Integrated Water Vapour

A GNSS water vapour tomography system developed to reconstruct spatially resolved humidity fields in the troposphere is described. The tomography system was designed to process the slant path delays of about 270 German GNSS stations in near real-time with a temporal resolution of 30 minutes, a horizontal resolution of 40 km and a vertical resolution of 500 m or better. After a short introduction to the GPS slant delay processing the framework of the GNSS tomography is described in detail. Different implementations of the iterative algebraic reconstruction techniques (ART) used to invert the linear inverse problem are discussed. It was found that the multiplicative techniques (MART) provide the best results with least processing time, i. e. a tomographic reconstruction of about 26000 slant delays on a 8280 cell grid can be obtained in less than 10 minutes. Different iterative reconstruction techniques are compared with respect to their convergence behaviour and some numerical parameters. The inversion can be considerably stabilized by using additional non-GNSS observations and implementing various constraints. Different strategies for initialising the tomography and utilizing extra information are discussed. At last an example of a reconstructed field of the wet refractivity is presented and compared to the corresponding distribution of the integrated water vapour, an analysis of a numerical weather model (COSMO-DE) and some radiosonde profiles.

A retrieval of total column water vapour (TCWV) from MODIS (Moderate-resolution Imaging Spectroradiometer) measurements is presented. The algorithm is adapted from a retrieval for MERIS (Medium Resolution Imaging Spectrometer) from Lindstrot et al. (2012). It obtains the TCWV for cloud-free scenes above land at a spatial resolution of 1 km × 1 km and provides uncertainties on a pixel-by-pixel basis. The algorithm has been extended by introducing empirical correction coefficients for the transmittance calculation within the forward operator. With that, a wet bias of the MODIS algorithm against ARM microwave radiometer data has been eliminated. The validation against other ground-based measurements (GNSS water vapour stations, GUAN radiosondes, and AERONET sun photometers) on a global scale reveals a bias between −0.8 and −1.6 mm and root mean square deviations between 0.9 and 2 mm. This is an improvement in comparison to the operational TCWV Level 2 product (bias between −1.9 and −3.2 mm and root mean square deviations between 1.9 and 3.4 mm). The comparison to MERIS TCWV for an example overpass exposes a systematic dry bias.

Meteorological and climate studies are enrichments with new observation technic and technology as well as secondary equipment's such as Global Positioning System GPS/ Global Navigation Satellite System (GNSS). To determine the accurate data in GNSS, it is need to know Integrated Water Vapour (IWV) which cause to tropospheric zenith delay. Vice versa IWV could be calculate from zenith travel time delays from GPS signals data with atmospheric pressure and temperature of GPS site. IWV which is produced from radiosonde data generally use as reference to determine the accuracy of GPS data. Nowadays GNSS meteorology is very familiar in Geomatics engineering. Perceptible Water Vapour (PWV) or Integrated Water Vapour (IWV) or Vertical Integrated Liquid (VIL) are different use in different meteorological systems and they are calculate from meteorological satellite data, radar data and radiosonde data. Spatial and temporal fluctuatings of water vapour content in the lower atmosphere cause time delays in signals propagating from space to targets on the ground. Different measurement methods exist to estimate water vapour. Global Navigation Satellite Systems (GNSS) provides continuous water vapour estimates. In this study, GNSS derived water vapour estimates are compared to radiosonde and radar observations. Statistical analysis of the differences between three data sets, GNSS, radar and radiosonde are summarized. In this study, it is intended to investigate relation between GNSS Ankara station's IWV, Ankara radiosonde station's IWV and Ankara Radar's VIL data. For this purpose, two term which are June 1 to 10 in 2010 and May 15 to 30 in 2015 are selected. These two term are consist of both dry and wet days. Data are obtained from NASA The Crustal Dynamics Data Information System (CDDIS) for GNSS IWV data, NOAA Integrated Global Radiosonde Archive (IGRA) for radiosonde IWV data and TSMS for radar VIL data. Radar make observation with its beam. Beam path is not goes strait ahead in atmosphere. It is goes like as curve which is suit to the world's roundness and when it crush to water droplet it turns back to RADAR antenna. The result of this, firstly if the droplet size is too small or moisture in atmosphere is in a vapour form such as in clear air RADAR may not be observed it. Secondly, due to RADAR beam shape is like curve it can not measure all layer moisture. So RADAR VIL values could not representative troposphere layer total moisture. To free from errors radiosonde values must be use with measurement points coordinates. If RADAR's value or meteorological satellite values use for comparing GNSS IWV values it is need to make a private study for this purpose. Stations geographic position IWV data of GNSS and Radiosonde (00Z and 12Z) COMPARISON OF WATER VAPOUR ESTIMATES IN ANKARA, TURKEY IRD.P21 Daily mean IWV value of RADAR, GNSS and Radiosonde for June 1 to 10 Daily mean IWV value of RADAR, GNSS and Radiosonde for May 15 to 30 IWV data of GNSS and Radiosonde (00Z and 12Z) CONCLUSION Comparing results are relation of GNSS and Radiosonde is quite good esp. during to precipitation and also Radar values get to closer to GNSS and Radiosonde during to precipitation. During to precipitation sky is covered by clouds and the water vapour distribute generally uniform in atmosphere esp. in stratiform type weather conditions. Causes of errors should be as follows;  Satellite signal which come from satellite to directly GNSS station pass throughout troposphere and its effected by troposphere humidity as a result GNSS IWV representative of troposphere layer water vapour. GNSS observations are stationary observations.  When radiosonde balloon is released it start to cruise freely in atmosphere and it's cruising depends on to winds in atmosphere and it can be go far away up to 300km in any directions. During to cruise while getting height it goes far away and also it collects data on its way. So it is naturally collect different values from stationary station.

