Pawan Bhartia - Profile on Academia.edu (original) (raw)
Papers by Pawan Bhartia
Space-Based Measurement of Chemical Tracers (gaseous) and Aerosol Pollutants: Past, Present, and Future Needs (Core Science Keynote)
Space-based Measurement of Gaseous and Aerosol Pollutants (Invited Presentation)
An assessment of the long-term drift in TOMS total ozone data, based on comparison with the Dobson Network
Geophysical Research Letters, 1988
Using techniques very similar to those used in comparing SBUV total ozone with Dobson [Fleig et a... more Using techniques very similar to those used in comparing SBUV total ozone with Dobson [Fleig et al. 1986A], seven years of total ozone data derived from the TOMS instrument on Nimbus‐7 are compared with results from 41 Dobson stations. In this study however, a ...
Journal of Geophysical Research, 2003
The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-vi... more The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-visible satellite spectrometer Global Ozone Monitoring Experiment (GOME) has been modeled by means of a feed forward neural network. This Neural Network Ozone Retrieval System (NNORSY) was trained exclusively on a data set of GOME radiances collocated with ozone measurements from ozonesondes, Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Polar Ozone and Aerosol Measurement III. Network input consists of a combination of spectral, geolocation, and climatological information (time and latitude). In the stratosphere the method globally reduces standard deviation with respect to an ozone climatology by around 40%. Tropospheric ozone can also be retrieved in many cases with corresponding reduction of 10-30%. All GOME data from January 1996 to July 2001 were processed. In a number of case studies involving comparisons with ozonesondes from Hohenpeissenberg, Syowa, and results from the classical Full Retrieval Method, we found good agreement with our results. The neural network was found capable of implicitly correcting for instrument degradation, pixel cloudiness, and scan angle effects. Integrated profiles generally agree to within ±5% with the monthly Total Ozone Mapping Spectrometer version 7 total ozone field. However, some problems remain at high solar zenith angles and very low ozone values, where local deviations of 10-20% have been observed in some cases. In order to better characterize individual ozone profiles, two local error estimation methods are presented. Vertical resolution of the profiles was assessed empirically and seems to be of the order of 4-6 km. Since neural network retrieval is a mathematically simple, one-step procedure, NNORSY is about 10 3-10 5 times faster than classical retrieval techniques based upon optimal estimation.
IEEE Transactions on Geoscience and Remote Sensing, 2013
The presence of absorbing aerosols above cloud decks reduces the amount of upwelling ultraviolet ... more The presence of absorbing aerosols above cloud decks reduces the amount of upwelling ultraviolet (UV), visible (VIS), and shortwave infrared radiation reaching the top of atmosphere. This effect is often referred to as "cloud darkening," which can be seen by eye in images and quantitatively in the spectral reflectance measurements made by passive sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) in the regions where light-absorbing carbonaceous and dust aerosols overlay low-level clouds. Radiative transfer simulations support the observational evidence and further reveal that the reduction in the spectral reflectance and color ratio between a pair of wavelengths is a function of both aerosol and cloud optical thickness (AOT and COT). For a prescribed set of aerosol and cloud properties and their vertical profiles, thus, the measured reflectance can be associated with a pair of AOT and COT. Based on these results, a retrieval technique has been developed, which is named as the "color ratio method," which utilizes the measurements at a shorter (470 nm) and a longer (860 nm) wavelength for the simultaneous derivation of AOT and COT. The retrieval technique has been applied to the MODIS 1-km reflectance measurements for the two distinct above-cloud smoke and dust aerosols events. This study is an extension of the previously developed near-UV method to the VIS spectral region. However, it constitutes the first attempt to use non-UV wavelengths to retrieve above-cloud AOT by a passive nonpolarized sensor. An uncertainty analysis has been presented, which estimates the expected error associated with these retrievals.
