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GPS/EGNOS Tropospheric Corrections for Mobility Applications

The use of ZTD Maps within the SCUTUM Project

C. Sciarretta, R. Pacione, B. Pace, D. Iacovone

A. Di Fazio

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Objective

• The work presents an experimental use for mobility applications of a GPS ZTD product, initially born to support operational Meteorology.

• European hourly gridded maps of ZTD values, interpolated (Ordinary Kriging) from few mm accuracy ZTD values (validated throughout a decadal activity in GPS Meteorology projects) estimated at GPS and EGNOS/RIMS locations, are used in the navigation solution of theTelespazio product for EGNOS/EDAS services called LCS to computethe position of a mobile GPS/EGNOS receiver.

• The experiment, carried out in the frame of the European projectSCUTUM, is to evaluate the enhancements possibly generated by punctual real-time ZTD corrections in the computed position in a mobility application such as the tracking & tracing of dangerousgoods.

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1. Heritage: A pointwise, very accurate, NRT GNSS ZTD product developed for meteo applications covering Europe and operational (used in E-GVAP project)

2. Adaptation to mobility applications/servicesa. Creation of a regional ZTD grid product at a uniform heightb. Rapid and accurate ZTD grid product elaboration inside LCSc. Continuous service flow guarantee (increasing robustness of

ZTD grid product and system architecture)

3. Enhancement to EDAS/RIMS data used. GNSS network densificatione. Data standardization

Activity phases

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Architecture

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ASI‐CGS ZTD Meteorological solution

ASI/CGS analysis center EGVAP (The EUMETNET GNSS water vapourprogramme, is set up to provide its EUMETNET partners with European GPS delay and water vapour measurements in Near-Real-Time foroperational meteorology.

E-GVAP operational data flow

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ASI‐CGS ZTD Map product

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ASI‐CGS ZTD Map product – Quality Check

We test the GTMC over 3 sites (BZRG, ZIMM, BRUS) and 1 week (March 2010) of ZTD estimates coming from 130 European GPS stations mostly belonging to the EPN Network.

Red: GPS ZTD Blue: ZTD Map Green: VMF1_Site

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ASI‐CGS ZTD Map product – Quality Check

25 IGS sites selected as benchmark (red): IGS ZTD values vs ZTD Map and UNB3M in March/May 2011

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Validation Methodology

• a calibration campaign, to tune the overall processing chain parameters in Telespazio (Rome) premises

• static field trials, at a fixed and controlled location in Telespazio (Rome) premises

• dynamic field trials, in real-life driving environments, in a small area in Southern Latium, around Ciampino where RIMS ROM is located

Three different LCS’s configurations (run in RT, simultaneously)1. “LCS baseline” (MOPS tropospheric corrections)2. “LCS enhanced” (GPS-only ZTD Map corrections)3. “LCS enhanced” (GPS+RIMS ZTD Map corrections)

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10 km

M0SEUniv. La Sapienza

ROMA EGNOS RIMS

TPZ1Calibration,

Static field trials

Validation campaign

TPZ2Dynamic field trials

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Calibration

Estimated coordinate

(deg, deg, m)

Formal uncertainty

(mm) LAT 41.929549053 1.003LON 12.572864907 2.093

H 97.2692 2.049

The processing flow has been set up (tuning of the parameters)

The expected impact of the experimental ZTD corrections has been quantified

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Field Trials measurements

Static field trial (20-21 July 2011) • positions & raw measurements from the fixed receiver (TPZ1)

used in the calibration phase, collected and processed by the LCS’s navigation solution in RT, simultaneously in the described three configurations w.r.t. the TPZ1 positions

Dynamic field trials (20 September 2011)• raw measurements from the GPS/EGNOS OBU and the fixed

GPS L1-L2 receiver (TPZ2) processed through a kinematic differential GPS method to compute a true path/reference trajectory

• positions from the GPS/EGNOS OBU, collected and processed by the LCS’s navigation solution in RT, simultaneously in the described three configurations w.r.t. the “true path”

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Static field trial ‐ Results

LCS configuration

HNSE (m)

VNSE (m)

Mean Median 95th percentile Mean Median 95th

percentile

“LCS baseline” 2.58 1.55 2.28 5.51 1.41 1.29 1.08 3.89

“LCS enhanced” ZTD GPS 2.58 1.54 2.29 5.51 1.35 1.25 1.04 3.79

“LCS enhanced” ZTD GPS + EDAS/RIMS

2.58 1.54 2.29 5.51 1.35 1.25 1.04 3.79

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Dynamic field trial ‐ Results

LCS configuration

HNSE (m)

VNSE (m)

Mean Median 95th percentile Mean Median 95th

percentile

“LCS baseline” 5.3 2.2 4.6 10.0 3.3 4.2 1.6 11.3

“LCS enhanced” ZTD GPS 5.3 2.1 4.6 9.9 3.1 4.2 1.4 11.0

“LCS enhanced” ZTD GPS + EDAS/RIMS

5.3 2.1 4.6 9.9 3.1 4.2 1.4 11.0

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Conclusions/Step forward (1/2)

• For a fixed receiver of known coordinates (mimic a rover), the height determination improvement is up to 8 centimetres (RMS of the residuals). No improvement is seen in the planar determination. Moreover, the inclusion of the EGNOS EDAS/RIMS in the ZTD Maps, as measured in the validation campaign has a low effect: the differences in the Up position error between ZTD maps with and without RIMS data are very tiny, below 1 cm, i.e. the order of magnitude of the georeferenced fixed point for the static campaign.

• For the SCUTUM uses, targeting a mobility application, the sensitivity of the LCS navigation solution to the inclusion of the ZTD experimental corrections is not meaningful.

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Conclusions/Step forward (2/2)

However, the SCUTUM activity enabled:

• To validate the hourly ASI-CGS ZTD Map product (>50 sites), customized to cope with the SCUTUM requirements

• To measure the inclusion of a RIMS data in the ZTD solution; thepotential contribution of the EGNOS RIMS network is valuable especially as it will allow to gauge the point-wise ZTD values when both the GPS and Galileo constellations will be operational. At this aim, it is crucial that the IGS/EUREF standards, followed by theinternational GPS community, are taken in by EGNOS/EDAS for the RIMS data dissemination.

• To possibly identify other sectors where realistic troposphericcorrections replacing modeled ones can be further exploited, such as the geolocation of SAR images from satellite missions.

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Thank you for your attention!

Contacts:Cecilia Sciarrettacecilia.sciarretta@e‐geos.it

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Back up

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SCUTUM LCS

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EGNOS Data Access Service

Provided data

• Raw GPS, GLONASS and EGNOS GEO observations and navigation data collected by the entire network of Ranging and Integrity Monitoring Stations (RIMS) and Navigation Land Earth Stations (NLES)

• EGNOS augmentation messages, as normally received by users via the EGNOS Geostationary satellites

Services

• Service Level 0 (SL0): subset of the data provided by SL1, encoded in ASN.1 format

• Service Level 1 (SL1): all EGNOS raw data encoded as RTCM messages

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Dynamic Field Trials features

Dynamic field trials were conducted using: • one OBU using GPS + EGNOS• the GPS L1-L2 frequencies receiver for the “true path”

measurement, installed on a test vehicle and connected to a common external GPS antenna

The reference GPS L1&L2 receiver (TPZ2) was installed near the test location with an inter-receiver distance not exceeding 20 km.

The GPS reference receiver was geo-referenced via a dedicated PPP (continuous/h24 for two days data collection campaign).