In this paper, MSMR geophysical products like Integrated Water Vapour (IWV), Ocean Surface Wind Speed (OWS) and Cloud Liquid Water (CLW) in different grids of 50, 75 and 150 kms are compared with similar products available from other satellites like DMSP-SSM/I and TRMM-TMI. MSMR derived IWV, OWS and CLW compare well with SSM/I and TMI finished products. Comparison of MSMR derived CLW with that derived from TMI and SSM/I is relatively in less agreement. This is possibly due to the use of 37 GHz in SSM/I and TMI that is highly sensitive to CLW, while 37 GHz channels are not available on MSMR. Monthly comparison of MSMR geophysical products with those from TMI is all carried out for climatological purpose. The monthly comparisons were much better compared to instantaneous comparisons. In this paper, details of the data analysis and comparison results are presented. The usefulness of the MSMR vis-à-vis other sensors is also discussed.

The content of precipitable water vapor (PWV) in the atmosphere is very important for astronomy in the infrared and radio (sub-millimeter) spectral regions. Therefore, the astrometeorology group has developed different methods to derive this value from measurements and making forecasts using a meteorological model. The goal is use that model to predict the atmospheric conditions and support the scheduling of astronomical observations. At ESO, several means to determine PWV over the observatories have been used, such as IR-radiometers (IRMA), optical and infrared spectrographs as well as estimates using data from GOES-12 satellite. Using all of these remote sensing methods a study undertaken to compare the accuracy of these PWV measurements to the simultaneous in-situ measurements provided by radiosondes. Four dedicated campaigns were conducted during the months of May, July, August and November of 2009 at the La Silla, APEX and Paranal observatory sites. In addition, the astrometeor...

In this paper, MSMR geophysical products like Integrated Water Vapour (IWV), Ocean Surface Wind Speed (OWS) and Cloud Liquid Water (CLW) in different grids of 50, 75 and 150 kms are compared with similar products available from other satellites like DMSP-SSM/I and TRMM-TMI. MSMR derived IWV, OWS and CLW compare well with SSM/I and TMI finished products. Comparison of MSMR derived CLW with that derived from TMI and SSM/I is relatively in less agreement. This is possibly due to the use of 37 GHz in SSM/I and TMI that is highly sensitive to CLW, while 37 GHz channels are not available on MSMR. Monthly comparison of MSMR geophysical products with those from TMI is all carried out for climatological purpose. The monthly comparisons were much better compared to instantaneous comparisons. In this paper, details of the data analysis and comparison results are presented. The usefulness of the MSMR vis-à-vis other sensors is also discussed.

