An increasing number of terrestrial‐ and space‐based radio‐communication systems are influenced by the ionospheric space weather, making the ionospheric state increasingly important to forecast. In ...this study, a novel extended encoder‐decoder long short‐term memory extended (ED‐LSTME) neural network, which can predict ionospheric total electron content (TEC) is proposed. Useful inherent features were automatically extracted from the historical TEC by LSTM layers, and the performance of the proposed model was enhanced by considering solar flux and geomagnetic activity data. The proposed ED‐LSTME model was validated using 15‐min TEC values from GPS measurements over one solar cycle (from January 2006 to July 2018) collected at 15 GPS stations in China. Different assessment experiments were conducted in different geographical locations and seasons as well as under varying geomagnetic activities, to comprehensively evaluate the model's performance. These comparative experiments were conducted using an ED‐LSTM, a traditional LSTM, a deep neural network, autoregressive integrated moving average, and the 2016 International Reference Ionosphere models. The results indicated that the ED‐LSTME model is superior to the other statistical models, with R2 and root mean square error values of 0.89 and 12.09 TECU, respectively. In addition, TEC was adequately predicted under different ionospheric conditions, and satisfactory results were obtained even under geomagnetically disturbed conditions. These results suggest that the prediction performance could be significantly improved by utilizing auxiliary data. These observations confirm that the proposed model outperforms several state‐of‐the‐art models in making predictions at different times and under diverse conditions.
Key Points
A novel extended encoder‐decoder long short‐term memory neural network (ED‐LSTME) for ionospheric total electron content (TEC) forecasting over China is developed
ED‐LSTME shows a strong capability in improving TEC forecasting at different geographical locations, seasons, and geomagnetic conditions
ED‐LSTME is robust and outperforms all the six selected baselines when comparing with the models in terms of their performance
A clear definition of the measurand is an essential precondition for measuring. When verifying conformity to ISO GPS tolerances (verification), the measurand is often unclear, particularly for ...geometrical tolerances. The tolerance zone is a portion of space whereas the measurand is a scalar quantity, and many such quantities may be derived from the same portion of space. We propose a unified derivation of the measurand in ISO GPS verification matching the designer's intent. Different types of tolerances are considered, from the easiest to the least obvious as to the derivation of the measurand.
Global positioning system (GPS) devices have been utilised in travel surveys since the late 1990s. Because GPS devices are very accurate at recording time and positional characteristics of travel, ...they can correct the trip-misreporting issue resulting from self-reports of travel and improve the accuracy of travel data. Although the initial idea of using GPS surveys in transport data collection was just to replace paper-based travel diaries, GPS surveys currently are being applied in a number of transport fields. Several general reviews have been done about GPS surveys in the literature review sections in some papers, but a detailed systematic review from GPS data collection to the whole procedure of GPS data processing has not been undertaken. This paper comprehensively reviews the development of GPS surveys and their applications, and GPS data processing. Different from most reviews in GPS research, this paper provides a detailed and systematic comparison between different methods from trip identification to mode and purpose detection, introduces the methods that researchers and planners are currently using, and discusses the pros and cons of those methods. Based on this review, researchers can choose appropriate methods and endeavour to improve them.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper reports on the progress of a wearable assistive technology (AT) device designed to enhance the independent, safe, and efficient mobility of blind and visually impaired pedestrians in ...outdoor environments. Such device exploits the smartphone’s positioning and computing capabilities to locate and guide users along urban settings. The necessary navigation instructions to reach a destination are encoded as vibrating patterns which are conveyed to the user via a foot-placed tactile interface. To determine the performance of the proposed AT device, two user experiments were conducted. The first one requested a group of 20 voluntary normally sighted subjects to recognize the feedback provided by the tactile-foot interface. The results showed recognition rates over 93%. The second experiment involved two blind voluntary subjects which were assisted to find target destinations along public urban pathways. Results show that the subjects successfully accomplished the task and suggest that blind and visually impaired pedestrians might find the AT device and its concept approach useful, friendly, fast to master, and easy to use.
•The potential of the use of smartphones in travel behaviour studies seems promising.•The use of smartphones could eliminate many problems that traditional surveys face.•Uneven distribution of mobile ...phones in the society causes sampling problems.•Important barriers are technological issues and limitations in big data analyses.•Broader use of smartphones in travel behaviour surveys is a distant perspective.
Human travel behaviour has recently been one of the most popular topics in transport studies. Therefore, the ability to obtain valuable sets of data has become one of the key challenges for researchers. Traditional mobility surveys have many important limitations. In this situation, the potential of the use of smartphones and dedicated applications in the identification of individual travel behaviour seem very promising. We set ourselves a goal to indicate strengths and weaknesses of data obtained with this method and assess the perspectives of its use for the needs of public policies. For these purposes we prepared a low-cost mobile application and conducted a pilot study among students in Poznań (Poland). In effect, trajectories of more than 100 people with almost 3 billion of location data were collected. Based on a literature review and our results we discuss the main problems, limitations and challenges of the broader use of the data obtained with smartphones. In the conclusion, we argue that there is a huge and increasing potential connected with mobile phones, but still some important barriers exist including sampling problems, limitations in big data analyses and technological issues. Therefore, a broader use of smartphones in travel behaviour surveys seems to be rather a distant perspective.
In this book, the reader will learn step by step how to use the Life Story method in qualitative research. In a clear and objective way, the authors expose practical examples of each instrument that ...composes the method and beyond, the analysis that best corresponds to this type of collection and the final format of the edited text in thesis, dissertation or others. Taking into account the doubts that arise when collecting, analyzing and writing the life history and noting the scarce literature in the area, this is a guide that brings together all the steps and mishaps that the future researcher may encounter in the process.
GNSS-R interferometric reflectometry (also known as GNSS-IR, or GPS-IR for GPS signals) is a technique that uses data from geodetic-quality GNSS instruments for sensing the near-field environment. In ...contrast to positioning, atmospheric, and timing applications of GNSS, GNSS-IR uses the signal-to-noise ratio (SNR) data. Software is provided to translate GNSS files, map GNSS-IR reflection zones, calculate GNSS-IR Nyquist frequencies, and estimate changes in the height of a reflecting surface from GNSS SNR data.
We studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS‐ total electron content (TEC) ...stations. It is observed that the vertical total electron content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17–18 March 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of the main phase toward the recovery phase. The first peak extended from beyond 0°S to 30°S, the second occurred from 6°S to 25°S, whereas the third diurnal peaks was confined from 13°S to 25°S. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on 18–19 March 2015. This ionospheric negative phase was stronger at low latitudes than in the equatorial region. Also, two latitudinal chains of GPS‐TEC stations from equatorial region to low latitudes in the east and west Brazilian sectors are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA) in the east and west Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.
Key Points
The 17 March 2015 St. Patrick´s day geomagnetic storm
Extreme ionospheric space weather event over the Brazilian sector
Anomalous behavior in EIA during main phase and recovery phases
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