Real Time Integrated Atmospheric Water Vapor and TEC from GPS



Index
Introduction
Processing Description
The GPS Data
Most recent 24-hour PWV Time Series Results
Map Plots of Results
Map Plot of Ionospheric TEC
Plots of azimuthal variation at Kansas & Oklahoma sites
Long Term Comparison Table between GPS PWV and RAOBS/WVRs
1-week Comparisons Plots of PWV Results Radiosondes/WVRs
Animations of Severe Storms, Tornados, Small Scale Water Vapor Features,
    and current Water Vapor
References to related papers



Current Precipitable Water Vapor (PWV) Distribution and GPS Sites Used to Estimate

( black squares show sites with both GPS and met data,
red squares indicate no met data)

[MAP PIC]

     Comparison most recent GOES PWV image





Current Total Electron Content (TEC) Distribution in TECU

[MAP PIC]

     JPL real time Ionospheric Total Electron Content for North America.



Introduction
Water vapor is a highly variable atmospheric constituent. It is fundamental to the transfer of energy in the atmosphere and in the formation and propagation of weather. Yet water vapor remains one of the most poorly characterized meteorological parameters. Improved knowledge of the water vapor field is needed for a variety of atmospheric research applications and for improved weather forecasting. Recently developed methods for sensing precipitable water vapor (PWV) with the Global Positioning System (GPS) promise improvement in short-term forecasting. To use PWV in forecasting it must be available close to real-time. GPS Science and Technology's (GST) GPS Research Group has been analyzing GPS data from the NOAA Forecast Systems Laboratory GPS network in near-real-time, and has started to analyze GPS data from the CORS network as well.


Processing Description
At present we process the GPS data in 1-hour segments. Once every hour our process transfers via ftp 1 hour of raw GPS data from the NOAA Forecast Systems Laboratory data hub. This one hour segment is translated from raw data to RINEX format using TEQC. Raw data from the Wasatch range, collected by the University of Utah is sent to UCAR via the IDD/LDM system developed by UNIDATA. Hourly RINEXfiles from the CORS network are ftp'd from the NGS CORS computer.
     The one-hour RINEX files are processed, with the Bernese software developed at the University of Berne Astronomical Institute. For the processing of PWV we constrain the station coordinates tightly to positions, obtained from processing daily solutions for the NOAA/FSL network. The normal equations (NEQ) file from the 1-hour analysis is stored. Then we stack the NEQ files from the last 24 1-hour solutions to obtain the equivalent of a 24-hour GPS solution. The main reason to apply this stacking technique, rather than re-processing many hours of data every hour is the significant savings in CPU time. This results in shorter latency with modest requirements in computing power. Presently the analysis of the roughly 50-station network takes about 30 minutes (plus about 10 minutes to prepare the plots). It takes about 10 minutes for the data to be downloaded to the FSL and CORS central sites, then ftp'd to our processing computer. Plots of the latest results are available about 50 minutes after real time.
     TEC analysis is done at zero-difference level with 1-hour phase files from all stations in the NOAA/FSL network. At present we compute an independent solution each hour and do not require continuity between the hourly TEC solutions.
     The software for real-time processing is operated by the Bernese Processing Engine (BPE), developed jointly by the University of Bern and the UCAR GPS Research Group. Processing is currently done with ultra rapid predicted GPS orbits from the IGS. These are formed by combining 12 hour orbit solutions + 24 hour predictions from major IGS orbit centers. The BPE operation for real-time GPS PWV processing was implemented by Teresa Van Hove, who is also responsible for the ongoing automated process.


The GPS Data
We are presently, on an experimental basis, processing data from about 50 sites operated by the NOAA Forecast Systems Laboratory , the NOAA/NGS GPS Continuously Operating Reference System (CORS) and by the University of Utah. NOAA/FSL is operating a 35 receiver network in the continental U.S. with 30 minute data downloading plus 3 sites in Alasks with daily downloading. The receivers are dual-frequency Trimble 4000SSE and 4000SSI instruments, with Trimble Compact L1/L2 antennas. The FSL GPS instruments are located at NOAA/FSL windprofiler sites and log data continuously at a sampling rate of 30 seconds. Phase-connected GPS data segments are transferred together with surface pressure, temperature, and humidity data via phone line to the NOAA hub in Boulder, Colorado every 30 minutes. The CORS network currently includes 120 sites including the FSL and U. Utah networks. We are processing 18 of the CORS sites operated by the U.S Coast Guard. 12 of theses sites mainly along the U.S. Gulf of Mexico and Atlantic Coastlines have collocated surface met packages with hourly met data files archived at CORS with the GPS data. The USCG sites are Ashtech Z_XII receivers and Ashtech Geodetic antennas. The U. Utah sites have Trimble SSI receivers with Trimble choke ring antennas.
     In addition we have begun to analyze data from contributing Universities. The University of Utah is operating a site in Yellowstone National Park and transmits the data in real time via satellite link to the UNAVCO facility. University of Utah also operates 5 GPS sites along the Wasatch range, using radio modems to download the receivers to a University of Utah school of mines computer and then pushing the data to UNAVCO via the internet using the ldm system developed by UNIDATA . The University of Utah department of Meteorology provides surface meteorological data for Red Butte; which is included in the water vapor processing.


