Within the framework of the Helmholtz Association Strategy Project ''GPS Atmosphere Sounding'' (GASP), an operational monitoring of integrated water vapor was established using 170 GPS sites in Germany and neighboring countries. The product, which can be obtained within 12-15 minutes of computer time on a single Linux PC, is generated each hour with a 30-minute time resolution and an accuracy of G1-2 mm in the precipitable water vapor. The GPS estimates are regularly validated using collocated instruments and the local model (LM) of the German Weather Service (DWD). First experiments for numerical weather predictions are performed at DWD and showed 2% improvement for the relative humidity in a 12-hour forecast, whilst the impact on the precipitation forecast over 24 hours is mixed up to now.

To study why, where, and when deep convection

With the increase of spatial resolution of weather forecast models to order O(1 km), the need for adequate observations for model validation becomes evident. Therefore, we designed and constructed the ''KITcube'', a mobile observation platform for convection studies of processes on the meso-c scale. The KITcube consists of in-situ and remote sensing systems which allow measuring the energy balance components of the Earth's surface at different sites; the mean atmospheric conditions by radiosondes, GPS station, and a microwave radiometer; the turbulent characteristics by a sodar and wind lidars; and cloud and precipitation properties by use of a cloud radar, a micro rain radar, disdrometers, rain gauges, and an X-band rain radar. The KITcube was deployed fully for the first time on the French island of Corsica during the HyMeX (Hydrological cycle in the Mediterranean eXperiment) field campaign in 2012. In this article, the components of KITcube and its implementation on the island are described. Moreover, results from one of the HyMeX intensive observation periods are presented to show the capabilities of KITcube.

Soil moisture is a geophysical key observable for predicting floods and droughts, modeling weather and climate and optimizing agricultural management. Currently available in situ observations are limited to small sampling volumes and restricted number of sites, whereas measurements from satellites lack spatial resolution. Global navigation satellite system (GNSS) receivers can be used to estimate soil moisture time series at an intermediate scale of about 1000 m 2 . In this study, GNSS signal-to-noise ratio (SNR) data at the station Sutherland, South Africa, are used to estimate soil moisture variations during 2008-2014. The results capture the wetting and drying cycles in response to rainfall. The GNSS Volumetric Water Content (VWC) is highly correlated (r 2 = 0.8) with in situ observations by time-domain reflectometry sensors and is accurate to 0.05 m 3 /m 3 . The soil moisture estimates derived from the SNR of the L1 and L2P signals compared to the L2C show small differences with a RMSE of 0.03 m 3 /m 3 . A reduction in the SNR sampling rate from 1 to 30 s has very little impact on the accuracy of the soil moisture estimates (RMSE of the VWC difference 1-30 s is 0.01 m 3 /m 3 ). The results show that the existing data of the global tracking network with continuous observations of the L1 and L2P signals with a 30-s sampling rate over the last two decades can provide valuable complementary soil moisture observations worldwide.

The Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (GFZ) is operating a worldwide Global Navigation Satellite Systems (GNSS) station network since many years. With recent developments in receiver technology and new upcoming navigation satellite systems like Galileo an upgrade of our stations was needed to track all GNSS. We will present the current status and setup of our station network and the plan for future upgrades. All modernized stations are presently contributing to the Multi-GNSS EXperiment (MGEX) of the International GNSS Service (IGS) as well as to the COoperative Network of GNSS Observations (CONGO). Selected results from a combined GPS/Galileo data processing will be shown. The used data were taken mainly from the public available MGEX network whereas the focus of analysis lies on precise orbit and clock determination of Galileo In-Orbit-Validation (IOV) satellites. Quality assessments are given which are based on orbit overlap statistics, clock stabilities as well as comparisons with external solutions. Additionally an independent validation of the orbits is derived through Satellite Laser Ranging (SLR) measurements. Furthermore some initial results of BeiDou data processing are shown which were derived with an experimental set of MGEX data.

[1] In order to improve the spatial resolution of GPS (Global Positioning System) derived zenith total delays (ZTD), existing GPS networks must be considerably densified. Due to economic reasons, this densification is recommended with single frequency receivers. We prove the epoch-differenced ionospheric delay is sufficient for estimating ZTD from single frequency GPS data. Based on this result, the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) is developed which uses the observations from surrounding dual frequency stations. With the derived ionospheric corrections, single frequency data is converted to dual frequency data which can be processed using any existing GPS processing software package. The approach is validated with regional GPS networks by comparing ZTDs from the converted and the observed dual frequency data. Their differences in RMS is about 3 mm which is negligible compared to the differences among various state-ofthe-art software packages. The easy implementation and the accuracy of the new approach may speed up the densification of existing networks with single frequency receivers. Citation: Deng, Z., M. Bender, G. Dick, M. Ge, J. Wickert, M. Ramatschi, and X. Zou (2009), Retrieving tropospheric delays from GPS networks densified with single frequency receivers, Geophys. Res. Lett., 36, L19802,

[1] The observation of GPS slant delays from ground GPS networks can be used to reconstruct spatially resolved humidity fields in the troposphere by means of tomographic techniques. Tomography is always related to the solution of inverse problems which are very sensitive to the quality of the input data. Prior to a tomographic reconstruction, it is therefore necessary to quantify the information provided by a given set of GPS slant delay data. This work describes the properties and the information content of more than two million GPS slant delays taken in March 2006 by a continuously operating German GPS network. The temporal and spatial distribution of the slant paths in the atmosphere and their angular distribution in the local system of the GPS station is given. These distributions depend on the satellite orbits and show some characteristic pattern.

Precipitable water vapor (PWV) is an important parameter for climate research and a crucial factor to achieve high accuracy in satellite geodesy and satellite altimetry. Currently Global Navigation Satellite System (GNSS) PWV retrieval using static Precise Point Positioning is limited to ground stations. We demonstrated the PWV retrieval using kinematic Precise Point Positioning method with shipborne GNSS observations during a 20‐day experiment in 2016 in Fram Strait, the region of the Arctic Ocean between Greenland and Svalbard. The shipborne GNSS PWV shows an agreement of ~1.1 mm with numerical weather model data and radiosonde observations, and a root‐mean‐square of ~1.7 mm compared to Satellite with ARgos and ALtiKa PWV. An improvement of 10% is demonstrated with the multi‐GNSS compared to the Global Positioning System solution. The PWV retrieval was conducted under different sea state from calm water up to gale. Such shipborne GNSS PWV has the promising potential to improve numerical weather forecasts and satellite altimetry.