S. A. Clough

Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, United States

Are you S. A. Clough?

Claim your profile

Publications (158)180.05 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Far-infrared (λ > 15.0 μm) (far-IR) radiative processes provide a large fraction of Earth's outgoing longwave radiation and influence upper tropospheric vertical motion. Water vapor, because of its abundance and strong absorption properties over an extended spectral range, is the primary source of these radiative processes. Historically, the lack of spectrally resolved radiometric instruments and the opacity of the lower atmosphere have precluded extensive studies of far-IR water vapor absorption properties. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program has organized a series of field experiments, the Radiative Heating in Underexplored Bands Campaigns (RHUBC), to address this deficiency. The first phase of RHUBC took place in 2007 at the ARM North Slope of Alaska Climate Research Facility. Measurements taken before and during this campaign have provided the basis for a clear-sky radiative closure study aimed at reducing key uncertainties associated with far-IR radiative transfer models. Extended-range Atmospheric Emitted Radiance Interferometer infrared radiance observations taken in clear sky conditions were compared against calculations from the Line-By-Line Radiative Transfer Model. The water vapor column amounts used in these calculations were retrieved from 183 GHz radiometer measurements. The uncertainty in these integrated water vapor retrievals is approximately 2%, a notable improvement over past studies. This far-IR radiative closure study resulted in an improvement to the Mlawer-Tobin Clough-Kneiyzs-Davies (MT_CKD) water vapor foreign continuum model and updates to numerous, far-IR water vapor line parameters from their values in the circa 2006 version of the HITRAN molecular line parameter database.
    Journal of Geophysical Research Atmospheres 09/2010; 115(D17):17106-. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Presented here are comparisons between the Infrared Atmospheric Sounding instrument (IASI) and the "Line-By-Line Radiative Transfer Model" (LBLRTM). Spectral residuals from radiance closure studies during the IASI JAIVEx validation campaign provide insight into a number of spectroscopy issues relevant to remote sounding of temperature, water vapor and trace gases from IASI. In order to perform quality IASI trace gas retrievals, the temperature and water vapor fields must be retrieved as accurately as possible. In general, the residuals in the CO2 ν2 region are of the order of the IASI instrument noise. However, outstanding issues with the CO2 spectral regions remain. There is a large residual ~−1.7 K in the 667 cm−1 Q-branch, and residuals in the CO2 ν2 and N2O/CO2 ν3 spectral regions that sample the troposphere are inconsistent, with the N2O/CO2 ν3 region being too negative (warmer) by ~0.7 K. Residuals on this lower wavenumber side of the CO2 ν3 band will be improved by line parameter updates, while future efforts to reduce the residuals reaching ~−0.5 K on the higher wavenumber side of the CO2 ν3 band will focus on addressing limitations in the modeling of the CO2 line shape (line coupling and duration of collision) effects. Brightness temperature residuals from the radiance closure studies in the ν2 water vapor band have standard deviations of ~0.2–0.3 K with some large peak residuals reaching ±0.5–1.0 K. These are larger than the instrument noise indicating that systematic errors still remain. New H2O line intensities and positions have a significant mbox{impact} on the retrieved water vapor, particularly in the upper troposphere where the water vapor retrievals are 10% drier when using line intensities compared with HITRAN 2004. In addition to O3, CH4, and CO, of the IASI instrument combined with an accurate forward model allows for the detection of minor species with weak atmospheric signatures in the nadir radiances, such as HNO3 and OCS.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2009; · 5.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 1] Remote measurements of trace gas profiles from nadir-viewing instruments are often retrieved and/or reported on a fine grid containing more levels than the number of independent pieces of information in the measurement. Such profiles contain a priori information, which complicates interpretation. For scientific analyses of these data it is desirable to move to a representation in which measurement information is dominant and the influence of a priori information is minimal. Presented here is a postprocessing approach using a simple algorithm to transform each retrieved profile to an appropriate, geographically varying coarse grid. The representation is chosen such that the averaging kernel is close to unity for regions of the atmosphere where the retrieval has most information. The approach takes advantage of the sensitivity characterization allowed by retrieval on a fine grid, while reducing the influence of the a priori, accounting for spatial and temporal variations in the sensitivity of the measurement to the true atmosphere, and preserving obvious physical meaning in the end product. The example used to demonstrate the approach is the methane product from the Tropospheric Emission Spectrometer (TES), which contains 0.5–2.0 degrees of freedom for signal, depending on season and location. The TES methane has been postprocessed, and the end product has been compared with results from GEOS-Chem, a global chemical model. Results show realistic latitudinal gradients from the TES data. Model/measurement differences also show large-scale features over Indonesia that we attribute to tropical biomass burning in the summer/fall.
