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Potentials Of The National Egyptian

Continuously Operating Reference Stations

(CORS) For River Nile Navigation

Moustafa A. Baraka

Adel H. El-Shazly

Professor of Surveying & Geodesy

Civil Engineering Program

German University in Cairo, Egypt

Professor of Surveying & Geodesy

Faculty of Engineering

Cairo University, Egypt

Introduction

With the recent development in Egypt especially inTransportation and Transportation logistics (3000 Km Newroads network, and Suez Canal development project ), It isnecessary to focus on the following:

1. Prepare suitable maps for navigation and tracking in terms of scales and accuracy.

2. The urgent need on supporting the River Nile Navigation for Transportation activities

3. Prepare Bathymetric maps for the Navigational water ways in Egypt including river Nile.

4. Prepare Electronic navigation chart with the safe navigation depth

5. Establish River Information System for Navigation and tracking

Introduction

6. Revise the current status of the real time positioning services in Egypt for navigation and tracking.

7. Revise the coverage and accuracy of DGPS support by EGNOS8. Revise the coverage and accuracy of DGPS support by Radio

Beacons9. The concept of the Network RTK and CORS in supporting the

real time activities for positioning, navigation and tracking 10. Main Structure of the CORS network and the implementation

of real time corrections.11. Examines the location, distribution and coverage of the

Egyptian CORS in relation to River Nile Navigation12. Current status of CORS network in Egypt and required

development to support the navigation and tracking motivation in Egypt especially for River Nile navigation.

Navigation in River Nile

• It is necessary to enhance the navigation through River Nile to support the transportation of cargo and tourism activities.

Navigation in River Nile • River Bus and River Tour services


• Support navigation of Floating hotels

METIS First Master Training& Seminar, Ifrane (Morocc),15,16.03.2007

7

• River Nile is a navigable marine waterway, and all the rules of

marine navigation should be applied.

• Suitable navigational aids and landmarks in River Nile should be

established.

Precise locations of buoys


• Preparation of electronic navigation chart for river Nile which includes bed levels determined by Hydrographic survey along the Nile corridor


• Yearly hydrographic survey for river Nile bed for maintenance and dredging process


• Safe Navigation requires minimum water depth along the river Nile all the year

• Regulation of water discharge should be controlled and arranged with the river navigation activities


• In addition, providing the instantaneous information about river traffic management

– Fairway Services

– Traffic Services

– Vessel Traffic Services

– Lock and Bridge management


AUTOMATIC IDENTIFICATION SYSTEM AIS

It is a system enables ship to identify their names, particulars, direction,

position and intention maneuvering in coastal and heavy trafficked areas

provided by AIS

Vessels Traffic And River Information ServicesVTS and RIS are shore based centers provide navigation services in

approaches of ports and Inland waterways

• It requires Real time position with enough accuracy for safe navigation

• GNSS code receivers offers Real time position with low accuracy

• DGPS can satisfy required accuracy for navigation in river Nile

GNSS for Navigation in River Nile

GNSS Positioning Techniques

Point Positioning Differential Positioning

Post Processing

Static

Pseudo kinematic

kinematic

Stop and Go

Rapid Static

Real Time

Carrier Phase

RTK

Pseudorange

(DGPS/DGNSS)

Fundamental DGPS/DGNSS system and correction data transmit

Purpose: improve accuracy & reliability

Ground Based Augmentation System

Space Based Augmentation Systems


• Errors in one position are similar to a local area• High performance GPS receiver at a known location.• Computes errors in the satellite info• Transmit this info in RTCM-SC 104 format to the remote GPS• Sub-meter accuracy near Beacons and worst away from Beacons

Radio Beacon Correction

DGPS Signal

GPS Receiver Station DGPS TransmitterShipboard GPS &

DGPS Receivers

Locations of Beacons Stations


IALA = International Association of Lighthouse Authorities


Accuracy

0.5 meter near the reference station

Add 1 meter/150 Km

Coverage of Six Beacons Stations in Egypt

Satellite Correction

• A subscription-based service that provides the user with corrections from a geo-stationary satellite.

The OmniSTAR DGPS System satisfies the following :

• Continental coverage

• Transmit RTCM format

• Sub-meter accuracy over the entire coverage area.

• Subscription service

• A system that automatically corrected a user's GPS position.

• The transmission of the real time corrections is from a geostationary satellite.