List of Stations/Results
The results, shown below, are EXPERIMENTAL and for TEST PURPOSES ONLY. These results are NOT intended for use in operational numerical weather forecast, and the quality of these results is still being tested.
     The time series display precipitable water vapor (PWV) and formal errors for the latest results. About 30 minutes after the raw data have been downloaded the results are plotted here. The bottom two panels display barometric pressure and temperature at the site.

    SUOMINET GPS-IPW SITES
  • UCAR Suominet site, Boulder, CO ...........postscript or gif image  map of PWV for region surrounding the UCAR Suominet site
  • MIT Suominet site, Haystack Observatory, MA ..........postscript or gif
  • GSFC1 Suominet site, Goddard Space Flight Center, MD ..........postscript or gif
  • Millersville Univ. Suominet site, PA ..........postscript or gif
  • Plymouth NH Suominet site ..........postscript or gif
  • CSU Suominet site, Ft Collins CO ..........postscript or gif
  • CSR1 Suominet site, UT, Austin ..........postscript or gif
  • UCAR Mesa Suominet site, Boulder, CO ..........postscript or gif
  • Univ. of Calgary Suominet site, Calgary, CA ..........postscript or gif
  • Univ. of Wyoming Suominet site, Laramie, WY ..........postscript or gif
  • Central Washington University Suominet site, Ellensburg, WA postscriptor gif
  • New Mexico Tech. Suominet site, Socorro, NM postscriptor gif
  • Suominet site, Friday Harbor, WA postscriptor gif
  • ARM Suominet site (SG01/EF13, Lamont, OK postscriptor gif
  • ARM Suominet site (SG04/EF09, Ashton, KA postscriptor gif
  • ARM Suominet site (SG08/EF12, Pawhuska, OK postscriptor gif
  • ARM Suominet site (SG11/EF08, Coldwater, KA postscriptor gif
  • ARM Suominet site (SG12/EF01, Parned, KA postscriptor gif
  • ARM Suominet site (SG13/EF05, Halstead, KA postscriptor gif
  • ARM Suominet site (SG14/EF06, Towanda, KA postscriptor gif
  • ARM Suominet site (SG16/EF07, Elk Falls, KA postscriptor gif
  • ARM Suominet site (SG17/EF25, Seminole, OK postscriptor gif
  • ARM Suominet site (SG18/EF24, Cyril, OK postscriptor gif
  • ARM Suominet site (SG19/EF22, Cyril, OK postscriptor gif
  • ARM Suominet site (SG20/EF22, El Reno, OK postscriptor gif

  • Plots of 3 hr azimuthal variation at Kansas/Oklahoma stations from latest daily solution
    • 0_3 HRs Azimuth variation at Kansas/Oklahoma sites .....gif image
    • 3_6 HRs Azimuth variation at Kansas/Oklahoma sites .....gif image
    • 6_9 HRs Azimuth variation at Kansas/Oklahoma sites .....gif image
    • 9_12 HRs Azimuth variation at Kansas/Oklahoma sites ....gif image
    • 12_15 HRs Azimuth variation at Kansas/Oklahoma sites ...gif image
    • 15_18 HRs Azimuth variation at Kansas/Oklahoma sites ...gif image
    • 18_21 HRs Azimuth variation at Kansas/Oklahoma sites ...gif image
    • 21_24 HRs Azimuth variation at Kansas/Oklahoma sites ...gif image


    Map Plots of PWV Results
    We display the current color contour PWV map based on our processing results (click here for postscript map). PWV is plotted in units of cm. You can also take a look at a near-real-time comparison GOES PWV image for the same area at The CIMSS Realtime GOES Page . At present there are 23 stations available for generating the PWV countour plots. The stations for which the wet delay was estimated in the last solution, shown as small triangles on the map, are used to generate the contours (GMT routines are used to generate the maps.) Also note that for regions with sparse or no wet delay sites the contour maps can look very strange because the data are so sparse. When surface pressure and temperature are not available we use default pressure and temperature for the dry delay computation. These stations, shown by grey circles are not used in generating the PWV contours. We have recently begun to generate total electron density maps for the region of the water vapor network. These maps are generated from 1 hour of dual frequency observations of the network and they display the total number of electrons in a vertical column of 1 square meter. Click for postscript total electron density maps.