    Information-centered J. Geophys. Res. 01/2009; 114.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Global high-spectral resolution (0.06 cm-1) nadir measurements from TES-Aura enable the simultaneous retrieval of a number of tropospheric pollutants and trace gases in addition to the TES standard operationally retrieved products (e.g. carbon monoxide, ozone). Ammonia (NH3) is one of the additional species that can be retrieved in conjunction with the TES standard products, and is important for local, regional, and global tropospheric chemistry studies. Ammonia emissions contribute significantly to several well-known environmental problems, yet the magnitude and seasonal/spatial variability of the emissions are poorly constrained. In the atmosphere, an important fraction of fine particulate matter is composed of ammonium nitrate and ammonium sulfate. These particles are statistically associated with health impacts. When deposited to ecosystems in excess, nitrogen, including ammonia can cause nutrient imbalances, change in ecosystem species composition, eutrophication, algal blooms and hypoxia. Ammonia is also challenging to measure in-situ. Observations of surface concentrations are rare and are particularly sparse in North America. Satellite observations of ammonia are therefore highly desirable. We recently demonstrated that tropospheric ammonia is detectable in the TES spectra and presented some corresponding preliminary retrievals over a very limited range of conditions (Beer et al., 2008). Presented here are results that expand upon these initial TES ammonia retrievals in order to evaluate/validate the retrieval results utilizing in-situ surface observations (e.g. LADCO, CASTNet, EPA /NC State) and chemical models (e.g. GEOS-Chem and CMAQ). We also present retrievals over regions of interest that have the potential to help further understand air quality and the active nitrogen cycle. Beer, R., M. W. Shephard, S. S. Kulawik, S. A. Clough, A. Eldering, K. W. Bowman, S. P. Sander, B. M. Fisher, V. H. Payne, M. Luo, G. B. Osterman, and J. R. Worden, First satellite observations of lower tropospheric ammonia and methanol, Geophysical Res. Letters, 35, L09801, doi:10.1029/2008GL033642, 2008.
    AGU Fall Meeting Abstracts; 12/2008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Results of validation studies for the Tropospheric Emission Spectrometer (TES) indicate that biases are present in the TES retrieved temperature. TES temperature is currently retrieved simultaneously with water vapor and ozone using the carbon dioxide, water vapor, and ozone spectral regions. We investigated several different TES temperature retrieval strategies for a number of selected cases. Presented are the resulting TES temperature retrievals and their impact on the water vapor and ozone retrievals. Radiance closure studies are also utilized in this study to provide additional insight. The results of this investigation will not only lead to improvements in future TES retrieval processor versions, but will also have relevance for other infrared sounders such as IASI.
    AGU Spring Meeting Abstracts; 05/2008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Tropospheric Emission Spectrometer (TES) on the EOS Aura satellite makes global measurements of infrared radiances which are used to derive profiles of species such as O3, CO, H2O, HDO and CH4 as routine standard products. In addition, TES has a variety of special modes that provide denser spatial mapping over a limited geographical area. A continuous-coverage mode (called “transect”, about 460 km long) has now been used to detect additional molecules indicative of regional air pollution. On 10 July 2007 at about 05:37 UTC (13:24 LMST) TES conducted such a transect observation over the Beijing area in northeast China. Examination of the residual spectral radiances following the retrieval of the TES standard products revealed surprisingly strong features attributable to enhanced concentrations of ammonia (NH3) and methanol (CH3OH), well above the normal background levels. This is the first time that these molecules have been detected in space-based nadir viewing measurements that penetrate into the lower atmosphere.
