Kharkov GPS Group

Software

• OCTAVA_PPA software architecture
• Carrier phase cycle slip detection procedure
• OCTAVA_PPA software testing results

Possibilities and features of the OCTAVA_PPA software

The Pre-Processing & Analyses software OCTAVA_PPA meets the following requirements.

1. The basis of the PPA software is the processing of not only the traditional double differences (or single differences "station-station") of carrier-phase observations but mainly "undifferenced" data of one separate (single) station.
2. Input data: RINEX-files of dual-frequency (and single-frequency) GPS/EGNOS unsmoothing raw data. The software carries out data processing at data rates 1/30 Hz - 1 Hz.
3. In the course of the processing the following operations are executed:
   • detection of carrier - phase slips at L1 and L2 GPS/EGNOS observations and repair of L1 and L2 (or L1 only) slips on the basis of processing the geometry-free linear combinations (LC) of code and phase data for each radiolink "satellite - GPS-station" separately as well as direct phase-only "satellite-satellite" single differences (the principle approach);
   • estimation of L1 and L2 code multipath effects;
   • QC-analyses of the code and carrier phase LC and estimation of RMS (multipath, noises) of the observations (C/A, P2, (L1-L2)) at both frequencies;
   • elimination (or flagging) of abnormal observations;
   • recovery of continuity of code observations (elimination of local time scale jumps typical for some type of the equipment);
   • calculation and QC of broadcast ephemeredes;
   • calculation and QC of satellite clock (frequency time) corrections (using broadcast GPS satellite messages) and correction of observations;
   • interpolation of the observations to GPS integer seconds;
   • smoothing the code observations using carrier-phase ones ("levelling") - for the purpose of further formation of WAD-corrections, estimation of current parameters of local ionospheric model, etc.;
   • data editing and formation of RINEX.OBS-file "cleared" from carrier-phase slips;
   • graphic and text displaying and registration of the processing results.
4. The software gives the opportunity of processing of the data obtained both in the static and kinematic modes. The full version of the PPA software complex will also allow one to carry out the analogous processing of such frequently used LC as single-differenced "station-station" observations and double-differenced observations.

The software complex will also include INTERNET WEB-FTP Server which must perform the functions of distribution of the archivized observations (RINEX), navigation and meteorology files and, also, "purified" observations and, in future, WAD/VRS corrections for network postprocessing.

Software applications

• Improvement of the reliability and quality of precise postprocessing GPS-positioning in geodesy, geodynamics, etc.;
• Sophisticated analysis of observations is clearing from slips and code multipath RINEX-files;
• Initial tool for all possible GPS applications;
• Software for teaching specialists and students;
• As an instrument for the delicate post-fly analysis of the results of mobile object trajectory determination in the automatic and interactive modes, including aircrafts (Flight Inspection Systems) and low-orbit space vehicles with on-board GPS equipment.

Users

• Developers of algorithms and software of processing GPS/GNSS observations (navigation, geodesy, cadactre, GIS, geodynamics, etc.);
• Specialists of various centers of processing GPS/GNSS observations;
• Sub-faculties of Universities specializing in radionavigation, satellite geodesy, GIS, etc.

Prospects of the software development

• Software adaptation to the observations of GLONASS and GALILEO;
• For reference permanent stations the software updating with the purpose of reducing the multipath effects in carrier-phase observations;
• Optional supplements formation of noiseless differential RTCM and WAD corrections (carrier-smoothed pseudorange corrections) and estimation of regional tropospheric and ionospheric models;
• Software adaptation for different programming languages;
• Development of the software version for functioning in real time mode.