– Costs $4500 + $800/yr


• World Differential G P S Coverage by privately owned satellites.

Omnistar provides differential GPS data from ground stations

via satellite.


Space Based Augmentation SystemDGPS (Aviation Applications)

• Satellite-based differential that is free of charge. • Corrects GPS positioning for use in aviation. • It corrects the atmospheric and orbital data so that

autonomous calculations can better determine true position.

Space Based Augmentation System

European Geostationary Navigation Overlay System (EGNOS)

Space Based Augmentation System

EGNOS Coverage Before 2013

EGNOS monitoring Stations

Standard (single-base station) RTK

Accuracy, Reliability, Availability

Good Bad

Standard (single-base station) RTK• Depends on the ability of the algorithms to resolve the integer

ambiguities and to model the differential errors that occur between the

RS and the rover.

• To solve the ambiguity, many conditions must exist, including a relatively

short distance between RS and rover.

No

rth

ing

(km

)

Easting (km)

Single baseline approach

City limits

**

No

rth

ing

(km

)

Easting (km)

Network approach

Ref.

Ref.

Ref. Ref.

Ref.

0

10

00

100

10

00

Network RTK (NRTK)Basics

City limits

0 100

Limited to short distances (~10 km) Long distances – over 100 km

Network RTK (NRTK) and Continuously Operating Reference Stations (CORS)

• Processing data from Multiple Reference Stations, and the

Providing of „Correction' information to users in Real-time

(X,Y,Z,t)

cm position accuracy

(X,Y,Z,t)(X,Y,Z,t)

Fix the

Ambiguity

(X,Y,Z,t)

Ref. Stn X,Y,Z

Pseudo-range + Corrn.

Carrier Phase + Corrn.

(X,Y,Z,t)

Real Time Position of Rover

Data CentreNMEA 0183

RTCM SC-104 Ver. 2.1

• Network-RTK’ approach, where the spatially correlated atmospheric and satellite orbit errors could be better mitigated using several continuously operating GPS reference stations surrounding the rover receiver.

• Rapid static and kinematic GPS techniques could be used over baselines that extend to tens of kilometers in length.

• Network based techniques enable cm-accuracy positioning with less dense reference stations

Network RTK (NRTK) and CORS systems

• CORS used to solve for the cost, accuracy, time consuming problems that came up with the traditional use of GNSS positioning techniques.

• CORS almost supports all applications of GNSS some of which are the Real Time Kinematics (RTK) and Differential GNSS (DGNSS).


• Improvement of accuracy versus single base RTK

• Reliability improvement• Productivity improvement • Positions are automatically

derived in a precise geodetic reference station system

• Real-time service for ionospheric disturbances can be provided

• Baseline Lengths

- Conventional : 30km-50km

- Correction Approach dependent?

- The new practical baseline: 70km

- Future: multi-constellations & 3 (or more frequencies):

100km - 200km?

• Based on practicalities: power, comms, sites, usage

• COST & RISK

• Extended capabilities: single-base and/or network

Network Design


Monumentation

Components of a CORS site

Hardware

Communications

Software

Photo Courtesy UNAVCO

Continuously Operating Reference Stations (CORS)

A CORS SITE

• Stable site (minimal local horizontal and vertica movement).

• Stable antenna mount.

• Minimum electromagnetic interference.

• Adequate security for equipment.

• Receiver and communications hub located inside a building

• Providing protection from weather and elements.

• Antenna located in a minimal Multipath environment.

• Continuous long-term operation

• Availability of power supplies and telecommunication

connection.

• DC from solar or a wind generation system.

• Communications solution depends on data requirement.

• Use of public Internet is generally preferred

Continuously Operating Reference Stations (CORS)

Network RTK (NRTK) and CORS systemsCommunication method

Duplex (bi-directional) communication or one-direction communication with these technical aspects:• expected signal strength at different locations,• number of users,• range and coverage,• transmission bandwidth,• protocol,• reliability and error correction,• latency (one second and shorter data transmission

latencies are required for cm level positioning accuracy).

Duplex communication mode is the mostly used method with:

• A cellular modem such as a General Packet Radio Service (GPRS) or Global System for Mobile Communications (GSM) are used.

• GPRS is usually preferred as it is more economical since the user pays for the data, not for the call duration.

• GPRS can provide a stable and reliable connection with latencies less than one second.