    Geophys. Res. Lett. 01/2008; 35(9):L09801.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 1] Comparisons of Tropospheric Emission Spectrometer (TES) water vapor retrievals with in situ measurements are presented. Global comparisons of TES water vapor retrievals with nighttime National Centers for Environmental Prediction RS90/RS92 radiosondes show a small (<5%) moist bias in TES retrievals in the lower troposphere (standard deviation of $20%), increasing to a maximum of $15% bias (with standard deviation reaching $40%) in the upper troposphere. This moist bias with respect to the sonde bias increases to a maximum of $15% in the upper troposphere between $300–200 hPa. The standard deviation in this region reaches values of $40%. It is important to note that the TES reported water vapor comparison statistics are not weighted by the water vapor layer amounts. Global TES/radiosonde results are comparable with the Atmospheric Infrared Sounder reported unweighted mean of 25% and root-mean-square of $55%. While such global comparisons help to identify general issues, inherent sampling errors and radiosonde measurement accuracy can limit the degree to which the radiosonde profiles alone can be used to validate satellite retrievals. In order to characterize the agreement of TES with in situ measurements in detail, radiance closure studies were performed using data from the Water Vapor Validation Experiment – Satellites/Sondes campaign from July 2006. Results indicate that estimated systematic errors from the forward model, TES measurements, in situ observations, retrieved temperature profiles, and clouds are likely not large enough to account for radiance differences between TES observations and forward model calculations using in situ profiles as input. Therefore, accurate validation of TES water vapor retrievals requires further campaigns with a larger variety of water vapor measurements that better characterize the atmospheric state within the TES field of view.
    Journal of Geophysical Research Atmospheres 01/2008; 113:15-24. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A primary component of the observed recent climate change is the radiative forcing from increased concentrations of long-lived greenhouse gases (LLGHGs). Effective simulation of anthropogenic climate change by general circulation models (GCMs) is strongly dependent on the accurate representation of radiative processes associated with water vapor, ozone, and LLGHGs. In the context of the increasing application of the Atmospheric and Environmental Research, Inc. (AER), radiation models within the GCM community, their capability to calculate longwave and shortwave radiative forcing for clear sky scenarios previously examined by the radiative transfer model intercomparison project (RTMIP) is presented. Forcing calculations with the AER line-by-line (LBL) models are very consistent with the RTMIP line-by-line results in the longwave and shortwave. The AER broadband models, in all but one case, calculate longwave forcings within a range of -0.20 to 0.23 W m-2 of LBL calculations and shortwave forcings within a range of -0.16 to 0.38 W m-2 of LBL results. These models also perform well at the surface, which RTMIP identified as a level at which GCM radiation models have particular difficulty reproducing LBL fluxes. Heating profile perturbations calculated by the broadband models generally reproduce high-resolution calculations within a few hundredths K d-1 in the troposphere and within 0.15 K d-1 in the peak stratospheric heating near 1 hPa. In most cases, the AER broadband models provide radiative forcing results that are in closer agreement with high-resolution calculations than the GCM radiation codes examined by RTMIP, which supports the application of the AER models to climate change research.
    Journal of Geophysical Research Atmospheres 01/2008; 113. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Air-broadened half-widths of the 22- and 183-GHz water-vapor lines and associated uncertainties have been determined using comparisons between ground-based radiometric measurements from Atmospheric Radiation Measurement sites in Oklahoma and Alaska, and MonoRTM, a radiative transfer model. Values of the widths obtained using the measurements are 0.0900 cm<sup>-1</sup>/atm with 1.6% uncertainty for the 22-GHz line and 0.0992 cm<sup>-1</sup>/atm with 2.4% uncertainty for the 183-GHz line. Also presented are spectroscopic parameters for these lines from new calculations performed using the complex implementation of the Robert-Bonamy theory (CRB). The CRB values of the air-broadened widths are 0.0913 cm<sup>-1</sup>/atm with 3% uncertainty and a temperature exponent of 0.755 for the 22-GHz line and 0.0997 cm<sup>-1</sup>/atm with 3% uncertainty and a temperature exponent of 0.769 for the 183-GHz line. The values for the air-broadened half-widths derived from the measurement/model comparisons show good agreement with the new CRB calculations. For future versions of MonoRTM, width values of 0.0900 and 0.0997 cm<sup>-1</sup>/atm are to be adopted with temperature dependences of 0.76 and 0.77 for the 22- and 183-GHz lines, respectively.
    IEEE Transactions on Geoscience and Remote Sensing 01/2008; 46:3601-3617. · 3.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 1] The fundamental measurement of the Tropospheric Emission Spectrometer (TES) on board the Aura spacecraft is upwelling infrared spectral radiances. Accurate TES retrievals of surface and atmospheric parameters such as trace gas amounts critically depend on well-calibrated radiance spectra. On-orbit TES nadir observations were evaluated using carefully selected, nearly coincident spectral radiance measurements from Atmospheric Infrared Sounder (AIRS) on Aqua and special scanning high-resolution interferometer sounder (SHIS) underflights. Modifications to the L1B calibration algorithms for TES version 2 data resulted in significant improvements for the TES-AIRS comparisons. The comparison of TES with SHIS (adjusted for geometric differences) show mean and standard deviation differences of less than 0.3 K at warmer brightness temperatures of 290–295 K. The TES/SHIS differences are less than 0.4 K at brightness temperatures of 265–270 K. There are larger TES/SHIS comparison differences for higher-frequency TES 1A1 filter, which has less upwelling radiance signal. The TES/ AIRS comparisons show mean differences of less than 0.3 K at 290–295 K and less than 0.5 K at 265–270 K with standard deviation less than 0.6 K for the majority of the spectral regions and brightness temperature range. A procedure to warm up the optical bench for better alignment in December 2005 gave a fourfold increase in the signal-to-noise ratio at higher frequency ranges. Recent results from a long-term comparison of TES sea surface temperature (SST) observations with the Reynolds optimally interpolated (ROI) SST product demonstrates TES radiometric stability.
