Time filter

Source Type

Knoxville, TN, United States

Smith D.A.,National Oceanic and Atmospheric Administration | Holmes S.A.,SGT Inc. | Li X.,ERT Inc. | Guillaume S.,ETH Zurich | And 4 more authors.
Journal of Geodesy | Year: 2013

A terrestrial survey, called the Geoid Slope Validation Survey of 2011 (GSVS11), encompassing leveling, GPS, astrogeodetic deflections of the vertical (DOV) and surface gravity was performed in the United States. The general purpose of that survey was to evaluate the current accuracy of gravimetric geoid models, and also to determine the impact of introducing new airborne gravity data from the 'Gravity for the Redefinition of the American Vertical Datum' (GRAV-D) project. More specifically, the GSVS11 survey was performed to determine whether or not the GRAV-D airborne gravimetry, flown at 11 km altitude, can reduce differential geoid error to below 1 cm in a low, flat gravimetrically uncomplicated region. GSVS11 comprises a 325 km traverse from Austin to Rockport in Southern Texas, and includes 218 GPS stations (σΔ h = 0.4 cm over any distance from 0.4 to 325 km) co-located with first-order spirit leveled orthometric heights (σ Δ H = 1.3 cm end-to-end), including new surface gravimetry, and 216 astronomically determined vertical deflections (σ DOV= 0.1′). The terrestrial survey data were compared in various ways to specific geoid models, including analysis of RMS residuals between all pairs of points on the line, direct comparison of DOVs to geoid slopes, and a harmonic analysis of the differences between the terrestrial data and various geoid models. These comparisons of the terrestrial survey data with specific geoid models showed conclusively that, in this type of region (low, flat) the geoid models computed using existing terrestrial gravity, combined with digital elevation models (DEMs) and GRACE and GOCE data, differential geoid accuracy of 1 to 3 cm (1 σ) over distances from 0.4 to 325 km were currently being achieved. However, the addition of a contemporaneous airborne gravity data set, flown at 11 km altitude, brought the estimated differential geoid accuracy down to 1 cm over nearly all distances from 0.4 to 325 km. © 2013 © Springer-Verlag (outside the USA). Source

Stone A.A.,State University of New York at Stony Brook | Stone A.A.,ERT Inc. | Schneider S.,State University of New York at Stony Brook | Broderick J.E.,State University of New York at Stony Brook | Schwartz J.E.,State University of New York at Stony Brook
Clinical Journal of Pain | Year: 2014

INTRODUCTION:: Pain diaries are important tools for clinical trials and optimal assay sensitivity of outcomes derived from these diaries is a worthwhile goal. Jensen and colleagues recently reported results suggesting that single-day diary-based outcomes could possibly be as psychometrically sound as outcomes based on taking the average of many diaries. MATERIALS AND METHODS:: In this paper, we attempted to replicate those results with several diary data sets. RESULTS AND DISCUSSION:: We come to a different conclusion than that advanced by Jensen and colleagues and conclude that their results were unusual in that very high test-retest reliability among days was found. With our 4 diary data sets we find that aggregating multiple diaries yields more reliable outcomes and improved sensitivity. We suggest that using single-day diaries will often lead to underpowered studies and that pretesting is advised before adopting single-day diaries. We also suggest that other researchers replicate these findings within their diary-based clinical trials. © 2013 by Lippincott Williams & Wilkins. Source

Stein A.F.,ERT Inc. | Saylor R.D.,National Oceanic and Atmospheric Administration
Atmospheric Chemistry and Physics | Year: 2012