• Number of users is limited by the ability of the NRTK processing center to simultaneously perform calculations for all users.

• For a limited number of users this latency is usually less than three seconds.


One-direction communication method mainly employs VHF or UHF broadcasting or encodes the RTK corrections into a broadcast TV audio sub-carrier signal with:

• For VHF broadcasting, allocation of suitable broadcast radio frequency and obtaining its license for development of NRTK.

• No restriction on the number of users concurrently using the NRTK.

• High cost of the infrastructure needed to build radio signal repeaters, if needed, to cover the whole area.

• Some problems due to the possibility of receiving signals of varying strength in different locations, and possible frequency jamming.

• A mix of both communication methods is however possible.


• The data transmission is mostly carried out via the Network Transport of RTCM via Internet Protocol (Ntrip).

• Ntrip is an open source and can be downloaded from the internet.

• Ntrip was built over the TCP/IP foundation and is an application–level protocol for streaming GNSS data over the internet.

• Ntrip uses HTTP and has three components: Ntrip Client, Server and Ntrip Caster.

• Ntrip is designed for distributing differential correction data (e.g. in the RTCM-SC104 format) or other kind of GNSS streaming data to stationary or mobile users over the internet.

• It allows simultaneous PC, Laptop, or receiver connections to a broadcasting host.

• Ntrip supports wireless internet access through mobile IP networks like GSM, GPRS.


NRTK Basics and Formats• Receiver collection rate – minimum 1Hz• Data formats

– Open standard– Compatibility

• RTCM SC-104 (data format related to GPS applications )– Developed by Radio Technical Commission for Maritime Services– RTCM Special Committee (SC) 104 is the one concerned

Differential Global Navigation Satellite System (DGNSS)– Only true ‘open’ protocol– RTCM-2.1 Added RTK messages for dm levels at short distances– RTCM-2.2 Expanded for differential operations with GLONASS

• CMR- Compact Measurement Record

RTCM Formats– RTCM-2.2, 2.3 RTK operations providing cm- level performance

at short distances

– RTCM-3.x More efficient; support RTK operations (GPS+GLONASS); network correction message

• Common message types 2.x

– Type 18, 20 – RTK uncorrected carrier phase data and carrier phase corrections

– Type 19, 21 – RTK uncorrected pseudo-range measurements and appropriate range corrections

• Common message types 3.x

– 1004 – full observables

– 1005 – reference station coordinates

– 1007 – antenna description

Network RTK Processing Techniques &

Applications

• Virtual Reference Station – VRS

• Area-Parameter Correction – FKP (Flächenkorrekturparameter)

• Master-Auxiliary Concept – MAC

Reference Station data

streams back to server

through LAN or

Internet

Virtual Reference Station – VRSData Flow

• VRS techniques is currently the most popular• Requires bi-directional communications• VRS observations constructed

Roving receiver sends

an NMEA string back to

server using cellular

modem - VRS position

is established

NMEA -

GGA

VRS


Server uses VRS

position to create

corrected observables

and broadcasts to

rover

VRS


a combined solution based on the

data from several reference stations

when the user is provided with a

software generated additional

information from a near-by virtualreference station

Rover surveys as in

normal RTK survey but

getting data as if

coming from the VRS

VRS


Area Correction Parameters - FKP

• Network described using coefficients for a surface

• Parallel surface with baselines less than 100 km

• Reference station at the center of the “surface”

Area Correction Parameters - FKP

• Software in rover receiver does the interpolation of corrections• Error information is provided for quality control and analysis• Single and bi-directional communications

Master Auxiliary Concept - MAC

Rover

Aux k3

Aux k4

Aux k2

Auxiliary k1Master j

70 km

• Rover position (NMEA) to

processing center

• Processing center chooses a

master station – usually

closest ref. station

• Auxiliary stations are chosen

from a 70 km catch circle

Master-Auxiliary Concept – MAC

• Rover receives MAC corrections via RTCM

• Rover decides on method of interpolation of corrections and how the position is determined – double difference, for example

Master-Auxiliary Concept – MAC

CORS distribution in Egypt

CORS distribution Around River Nile

Coverage Areas for CORS in Egypt

Continuously Operating Reference Stations (CORS) in Egypt

• Network consists from 40 CORS Sites

• Distributed along Delta and Nile Valley

• Fixed at roof of the Surveying Authority buildings or any

governmental buildings.

