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Although vertical total electron content (VTEC) forecasting is still an open subject of research, the use of predictions of the ionospheric state at a scale of several days is an area of increased interest. A global VTEC forecast product for two days ahead, which is based exclusively on actual Global Positioning System (GPS) data, has been developed in the frame of the International Global Navigation Satellite Systems (GNSS) Service (IGS) Ionospheric Working Group (IGS Iono‐WG). The UPC ionospheric VTEC prediction model is based on the Discrete Cosine Transform (DCT), which is widely used in image compression (for instance, in JPEG format). Additionally, a linear regression module is used to forecast the time evolution of each of the DCT coefficients. The use of the DCT coefficients is justified because they represent global features of the whole two‐dimensional VTEC map/image. Also, one can therefore introduce prior information affecting the VTEC, for instance, smoothness or the distribution of relevant features in different directions. For this purpose, the use of a long time series of final/rapid UPC VTEC maps is required. Currently, the UPC Predicted product is being automatically generated in test mode and is made available through the main IGS server for public access. This product is also used to generate two days ahead preliminary combined IGS Predicted product. Finally, the results presented in this work suggest that the two days ahead UPC Predicted product could become an official IGS product in the near future.

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In this work, a new GPS carrier phase-based\ud velocity and acceleration determination method is presented\ud that extends the effective range of previous techniques. The\ud method is named ‘EVA’, and may find applications in fields\ud such as airborne gravimetry when rough terrain orwater bodies\ud make difficult or impractical to set up nearby GPS reference\ud receivers. The EVA method is similar to methods such\ud as Kennedy (Precise acceleration determination from carrier\ud phase measurements. In: Proceedings of the 15th international\ud technical meeting of the satellite division of the Institute\ud of Navigation. ION GPS 2002, Portland pp 962–972,\ud 2002b) since it uses L1 carrier phase observables for velocity\ud and acceleration determination. However, it introduces\ud a wide network of stations and it is independent of precise\ud clock information because it estimates satellite clock\ud drifts and drift rates ‘on-the-fly’, requiring only orbit data\ud of sufficient quality. Moreover, with EVA the solution rate\ud is only limited by data rate, and not by the available precise\ud satellite clocks data rate. The results obtained are more\ud robust for long baselines than the results obtained with the\ud reference Kennedy method. An advantage of being independent\ud of precise clock information is that, beside IGS Final\ud products, also the Rapid, Ultra-Rapid (observed) and Ultra-\ud Rapid (predicted) products may be used. Moreover, the EVA\ud technique may also use the undifferenced ionosphere-free\ud carrier phase combination (LC), overcoming baseline limitations\ud in cases where ionosphere gradients may be an issue\ud and very low biases are required. During the development of\ud this work, some problems were found in the velocity estimation\ud process of the Kennedy method. The sources of the problems were identified, and an improved version of the\ud Kennedy method was used for this research work. An experiment\ud was performed using a light aircraft flying over the Pyrenees,\ud showing that both EVA and the improved Kennedy\ud methods are able to cope with the dynamics of mountainous\ud flight. A RTK-derived solution was also generated, and\ud when comparing the three methods to a known zero-velocity\ud reference the results yielded similar performance. The EVA\ud and the improved-Kennedy methods outperformed the RTK\ud solutions, and the EVA method provided the best results in\ud this experiment. Finally, both the improved version of the\ud Kennedy method and the EVA method were applied to a network\ud in equatorial South America with baselines of more\ud than 1,770 km, and during local noon. Under this tough scenario,\ud the EVAmethod showed a clear advantage for all components\ud of velocity and acceleration, yielding better and more\ud robust results.Peer ReviewedPostprint (published version

We organize complex problems in simple ways\ud using a GNSS data management strategy based on ‘‘GNSS\ud Data Structures’’ (GDS), coupled with the open source\ud ‘‘GPS Toolkit’’ (GPSTk) suite. The code resulting from\ud using the GDS and their associated ‘‘processing paradigm’’\ud is remarkably compact and easy to follow, yielding better\ud code maintainability. Furthermore, the data abstraction\ud allows flexible handling of concepts beyond mere data\ud encapsulation, including programmable general solvers. An\ud existing GPSTk class can be modified to achieve the goal.\ud We briefly describe the ‘‘GDS paradigm’’ and show how\ud the different GNSS data processing ‘‘objects’’ may be\ud combined in a flexible way to develop data processing\ud strategies such as Precise Point Positioning (PPP) and\ud network-based PPP that computes satellite clock offsets\ud on-the-fly.Peer ReviewedPostprint (published version