The local distribution of water vapour in the urban area of Rome has been studied using both a high resolution mesoscale model (MM5) and Earth Remote Sensing-1 (ERS-1) satellite radar data. Interferometric Synthetic Aperture Radar (InSAR) techniques, after the removal of all other geometric effects, estimate excess path length variation between two different SAR acquisitions (Atmospheric Phase Screen: APS). APS are strictly related to the variations of the water vapour content along the radar line of sight. To the aim of assessing the MM5 ability to reproduce the gross features of the Integrated Water Vapour (IWV) spatial distribution, as a first step ECMWF IWV has been used as benchmark against which the high resolution MM5 model and InSAR APS maps have been compared. As a following step, the high resolution IWV MM5 maps have been compared with both InSAR and surface meteorological data. The results show that the high resolution IWV model maps compare well with the InSAR ones. Support to this finding is obtained by semivariogram analysis that clearly shows good agreement beside from a model bias.

Meteorological and climate studies are enrichments with new observation technic and technology as well as secondary equipment's such as Global Positioning System GPS/ Global Navigation Satellite System (GNSS). To determine the accurate data in GNSS, it is need to know Integrated Water Vapour (IWV) which cause to tropospheric zenith delay. Vice versa IWV could be calculate from zenith travel time delays from GPS signals data with atmospheric pressure and temperature of GPS site. IWV which is produced from radiosonde data generally use as reference to determine the accuracy of GPS data. Nowadays GNSS meteorology is very familiar in Geomatics engineering. Perceptible Water Vapour (PWV) or Integrated Water Vapour (IWV) or Vertical Integrated Liquid (VIL) are different use in different meteorological systems and they are calculate from meteorological satellite data, radar data and radiosonde data. Spatial and temporal fluctuatings of water vapour content in the lower atmosphere cause time delays in signals propagating from space to targets on the ground. Different measurement methods exist to estimate water vapour. Global Navigation Satellite Systems (GNSS) provides continuous water vapour estimates. In this study, GNSS derived water vapour estimates are compared to radiosonde and radar observations. Statistical analysis of the differences between three data sets, GNSS, radar and radiosonde are summarized. In this study, it is intended to investigate relation between GNSS Ankara station's IWV, Ankara radiosonde station's IWV and Ankara Radar's VIL data. For this purpose, two term which are June 1 to 10 in 2010 and May 15 to 30 in 2015 are selected. These two term are consist of both dry and wet days. Data are obtained from NASA The Crustal Dynamics Data Information System (CDDIS) for GNSS IWV data, NOAA Integrated Global Radiosonde Archive (IGRA) for radiosonde IWV data and TSMS for radar VIL data.  Radar make observation with its beam. Beam path is not goes strait ahead in atmosphere. It is goes like as curve which is suit to the world's roundness and when it crush to water droplet it turns back to RADAR antenna. The result of this, firstly if the droplet size is too small or moisture in atmosphere is in a vapour form such as in clear air RADAR may not be observed it. Secondly, due to RADAR beam shape is like curve it can not measure all layer moisture. So RADAR VIL values could not representative troposphere layer total moisture. To free from errors radiosonde values must be use with measurement points coordinates. If RADAR's value or meteorological satellite values use for comparing GNSS IWV values it is need to make a private study for this purpose. Stations geographic position IWV data of GNSS and Radiosonde (00Z and 12Z) COMPARISON OF WATER VAPOUR ESTIMATES IN ANKARA, TURKEY IRD.P21 Daily mean IWV value of RADAR, GNSS and Radiosonde for June 1 to 10 Daily mean IWV value of RADAR, GNSS and Radiosonde for May 15 to 30 IWV data of GNSS and Radiosonde (00Z and 12Z) CONCLUSION Comparing results are relation of GNSS and Radiosonde is quite good esp. during to precipitation and also Radar values get to closer to GNSS and Radiosonde during to precipitation. During to precipitation sky is covered by clouds and the water vapour distribute generally uniform in atmosphere esp. in stratiform type weather conditions. Causes of errors should be as follows;  Satellite signal which come from satellite to directly GNSS station pass throughout troposphere and its effected by troposphere humidity as a result GNSS IWV representative of troposphere layer water vapour. GNSS observations are stationary observations.  When radiosonde balloon is released it start to cruise freely in atmosphere and it's cruising depends on to winds in atmosphere and it can be go far away up to 300km in any directions. During to cruise while getting height it goes far away and also it collects data on its way. So it is naturally collect different values from stationary station.

