Air-broadened half-widths of the 22 GHz and 183 GHz water...
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Vivienne H. Payne 1 , Jennifer S. Delamere 1 , Karen E. Cady-Pereira 1 , Robert R. Gamache 2 , Eli J. Mlawer 1 , Jean-Luc Moncet 1 , Shepard. A. Clough 3 [email protected] 1 Atmospheric and Environmental Research Inc., 131 Hartwell Ave., Lexington, MA, 02421-3626, USA 2 University of Massachusetts, Lowell, MA, USA 3 Clough Associates, Lexington, MA, USA Air-broadened half-widths of the 22 GHz and 183 GHz water vapor lines Model: MonoRTM Microwave radiative transfer model, developed at AER, Inc. Summary • Air-broadened half-widths of the 22 GHz and 183 GHz water vapor lines and associated uncertainties have been determined using comparisons between ground-based radiometric measurements and a radiative transfer model. • Width values and associated temperature dependences are also presented from new state-of-the-art spectroscopic calculations. • Width values derived from radiometer measurements are in good agreement with the new calculations. • Values for the half-width (γ) of the 22 and 183 GHz lines at 296 K adopted in the latest version of AER’s line-by-line models: Introduction The 22.24 GHz and 183.31 GHz water vapor lines are two of the most important spectroscopic lines for remote sensing of the Earth’s atmosphere. These lines are utilized by a wide variety of instruments that measure water vapor for atmospheric studies and weather prediction, including instruments at the surface, on high-altitude research aircraft and on satellites. These measurements are used for retrievals of atmospheric water vapor and as input to data assimilation schemes. The accuracy of the retrievals and the forecasts from the assimilation schemes directly depend on the accuracy of the line parameters used as input to the relevant radiative transfer models. Air-broadened half-widths of (a) the 22 GHz and (b) the 183 GHz lines: laboratory measurements, calculations and values from recent versions of the HITRAN database, displayed in order of publication. Vertical dotted lines represent values obtained in this work using the MWRP (22 GHz) and GVR (183 GHz) measurements. Shaded bars show error bounds for these values (Payne et al., 2008 and references therein). 22 GHz • ARM Southern Great Plains (SGP) site • Data used: March 2000 to February 2002 • MicroWave Radiometer Profiler (MWRP) • 12 channels from 22-60 GHz • Built by Radiometrics • (http://www.radiometrics.com) • RS-80 radiosondes 1. Model simulations with clear-sky radiosondes 2. Removal of dry bias from RS-80s 3. Estimation of channel-dependent offsets 4. Scaling of PWV using 23.835 GHz channel 5. Retrieval of 22GHz line width 183 GHz • ARM North Slope of Alaska (NSA) site • Data used: January to October 2007 • Includes data from RHUBC campaign • G-band Vapor Radiometer (GVR) • 4 channels around 183 GHz (Pazmany et al. 2007) • Built by Prosensing (http://www.prosensing.com) • RS-92 radiosondes 1. Model simulations with clear-sky radiosondes 2. Estimation of channel offsets for +/-1, +/-3 GHz channels 3. Scaling of PWV using +/-3 GHz channel 4. Retrieval of 183 GHz line width 5. Scaling of PWV using +/-7 GHz channel in linear regime 6. Second iteration of line width retrieval References • Payne, V. H. et al., Air-broadened half-widths of the 22 GHz and 183 GHz water vapor lines, IEEE TGRS, in review, 2008 • Pazmany, A. L., et al., A compact 183 GHz radiometer for water vapor and liquid sensing, IEEE TGRS, vol. 45, No. 7, pp2202-2207, July 2007 Acknowledgements This research was supported by the Office of Biological and Environmental Research of the U.S. Department of Energy as part of the Atmospheric Radiation Measurement Program and by the Joint Center for Satellite Data Assimilation. One of the authors (R. R. Gamache) is pleased to acknowledge support of this research by the National Science Foundation (NSF) through Grant No. ATM- 0242537. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Complex Robert-Bonamy (CRB) calculations Uncertainties , Model/measurement differences for “raw” sondes Model/measurement differences for scaled sonde after removal of channel-dependent offsets, using width value of 0.0900 cm -1 /atm Model/measurement differences for scaled sondes after removal of channel-dependent offsets, using width value of 0.0959 cm -1 /atm Model/measurement differences for “raw” sondes using width value of 0.0989 cm -1 /atm Model/measurement differences for “raw” sondes using width value of 0.95*0.0989 cm -1 /atm Model/measurement differences using final width value of 0.0997 cm -1 /atm (after final scaling of PWV) Error source Contribution Random retrieval error 0.1 % 1 K temperature uncertainty 0.3 % 3 % continuum uncertainty 0.6 % 10 % column ozone uncertainty 0.02% 1.5 % PWV uncertainty 1.5 % 0.5% intensity uncertainty 0.25% Water vapor profile shape uncertainty 0.4 % 1 K instrument calibration uncertainty 1.6% Total 2.4 % Error source Contribution Random retrieval error Less than 0.001 % 1 K temperature uncertainty Less than 0.1 % 3 % continuum uncertainty 0.2 % 1.5 % PWV uncertainty 1.5 % 0.5% intensity uncertainty 0.5% 5% self-broadened halfwidth uncertainty 0.2% Total 1.6 % 22 GHz 183 GHz Transition (cm -1 atm -1 ) n (cm -1 atm - 1 ) 22.24 GHz 6 1 6 5 2 3 0.0913 0.755 -0.000882 183.31 GHz 3 1 3 2 2 0 0.0997 0.769 -0.00269 Half-width (γ), temperature dependence of the half-width (n), and line shift (δ) for the 22 and 183 GHz lines at 296 K with air as the buffer gas from new CRB calculations by R. R. Gamache. 2.4% 0.0997 183.31 GHz 1.6% 0.0900 22.24 GHz Uncertainty γ (cm -1 /atm) Water line
Transcript of Air-broadened half-widths of the 22 GHz and 183 GHz water...