• Baselines lengths among CORS stations are 50 to 70 km

• The CORS are equipped with dual frequency GNSS receivers

(Trimble Net R5)

• Each receiver works with A.C. with 220 volt with adapter as

alternative DC power source.

• Each receiver with internal memory 2Giga bytes to store data

for five days.

• Each receiver with one Ethernet Rj5 port, 1 serial port, an 3

USB ports.

• Each station equipped with router ( Sarian) model DR6410

with adapter.

• CORS collect observations and send them to Control Center

• Control Center is located at Egyptian Surveying Authority

Building Dokki, Giza.

• Control center consists from 2 Servers to store observations

from 40 CORS and monitor the status for each station.

• Communications between each station and control center

consist from 40 ADSL lines and 2 SIM Cards for each CORS

and one Telephone line

• Collected data from 40 ADSL lines are then collected through

2 leased lines and then to Router and then to Server

Continuously Operating Reference Stations (CORS) in Egypt

CORS Station Example In Egypt

mom

40Stations

Modem

Modem

Router

Switch

1

Switch2

Server

1

Server2

4MB

Leased1

Leased2

2MB

2MB

4MB

4MB

40ADS

L

Control center communications

Examples of

Advanced Network Rover

SPS855 Modular Receiver

Supports base, rover, rugged and Beacon antennas

Semi permanent base station or rover GNSS capable

Internal battery for upto13 hours operation

Marine rover use –DGPS up to Precision. Single or dual antennas

Flexible interfacing –Bluetooth, Internet, Serial

Scalable accuracy modes – Location through to Precision

Heading Add On GNSS receiver for heading

Internal wideband 410-470 MHz, or external cellular modem

What's standard on board• SPS855 GNSS Dual Frequency Supports the following satellite systems and

correction sources– GPS, GLONASS, Galileo and Compass– Satellite-based Augmentation Systems such as WAAS, EGNOS, MSAS, and QZSS– MarineSTAR & OmniSTAR™ VBS, XP or HP– Precision GNSS base station (RTK corrections)– DGPS using UHF radio links (RTCM, CMR, CMR+, CMRX)– Virtual Reference Station (VRS)– Trimble Internet Base Station Service (IBSS)

• Technical – 440 channels– 28 Mb internal memory – 20Hz output– Upgradable to Location RTK (10/10), Location RTK & Precise vertical (10/2) and

Precision RTK (1/2)– Serial, Bluetooth & Internet– Internal battery– Internal wide band 410-470 MHz UHF Radio

Trimble Geo 7X Handheld

ConclusionsTowards the implementation of proper River Nile Navigationsystem, It is required to:

1. Prepare bathymetric map for river Nile

2. Adopt maintenance system for the river Nile with continuousmeasurement of bed levels

3. Continuous monitoring for Rive Nile water surface along thenavigation way

4. Prepare electronic navigation chart to be the base for RiverInformation System

5. Establish Navigation Aids along the River Nile

6. Prepare the navigation ships or boats with suitable GNSSreceivers capable of define position with 1 to 3 m accuracy

• Based on the current GNSS positioning and the future situationfor supporting navigation activities it is necessary to mention:

1. The limited coverage and accuracy of EGNOS correction for GPSposition in Egypt is not suitable to support the navigationthrough River Nile.

2. With the implementation of more monitor stations in Africa forEGNOS system the accuracy for GNSS position with EGNOScorrection should be tested.

3. The GBAS service or radio Beacons corrections do not cover thenavigation water way of river Nile and require single frequencyreceiver capable of receiving correction in RTCM format.

4. Network RTK is ideal solution to define real time positions withcm accuracy or dm accuracy depends on the used rover receiver.

Conclusions

Conclusions5. CORS network ,with 40 stations, in Egypt Covers Delta and Nile

Valley with spacing 50- 70 km. Accordingly it covers the RiverNile up to Aswan.

6. No Coverage for the network in Eastern and Western deserts.

7. Currently, ESA operates the national Egyptian CORS to supportnon-navigation, in post-processing modes of GPS.

8. Working with Egyptian CORS in real time will strongly affect thenew development activities in Egypt.

9. ESA, along with other national Egyptian stakeholders, areencouraged to review the Egyptian CORS scope and strategies inorder to maximize the national CORS services, for both publicand private sectors.

THANK YOU

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