Journal of Geophysical Research, 2003
The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-vi... more The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-visible satellite spectrometer Global Ozone Monitoring Experiment (GOME) has been modeled by means of a feed forward neural network. This Neural Network Ozone Retrieval System (NNORSY) was trained exclusively on a data set of GOME radiances collocated with ozone measurements from ozonesondes, Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Polar Ozone and Aerosol Measurement III. Network input consists of a combination of spectral, geolocation, and climatological information (time and latitude). In the stratosphere the method globally reduces standard deviation with respect to an ozone climatology by around 40%. Tropospheric ozone can also be retrieved in many cases with corresponding reduction of 10-30%. All GOME data from January 1996 to July 2001 were processed. In a number of case studies involving comparisons with ozonesondes from Hohenpeissenberg, Syowa, and results from the classical Full Retrieval Method, we found good agreement with our results. The neural network was found capable of implicitly correcting for instrument degradation, pixel cloudiness, and scan angle effects. Integrated profiles generally agree to within ±5% with the monthly Total Ozone Mapping Spectrometer version 7 total ozone field. However, some problems remain at high solar zenith angles and very low ozone values, where local deviations of 10-20% have been observed in some cases. In order to better characterize individual ozone profiles, two local error estimation methods are presented. Vertical resolution of the profiles was assessed empirically and seems to be of the order of 4-6 km. Since neural network retrieval is a mathematically simple, one-step procedure, NNORSY is about 10 3-10 5 times faster than classical retrieval techniques based upon optimal estimation.
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resol... more The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO 2). This paper describes an OMI SO 2 algorithm (the band residual difference) that uses calibrated residuals at SO 2 absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO 2 , the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO 2. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO 2 and of heavy anthropogenic SO 2 pollution to provide new information on the relative importance of these sources for climate studies.
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resol... more The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO 2). This paper describes an OMI SO 2 algorithm (the band residual difference) that uses calibrated residuals at SO 2 absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO 2 , the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO 2. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO 2 and of heavy anthropogenic SO 2 pollution to provide new information on the relative importance of these sources for climate studies.
IEEE Transactions on Geoscience and Remote Sensing, 2006
Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. ... more Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). With the exception of HIRDLS, all of the instruments are performing as expected, and HIRDLS will likely be able to deliver most of their planned data products. We summarize the mission, instruments, and synergies in this paper.
Global pictures of the ozone field, from high altitudes, from DE-I
Advances in Space Research, 1982
... REFERENCES 1. GHB Dobson and DN Harrison, Proc. Roy. Soc., Ser. A 110, 660 (1926) 2. FE Fowle... more ... REFERENCES 1. GHB Dobson and DN Harrison, Proc. Roy. Soc., Ser. A 110, 660 (1926) 2. FE Fowle, Smithsonian Miscellaneous Collections 81, 1 (1929) 3. GM Keating, L. Frank, JD Craven, D. Young, J. Nicholson, P. Bhartia, D. Gordon, EOS, Trans. ...
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) flies on NASA's Earth Observing System AURA satellite, laun... more The Ozone Monitoring Instrument (OMI) flies on NASA's Earth Observing System AURA satellite, launched in July 2004. OMI is an ultraviolet/visible (UV/VIS) nadir solar backscatter spectrometer, which provides nearly global coverage in one day, with a spatial resolution of 13 km 24 km. Trace gases measured include O 3 , NO 2 , SO 2 , HCHO, BrO, and OClO. In addition OMI measures aerosol characteristics, cloud top heights and cloud coverage, and UV irradiance at the surface. OMI's unique capabilities for measuring important trace gases with daily global coverage and a small footprint will make a major contribution to our understanding of stratospheric and tropospheric chemistry and climate change along with Aura's other three instruments. OMI's high spatial resolution enables detection of air pollution at urban scales. Total Ozone Mapping Spectrometer and differential optical absorption spectroscopy heritage algorithms, as well as new ones developed by the international (Dutch, Finnish, and U.S.) OMI science team, are used to derive OMI's advanced backscatter data products. In addition to providing data for Aura's prime objectives, OMI will provide near-real-time data for operational agencies in Europe and the U.S. Examples of OMI's unique capabilities are presented in this paper. Index Terms-Air quality, atmospheric composition, ozone monitoring, satellite measurements. I. INTRODUCTION T HE Ozone Monitoring Instrument (OMI), a contribution of the Netherlands Agency for Aerospace Programs (NIVR) in collaboration with Finnish Meteorological Institute (FMI) to the Nationa Aeronautics and Space Administration's (NASA) Aura mission, is orbiting the Earth on the Aura spacecraft. Aura is part of NASA's long-term Earth Observing System (EOS) mission and was launched in July 2004 from Vandenberg Air Force base in California into a polar sun-synchronous orbit.
