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ŠUMARSKI LIST 7-8/2016 str. 41     <-- 41 -->        PDF

the GNSS standards all around the world, has an important mission to archiving and presenting the information such as GPS/GLONASS satellite ephemerides data, earth rotation parameters, coordinates and velocity data of IGS stations, clock data of GPS/GLONASS satellites and IGS stations, ionospheric and tropospheric data. Moreover, not only IGS but also several organizations such as Jet Propulsion Laboratory (JPL), Natural Resources Canada (NRCan), Center for Orbit Determination in Europe (CODE) and Bundesamt für Kartographie und Geodäsie (BKG) have a significant role in terms of data providing for GPS/GNSS positioning.
The raw data collected from anywhere in the world with only one dual frequency geodetic grade GPS receiver may be converted to the Receiver Independent EXchange (RINEX) format, and may be uploaded to one of these services to process. However, there are some specific factors such as data processing solution techniques, solution algorithms (mathematical model), products used and accuracies of them (reference station coordinates, satellite ephemerides and clock corrections, atmospheric parameters etc.) and observation duration to estimate high accurate point positions. These services aid to the users in traditional GPS survey and processing studies with several advantages in terms of software, hardware, equipment, personnel and logistics costs.
Table 1 shows the specifications and classifications of these services, of which give especially effective solutions for static GPS observation data with long observation durations (2 hours and over). The services listed, which have different technical specifications, have been commonly used by several disciplines for precise positioning. These services when compared with the commercial and scientific software, that are not required long term training and easy use, have made the use of PPP technique common. Since these services have some differences with respect to service features such as membership requirement, storage limitation of the GPS/GNSS RINEX data to be uploaded, process in static/kinematic modes, evaluation the data collected by single/dual or multi frequency receiver, GPS/GNSS antenna type selection, users are interested in them (URL-2; URL-3; URL-4; URL-5; URL-6; URL-7; URL-8).
The aim of the study is to investigate the positioning accuracy of the PPP method and also to expose the accuracy assessment of PPP technique by using different web based online services under the forest environment. Moreover, the study investigates decrease the survey budget and equipment in terms of using web based online services and single GPS receiver to provide high accurate point positions. For this purpose, two station points, which one of them is in the forest area and the other is close to the forest environment, have been established around the forest environment, and then long-term and repeated static GPS observations have been collected. The data collected have been processed by commercial software (Topcon Tools v8.2) and web-based online services (OPUS, AUSPOS, CSRS-PPP, GAPS, APPS) to research especially accuracy of the GPS PPP technique. Since there are some restrictions for use of GPS in the forest environment, it is effectively used for surveying applications by different disciplines. Thus, performance of GPS PPP technique is investigated especially in forest environment for point-positioning applications using web based online services.
Definition of The Study Area
Definicija područja istraživanja