The processes of aerosol sulfate formation are vital components in the scientific understanding of perturbations of earth's radiative balance via aerosol direct and indirect effects. In this work, an analysis of the influence of changes in oxidant levels and sulfur dioxide oxidation pathways was performed to study the underlying pathways for sulfate formation. Sensitivities of this constituent were calculated from a series of photochemical model simulations with varying rates of NOx and VOC emissions to produce variations in oxidant abundances using a photochemical model (CMAQ) that covers the eastern US for part of the ICARTT 2004 campaign. Three different chemical mechanisms (CBIV, CB05, and SAPRC99) were used to test model responses to changes in NOx and VOC concentrations. Comparison of modeled results and measurements demonstrates that the simulations with all three chemical mechanisms capture the levels of sulfate reasonably well. However, the three mechanisms are shown to have significantly different responses in sulfate formation when the emissions of NOx and/or VOC are altered, reflecting different photochemical regimes under which the formation of sulfate occurs. Also, an analysis of the oxidation pathways that contribute to sulfur dioxide conversion to sulfate reveals substantial differences in the importance of the various pathways among the three chemical mechanisms. These findings suggest that estimations of the influence that future changes in primary emissions or other changes which perturb SO2 oxidants have on sulfate abundances, and on its direct and indirect radiative forcing effects, may be dependent on the chemical mechanism employed in the model analysis. © 2012 Author(s). Source

Yu F.,ERT Inc. | Wu X.,National Oceanic and Atmospheric Administration
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

During the Geostationary Operational Environmental Satellite (GOES)-14 and -15 post-launch test (PLT) for science periods, an up to ∼2 K mean brightness temperature (Tb) bias with respect to collocated Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI) observations was observed in the absorptive IR channels of the GOES-14/15 Imagers. These large scene-dependent biases were believed to be caused mainly by spectral characterization errors. In this paper, we refined the spectral response function (SRF) shift algorithm which was developed during the GOES-13 PLT period to improve the GOES-14/15 Imager IR radiometric calibration accuracy by accurately calculating the impact of blackbody on the calibrated scene radiance. The uncertainty of the SRF shift algorithm was estimated and used to guide the final selection of the total amount of central wave-number shift. This refined algorithm was first verified with GOES-13 Imager Ch6 data and then used to evaluate and further revise the audited GOES-14/15 SRFs provided by the instrument vendor. Based on this algorithm, the optimal SRF shifts were -1.98cm-1 for GOES-13 Ch6, -8.25cm-1 for GOES-14 Ch3, -0.25cm-1 for GOES-14 Ch6, -6.25cm-1 for GOES-15 Ch3 and +0.50cm-1 for GOES-15 Ch6. The newly shifted SRFs were operationally implemented into the GOES-14/15 Imager IR calibrations in the August of 2011 and successfully reduced the mean all-sky Tb bias with respect to the reference instrument to less than 0.15 K. The scene-dependent bias, which can be nonlinear at large erroneous SRF, was also greatly reduced. The same method was applied to correct the GOES-12 Imager Ch6 SRF which has a changing SRF error during its mission life. A strong linear relationship between the optimal SRF shifts and the mean Tb bias with respect to the AIRS data was observed at this channel. This strong linear relationship can be used to revise the GOES-12 Ch6 SRF for a better radiance simulation. The method described in this paper is particularly important to evaluate and revise the erroneous SRF, if it exists, after satellite launch yet before it becomes fully operational. © 2012 IEEE. Source

Kunkel K.E.,North Carolina State University | Kunkel K.E.,National Oceanic and Atmospheric Administration | Karl T.R.,National Oceanic and Atmospheric Administration | Easterling D.R.,National Oceanic and Atmospheric Administration | And 5 more authors.
Geophysical Research Letters | Year: 2013

Probable maximum precipitation (PMP) is the greatest accumulation of precipitation for a given duration meteorologically possible for an area. Climate change effects on PMP are analyzed, in particular, maximization of moisture and persistent upward motion, using both climate model simulations and conceptual models of relevant meteorological systems. Climate model simulations indicate a substantial future increase in mean and maximum water vapor concentrations. For the RCP8.5 scenario, the changes in maximum values for the continental United States are approximately 20%-30% by 2071-2100. The magnitudes of the maximum water vapor changes follow temperature changes with an approximate Clausius-Clapeyron relationship. Model-simulated changes in maximum vertical and horizontal winds are too small to offset water vapor changes. Thus, our conclusion is that the most scientifically sound projection is that PMP values will increase in the future due to higher levels of atmospheric moisture content and consequent higher levels of moisture transport into storms. Key Points Maximum atmospheric water vapor will increase in the future Estimates of Probable Maximum Precipitation will increase commensurately Dams and other similar structures are vulnerable to future climate change ©2013. American Geophysical Union. All Rights Reserved. Source

Discover hidden collaborations