Evaluation of tropospheric ozone residual measurements derived from TOMS-V9 and hyper-spectral total ozone algorithms
<p>The NASA TOMS V9 (TOMS-V9) total ozone retrieval algorithm is tested<br>for sensit... more <p>The NASA TOMS V9 (TOMS-V9) total ozone retrieval algorithm is tested<br>for sensitvity to boundary-layer ozone and suitability to make daily<br>maps of tropospheric ozone residual (TOR).  Daily maps of TOR are<br>derived by differencing co-located MERRA-2 assimilated MLS<br>stratospheric column ozone (SCO) from total column ozone from the Aura<br>Ozone Monitoring Instrument (OMI).  The TOMS-V9 algorithm uses a few<br>discrete channels with an order of magnitude range in ozone<br>senstivity. We compare the TOR results from TOMS-V9 with results from<br>several hyper-spectral total ozone retrievals: GODFIT v4 (BIRA-IASB),<br>OMI-DOAS (KNMI), and total ozone from the SAO PROFOZ algorithm. We<br>compare all satellite-retrieved TOR with TOR derived from ozonesondes,<br>lidar, and the Goddard Modeling Initiative (GMI) model simulation.</p><p> </p><p> </p>
OMPS Limb Profiler Gridded Level 1 Ancillary Product
An assessment of OMI retrievals of aerosol properties is presented. We compare OMI retrieved valu... more An assessment of OMI retrievals of aerosol properties is presented. We compare OMI retrieved values of extinction and absorption optical depth, and aerosol single scattering albedo to AERONET ground-based measurements. An evaluation of the accuracy of the retrievals for a limited number of observations under cloud-free conditions shows a positive offset of about 0.03 in retrieved optical depth. This small offset is an indication of accurate sensor calibration to the 1% level. The retrieved SSA values agree well with RMS differences of 0.02-0.03 compared with the AERONET observations. This result shows that the UV technique is a very valuable tool for measuring aerosol absorption from space.
Scientific Results from the OMPS Limb Profiler Sensor on Suomi NPP satellite
The Community Workshop on Air Quality Remote Sensing from Space was held in Boulder, Colorado, Fe... more The Community Workshop on Air Quality Remote Sensing from Space was held in Boulder, Colorado, February 21-23, 2006, to examine what observational characteristics are required for the successful use of satellite remote sensing to measure environmentally significant pollutant trace gases and aerosols. Air quality (AQ) measurements are urgently needed to understand the complex consequences of increasing anthropogenic emissions, the biogenic response to changing temperature and humidity, and the escalating incidence of fire. The acknowledged urgency of this endeavor was reflected in the fact that the Workshop engaged more than 150 scientists and other AQ stakeholders with the primary goal of developing a strategy for future space-based capabilities. Four principal areas in which satellite observations are crucial for future AQ basic research and operational needs were identified: (1) AQ characterization for retrospective assessments and forecasting to support air program management and public health advisories; (2) Quantification of emissions of ozone and aerosol precursors; (3) Long-range transport of pollutants extending from regional to global scales; and (4) Large puff releases from environmental disasters. The recent advances in tropospheric remote sensing from low-Earth orbit (LEO) instruments such as MOPITT, GOME, MODIS, MISR, SCIAMACHY, OMI and TES have demonstrated the value of using satellites for both scientific studies and environmental applications. The Workshop agreed that the measurement capabilities for tropospheric O 3 , CO, NO 2 , HCHO, SO 2 and aerosols need to be continued and, at the same time, instrument capabilities and measurement algorithms for these species improved. Ideally, the AQ community envisions a scientific and observing framework for atmospheric composition that is analogous to that achieved for weather forecasting. In particular, our national weather prediction system relies on the combination of observations from geostationary Earth orbit (GEO), LEO, suborbital and surface platforms to derive a 4-dimensional view (3 spatial plus temporal) of the physical state of the atmosphere. Similar capability for AQ constituents will be required for AQ characterization and "chemical weather" forecasting. Workshop participants reached a consensus that multi-spectral sentinel missions (GEO or Lagrangian (L-1) orbit) that have high spatial and temporal resolution, and which are able to provide some species concentrations within the boundary layer, would be most beneficial to the AQ community. At the present time, GEO meets this measurement capability with the least amount of risk, and the greatest societal benefit from a U.S. perspective would be derived from placing such a satellite in an orbit capable of observing North America. The NOAA GOES-R operational suite of measurements from GEO will have some AQ relevant capability for ozone, carbon monoxide and aerosol. However, since NOAA's primary objective is improving weather forecasting, observations are not currently optimized for AQ applications and critical multi-spectral measurements in the UV and near-IR are not planned. Thus the Workshop stated the need for a new generation of dedicated AQ satellite missions that will also be part of an integrated observing
We discuss collection 2 SO2 data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) on boar... more We discuss collection 2 SO2 data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) on board NASA EOS/Aura spacecraft and show examples of detected volcanic and anthropogenic SO2 emissions. Quantification of anthropogenic SO2 emissions requires collection 3 reprocessing available in the fall 2007.
