Baseline Calibration

There is a need and often a legal requirement to have your instrument checked over an official baseline, typically once per year - after your annual service would be a good time!
The procedures and calculations differ by state.

Below we have specified the parameters you will need to feed into the baseline calculation softwares. Note that the C and D parameters as used in Rüeger's formula (see below) have been derived from the ppm formula listed in the operators manuals. Similarly, the Unit of Length is derived from the modulating frequency which is listed in Sokkia's service manuals. E.g. a Unit of length of 2 meters corresponds to a wavelength of 4 meters which (rounded) corresponds to a 75MHz frequency. The value of the Unit of Length determines what baseline lengths to use, so what pillar combinations to set up on. So before you go out into the field, you'll need to know what the Unit of Length of your total station is.

Sometimes the available pillars are a legacy from the past, e.g. only a multiple of 10.0000 meters is available. In that case cyclic errors have to be identified in a different manner (NSW)
Talking legacy, have a look at the US NGS service - a 1977 manual on the use of baselines.

 EDM type/
 Instrument Series 		Unit of Length
(=half of modulation  wavelength)		 EDM source C
(Rüeger)		 D
(Rüeger)		  modulation frequency
   (rounded, in MHz)
 SRX (SRX1,2,3,5)    (RedTech EX)
 SET X		 0.8m Red Laser diode
(690 nm)		 282.324 80.405 187
30R  (RedTech and RedTech II)
30R,130R,030R instruments  (R and R3)
  e.g. SET230R, SET530RK3, SET4230RM		 2m Red Laser diode
(690 nm )		 282.59 80.361 75MHz
 NET1200 2m Infrared LED 282.59 80.361 75MHz
 EZStation 20/20A,21/21A 2.5m 660nm red laser !     60MHz
 SET 3110R,4110R 5 830nm infrared LED !     30MHz
           
SET220 series (SET2220,3220,4220) 
SET110M series (SET3110M,4110M)
SET110 series (SET2110,3110,4110)
SET010 series (SET1010,2010,3010,4010)
SET000 series (PowerSET1000,2000,3000,4000)
SET 10 series (SET310,510,610)
SET100 series (SET 2100,3100,4100)
SET00 series (SET300,500,600, incl S models)
SET5W,SET3Bii
SET3E,SET4E
SET3F,SET5F
BII series: SET2BII,3BII,4BII
CII series: SET2Cii,3Cii,4Cii		 5m 860nm Infrared LED     30MHz
           
 SET2,3,4  SET4A
 SET2B,3B,4B, (not: SET2Bii,3Bii,4Bii,)
 SET2C,3C,4C
 all RED's, all SDM's		 10m 860nm Infrared LED 278.96 79.323 15MHz
 SET5,6      + S models
 SET5A
 SET5E,6E
 SET6F		 20m 860nm Infrared LED     7.5MHz

In the EDM handbooks issued in SA and VIC the unit of length is listed for a large number of survey instruments, sometimes different from the above ...

SA     landservices.sa.gov.au 

VIC    EDM handbook v9 , Vict Lands

Handbooks:for other States:

NSW  Direction No 5 - verification of Distance Measurement Equipment

ACT   EDM calibration handbook

WA    EDM Calibration


The correction Ka to be added to the measured distance dmeas , can be calculated using Rüeger's formula,

from NSW Surveyors General's Directions No5, Aug 2004:

Ka = [ C - D * p      +   11.27 e  ] 10-6 dmeas

          273.15+t       273.15+t

Where

'p'= pressure in millibars

't'= temperature in degrees Celcius

'e'=partial water vapour pressure (mb) ; (pmillimetres = 0.75006 pmillibars)

'C' and 'D' are parameters specific to the modulation frequency and the carrier wavelength

respectively of the EDM instrument.
 

Sokkia uses a different representation of the same formula, e.g. from the manual for the x30R instruments:
(just multiply below and above the dividers with 273.15 to see Rüeger's formula appear)

Atmospheric Correction Factor

(282.59 -  0.2942 * p   + 0.0416 *e     ) * 10-6
           1+0.003661*t   1+0.003661*t

t: Air temperature in °C

p: Pressure in hPa

e: Water vapour pressure in hPa

h: Humidity in %

ew = Saturated water vapour pressure