    Journal of Geophysical Research Atmospheres 01/2008; 113:15-5. · 3.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT Accurate water vapor profiles from radiosondes are essential for long-term climate prediction, weather prediction, validation of remote sensing retrievals, and other applications. The Vaisala RS80, RS90, and RS92 radiosondes are among the more commonly deployed radiosondes in the world. However, numerous investigators have shown,that the daytime,water vapor profiles measured,by these instruments,present a significant dry bias due to the solar heating of the humidity,sensor. This bias in the column-integrated precipitable water vapor (PWV), along with variability due to calibration, can be removed by scaling the humidity profile to agree with the PWV retrieved from a microwave radiometer (MWR), as has been demonstrated,by several previous studies. Infrared radiative closure analyses have,shown,that the MWR PWV does not present daytime versus nighttime differences; thus, scaling by the MWR is a possible approach for removing the daytime dry bias. However, MWR measurements are not routinely available at all radiosonde,launch sites. Starting from,a long-term series of sonde and MWR PWV measurements,from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site, the authors have developed a simple correction to the column-integrated sonde PWV, derived from an analysis of the ratio of the MWR and sonde,measurements;,this correction is a function of the atmospheric,transmittance,as determined by the solar zenith angle, and it effectively removes the daytime dry bias at all solar zenith angles. The correction was validated by successfully applying it to an independent,dataset from,the ARM tropical western Pacific (TWP) site.
    Journal of Atmospheric and Oceanic Technology - J ATMOS OCEAN TECHNOL. 01/2008; 25(6).
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Tropospheric Emission Spectrometer (TES) on the EOS Aura satellite makes global measurements of infrared radiances that are used to derive profiles of species such as O3, CO, H2O and CH4 as routine standard products. In addition, TES has a variety of special modes that provide denser spatial mapping at the expense of reduced coverage. One of these modes (called "transect") has now been used to detect additional molecules indicative of regional air pollution. On July 10 2007 at about 05:37 UTC (13:24 LMST) TES conducted such a transect observation over northeast Asia between latitudes +37.988 & +41.998, east longitudes 117.014 & 115.746 (some 460 km long). Examination of the spectral residuals (observed - calculated) following the retrieval of the TES standard products revealed surprisingly strong features attributable to enhanced concentrations of ammonia (NH3) and methanol (CH3OH), well above the normal background levels. This is the first time that these molecules have been detected in nadir viewing measurements that penetrate into the lower atmosphere. The paper will discuss the concentration and distribution of these species over this area and offer suggestions as to their origin. This work was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, under contract with the National Aeronautics and Space Administration.
    AGU Fall Meeting Abstracts; 12/2007
  • [Show abstract] [Hide abstract]
    ABSTRACT: Climate and weather prediction models require accurate calculations of vertical profiles of radiative heating. In contrast to calculations of radiance and irradiance at the surface and top-of-atmosphere (TOA), heating rate calculations cannot be directly validated due to the lack of corresponding observations. However, surface and TOA measurements can indirectly establish the quality of computed heating rates through validation of the calculated irradiances at the atmospheric boundaries. The Atmospheric Radiation Measurement (ARM) program has produced continuous profiles of computed radiative heating rates at its Climate Research Facilities that have been validated using this approach. The computed surface and TOA irradiances have been subject to extensive radiative closure analysis, an effort that has led to significant advancements in the three components of radiative closure studies: model calculations, including spectroscopic parameters; radiometric measurement accuracy; and the specification of the atmospheric state in the radiating column. In particular, this effort has taken advantage of ARM's substantial set of active and passive sensors that are sensitive to the cloud properties within the radiating column to evaluate numerous cloud property retrieval algorithms. This effort, named the ARM Broadband Heating Rate Profile (BBHRP) project, is a collaboration of all the working groups in the program. This presentation will present selected results from this closure study for both clear and cloudy conditions, including an analysis of the relative model-measurement agreement resulting from the use of various cloud property retrieval algorithms. Focus will be placed on results from the ARM North Slope of Alaska site, including the presentation of computed heating rates for cases of interest.
