1 SVY 207: Lecture 14 Instruments and Applications Aim of this lecture: –To learn GPS specifications appropriate to different applications Short lecture (15 min) –Receivers –Antennas –Applications –Specifications Practical example to think about! (35 min) –Work in pairs –Report back to class Quiz (5 min)

2 Receivers Receiver types –In order of historical development for civilian surveying: TYPESINGLE-FREQDUAL-FREQExample Squaring:  1 2  2 2 Series-X P code:  1(P), P1(P)  2(P), P2(P)Rogue, Z-12 Single frequency:  1(C), P1(C)Hand helds C/A with squaring:  1(C), P1(C)  2 2 Old Ashtechs Cross correlating:  1(C), P1(C)  X), P2(X)Rogue Z-tracking:  1(C), P1(C)  Z), P2(Z)Z-12 –Cross correlation actually measures: PX  (P1  P2) because P code is same  X  (  1   2) –Receiver then constructs following observations: P2(X)  P1(C)  PX  2(X)   1(C)   X –Z-tracking uses some non-secret knowledge about encryption –Note: receivers can switch to P code if A/S is off

3 Receivers Size and Portability –Rack mounted –Portable –Hand held Software –Measurement software (code correlation, etc.) –Data management (tapes, RAM, flashcards, etc.) –Radio link (differential or RTK) –Interface (keypad, display, PC, modem) –Navigation solution (where am I, which way am I going?) –GIS (where am I on a map? ) –Kalman filter, and integration with other data types

4 Antennas Antenna types –single or dual frequency –Helical (bulky) or microstrip (flat) Backplanes –antenna often bolted down on top of a backplane –to reduce multipathing –can be a large metallic disc –can be a “choke ring” Size/Portability –Backplanes are obviously heavier and larger –Antennas can be »mounted on ground (reduce multipath) »placed on tripod (improve horizon) »fixed to a “bipod” for large scale surveying »can be physically integrated with receiver

5 Applications –navigation –geophysics –photo-control –civil-engineering control –seismic surveying –agriculture –in-car navigation (+ GIS) –connecting reference systems (e.g., channel tunnel) –large scale mapping

6 Specifications Considerations: –quality: precision, accuracy, reliability »type of data: L1, P1, L2, P2 (all or some?) »type of receiver, antenna, software »point, differential, or relative positioning »redundancy (e.g., guard against blunders, fatal errors) –latency: real-time or post-processing »radio link »broadcast or IGS orbits –frequency: solution rate »kinematic or static »data logging rate –portability versus permanence »weight, ruggedness, number of operators »type of receiver, antenna, antenna mount (tripod,..)

7 A practical example to think about! –As the senior surveyor working for a large engineering company you have been asked to plan the field work and data analysis for a GPS campaign. The campaign requires a high precision (1 cm) GPS survey of a network of several points over distances of up to 30km. –List the factors you should consider when planning the campaign.

8 Quiz For each of the following applications, state the specifications on the GPS equipment and method: (1) Establish a global control network with highest accuracy (2) Position an oil tanker as it comes into port

9 (3) Land an aircraft automatically (4) Position a hiker

10 (5) Provide positions to a car driver (6) Survey a 8 points crossing an earthquake fault over distances of up to 50 km

11 (7) Survey 40 points on a volcano over distances of up to 5 km (8) Determine if any subsidence is occuring at the level of 1 cm per year on an offshore oil rig.