Vivienne H. Payne1, Jennifer S. Delamere1, Karen E. Cady-Pereira1, Robert R. Gamache2, Eli J. Mlawer1,Jean-Luc Moncet1, Shepard. A. Clough3
[email protected] and Environmental Research Inc., 131 Hartwell Ave., Lexington, MA, 02421-3626, USA
2University of Massachusetts, Lowell, MA, USA3Clough Associates, Lexington, MA, USA
Air-broadened half-widths of the 22 GHz and 183 GHz water vapor lines
Model: MonoRTM
Microwave radiative transfer model, developed at AER, Inc.
Summary
• Air-broadened half-widths of the 22 GHz and 183 GHz water vaporlines and associated uncertainties have been determined usingcomparisons between ground-based radiometric measurements anda radiative transfer model.
• Width values and associated temperature dependences are alsopresented from new state-of-the-art spectroscopic calculations.
• Width values derived from radiometer measurements are in goodagreement with the new calculations.
• Values for the half-width (γ) of the 22 and 183 GHz lines at 296 Kadopted in the latest version of AER’s line-by-line models:
Introduction
The 22.24 GHz and 183.31 GHz water vapor lines are two of themost important spectroscopic lines for remote sensing of the Earth’satmosphere. These lines are utilized by a wide variety of instrumentsthat measure water vapor for atmospheric studies and weatherprediction, including instruments at the surface, on high-altituderesearch aircraft and on satellites. These measurements are used forretrievals of atmospheric water vapor and as input to dataassimilation schemes. The accuracy of the retrievals and theforecasts from the assimilation schemes directly depend on theaccuracy of the line parameters used as input to the relevantradiative transfer models.
Air-broadened half-widths of(a) the 22 GHz and (b) the183 GHz lines: laboratorymeasurements, calculationsand values from recentversions of the HITRANdatabase, displayed in orderof publication. Vertical dottedlines represent valuesobtained in this work usingthe MWRP (22 GHz) andGVR (183 GHz)measurements. Shaded barsshow error bounds for thesevalues (Payne et al., 2008and references therein).
22 GHz• ARM Southern Great Plains (SGP) site• Data used: March 2000 to February 2002• MicroWave Radiometer Profiler (MWRP)
• 12 channels from 22-60 GHz• Built by Radiometrics• (http://www.radiometrics.com)
• RS-80 radiosondes
1. Model simulations with clear-sky radiosondes2. Removal of dry bias from RS-80s3. Estimation of channel-dependent offsets4. Scaling of PWV using 23.835 GHz channel5. Retrieval of 22GHz line width
183 GHz• ARM North Slope of Alaska (NSA) site• Data used: January to October 2007
• Includes data from RHUBC campaign• G-band Vapor Radiometer (GVR)
• 4 channels around 183 GHz (Pazmany et al. 2007)• Built by Prosensing (http://www.prosensing.com)
• RS-92 radiosondes
1. Model simulations with clear-sky radiosondes2. Estimation of channel offsets for +/-1, +/-3 GHz channels3. Scaling of PWV using +/-3 GHz channel4. Retrieval of 183 GHz line width5. Scaling of PWV using +/-7 GHz channel in linear regime6. Second iteration of line width retrieval
References• Payne, V. H. et al., Air-broadened half-widths of the 22 GHz and 183 GHz watervapor lines, IEEE TGRS, in review, 2008• Pazmany, A. L., et al., A compact 183 GHz radiometer for water vapor and liquidsensing, IEEE TGRS, vol. 45, No. 7, pp2202-2207, July 2007
Acknowledgements
This research was supported by the Office of Biological and Environmental Research of theU.S. Department of Energy as part of the Atmospheric Radiation Measurement Programand by the Joint Center for Satellite Data Assimilation. One of the authors (R. R. Gamache)is pleased to acknowledge support of this research by the National Science Foundation(NSF) through Grant No. ATM- 0242537. Any opinions, findings and conclusions orrecommendations expressed in this material are those of the authors and do not necessarilyreflect the views of the National Science Foundation.
Complex Robert-Bonamy (CRB) calculations
Uncertainties
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Error source Contribution
Random retrieval error 0.1 %
1 K temperature uncertainty 0.3 %
3 % continuum uncertainty 0.6 %
10 % column ozone uncertainty 0.02%
1.5 % PWV uncertainty 1.5 %
0.5% intensity uncertainty 0.25%
Water vapor profile shape uncertainty 0.4 %
1 K instrument calibration uncertainty 1.6%
Total 2.4 %
Error source Contribution
Random retrieval error Less than 0.001 %
1 K temperature uncertainty Less than 0.1 %
3 % continuum uncertainty 0.2 %
1.5 % PWV uncertainty 1.5 %
0.5% intensity uncertainty 0.5%
5% self-broadened halfwidth uncertainty 0.2%
Total 1.6 %
22 GHz183 GHz
Transition (cm-1 atm-1) n (cm-1 atm-
1) 22.24 GHz
6 1 6 5 2 3 0.0913 0.755 -0.000882
183.31 GHz 3 1 3 2 2 0
0.0997 0.769 -0.00269
Half-width (γ), temperaturedependence of the half-width(n), and line shift (δ) for the 22and 183 GHz lines at 296 Kwith air as the buffer gas fromnew CRB calculations by R. R.Gamache.
2.4%0.0997183.31 GHz1.6%0.090022.24 GHz
Uncertaintyγ (cm-1/atm)Water line