Measurements of tropospheric integrated water vapour (IWV) made with two microwave radiometers (AS-MUWARA, TP/WVP-3000), GPS, and radiosondes (SRS 400) during the Temperature, hUmidity, and Cloud (TUC) profiling campaign under mid-latitude conditions in Payerne, Switzerland, in winter 2003/2004 are compared. All methods provide robust IWV retrievals in clear sky and cloudy situations. The mean difference between radiometric and radiosonde IWV is less than 0.15 kgm −2 being not significant with respect to the standard deviation and to the theoretical accuracy. The GPS IWV measurements have a persistent significant dry bias of approx. 0.5 kgm −2 with respect to radiometers and radiosondes. The different temporal and spatial resolutions of the instruments were found to have a strong influence on the standard deviation. A characteristic diurnal cycle of the GPS and radiometric IWV was observed.

The content of precipitable water vapor (PWV) in the atmosphere is very important for astronomy in the infrared and radio (sub-millimeter) spectral regions. Therefore, the astrometeorology group has developed different methods to derive this value from measurements and making forecasts using a meteorological model. The goal is use that model to predict the atmospheric conditions and support the scheduling of astronomical observations. At ESO, several means to determine PWV over the observatories have been used, such as IR-radiometers (IRMA), optical and infrared spectrographs as well as estimates using data from GOES-12 satellite. Using all of these remote sensing methods a study undertaken to compare the accuracy of these PWV measurements to the simultaneous in-situ measurements provided by radiosondes. Four dedicated campaigns were conducted during the months of May, July, August and November of 2009 at the La Silla, APEX and Paranal observatory sites. In addition, the astrometeorological group employs the WRF meteorological model with the goal of simulating the state of the atmosphere (every 6 hours) and forecasting the PWV. With these simulations, plus satellite images, radiosonde campaign data can be classified synoptically and at the same time the model can be validated with respect to PWV.

The measurement of the atmospheric delay of radio signals from navigation system satellites, such as the Global Positioning System (GPS) satellites, offer an opportunity for the NWP community to get access to high quality atmospheric moisture informa- tion from already established networks of GPS ground stations. Considerable progress has been achieved both the COST 716 action (Exploitation of Ground-based GPS for Climate and Numerical Weather Prediction Analysis) and within the MAGIC project (Meteorological Applications of GPS Integrated Water Vapour Measurements in the Western Mediterranean) and other pioneer projects. The quality of the data has steadily improved. The extraction techniques now work in near real time, as necessary for NWP. Use of GPS data are approaching operational status in Europe. In this presentation the TOUGH project will be described. The general objectives of the project are to improve the use of GPS data for NWP and climate monitoring. This shall be done b...

The zenith total delay (ZTD), which can be measured using ground based GPS receivers, depends mainly on the local pressure at and the integrated water vapour above the GPS sites. Both properties are vital to numerical weather prediction (NWP) models and to meteorology in general. It is expected therefore, but has yet to be demonstrated, that utilising ZTD's will improve the skill of NWP forecasts.

The spatial and temporal variations of atmospheric precipitable water (PW) content anomalies were analysed over Europe from 1973 to 2003 using daily data (0000 and 1200 UTC) from National Center of Environmental Prediction and National Center of Atmospheric Research Reanalysis project (NCEP-1) and in situ radiosonde data. Mann-Kendall trend tests were applied to long-term PW time series. Technology changes influence PW radiosonde trends, although these are in agreement with NCEP-1 trends. Over the south of the Iberian Peninsula, trends are negative and statistically significant (<−0.04 mm year −1 ; p < 0.05) and positive over the Central European Mountains (The Alpes) and the North Atlantic Ocean (>0.04 mm year −1 ; p < 0.05). Seasonal trends revealed negative and significant trends over the Iberian Peninsula for all seasons (<−0.03 mm year −1 ; p < 0.05).

