Pieternel F. Levelt

Aerosols and surface UV products from Ozone Monitoring Instrument observations: An overview

We present an overview of the theoretical and algorithmic aspects of the Ozone Monitoring Instrument (OMI) aerosol and surface UV algorithms. Aerosol properties are derived from two independent algorithms. The nearUV algorithm makes use of OMI observations in the 350-390 nm spectral region to retrieve information on the absorption capacity of tropospheric aerosols. OMI-derived information on aerosol absorption includes the UV Aerosol Index and absorption optical depth at 388 nm. The other algorithm makes use of the full UV-to-visible OMI spectral coverage to derive spectral aerosol extinction optical depth. OMI surface UV products include erythemally weighted daily dose as well as erythemal dose rate and spectral UV irradiances calculated for local solar noon conditions. The advantages and limitations of the current algorithms are discussed, and a brief summary of several validation and evaluation analysis carried out to assess the current level of uncertainty of these products is presented. Copyright 2007 by the American Geophysical Union. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: D24S47

OMI level 0 to 1b processing and operational aspects

The Ozone Monitoring Instrument (OMI) was launched on July 15, 2004 on the National Aeronautics and Space Administrations Earth Observing System Aura satellite. OMI is an ultraviolet-visible imaging spectrograph providing daily global coverage with high spatial resolution. This paper discusses the ground data processing software used for Level 0 to Level 1b processing of OMI data. In addition, the OMI operations scenario is described together with the data processing concept. This paper is intended to serve as a reference guide for users of OMI (Level 1b) data.

TROPOMI and TROPI: UV/VIS/NIR/SWIR instruments

TROPOMI (Tropospheric Ozone-Monitoring Instrument) is a five-channel UV-VIS-NIR-SWIR non-scanning nadir viewing imaging spectrometer that combines a wide swath (114°) with high spatial resolution (10 × 10 km2 ). The instrument heritage consists of GOME on ERS-2, SCIAMACHY on Envisat and, especially, OMI on EOS-Aura. TROPOMI has even smaller ground pixels than OMI-Aura but still exceeds OMIs signal-to-noise performance. These improvements optimize the possibility to retrieve tropospheric trace gases. In addition, the SWIR capabilities of TROPOMI are far better than SCIAMACHYs both in terms of spatial resolution and signal to noise performance. TROPOMI is part of the TRAQ payload, a mission proposed in response to ESAs EOEP call. The TRAQ mission will fly in a non-sun synchronous drifting orbit at about 720 km altitude providing nearly global coverage. TROPOMI measures in the UV-visible wavelength region (270-490 nm), in a near-infrared channel (NIR) in the 710-775 nm range and has a shortwave infrared channel (SWIR) near 2.3 μm. The wide swath angle, in combination with the drifting orbit, allows measuring a location up to 5 times a day at 1.5-hour intervals. The spectral resolution is about 0.45 nm for UVVIS- NIR and 0.25 nm for SWIR. Radiometric calibration will be maintained via solar irradiance measurements using various diffusers. The instrument will carry on-board calibration sources like LEDs and a white light source. Innovative aspects include the use of improved detectors in order to improve the radiation hardness and the spatial sampling capabilities. Column densities of trace gases (NO2, O3, SO2 and HCHO) will be derived using primarily the Differential Optical Absorption Spectroscopy (DOAS) method. The NIR channel serves to obtain information on clouds and the aerosol height distribution that is needed for tropospheric retrievals. A trade-off study will be conducted whether the SWIR channel, included to determine column densities of CO and CH4, will be incorporated in TROPOMI or in the Fourier Transform Spectrometer SIFTI on TRAQ. The TROPI instrument is similar to the complete TROPOMI instrument (UV-VIS-NIR-SWIR) and is proposed for the CAMEO initiative, as described for the U.S. NRC Decadal Study on Earth Science and Applications from Space. CAMEO also uses a non-synchronous drifting orbit, but at a higher altitude (around 1500 km). The TROPI instrument design is a modification of the TROPOMI design to achieve identical coverage and ground pixel sizes from a higher altitude. In this paper capabilities of TROPOMI and TROPI are discussed with emphasis on the UV-VIS-NIR channels as the TROPOMI SWIR channel is described in a separate contribution [5].