The Ozone Mapping and Profiler Suite represents a new generation of the US ozone measuring instru... more The Ozone Mapping and Profiler Suite represents a new generation of the US ozone measuring instruments aimed to monitor the ozone recovery associated to the reduction in levels of manmade ozone depleting substances regulated by the Montreal protocol. The first OMPS was launched on board of the Suomi NPP satellite in October 2011. The Limb Profiler is a part of the OMPS instrumental suite, and it collects solar radiances scattered from the atmospheric limb in the UV and VIS spectral ranges. The next OMPS Limb Profiler is scheduled to launch in 2022 on board of NASA/NOAA JPSS-2 mission. These limb scattering measurements allow to retrieve vertical ozone profiles from the tropopause up to the mesosphere with a high vertical resolution (~2 km). The expected ozone recovery is almost three times slower than the ozone loss observed in 1980s and 1990s. To detect such small trends in ozone concentration, the instrument calibrations should be extremely accurate. Comparisons of ozone retrievals from OMPS LP with the correlative satellite measurements from Aura MLS and ISS SAGE III revealed that OMPS LP retrievals accurately characterize the vertical ozone distribution in different atmospheric regions which are most sensitive to changes in the stratospheric composition and dynamics. Between 18 and 42 km the mean differences between LP and correlative measurements are within ±10%, except for the northern high latitudes where between 20 and 32 km biases exceed 10% due to the measurement errors. We also found a small positive drift of ~0.5%/yr against MLS with a pattern that is consistent with the ~150-meter drift (over 7 years) in sensor pointing detected by one of our altitude resolving methods. The spatial patterns in the ozone biases and drifts suggest that remaining errors in the LP ozone retrievals are due to errors in altitude registration and instrument calibrations. We present a study where we evaluate calibrations of the OMPS LP by converting ozone differences between OMPS LP and Aura MLS into differences in radiances. Then these radiance differences are compared with the LP measured radiances to determine errors in OMPS LP calibrations. Since the OMPS LP has three slits, some of the errors, like a drift in the altitude registration, should be common across all three slits, but other errors will be unique for each slit, helping to isolate different sources of errors. This approach can be extended to earlier ESA's limb scattering missions, like SCIAMACHY and OSIRIS, since MLS has long overlap with the ENVISAT and Odin missions.
Atmospheric Measurement Techniques
We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud ... more We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud optical centroid pressure (OCP), from oxygen dimer (O 2 -O 2 ) absorption at 477 nm after determining an effective cloud fraction (ECF) at 466 nm, a wavelength not significantly affected by trace-gas absorption and rotational Raman scattering. The retrieved cloud products are intended for use as inputs to the operational nitrogen dioxide (NO 2 ) retrieval algorithm for the Ozone Monitoring Instrument (OMI) flying on the Aura satellite. The cloud algorithm uses temperature-dependent O 2 -O 2 cross sections and incorporates flexible spectral fitting techniques that account for specifics of the surface reflectivity. The fitting procedure derives O 2 -O 2 slant column densities (SCDs) from radiances after O 3 , NO 2 , and H 2 O absorption features have been removed based on estimates of the amounts of these species from independent OMI algorithms. The cloud algorithm is based on the frequently used mixed Lambertian-equivalent reflectivity (MLER) concept. A geometry-dependent Lambertian-equivalent reflectivity (GLER), which is a proxy of surface bidirectional reflectance, is used for the ground reflectivity in our implementation of the MLER approach. The OCP is derived from a match of the measured O 2 -O 2 SCD to that calculated with the MLER method. Temperature profiles needed for computation of vertical column densities are taken from the Global Modeling Initiative (GMI) model. We investigate the effect of using GLER instead of climatological LER on the retrieved ECF and OCP. For evaluation purposes, the retrieved ECFs and OCPs are compared with those from the operational OMI cloud product, which is also based on the same O 2 -O 2 absorption band. Impacts of the application of the newly developed cloud algorithm to the OMI NO 2 retrieval are discussed.
