Surveying II UNIT IV GPS SURVEYING

Basic concepts – Different segments – space control and user segments – satellite configuration- signal structure – orbit determination and representation – antispoofing – and selective availability – Task control segment -Hand held and Geodetic receivers – data processing – Traversing – and triangulation 4/28/2017

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parts of system include: space (GPS satellite vehciles, or SVs) control (tracking stations) users first one launched in 1978 ….June 26, 1993 Air Force launched 24th SV 4/28/2017

Design Objectives of GPS Suitable for different platforms: aircraft, ship, land-based and space (missiles and satellites), Ability to handle a wide variety of dynamics, Real-time positioning, velocity and time determination capability to an appropriate accuracy, Single global geodetic datum (reference system) for defining position, Differential accuracy standards: highest accuracy to be restricted to a certain class of authorized users, Resistant to jamming (intentional and unintentional), Redundancy provisions to ensure the survivability of the system, Passive positioning system that does not require the transmission of signals from the user to the satellite(s), Ability to provide the service to an unlimited number of users and world-wide coverage Low cost, low power, therefore highly complex satellite segment, Total replacement of the Transit 1 satellite and other terrestrial navigation aid systems. 4/28/2017

Signal Measurement Techniques Geocentric & geodetic Reference Systems Introduction Signal Measurement Techniques Geocentric & geodetic Reference Systems Time Systems Satellite Configuration 4/28/2017

Principles Of Global Positioning System (GPS) What is GPS? The GPS reference system The GPS system components The space segment The control segment The user segment GPS positioning principles 4/28/2017

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Basic functions of satellites include: Space Segment Constitutes satellite constellation which downlinks data including coded ranging signals, position information, atmospheric data, and almanac (data about approximate orbit information of all satellites). Basic functions of satellites include: Receive and store information transmitted by the control station Perform limited data processing by its own computer Maintain very accurate time by means of onboard 2 cesium and 2 rubidium oscillators Transmit information to the user by the signal message Maneuver to position in space controlled by the control segment 4/28/2017

Figure 5.1 GPS constellation consisting of six orbital planes with four satellites in each plane. Each satellite is identified with a two-character code: a letter identifies the orbital plane (A through F) and a number identifies the satellite number in the plane (Enge and Misra, 1999) 4/28/2017

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Control Segment I It consists of 5 tracking station to collect data based on observing satellite in their orbits. Tracking is executed with two frequency receivers equipped with highly precise cesium oscillators. Meteorological data is also collected for accurate evaluation of tropospheric delay (explained later in Lecture 10). 4/28/2017

Control Segment II One MCS, takes data from other 5 tracking stations and consequently predicts satellites orbits by extrapolation. Computes clock correction for satellite time referred to GPS time frame. Satellite time synchronization is carried out by connecting MCS to US Naval Observatory (USNO) in Washington DC. The clock correction data is then sent to transmitting station for uploading. 4/28/2017

Control Segment III Three transmitting stations are involved for transmitting recent data (including broadcast message) to satellites. These stations also send telemetry commands for repositioning, switching spare components etc. 4/28/2017

User Segment Consists of GPS receiver units with capability to obtain real time positioning. GPS receivers are hand-held radio-receivers/computers which measure the time that the radio signal takes to travel from a GPS satellite until it arrives at the GPS antenna. Using the travel time multiplied by the speed of light provides a calculation of range to each satellite in view. From this and additional information on the satellites orbit and velocity, the internal GPS receiver software calculates its position through a process of resection.  4/28/2017

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Advantages of GPS Unlike conventional surveying procedures, there is no need for intervisibility between stations. Independent of weather conditions as a result of using radio frequencies to transmit the signals. Use of same field and data reduction procedures results in position accuracy which independent of network shape or geometry and are primarily a function of inter-station distance. GPS surveying provides generally homogeneous accuracy. Hence, geodetic network planning in the classical sense is longer relevant. The points can be established wherever they are required need not be located at evenly distributed sites atop mountains to satisfy intervisibility, or network geometry criteria. GPS surveying is more efficient, more flexible and less time consuming positioning technique than using conventional terrestrial survey technologies. GPS can be used to obtain high accuracy three dimensional (3D) information, anywhere and time with relatively little effort on a global datum . The GPS instrumentation and the data processing software do not radically even if very high or moderately high accuracies are required (from 1 part in 104 to 1 part in 106 ). 4/28/2017

Applications Natural resources Precision farming Civil Engineering applications Structural deformations Open pit mining Land and marine seismic surveying Airborne mapping Seafloor mapping Vehicle navigation Transit system Retail industry Cadastral surveying Stakeout (waypoint navigation) Location based services (LBS) 4/28/2017

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GPS Observativations Carrier phases Differential GPS Relative positioning 4/28/2017

Sources of Error in GPS Surveying Clock error Atmospheric inferences Multipath Satellites configuration Instrument setup 4/28/2017

GPS Surveying Techniques Static FastStatic Post-processed Kinematic RTK 4/28/2017

Data transfer between controller and office computer Post Processing Data transfer between controller and office computer Using office software to process and adjust data Import and export data and graphs to CAD and GIS programs Generate drawings and reports 4/28/2017

Use of CORS in GPS Surveying The Continuously Operating Reference Stations (CORS) The Network CORS Data File Use of CORS in GPS Surveying 4/28/2017

Setting auto time features Viewing satellite graphs Editing a session Defining and viewing curtains Designing a network Static surveying FastStatic surveying Post-processed Kinematic surveying Setting up and configuring the radio for RTK 4/28/2017

Real-Time Kinemeatic (RTK) surveying Performing site calibration Staking out a point Performing GPS survey with CORS Data transfer Creating and configuring a processing style Processing baseline Performing network adjustment Importing and exporting to CAD and GIS software 4/28/2017

Describe the principles of GPS surveying. Learning outcomes: Describe the principles of GPS surveying. Perform planning and network design. Setup a GPS system for surveying. Perform Post-processed and RTK surveys and acquire appropriate GPS data. Perform data transfer. Post process the GPS data. Perform error analysis of the acquired GPS and other measured data. Generate field notes appropriate to GPS surveying. Produce written reports to communicate results of field surveys. 4/28/2017

Review the history of GPS surveying. Assignments Review the history of GPS surveying. Explain the advantages of GPS surveying. Estimate the accuracy of GPS surveying. Study the three segments of the GPS surveying. Differentiate the types of receivers. Determine the coordinates of a point in space when the distance between the point and a known point is given. Determine distance with code-ranging method. 4/28/2017

Determine distance with carrier-phase method. Assignments Determine distance with carrier-phase method. Explain how the integer of ambiguity is resolved in carrier-phase measurement. Explain relative positioning and differential GPS. Study the sources of errors in GPS surveying. Explain Static, FastStatic, Post-processed Kinematic and RTK surveys, their accuracies and applications. Design networks. 4/28/2017

Chris Rizos, Principles and Practice of GPS Surveying, UNSW 1997 Textbooks Chris Rizos, Principles and Practice of GPS Surveying, UNSW 1997 Paul Wolf, Elementary Surveying, Prentice Hall, 2002 Alfred Leick, GPS Satellite Surveying, 2nd ed., Wiley, 1995 Simon McElroy, Getting Started with GPS Surveying, GPSCO, 1996 Abdie Tabrizi, Lecture notes, 2004 Trimble Training Manuals, 2005 4/28/2017