    Long Term Comparison Table
    This Table below summarizes the comparison of real-time and post - processed GPS PWV results with each other and with radiosondes and WVRs for stations in the inner network. The comparisons are based on the results from the first 121 days of 1997. This table summarizes comparisons of the real-time results computed with one hour latency (1 hour after downloading of the data) in black and results with zero-hour latency (processed immediately after downloading 1 hour of data from NOAA/FSL) in red. Thus reducing the latency by 1 hour increases the error in our results slightly.

      post processed vs. realtime GPS
    rms [mm]/ bias [mm]/ # points
    RAOBS vs. realtime GPS
    rms [mm]/ bias [mm]/ # points
    WVR vs. realtime GPS
    rms [mm]/ bias [mm]/ # points
    RAOBS vs. post processed GPS
    rms [mm]/ bias [mm]/ # points
    HBRK 1.3 / 0.0 / 4725
    1.5 / 0.0 / 4745
    1.5 / -0.1 / 196
    1.7 / -0.1 / 196
    1.6 / 0.4 / 3827
    1.7 / 0.4 / 3846
    1.0 / -0.1 / 196
    HKLO 1.6 / 0.0 / 5301
    1.8 / 0.0 / 5325
    2.3 / 0.3 / 162
    2.5 / 0.3 / 162
    2.2 / 1.3 / 2468
    2.4 / 1.3 / 2480
    1.5 / 0.3 / 162
    LMNO 1.4 / 0.0 / 5170
    1.6 / 0.0 / 5186
    2.0 / -0.6 / 473
    2.1 / -0.6 / 472
    2.0 / -1.0 / 3913
    2.2 / -1.0 / 3927
    1.4 / -0.6 / 467
    PRCO 1.6 / -0.1 / 5157
    1.8 / -0.1 / 5180
    2.0 / -0.8 / 181
    2.1 / -0.8 / 181
    1.8 / 0.1 / 4141
    1.7 / 0.1 / 4186
    1.2 / -0.5 / 181
    VCIO 1.6 / -0.2 / 5206
    1.7 / -0.2 / 5222
    1.8 / 0.0 / 197
    1.9 / 0.0 / 197
    1.7 / -0.8 / 4408
    1.7 / -0.8 / 4422
    1.5 / 0.3 / 197


    Weekly Comparison of GPS PWV Results with RAOBS and WVRs
    These plots display comparisons of the near-real-time PWV estimates with estimates obtained with post-processed CODE or IGS orbits. PWV from radiosonde data (RAOBS) are also plotted for comparison with the GPS solutions when available. A time span of one week is shown for each station. The plots are updated daily when new RAOBS data become available.
         Only the near-real-time PWV estimates (the last 1-hour segment of each hourly 24-hour solution) are compared to the post-processed solution and to RAOBS, because these are the values that an operational forecasting system would assimilate. Data gaps indicate problems with data availability in near real time. Often data, that were not available in near-real-time become available with the daily files provided by NOAA. Select any station below to view a weekly comparison plot.

