Sect_4.2.2

4.2.2 GPS Hardware for Surveying:

HARDWARE CHARACTERISTICS

The following are some characteristics of GPS receiver hardware to be considered by a user or purchaser:

P/Y code, C/A code pseudo-range measurements, as well as carrier phase?
Code-correlation, or squaring, or other proprietary phase tracking techniques?
Single frequency or dual-frequency capability?
Continuous or switching, or hybrid tracking channel architecture? How many channels?
External clock input?
Strobe timing output?
Type of data storage, and capacity?
Power requirements and options?
Antenna type, and antenna-receiver configuration?
Nature of "packaging": backpack, handheld, tripod-mounted or rack-mounted?
Real-time operation, or post-processing mode?
Availability and sophistication of software?

Some of these characteristics have already been discussed in earlier sections. GPS receivers to be used for high precision surveying applications generally have the following features:

Able to measure the integrated carrier phase on at least one of the two L-band carrier frequencies.
Have the capability of tracking substantially more than the minimum four satellites simultaneously (preferably an "all-in-view" capability).
Record the data for subsequent post-mission processing.
Typical data measuring rate of 15-60 seconds (much higher for kinematic applications, perhaps 10-20Hz for some models).
Antennas are chosen with stability and quality in mind so as to minimise phase centre variations and sensitivity to multipath, with the phase centre and point to which antenna height measurements are made clearly marked on the antenna housing.
Must be of rugged construction, light and portable.

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