Water vapour plays a major role in atmospheric processes but remains difficult to quantify due to its high variability in time and space and the sparse set of available measurements. The GPS has proved its capacity to measure the integrated water vapour at zenith with the same accuracy as other methods. Recent studies show that it is possible to quantify the integrated water vapour in the line of sight of the GPS satellite. These observations can be used to study the 3D heterogeneity of the troposphere using tomographic techniques. We develop three-dimensional, tomographic software to model the three-dimensional distribution of the tropospheric water vapor from GPS data. First the tomographic software is validated by simulations based on the realistic ESCOMPTE GPS network configuration. Without a priori information the absolute value of water vapour is less resolved as opposed to relative horizontal variations. During the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers was operated for two weeks within a 20km x 20km area around Marseille (Southern France). The network extends from sea level to the top of the Etoile chain (~700m high). Optimal results have been obtained with a time windows of 30min intervals and input data evaluation every 15 min. The optimal grid for the ESCOMTE geometrical configuration has a horizontal step size of 0.05° by 0.05°, and 500 m vertical step size. Second we have compared the results of real data inversions with independent observations. Three inversions have been compared to three successive radiosonde launches and shown to be consistent. A good resolution compared to the a priori information is obtained up to heights of 3000 m. A humidity spike at 4000 m altitude remains unresolved. The reason is probably that the signal is spread homogeneously over the whole network and that such a feature is not resolvable by tomographic techniques. The results of our pure GPS inversion show a correlation with meteorological phenomena. Our measurements could be related to the land/sea breeze. Undoubtedly, tomography has some interesting potential for the water vapor cycle studies at small temporal and spatial scales.

The spatial and temporal variations of atmospheric precipitable water (PW) content anomalies were analysed over Europe from 1973 to 2003 using daily data (0000 and 1200 UTC) from National Center of Environmental Prediction and National Center of Atmospheric Research Reanalysis project (NCEP-1) and in situ radiosonde data. Mann-Kendall trend tests were applied to long-term PW time series. Technology changes influence PW radiosonde trends, although these are in agreement with NCEP-1 trends. Over the south of the Iberian Peninsula, trends are negative and statistically significant (<−0.04 mm year −1 ; p < 0.05) and positive over the Central European Mountains (The Alpes) and the North Atlantic Ocean (>0.04 mm year −1 ; p < 0.05). Seasonal trends revealed negative and significant trends over the Iberian Peninsula for all seasons (<−0.03 mm year −1 ; p < 0.05).

The zenith total delay (ZTD), which can be measured using ground based GPS receivers, depends mainly on the local pressure at and the integrated water vapour above the GPS sites. Both properties are vital to numerical weather prediction (NWP) models and to meteorology in general. It is expected therefore, but has yet to be demonstrated, that utilising ZTD's will improve the skill of NWP forecasts.

Water vapour plays a major role in atmospheric processes but remains difficult to quantify due to its high variability in time and space and the sparse set of available measurements. The GPS has proved its capacity to measure the integrated water vapour at zenith with the same accuracy as other methods. Recent studies show that it is possible to quantify the integrated water vapour in the line of sight of the GPS satellite. These observations can be used to study the 3D heterogeneity of the troposphere using tomographic techniques. We develop three-dimensional tomographic software to model the three-dimensional distribution of the tropospheric water vapour from GPS data. First, the tomographic software is validated by simulations based on the realistic ESCOMPTE GPS network configuration. Without a priori information, the absolute value of water vapour is less resolved as opposed to relative horizontal variations. During the ESCOMPTE field experiment, a dense network of 17 dual frequ...

We present results on the microwave absorbing material in different geometries around ground-based Global Navigation Satellite System (GNSS) antennas in order to mitigate multipath effects on the estimates of coordinates and atmospheric water vapour. The influence of the installation of a hemispheric radome on the antenna was also investigated. Two GNSS stations at the Onsala Space Observatory were used forming a 12 m baseline. Nearly one year of data starting from Oct. 2008, was analyzed by the GIPSY/OASIS II software using the Precise Point Positioning (PPP) processing strategy with the Niell Mapping Function (NMF), and for five different elevation cutoff angles from 5 • to 25 • . We found that the use of the absorbing material decreases the offset in the estimated vertical component of the baseline from ∼27 mm to ∼4 mm when the elevation cutoff angle varies from 5 • to 20 • . Two different configurations of the absorber give similar results with a mean difference less than 3 mm. The horizontal components are much less affected. The changes within 5 mm in the offsets in the vertical component of the baseline are seen for all five elevation cutoff angle solutions when the antenna was covered by a hemispheric radome. The offset, also from 5 • to 20 • , in the estimates of the atmospheric Integrated Water Vapour (IWV) decreases from ∼1.6 kg/m 2 to ∼0.3 kg/m 2 . Using the radome affects the IWV estimates less than 0.4 kg/m 2 for all different solutions. IWV comparisons between a Water Vapour Radiometer (WVR) and the GPS data give consistent results.