    AGU Fall Meeting Abstracts. 12/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Longwave radiative cooling in the upper troposphere significantly influences Earth's climate. With water vapor dominating this cooling, the spectral regions in which the greatest upper tropospheric cooling occurs are opaque when viewed from the vast majority of surface locations. While the opacity of the lower atmosphere is a formidable obstacle in studying upper tropospheric radiative processes from the surface, a greater obstacle has been the lack of radiometric instrumentation in the most critical spectral region for these processes, the far- infrared (lambda > 15 mum). These obstacles have led to a relatively high uncertainty in our knowledge of upper tropospheric radiative processes. In the spring of 2007, the Radiative Heating in Underexplored Bands Campaign (RHUBC) was conducted at the Atmospheric Radiation Measurement Program's (ARM) North Slope of Alaska Climate Research Facility (NSA). The experiment was designed to make detailed observations of the downwelling infrared radiation in the pure rotation (17--100 mum; 100--600 cm-1) and the 6.7 mum (1350--1850 cm-1) nu2 water vapor bands under the extremely dry and cold conditions found at the NSA location. High-spectral-resolution observations were collected by two state-of-the-art Fourier Transform Spectrometers: the ARM AERI-ER (400-- 3000 cm-1) and the Imperial College TAFTS (80--650 cm-1). Also, three state-of-the-art microwave radiometers observing emission at 183 GHz were deployed to the NSA site during RHUBC. From these microwave measurements, the total atmospheric water vapor column can be accurately retrieved. With numerous radiosondes launched in conditions with less than 3 mm of total precipitable water vapor, RHUBC provided the opportunity for extensive clear-sky high-spectral-resolution comparisons between model calculations and measurements. This presentation will discuss the infrared radiance measurements, radiative transfer models and specification of the atmospheric state used in these radiative closure studies, as well as the initial efforts to reduce key uncertainties in water vapor spectroscopy. RHUBC is anticipated to improve calculations of polar surface radiative fluxes and mid-to-upper tropospheric radiative cooling, ultimately resulting in improved simulations of Earth's present and future climate.
    AGU Fall Meeting Abstracts. 12/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The current edition of the HITRAN compilation employed a sophisticated algorithm for combining measurements available for the air-broadened half-widths of water-vapor absorption lines with theoretical values. Nevertheless, some of the values in the HITRAN database were found to be far from ideal, due to large dispersions that still exist in the experimental or theoretical methods. Therefore, new criteria were developed for introducing the best available air-broadened half-widths into HITRAN, based on physical principles and statistics. This update concerns the three most abundant isotopologues of water, with the values for H217O and H218O being the ones from analogous transitions of the principal isotopologues. The new parameters have been tested in different remote-sensing applications and improved constituent profiles were obtained. In total, air-broadened half-width values were updated for 11,787 transitions of water vapor in the HITRAN database (6789 for H216O, 2906 for H217O, and 2092 for H218O). Some additional updates to the water-vapor line list are also presented. The resultant file (01_hit06.par) was uploaded to the HITRAN website (http://www.cfa.harvard.edu/hitran/) in September 2006.
    Journal of Quantitative Spectroscopy and Radiative Transfer 12/2007; · 2.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Atmospheric Radiation Measurement (ARM) Program maintains a suite of instruments in various locations to provide continuous monitoring of atmospheric parameters. Temperature and humidity retrievals are two of the key parameters used by the climate-modeling community. Accuracy in the spectroscopy adopted by the various radiative transfer models is crucial for obtaining accurate retrievals. While the accuracy of the spectroscopic parameters used for water-vapor retrievals is satisfactory, temperature retrievals continue to be affected by uncertainties in oxygen line parameters leading to discrepancies between the modeled and observed brightness temperatures. In this paper, we compare the model calculations in the oxygen-band channels with the measurements collected by the ARM-operated 12-channel Microwave Radiometer Profiler (MWRP). The dataset used spans a wide range of atmospheric temperature conditions, with ground temperatures varying between -40degC and +20degC. Model calculations are performed by using line parameters from the high-resolution transmission molecular-absorption (HITRAN) database and from a set of newly published parameters. Our comparison shows that the newly published parameters agree more closely with the MWRP measurements and confirms the need to update the HITRAN database for the oxygen lines. We show the effect of line parameters on the retrievals of temperature, water vapor, and liquid water, and show that improved oxygen absorption is essential to reduce the clear-sky bias in the liquid-water path retrievals.