Ozone monitoring instrument flight-model on-ground and inflight calibration

The Ozone Monitoring Instrument (OMI) is an ultravioletvisible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a 114 degrees wide swath combined with an unprecedented small ground pixel (nominally 13 x 24 km2), which in turn enables global daily ground coverage with high spatial resolution. The OMI instrument is part of NASA’s EOSAURA satellite, which will be launched in the second half of 2004. The on-ground calibration of the instrument was performed in 2002. This paper presents and discusses results for a number of selected topics from the on-ground calibration: the radiometric calibration, the spectral calibration and spectral slit function calibration. A new method for accurately calibrating spectral slit functions, based on an echelle grating optical stimulus, is discussed. The in-flight calibration and trend monitoring approach and facilities are discussed.

In-flight calibration of the ozone monitoring instrument

This paper discusses various aspects of the on-ground and in-flight calibration of the OMI instrument.

Compact hyperspectral instrument for NO2 remote sensing

The impact of NO2 and other atmospheric trace gases on health and the environment is now acknowledged by governments around the world. The sources, both natural and anthropogenic, have been shown to affect the quality of life due to low air quality in densely populated areas. Consequently, the need for accurate global NO2 measurements with high spatial- and temporal resolution to monitor NO2 is becoming ever more important. Through an ESA study, TNO and KNMI have been evaluating measurement requirements and an instrument design for a ‘Compact NO2 Spectrometer’, based on a hyperspectral imaging instrument operating in the VIS (405-490nm] spectral range and aimed at combining the performance of state-of-the-art instruments with fine spatial sampling (0.5x0.5 km2). By use of a novel free-form optics a very compact low volume and low mass design has been achieved. Combining this with other small satellite design approaches for components the aim is to create a low cost instrument capable of being flown on a wide variety of space platforms. Global daily coverage can then be achieved with a relatively small constellation of instruments. The key design features are described for a ‘Compact NO2 Spectrometer’, such as the optical design approach, the use of free-form optics, an ‘athermal’ all aluminium approach. An overview of the development and airborne results from a breadboard of a small prototype system (Spectrolite) developed by TNO which uses many of the design features envisaged for this new instrument is given.

EOS-AURA ozone monitoring instrument: scientific results of nearly two years successful operation and in-flight calibration and performance

The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115° wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents a number of examples of scientific results from the first two years in orbit, as well as a selection of in-flight radiometric, spectral and CCD detector performance and calibration results. The scientific results will show the OMI capability of measuring atmospheric phenomena with high spatial and temporal resolution. It will be shown that the OMI radiometric and spectral calibration are accurately understood. Radiation damage effects on the CCD detectors will be discussed in detail and it will be shown that it is possible to correct for the consequences to a large extent in order to minimise the impact on the scientific level-1 and level-2 data products.

TROPOMI end-to-end performance studies

The TROPOspheric Monitoring Instrument (TROPOMI) is a UV/VIS/NIR/SWIR non-scanning nadir viewing imaging spectrometer that combines a wide swath (110°) with high spatial resolution (8 x 8 km). Its main heritages are from the Ozone Monitoring Instrument (OMI) and from SCIAMACHY. Since its launch in 2004 OMI has been providing, on a daily basis and on a global scale, a wealth of data on ozone, NO2 and minor trace gases, aerosols and local pollution, a scanning spectrometer launched in 2004. The TROPOMI UV/VIS/NIR and SWIR heritage is a combination of OMI and SCIAMACHY. In the framework of development programs for a follow-up mission for the successful Ozone Monitoring Instrument, we have developed the so-called TROPOMI Integrated Development Environment. This is a GRID based software simulation tool for OMI follow-up missions. It includes scene generation, an instrument simulator, a level 0-1b processing chain, as well as several level 1b-2 processing chains. In addition it contains an error-analyzer, i.e. a tool to feedback the level 2 results to the input of the scene generator. The paper gives a description of the TROPOMI instrument and focuses on design aspects as well as on the performance, as tested in the end-to-end development environment TIDE.