Comptes Rendus Geoscience
Space-Based Measurement of Chemical Tracers (gaseous) and Aerosol Pollutants: Past, Present, and Future Needs (Core Science Keynote)
Space-based Measurement of Gaseous and Aerosol Pollutants (Invited Presentation)
An assessment of the long-term drift in TOMS total ozone data, based on comparison with the Dobson Network
Geophysical Research Letters, 1988
Using techniques very similar to those used in comparing SBUV total ozone with Dobson [Fleig et a... more Using techniques very similar to those used in comparing SBUV total ozone with Dobson [Fleig et al. 1986A], seven years of total ozone data derived from the TOMS instrument on Nimbus‐7 are compared with results from 41 Dobson stations. In this study however, a ...
Journal of Geophysical Research, 2003
The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-vi... more The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-visible satellite spectrometer Global Ozone Monitoring Experiment (GOME) has been modeled by means of a feed forward neural network. This Neural Network Ozone Retrieval System (NNORSY) was trained exclusively on a data set of GOME radiances collocated with ozone measurements from ozonesondes, Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Polar Ozone and Aerosol Measurement III. Network input consists of a combination of spectral, geolocation, and climatological information (time and latitude). In the stratosphere the method globally reduces standard deviation with respect to an ozone climatology by around 40%. Tropospheric ozone can also be retrieved in many cases with corresponding reduction of 10-30%. All GOME data from January 1996 to July 2001 were processed. In a number of case studies involving comparisons with ozonesondes from Hohenpeissenberg, Syowa, and results from the classical Full Retrieval Method, we found good agreement with our results. The neural network was found capable of implicitly correcting for instrument degradation, pixel cloudiness, and scan angle effects. Integrated profiles generally agree to within ±5% with the monthly Total Ozone Mapping Spectrometer version 7 total ozone field. However, some problems remain at high solar zenith angles and very low ozone values, where local deviations of 10-20% have been observed in some cases. In order to better characterize individual ozone profiles, two local error estimation methods are presented. Vertical resolution of the profiles was assessed empirically and seems to be of the order of 4-6 km. Since neural network retrieval is a mathematically simple, one-step procedure, NNORSY is about 10 3-10 5 times faster than classical retrieval techniques based upon optimal estimation.
IEEE Transactions on Geoscience and Remote Sensing, 2013
The presence of absorbing aerosols above cloud decks reduces the amount of upwelling ultraviolet ... more The presence of absorbing aerosols above cloud decks reduces the amount of upwelling ultraviolet (UV), visible (VIS), and shortwave infrared radiation reaching the top of atmosphere. This effect is often referred to as "cloud darkening," which can be seen by eye in images and quantitatively in the spectral reflectance measurements made by passive sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) in the regions where light-absorbing carbonaceous and dust aerosols overlay low-level clouds. Radiative transfer simulations support the observational evidence and further reveal that the reduction in the spectral reflectance and color ratio between a pair of wavelengths is a function of both aerosol and cloud optical thickness (AOT and COT). For a prescribed set of aerosol and cloud properties and their vertical profiles, thus, the measured reflectance can be associated with a pair of AOT and COT. Based on these results, a retrieval technique has been developed, which is named as the "color ratio method," which utilizes the measurements at a shorter (470 nm) and a longer (860 nm) wavelength for the simultaneous derivation of AOT and COT. The retrieval technique has been applied to the MODIS 1-km reflectance measurements for the two distinct above-cloud smoke and dust aerosols events. This study is an extension of the previously developed near-UV method to the VIS spectral region. However, it constitutes the first attempt to use non-UV wavelengths to retrieve above-cloud AOT by a passive nonpolarized sensor. An uncertainty analysis has been presented, which estimates the expected error associated with these retrievals.