      NOAA FSL GPS-IPW SITES
    • Aztec, NM ...........postscript or gif image of weekly comparison 
    • Blacksburg, VA ...........postscript or gif image of weekly comparison 
    • Bloomfield, MO ...........postscript or gif image of weekly comparison 
    • Blue River, WI ...........postscript or gif image of weekly comparison 
    • Boulder, CO ...........postscript or gif image of weekly comparison 
    • Conway, MO ...........postscript or gif image of weekly comparison 
    • DeQueen, AR ...........postscript or gif image of weekly comparison
    • Fairbury, NE ...........postscript or gif image of weekly comparison 
    • Granada, CO ...........postscript or gif image of weekly comparison
    • Haskel, OK ............postscript or gif image of weekly comparison
    • Haviland, KS ..........postscript or gif image of weekly comparison
    • Hillsboro, KS .........postscript or gif image of weekly comparison
    • Jayton, TX .............postscript or gif image of weekly comparison
    • Lamont, OK ............postscript or gif image of weekly comparison
    • Lathrop, MO ............postscript or gif image of weekly comparison 
    • Medicine Bow, WY ..... postscript or gif image of weekly comparison
    • Merriman, NE ......... postscript or gif image of weekly comparison
    • Nat. Buoy D. Cent., MI postscript or gif image of weekly comparison
    • Neodesha, KS ..........postscript or gif image of weekly comparison
    • Neligh, NE ..........postscript or gif image of weekly comparison 
    • Okolona, MS ..........postscript or gif image of weekly comparison 
    • Palestine, TX ...........postscript or gif image of weekly comparison
    • Platteville, CO .......postscript or gif image of weekly comparison
    • Purcell, OK ...........postscript or gif image of weekly comparison
    • Seattle, WA ............postscript or gif image of weekly comparison
    • Slater, IA ............postscript or gif image of weekly comparison 
    • Syracuse, NY ............postscript or gif image of weekly comparison 
    • Tucumcari, NM ...........postscript or gif image of weekly comparison
    • Vici, OK ..............postscript or gif image of weekly comparison
    • White Sands, NM .......postscript or gif image of weekly comparison
    • Winnfield, LA .........postscript or gif image of weekly comparison
    • Wolcott, IA ...........postscript or gif image of weekly comparison
    • Wood Lake, MN ...........postscript or gif image of weekly comparison 

    • USGC DGPS SITES
    • Aransas Pass, TX ...........postscript or gif image of weekly comparison 
    • Cape Canaveral, FL ...........postscript or gif image of weekly comparison 
    • Charleston, SC ...........postscript or gif image of weekly comparison 
    • Mac Dill AFB, FL ...........postscript or gif image of weekly comparison 
    • English Turn, LA ...........postscript or gif image of weekly comparison 
    • Fort Macon, NC ...........postscript or gif image of weekly comparison 
    • Galvaston, TX ...........postscript or gif image of weekly comparison 
    • Key West, FL ...........postscript or gif image of weekly comparison 
    • Mac Dill AFB, FL ...........postscript or gif image of weekly comparison 
    • Mobile Pt, AL ...........postscript or gif image of weekly comparison 
    • Moriches, NY ...........postscript or gif image of weekly comparison 
    • Sandy Hook, NJ ...........postscript or gif image of weekly comparison 
    • Savannah GA ...........postscript or gif image of weekly comparison 

    • DoT NDGPS SITES
    • Clark, SD ....... ....postscript or gif image of weekly comparison 
    • Whitney, NE ...........postscript or gif image of weekly comparison 



    MPEG Animations
    Click here for an animation of a dry line moving into the state of Oklahoma on May 26, 1996 (day 147). This animation, which is composed of our 30-minute solutions shows a dry line that brought severe storms into the area of the GPS network.

    Click here for an even more extreme dry line and water vapor gradient in Oklahoma on May 7. 1995. This dry line was associated with tornados in the area.

    Click here for the animation of results from the 1996 NCAR/ATD GPS experiment which shows evidence of small-scale water vapor variations within the 14-station GPS network on the Oklahoma/Kansas border. The animation shows hourly snapshots of the 3-week experiment. The GPS data have been collected by NCAR's Atmopsheric Technology Division (ATD) using NCAR's and NOAA's receivers. ATD GPS data were analyzed together with data from the NOAA FSL network with 30 minute resolution by Teresa VanHove at UCAR/UNAVCO.



    References to related publications
    Below we list some references to papers related to estimating atmospheric water vapor with GPS. This is not a complete reference list on the subject but rather a list of some papers that our group has collaborated on.

      Alber, C., R. Ware, C. Rocken and F. Solheim, GPS surveying with 1 mm precision using corrections for atmospheric slant path delay, Geophysical Research Letters, Vol. 24, No. 15, pp 1859-1862, August 1997.

      Anthes, R., M. Exner, C. Rocken, and R. Ware, Results from the GPS/MET Experiment and Potential Applications to GEWEX, GEWEX News, 7, 3-6, Feb., 1997.

      Bevis, M., S. Businger, S. Chiswell, T.A. Herring, R.A. Anthes, C. Rocken and R.H. Ware, GPS Meteorology: Mapping zenith wet dealys onto precipitable water, Journal of Applied Meteorology, 379-386, 1994.

      Bevis M., S. Businger, T.A. Herring, C. Rocken, R.A. Anthes and R.H. Ware, GPS Meteorology: Remote Sensing of Atmospheric Water Vapor Using the Global Positioning System, Journal of Geophys. Research, Vol. 97, No. D14, pp 15,787-15,801, October, 1992.

