“EGNOS Workshop – application” Cracow , 24th September 2004

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““EGNOS Workshop – application”EGNOS Workshop – application”CracowCracow, , 24th September 200424th September 2004

MAIN ASTRONOMICAL OBSERVATORYNATIONAL ACADEMY OF SCIENCES OF UKRAINE

GPS/EGNOS Pre-Processing experimental software "OCTAVA_PPA":

concept, possibilities, initial test results

Dr. Alexey A. Zhalilo, Natalya V. Sadanova

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CONTENTS

Possibilities and Features of "OCTAVA_PPA" software Observation equations Software block-diagram General distinctions from conventional analogues Examples of the results of processing the GPS observations

· IGS stations, GPS observations (RINEX v. 2.10) · NovAtel OEM4-G2W ref. receiver (JSC "NIIRI", Kharkov), GPS/EGNOS observations (RINEX v. 2.10)

Software Applications Users Prospects of the software development Acknowledgements Contacts

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Possibilities and Features of "OCTAVA_PPA" software

The “Pre-Processing” software is being created within the framework of the Program of regional geodynamic and ecological monitoring of the Crimea as part of WAD/VRS algorithmic and software complex

Scientific Supervisor – Prof. Yaroslav S. Yatskiv,Academician of the National Academy of Sciences of Ukraine

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Possibilities and Features of "OCTAVA_PPA" software (1/5)

1. The basis of the Pre-Processing&Analyses (experimental) software "OCTAVA_PPA“ 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. PPA carry out data processing at data rates 1/30 Hz and 1 Hz. PPA software admits the processing of RINEX-files, in which Doppler observations are absent.

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3. In the course of processing the following operations are executed: detection of carrier phase slips at L1 and L2 GPS/EGNOS observations, continuity recovery (where it is possible); detection, estimation and correction of L1 and L2 (or L1 only) phase slips both for static and kinematic modes of measuring 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 (key) approach);

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estimation and mitigation of L1 & L2 code multipath effects;

QC-analyses of the code and carrier phase LC and estimation of RMS observations (C/A, P2, L1, L2) at both frequencies (multipath, noises);

elimination (or flagged ) of abnormal observations;

recovery of continuity of code and phase observations (elimination of local time scale jumps typical for some type of the equipment);

calculation of ephemeredes;

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synchronization (interpolation to GPS integer seconds) of observations;

calculation of satellite clock (frequency–time) corrections (using broadcast GPS satellite messages) and correction of observations;

correct filtering of code observations by using carrier-phase ones (“levelling”) - for the purpose of further formation of WAD-corrections, estimation of current parameters of local ionospheric model, etc. – optionally;

data editing and formation of RINEX.OBS-file "cleared" from carrier-phase slips and pseudorange multipath;

graphic and text displaying and registration of the results of processing

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4. The software gives the opportunity of processing the data obtained both in the static and kinematic modes including the objects with high dynamics.

The full version of the PPA software complex will also allow to carry out the analogous processing of such frequently used LC, as single-differenced "station-station" observations and double-differenced observations.

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Observation equations (1/2)

“Geometry-free” linear combinations (LC) of observations:

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Observation equations (2/2)

Carrier-phase single differences“ith satellite – jth satellite”

ij2

2

wij1

1

wijwl

ij22l

ij2

ijL2

ij2часыij

ijij2

ij11k

ij1

ijL1

ijчасыij

ijij1

L̂)( L̂)( L̂

:LC Lane - Wideand

L )t( N C I }LF{ L̂

L )t( N C I }LF{ L̂

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“OCTAVA_PPA” software block diagram (1/9)

Mode of post-processing of (daily) sessions of dual frequency observations

of separate stations Trimble 4000SSI, NovAtel OEM4-G2W

Registration rates – 1/30 Hz, 1 Hz

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7

4

1 2

3 5 DB

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8

9

10

11

DB

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””Cleared”Cleared” RINEXRINEX

END of processing (i-th station)

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RINEX 2.10(OBS- and NAV- files)

A priori information 2

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Reading of RINEX.NAV file. Formation of intermediate data for calculation of frequency and time corrections and ephemeredes

