Sect_10.3.4

10.3.4 GPS Surveying Specifications & Recommended Practices

FIELD PROCEDURE SPECIFICATIONS

Specifying such things as the number of receivers to observe simultaneously, length of observation span, number of satellites to be observed, cutoff elevation angle, measurement of meteorological parameters, etc.

Therefore, specifications for field procedures must include (beyond those existing for conventional techniques), as a function of desired accuracy:

time per station occupation (if possible, as a function of satellite geometry),
whether single or dual-frequency instrumentation is to be used,
the GPS technique to be used,
number of receivers deployed,
satellite geometry,
data rates and the number of satellites tracked,
number of independent occupations per site,
number of repeated baselines,
cutoff elevation for tracking,
quantity and quality of meteorological data to be collected, and
antenna setup specifications, etc.

The Table in section 10.3.2 and the Table below give the Australian observation requirements for GPS surveys (note that the modern GPS techniques are included). In the Table below an effort has been made to provide recommendations with regards to the GPS surveying technique that should be used as a function of antenna spacing. Table in section 10.3.2 makes suggestions concerning which GPS surveying technique should be used as a function of the desired ORDER of the survey.

Australian observation requirements for GPS surveys (ICSM, 1994).

initialisation dual / single frequency common sats continuous lock during travel maximum spacing PDOP

STATIC GPS METHODS

Classic-static no opt. 4 no > 500 kms * e

Pseudo kinematic no opt. 4
* a no, only at base <20 kms * e

Quick static methods no opt.
* d 4 no <10 kms * e

KINEMATIC GPS METHODS

Continuous Kinematic yes
* b opt.
* c 5 preferred
4 possible yes <20 kms <10
* f

Stop & Go yes single 5 preferred
4 possible yes <20 kms <10
* f

" Ambiguity resolution on the fly " --
kinematic no dual, also single 5 preferred
4 possible preferred but not necessary <20 kms
7-10 kms best

	initialisation	dual / single frequency	common sats	continuous lock during travel	maximum spacing	PDOP
STATIC GPS METHODS
Classic-static	no	opt.	4	no	> 500 kms	* e
Pseudo kinematic	no	opt.	4 * a	no, only at base	<20 kms	* e
Quick static methods	no	opt. * d	4	no	<10 kms	* e

KINEMATIC GPS METHODS
Continuous Kinematic	yes * b	opt. * c	5 preferred 4 possible	yes	<20 kms	<10 * f
Stop & Go	yes	single	5 preferred 4 possible	yes	<20 kms	<10 * f
" Ambiguity resolution on the fly " -- kinematic	no	dual, also single	5 preferred 4 possible	preferred but not necessary	<20 kms 7-10 kms best

Notes:

*a: Four satellites required in both observation sessions, 5 or more an advantage.

*b: Observe a known baselines (at beginning or end) and solve all ambiguities, or do an antenna or return to the starting point the end of the survey.

*c: Dual frequency receivers give an advantage.

*d: Dual frequency P-code will enhance the speed of the solution.

*e: Sufficiently changing geometry during a recording session assists in the determination of ambiguities and, where they have been resolved, PDOP should be low at some stage in the processed data.

*f: The ambiguities are resolved through the initialisation and the PDOP should be low at some stage during each station occupation from that moment (refer to manufacturers specifications).

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