Journal of Geophysical Research, 2003
The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-vi... more The inverse radiative transfer equation to retrieve atmospheric ozone distribution from the UV-visible satellite spectrometer Global Ozone Monitoring Experiment (GOME) has been modeled by means of a feed forward neural network. This Neural Network Ozone Retrieval System (NNORSY) was trained exclusively on a data set of GOME radiances collocated with ozone measurements from ozonesondes, Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Polar Ozone and Aerosol Measurement III. Network input consists of a combination of spectral, geolocation, and climatological information (time and latitude). In the stratosphere the method globally reduces standard deviation with respect to an ozone climatology by around 40%. Tropospheric ozone can also be retrieved in many cases with corresponding reduction of 10-30%. All GOME data from January 1996 to July 2001 were processed. In a number of case studies involving comparisons with ozonesondes from Hohenpeissenberg, Syowa, and results from the classical Full Retrieval Method, we found good agreement with our results. The neural network was found capable of implicitly correcting for instrument degradation, pixel cloudiness, and scan angle effects. Integrated profiles generally agree to within ±5% with the monthly Total Ozone Mapping Spectrometer version 7 total ozone field. However, some problems remain at high solar zenith angles and very low ozone values, where local deviations of 10-20% have been observed in some cases. In order to better characterize individual ozone profiles, two local error estimation methods are presented. Vertical resolution of the profiles was assessed empirically and seems to be of the order of 4-6 km. Since neural network retrieval is a mathematically simple, one-step procedure, NNORSY is about 10 3-10 5 times faster than classical retrieval techniques based upon optimal estimation.
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resol... more The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO 2). This paper describes an OMI SO 2 algorithm (the band residual difference) that uses calibrated residuals at SO 2 absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO 2 , the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO 2. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO 2 and of heavy anthropogenic SO 2 pollution to provide new information on the relative importance of these sources for climate studies.
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resol... more The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO 2). This paper describes an OMI SO 2 algorithm (the band residual difference) that uses calibrated residuals at SO 2 absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO 2 , the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO 2. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO 2 and of heavy anthropogenic SO 2 pollution to provide new information on the relative importance of these sources for climate studies.
IEEE Transactions on Geoscience and Remote Sensing, 2006
Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. ... more Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). With the exception of HIRDLS, all of the instruments are performing as expected, and HIRDLS will likely be able to deliver most of their planned data products. We summarize the mission, instruments, and synergies in this paper.
Global pictures of the ozone field, from high altitudes, from DE-I
Advances in Space Research, 1982
... REFERENCES 1. GHB Dobson and DN Harrison, Proc. Roy. Soc., Ser. A 110, 660 (1926) 2. FE Fowle... more ... REFERENCES 1. GHB Dobson and DN Harrison, Proc. Roy. Soc., Ser. A 110, 660 (1926) 2. FE Fowle, Smithsonian Miscellaneous Collections 81, 1 (1929) 3. GM Keating, L. Frank, JD Craven, D. Young, J. Nicholson, P. Bhartia, D. Gordon, EOS, Trans. ...
IEEE Transactions on Geoscience and Remote Sensing, 2006
The Ozone Monitoring Instrument (OMI) flies on NASA's Earth Observing System AURA satellite, laun... more The Ozone Monitoring Instrument (OMI) flies on NASA's Earth Observing System AURA satellite, launched in July 2004. OMI is an ultraviolet/visible (UV/VIS) nadir solar backscatter spectrometer, which provides nearly global coverage in one day, with a spatial resolution of 13 km 24 km. Trace gases measured include O 3 , NO 2 , SO 2 , HCHO, BrO, and OClO. In addition OMI measures aerosol characteristics, cloud top heights and cloud coverage, and UV irradiance at the surface. OMI's unique capabilities for measuring important trace gases with daily global coverage and a small footprint will make a major contribution to our understanding of stratospheric and tropospheric chemistry and climate change along with Aura's other three instruments. OMI's high spatial resolution enables detection of air pollution at urban scales. Total Ozone Mapping Spectrometer and differential optical absorption spectroscopy heritage algorithms, as well as new ones developed by the international (Dutch, Finnish, and U.S.) OMI science team, are used to derive OMI's advanced backscatter data products. In addition to providing data for Aura's prime objectives, OMI will provide near-real-time data for operational agencies in Europe and the U.S. Examples of OMI's unique capabilities are presented in this paper. Index Terms-Air quality, atmospheric composition, ozone monitoring, satellite measurements. I. INTRODUCTION T HE Ozone Monitoring Instrument (OMI), a contribution of the Netherlands Agency for Aerospace Programs (NIVR) in collaboration with Finnish Meteorological Institute (FMI) to the Nationa Aeronautics and Space Administration's (NASA) Aura mission, is orbiting the Earth on the Aura spacecraft. Aura is part of NASA's long-term Earth Observing System (EOS) mission and was launched in July 2004 from Vandenberg Air Force base in California into a polar sun-synchronous orbit.
