Teresa Van Hove

Sensing atmospheric water vapor with the global positioning system

Global Positioning System (GPS) receivers, water vapor radiometers (WVRs), and surface meteorological equip- ment were operated at both ends of a 50-kin baseline in Colorado to measure the precipitable water vapor (PWV) and wet delay in the line-of-sight to GPS satellites. Using high pre- cision orbits, WVR-measured and GPS-inferred PWV differences between the two sites usually agreed to better than 1 min. Using less precise on-line broadcast orbits increased the discrepancy by 30%. Data simulations show that GPS mea- surements can provide ram-level separate PWV estimates for the two sites, as opposed to just their difference, if baselines exceed 500 km and the highest accuracy GPS orbits are used.

GPS/STORM—GPS Sensing of Atmospheric Water Vapor for Meteorology

Abstract Atmospheric water vapor was measured with six Global Positioning System (GPS) receivers for 1 month at sites in Colorado, Kansas, and Oklahoma. During the time of the experiment from 7 May to 2 June 1993, the area experienced severe weather. The experiment, called “GPS/STORM,” used GPS signals to sense water vapor and tested the accuracy of the method for meteorological applications. Zenith wet delay and precipitable water (PW) were estimated, relative to Platteville, Colorado, every 30 min at five sites. At three of these five sites the authors compared GPS estimates of PW to water vapor radiometer (WVR) measurements. GPS and WVR estimates agree to 1–2 mm rms. For GPS/STORM site spacing of 500–900 km, high-accuracy GPS satellite orbits are required to estimate 1–2-mm-level PW. Broadcast orbits do not have sufficient accuracy. It is possible, however, to estimate orbit improvements simultaneously with PW. Therefore, it is feasible that future meteorological GPS networks provide near-real-time hig...

Near real-time GPS sensing of atmospheric water vapor

We describe sensing of atmospheric column water vapor in near real-time using the Global Positioning System (GPS). We use predicted GPS orbits for automated computation of vertical column water vapor within 30 minutes of GPS data collection. Based on a 4 month comparison, near real-time GPS column water vapor agrees with radiosondes and radiometers within 2 mm rms. Our near real-time column water vapor data are posted hourly at www.unavco.ucar.edu. They are available for assimilation in numerical weather models and for other applications.

Quality-Controlled Upper-Air Sounding Dataset for DYNAMO/CINDY/AMIE: Development and Corrections

AbstractThe upper-air sounding network for Dynamics of the Madden–Julian Oscillation (DYNAMO) has provided an unprecedented set of observations for studying the MJO over the Indian Ocean, where coupling of this oscillation with deep convection first occurs. With 72 rawinsonde sites and dropsonde data from 13 aircraft missions, the sounding network covers the tropics from eastern Africa to the western Pacific. In total nearly 26 000 soundings were collected from this network during the experiment’s 6-month extended observing period (from October 2011 to March 2012). Slightly more than half of the soundings, collected from 33 sites, are at high vertical resolution. Rigorous post–field phase processing of the sonde data included several levels of quality checks and a variety of corrections that address a number of issues (e.g., daytime dry bias, baseline surface data errors, ship deck heating effects, and artificial dry spikes in slow-ascent soundings).Because of the importance of an accurate description of ...

Pointed water vapor radiometer corrections for accurate global positioning system surveying

Delay of the Global Positioning System (GPS) signal due to atmospheric water vapor is a major source of error in GPS surveying. Improved vertical accuracy is impor- tant for sea level and polar isostasy measurements, geodesy, normal fault motion, subsidence, earthquake studies, air and ground-based gravimetry, ice dynamics, and volcanology. We conducted a GPS survey using water vapor radiometers (WVRs) pointed toward GPS satellites to correct for azi- muthal variations in water vapor. We report 2.6 mm vertical precision on a 50-km baseline for 19 solution days. Kalman filter or least-square corrections to the same data do not account for azimuthal distribution of water vapor and are degraded by 70%.

Precipitable water from GPS over the continental United States: Diurnal cycle, intercomparisons with NARR, and link with convective initiation

AbstractThe variation of precipitable water vapor (PW) over the continental United States is examined at various time scales using spatial maps of a column-averaged mixing ratio (CAMR) that is derived from integrated column PW from both observations and reanalysis data. CAMR spatial maps are generated utilizing PW measurements obtained from a network of ground-based global positioning system (GPS) receivers and the North American Regional Reanalysis (NARR) over a time span of 4 yr (February 2009–January 2013). The effect of topography on PW is mitigated by vertically averaging the mixing ratio instead of integrating the absolute humidity. An ordinary kriging interpolation technique is used to generate spatial maps of CAMR. The observed and predicted PW derived by GPS and NARR correlate well with each other at annual and monthly scales. When focusing on its diurnal cycle, moisture peaks in the late afternoon over the Great Plains and late night over the Rockies. It is also found that atmospheric moisture w...