using gps to measure precipitable water vapor in antarctica
TRANSCRIPT
Using Global Positioning System to Measure
Precipitable Water Vapor in AntarcticaAmanda Murray, Mike Willis and Terry Wilson
School of Earth Sciences and Byrd Polar Research Center, Ohio State University,
Columbus, Ohio 43210; [email protected]
Moisture (mm)Southern Victoria Land; Jan 21, 2005
Pressure (hPa) Temperature (k)
Location of GPS Sites in Southern Victoria Land, Antarctica
Moisture Time Series for 4 GPS Sites
Background:• The GPS signal is broadcast on two frequencies (L1 and L2).
• Precipitable Water Vapor can be extracted from delay of radio signalsas they pass through the atmosphere.• Delay can be broken into Zenith Path Delay (ZPD), Zenith Hydrostatic"Dry" Delay (ZHD) and Zenith Wet Delay (ZWD).•ZWD is caused by the water vapor in the troposphere.• ZPD is from GPS, ZHD from atmospheric model and formula leaving ZWD.• ZWD is converted to PWD.•Z HD error is nearly eliminated because the L1 and L2 signals are spaced apart and can be combined.• Model data downloaded from the Antarctic Mesoscale Prediction System (AMPS) is compared to GPS data.•The resulting improvement in our knowledge of water vapor distribution will enable more accurate weather forecasts and will contribute to studies of climate change (Bevis et al. 1994).
Manipulating the Data:•AMPS model data were downloaded into directories in Linux.•Surface pressure (hPa), 2-meter temperature (K), and moisture (mm) data were all examined for the year 2005.•All were geocoded to a 30km by 30km grid across Antarctica in order to produce maps of these variables. • There were 31 GPS sites examined for this study and the values from the variables were interpolated for each GPS station.• The coordinates of the GPS sites are used as interpolation points from the AMPS 30km by 30km gridded data. • Time series of moisture (see below) were created for each GPS site from the interpolation.• AMPS model pressure data were used to calculate the ZHDs for GPS sites. • ZNDs from each GPS site were given to us for this study.
Formulas:ZHD = 2.2779*(Ps/(1-0.00266*COS(2λ)-0.00028*H))Where Ps = surface pressure, λ = latitude andH = height above ellipsoid in km
Precipitable Water = ∏ * ZWD∏^-1 = 10^-6ρRv[(k3/Tm)+K'2] k'2 = k2 -mk1 Tm = ∫((Pv/T)dz)/((Pv/T2)dz) ≈ ∑^N ((Pvi/Ti)∆zi)/∑^N((Pvi/Ti^2)∆zi) ρ = density of liquid water, Rv = specific gas constant, m = ratio of molar constants, Pv = partial pressure of water, T = temperature in Kelvin, i= each discrete level, N = number of layers, Z = height in m
References:Bevis, M., S. Businger, S. Chishwell, T. A. Herring, R. A. Anthes, C. Rocken and R. H. Ware, 1994: GPS meteorology: mapping zenith wet delays onto precipitablewater. Journal of Applied Meteorology. Vol. 33, 379-386.
Acknowledgements:A. Murray thanks Kelly Carroll for the support and for this research opportunity, Dr. Diem and Dr. Cramptonfor the references, everyone involved in the OSU SROP program and especially NSF (grant 60008970) and POLENET for making this opportunity available.
Comparisons:• AMPS is at present a reliable source for prediction ofpressure and temperature.• Model predictions may be inaccurate if the model data isdifferent from the GPS data.• Any patterns and correlations between the GPS data andmodel output will be analyzed.• For the ZNDs from each GPS site, there are days with nodata and it is different for each site.
Work in Progress:• ZHDs are still being calculated.
• ZWDs have yet to be calculated.• ZNDs for more GPS sites were acquired than anticipated.• More charts and maps are to come!
Interpolation:Coordinates for GPS sites (stars – above and below) were interpolated.
This below was one of the first maps.