    IEEE Transactions on Geoscience and Remote Sensing 08/2007; · 3.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Many of the clouds important to the Earth’s energy balance, from the tropics to the Arctic, are optically thin and contain liquid water. Longwave and shortwave radiative fluxes are very sensitive to small perturbations of the cloud liquid water path (LWP) when the LWP is small (i.e.,
    Bulletin of the American Meteorological Society 02/2007; 88(2). · 11.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ground-based two-channel microwave radiometers have been used for over 15 years by the Atmospheric Radiation Measurement (ARM) program to provide observations of downwelling emitted radiance from which precipitable water vapor (PWV) and liquid water path (LWP) – twp geophysical parameters critical for many areas of atmospheric research – are retrieved. An algorithm that utilizes two advanced retrieval techniques, a computationally expensive physical-iterative approach and an efficient statistical method, has been developed to retrieve these parameters. An important component of this Microwave Retrieval (MWRRET) algorithm is the determination of small (< 1K) offsets that are subtracted from the observed brightness temperatures before the retrievals are performed. Accounting for these offsets removes systematic biases from the observations and/or the model spectroscopy necessary for the retrieval, significantly reducing the systematic biases in the retrieved LWP. The MWRRET algorithm provides significantly more accurate retrievals than the original ARM statistical retrieval which uses monthly retrieval coefficients. By combining the two retrieval methods with the application of brightness temperature offsets to reduce the spurious LWP bias in clear skies, the MWRRET algorithm provides significantly better retrievals of PWV and LWP from the ARM 2-channel microwave radiometers compared to the original ARM product.
    IEEE Transactions on Geoscience and Remote Sensing 01/2007; 45:3680-3690. · 3.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS)-Aura spacecraft measures global profiles of atmospheric ozone with vertical resolution of 6-7 km in the troposphere for the nadir view. For a first validation of TES ozone measurements we have compared TES-retrieved ozone profiles to ozonesondes from fall, 2004. In some cases the ozonesonde data are from dedicated launches timed to match the Aura overpass, while other comparisons are performed with routine data available from the Southern Hemisphere Additional Ozonesonde (SHADOZ) archive and World Ozone and Ultraviolet Data Center (WOUDC) data archives. We account for TES measurement sensitivity and vertical resolution by applying the TES-averaging kernel and constraint to the ozonesonde data before differencing the profiles. Overall, for V001 data, TES ozone profiles are systematically higher than sondes in the upper troposphere but compare well in the lower troposphere, with respect to estimated errors. These comparisons show that TES is able to detect relative variations in the coarse vertical structure of tropospheric ozone.
    Journal of Geophysical Research Atmospheres 01/2007; 112. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe the approach for the estimation of the atmospheric state, e.g., temperature, water, ozone, from calibrated, spectral radiances measured from the Tropospheric Emission Spectrometer (TES) onboard the Aura spacecraft. The methodology is based on the maximum a posteriori estimate, which mathematically requires the minimization of the difference between observed spectral radiances and a nonlinear model of radiative transfer of the atmospheric state subject to the constraint that the estimated state must be consistent with an a priori probability distribution for that state. The minimization techniques employed here are based on the trust-region Levenberg-Marquardt algorithm. An analysis of the errors for this estimate include smoothing, random, spectroscopic, "cross-state", representation, and systematic errors. In addition, several metrics and diagnostics are introduced that assess the resolution, quality, and statistical significance of the retrievals. We illustrate this methodology for the retrieval of atmospheric and surface temperature, water vapor, and ozone over the Gulf of Mexico on November 3, 2004.
    IEEE Transactions on Geoscience and Remote Sensing 06/2006; · 3.47 Impact Factor

Publication Stats

5k Citations
180.05 Total Impact Points

Institutions

  • 2–2008
    • Atmospheric and Environmental Research, Inc.
      Lexington, Massachusetts, United States
    • Pennsylvania State University
      University Park, Maryland, United States
  • 2005
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 2003
    • University of Denver
      Denver, Colorado, United States
  • 1997
    • University of Colorado at Boulder
      • Cooperative Institute for Research in Environmental Sciences (CIRES)
      Boulder, CO, United States
  • 1973
    • Air Force Research Laboratory
      Washington, Washington, D.C., United States