Evaluation of tropospheric ozone residual measurements derived from TOMS-V9 and hyper-spectral total ozone algorithms
<p>The NASA TOMS V9 (TOMS-V9) total ozone retrieval algorithm is tested<br>for sensit... more <p>The NASA TOMS V9 (TOMS-V9) total ozone retrieval algorithm is tested<br>for sensitvity to boundary-layer ozone and suitability to make daily<br>maps of tropospheric ozone residual (TOR).  Daily maps of TOR are<br>derived by differencing co-located MERRA-2 assimilated MLS<br>stratospheric column ozone (SCO) from total column ozone from the Aura<br>Ozone Monitoring Instrument (OMI).  The TOMS-V9 algorithm uses a few<br>discrete channels with an order of magnitude range in ozone<br>senstivity. We compare the TOR results from TOMS-V9 with results from<br>several hyper-spectral total ozone retrievals: GODFIT v4 (BIRA-IASB),<br>OMI-DOAS (KNMI), and total ozone from the SAO PROFOZ algorithm. We<br>compare all satellite-retrieved TOR with TOR derived from ozonesondes,<br>lidar, and the Goddard Modeling Initiative (GMI) model simulation.</p><p> </p><p> </p>
OMPS Limb Profiler Gridded Level 1 Ancillary Product
An assessment of OMI retrievals of aerosol properties is presented. We compare OMI retrieved valu... more An assessment of OMI retrievals of aerosol properties is presented. We compare OMI retrieved values of extinction and absorption optical depth, and aerosol single scattering albedo to AERONET ground-based measurements. An evaluation of the accuracy of the retrievals for a limited number of observations under cloud-free conditions shows a positive offset of about 0.03 in retrieved optical depth. This small offset is an indication of accurate sensor calibration to the 1% level. The retrieved SSA values agree well with RMS differences of 0.02-0.03 compared with the AERONET observations. This result shows that the UV technique is a very valuable tool for measuring aerosol absorption from space.
Scientific Results from the OMPS Limb Profiler Sensor on Suomi NPP satellite
The Community Workshop on Air Quality Remote Sensing from Space was held in Boulder, Colorado, Fe... more The Community Workshop on Air Quality Remote Sensing from Space was held in Boulder, Colorado, February 21-23, 2006, to examine what observational characteristics are required for the successful use of satellite remote sensing to measure environmentally significant pollutant trace gases and aerosols. Air quality (AQ) measurements are urgently needed to understand the complex consequences of increasing anthropogenic emissions, the biogenic response to changing temperature and humidity, and the escalating incidence of fire. The acknowledged urgency of this endeavor was reflected in the fact that the Workshop engaged more than 150 scientists and other AQ stakeholders with the primary goal of developing a strategy for future space-based capabilities. Four principal areas in which satellite observations are crucial for future AQ basic research and operational needs were identified: (1) AQ characterization for retrospective assessments and forecasting to support air program management and public health advisories; (2) Quantification of emissions of ozone and aerosol precursors; (3) Long-range transport of pollutants extending from regional to global scales; and (4) Large puff releases from environmental disasters. The recent advances in tropospheric remote sensing from low-Earth orbit (LEO) instruments such as MOPITT, GOME, MODIS, MISR, SCIAMACHY, OMI and TES have demonstrated the value of using satellites for both scientific studies and environmental applications. The Workshop agreed that the measurement capabilities for tropospheric O 3 , CO, NO 2 , HCHO, SO 2 and aerosols need to be continued and, at the same time, instrument capabilities and measurement algorithms for these species improved. Ideally, the AQ community envisions a scientific and observing framework for atmospheric composition that is analogous to that achieved for weather forecasting. In particular, our national weather prediction system relies on the combination of observations from geostationary Earth orbit (GEO), LEO, suborbital and surface platforms to derive a 4-dimensional view (3 spatial plus temporal) of the physical state of the atmosphere. Similar capability for AQ constituents will be required for AQ characterization and "chemical weather" forecasting. Workshop participants reached a consensus that multi-spectral sentinel missions (GEO or Lagrangian (L-1) orbit) that have high spatial and temporal resolution, and which are able to provide some species concentrations within the boundary layer, would be most beneficial to the AQ community. At the present time, GEO meets this measurement capability with the least amount of risk, and the greatest societal benefit from a U.S. perspective would be derived from placing such a satellite in an orbit capable of observing North America. The NOAA GOES-R operational suite of measurements from GEO will have some AQ relevant capability for ozone, carbon monoxide and aerosol. However, since NOAA's primary objective is improving weather forecasting, observations are not currently optimized for AQ applications and critical multi-spectral measurements in the UV and near-IR are not planned. Thus the Workshop stated the need for a new generation of dedicated AQ satellite missions that will also be part of an integrated observing
We discuss collection 2 SO2 data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) on boar... more We discuss collection 2 SO2 data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) on board NASA EOS/Aura spacecraft and show examples of detected volcanic and anthropogenic SO2 emissions. Quantification of anthropogenic SO2 emissions requires collection 3 reprocessing available in the fall 2007.