      Businger, S., S.R. Chiswell, M. Bevis, J. Duan, R. A. Anthes, C. Rocken, R. H. Ware, T. VanHove, and F. S. Solheim, The Promise of GPS in Atmospheric Monitoring, Bull. Am. Meteor. Sco., 77, pp 5-18, 1996.

      Chiswell, S., S. Businger, M. Bevis, F. Solheim, C. Rocken, and Randolph Ware, Improved Retrieval of Integrated Water Vapor from Water Vapor Radiometer Measurements Using Numerical Weather Prediction Models, Journal of Atm. and Ocean. Tech, Vol. 11, No.5 , October 1994.

      Chiswell, S., S. Businger, M. Bevis, J. Duan, C. Rocken, Randolph Ware, F. Solheim, and T. Van Hove, Application of GPS Water Vapor Data in the Analysis of Severe Weather, submitted to Monthly Weather Review, January, 1995.

      Duan, J., M. Bevis, P. Fang, Y.Bock, S. Chiswell, S. Businger, C. Rocken, F. Solheim, T. VanHove, R. Ware, S. Mc Clusky, T. A. Herring, and R. W. King, GPS Meteorology: Direct Estimation of the Absolute Value of Precipitable Water, J. of Applied Met., Vol. 35, No. 6, pp 830-838, June 1996.

      Gutman, S., R. Chadwick, D. Wolfe, A. Simon, T. VanHove, and C. Rocken, Toward an Operational Water Vapor Remote Sensing System Using GPS, FSL Forum, September 1994.

      Rocken C., The Global Positioning System: A New Tool for Tectonic Studies, Ph.D. Thesis, University of Colorado at Boulder, 298 pp., 1988.

      Rocken, C., J. Johnson, R.E. Neilan, M. Cerezo, J. Jordan, M. Falls, L. Nelson, R. Ware, M. Hayes, The Measurement of Atmospheric Water Vapor: Radiometer Comparison and Spatial Variations, IEEE Trans. on Geosci. and Remote Sens., Vol., 29., No.1, pp. 3 - 8, Jan., 1991.

      Rocken, C. R. H. Ware, T. Van Hove, F. Solheim, C. Alber, J. Johnson, M. Bevis, S. Businger, Sensing Atmospheric Water Vapor with the Global Positioning System, Geophys. Res. Letters, Vol. 20, No. 23, pp 2631-2634, Dec., 1993.

      Rocken, C. T. Van Hove, J. Johnson, F. Solheim, R. H. Ware, M. Bevis, S. Businger, S. Chiswell, GPS/STORM - GPS Sensing of Atmospheric Water Vapor for Meteorology, Journal of Atmos. and Ocean. Tech., Vol. 12, No. 3, pp 468-478, June 1995.

      Rocken, C, F S Solheim, R H Ware, M Exner, D Martin, M Rothacher, Application of IGS Data to GPS Sensing of the Atmopsphere for Weather and Climate Research, Proceeding for the 1995 IGS Meeting, Potsdam, Germany, May 15-17, 1995.

      Rocken, C., R. Anthes, M. Exner, D. Hunt, S. Sokolovsky, R. Ware, M. Gurbunov, W. Schreiner, D. Feng, B. Herman, Y.-H. Kuo, X. Zou, Verification of GPS/MET Data in the Neutral Atmosphere, J. of Geophys. Research, accepted for pub., Nov., 1997.

      Rocken, C., T. VanHove. R. Ware, Near real-time GPS sensing of atmospheric water vapor, Geophys. Res. Let., Vol. 24, No. 24, pp 3221-3224, 1997.

      Ware, R.H., M. Exner, D. Feng, M. Gorbunov, K. Hardy, B. Herman, Y. Kuo, T. Meehan, W. Melbourne, C. Rocken, W. Schreiner, S. Sokolovskiy, F. Solheim, X. Zou, R. Anthes, S. Businger and K. Trenberth, GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results, Bull. Am. Meteor. Sco., 77, pp 19-40, 1996.

      Ware, R.H., C. Alber, C. Rocken, F. Solheim, Sensing integrated water vapor along GPS ray paths, Geophys. Res. Let., Vol. 24, No. 4, pp 417-420, Feb. 15, 1997.

      Yuan L., R. A. Anthes, R.H. Ware, C. Rocken, W. Bonner, M. Bevis and S. Businger, Sensing Climate Change Using the Global Positioning System, Journal of Geophys. Res., Vol. 98, No. D8, pp 14,925-14,937, 1993.





    Comments: dhunt@ucar.edu
    Last Modified: Tue May 18 17:41:41 1999
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