1

SVY 207: Lecture 14Instruments 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:

TYPE SINGLE-FREQ DUAL-FREQ Example

Squaring: 12 22 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) 22 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.