The Ozone Mapping and Profiler Suite represents a new generation of the US ozone measuring instru... more The Ozone Mapping and Profiler Suite represents a new generation of the US ozone measuring instruments aimed to monitor the ozone recovery associated to the reduction in levels of manmade ozone depleting substances regulated by the Montreal protocol. The first OMPS was launched on board of the Suomi NPP satellite in October 2011. The Limb Profiler is a part of the OMPS instrumental suite, and it collects solar radiances scattered from the atmospheric limb in the UV and VIS spectral ranges. The next OMPS Limb Profiler is scheduled to launch in 2022 on board of NASA/NOAA JPSS-2 mission. These limb scattering measurements allow to retrieve vertical ozone profiles from the tropopause up to the mesosphere with a high vertical resolution (~2 km). The expected ozone recovery is almost three times slower than the ozone loss observed in 1980s and 1990s. To detect such small trends in ozone concentration, the instrument calibrations should be extremely accurate. Comparisons of ozone retrievals from OMPS LP with the correlative satellite measurements from Aura MLS and ISS SAGE III revealed that OMPS LP retrievals accurately characterize the vertical ozone distribution in different atmospheric regions which are most sensitive to changes in the stratospheric composition and dynamics. Between 18 and 42 km the mean differences between LP and correlative measurements are within ±10%, except for the northern high latitudes where between 20 and 32 km biases exceed 10% due to the measurement errors. We also found a small positive drift of ~0.5%/yr against MLS with a pattern that is consistent with the ~150-meter drift (over 7 years) in sensor pointing detected by one of our altitude resolving methods. The spatial patterns in the ozone biases and drifts suggest that remaining errors in the LP ozone retrievals are due to errors in altitude registration and instrument calibrations. We present a study where we evaluate calibrations of the OMPS LP by converting ozone differences between OMPS LP and Aura MLS into differences in radiances. Then these radiance differences are compared with the LP measured radiances to determine errors in OMPS LP calibrations. Since the OMPS LP has three slits, some of the errors, like a drift in the altitude registration, should be common across all three slits, but other errors will be unique for each slit, helping to isolate different sources of errors. This approach can be extended to earlier ESA's limb scattering missions, like SCIAMACHY and OSIRIS, since MLS has long overlap with the ENVISAT and Odin missions.
Atmospheric Measurement Techniques
We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud ... more We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud optical centroid pressure (OCP), from oxygen dimer (O 2 -O 2 ) absorption at 477 nm after determining an effective cloud fraction (ECF) at 466 nm, a wavelength not significantly affected by trace-gas absorption and rotational Raman scattering. The retrieved cloud products are intended for use as inputs to the operational nitrogen dioxide (NO 2 ) retrieval algorithm for the Ozone Monitoring Instrument (OMI) flying on the Aura satellite. The cloud algorithm uses temperature-dependent O 2 -O 2 cross sections and incorporates flexible spectral fitting techniques that account for specifics of the surface reflectivity. The fitting procedure derives O 2 -O 2 slant column densities (SCDs) from radiances after O 3 , NO 2 , and H 2 O absorption features have been removed based on estimates of the amounts of these species from independent OMI algorithms. The cloud algorithm is based on the frequently used mixed Lambertian-equivalent reflectivity (MLER) concept. A geometry-dependent Lambertian-equivalent reflectivity (GLER), which is a proxy of surface bidirectional reflectance, is used for the ground reflectivity in our implementation of the MLER approach. The OCP is derived from a match of the measured O 2 -O 2 SCD to that calculated with the MLER method. Temperature profiles needed for computation of vertical column densities are taken from the Global Modeling Initiative (GMI) model. We investigate the effect of using GLER instead of climatological LER on the retrieved ECF and OCP. For evaluation purposes, the retrieved ECFs and OCPs are compared with those from the operational OMI cloud product, which is also based on the same O 2 -O 2 absorption band. Impacts of the application of the newly developed cloud algorithm to the OMI NO 2 retrieval are discussed.
Comptes Rendus Geoscience