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Reading of RINEX.OBS file and transformation into internal MatLab TNP

working structure 4

Reading the header of RINEX.OBS file.Calculation of the Antenna Phase Center data

tying to the geodetic marker 5

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Calculations for each epoch: Δtrec , ephemeredes, frequency and time corrections and other data for synchronization (interpolation to GPS integer seconds) and consequent processing 6

Editing of TNP data: By elevation angle β≥βmin = (5о ÷ 15о) By the results of preliminary data analysis

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Formation of “geometry-free”(GF) code and carrier-phase linear combinations (LC) of dual frequency observations “Satellite-by-satellite” processing: detection, estimation, identification and elimination of carrier-phase “big” slips of L1 and L2


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Formation and Processing (detection, estimation, identification) of single

differences (between satellites) of L1 and L2 carrier-phase observations.

Processing of undifferenced (one-way) carrier-phase observations (in case of external atomic clock use)

The elimination of “small” slips –the final correcting of slips


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Estimation of code observation multipath using the filtering of “slipless” code and carrier-phase linear combinations

Multipath compensation (correction) Estimation of observations (C/A, P2, L1, L2) RMS Marking of abnormal observations (outliers)


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Formation of RINEX.OBS-file ”cleared” from slips and pseudorange multipath


11Interpolation of the observations to integer GPS seconds and elaboration of frequency-time corrections, ephemeredes (using SV navigation message) and navigation solution 12

Termination of processing of the session.Passing to session processing

of another station

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General distinctions from conventional analogues (1/2)

For the determination and elimination of carrier-phase slips the software performs the processing of “undifferenced” observations of a separate (single) station or receiver – the standard approach usually uses double differencesTwo-stage approach of detection and elimination of “big” and “small” slips at the expense of using the LC of observations with “low”dynamics (Stage 1) and direct (with high dynamics) observations of carrier-phase single differences between satellites is used (Stage 2)

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The software uses new original algorithms of detection and estimation of carrier-phase slips in conditions of high dynamics and observation lapses

The principle of correlation filtering of code and carrier-phase linear combinations for detection and estimation of carrier-phase slips is used

General distinctions from conventional analogues (2/2)

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Examples of the results of processing the GPS observations of IGS stations (1/5)Detection, estimation, identification of “big”carrier-phase cycle slips

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Examples of the results of processing the GPS observations of IGS stations (1/3)Detection, estimation, identification of “small”carrier-phase cycle slips (at the example of “Wide-Lane” LC processing )

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Examples of the results of processing the GPS observations of IGS stations (2/3)Detection, estimation, identification of “small”carrier-phase cycle slips (at the example of “Wide-Lane” LC processing)

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Examples of the results of processing the GPS observations of IGS stations (3/3)Detection, estimation, identification of “small”carrier-phase cycle slips (at the example of “Wide-Lane” LC processing)

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Examples of the results of processing the GPS observations of IGS stations (1/7)Multipath estimation

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Examples of the results of processing the GPS observations of IGS stations (2/7)Multipath estimation

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Examples of the results of processing the GPS observations of IGS stations (3/7)Multipath Effect (Correlator Output)

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Examples of the results of processing the GPS observations of IGS stations (4/7)Multipath Effect is eliminated (Correlator Output)

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Examples of the results of processing the GPS observations of IGS stations (5/7)Multipath Effect + Cycle Slip

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Examples of the results of processing the GPS observations of IGS stations (6/7)Multipath Effect + Cycle Slip (Correlator Output)

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Examples of the results of processing the GPS observations of IGS stations (7/7)Correlator Output:detection of Cycle Slip (Multipath Effect is eliminated )

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Examples of the results of processing the GPS/EGNOS observations of NovAtel OEM4-G2W receiver (1/21)

ZONES OF RADIOVISIBILITY OF GPS SATELLITES

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Session of observations №1060 dt. 15 April 2004;the processing interval included 17700 epochs at rate 1 Hz;

beginning of the session – 10 minutes and 22 seconds past 7 a.m.

2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

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Documents

“EGNOS Workshop – application” Cracow , 24th September 2004