 load estimated over the extended Balkan region with the use of the high spatial resolution Comprehensive Air Quality Model with extensions (CAMx) modelling results. Two years of satellite and modelling estimates have been analysed so as to pin-point locations of constantly high SO2 loading, locations with a marked seasonal variability as well as locations with high expected loading that might not be visible from the satellite orbit. Regions of specific interest will be chosen for further investigation and algorithm development based on updated modelling input parameters such as the SO2 loading profile.