Sokkia SRX1, Руководство оператора, Страница: 179 / 184

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30. EXPLANATION
• Need for atmospheric correction
The SRX measures the distance with a beam of light, but the velocity of this light varies according
to the index of refraction of light in the atmosphere. This index of refraction varies according to the
temperature and pressure. Near normal temperature and pressure conditions:
With constant pressure, a temperature change of 1°: an index change of 1 ppm.
With constant temperature, a pressure change of 3.6 hPa: an index change of 1 ppm.
To perform high accuracy measurements, it is necessary to find the atmospheric correction factor
from even more accurate temperature and pressure measurements and perform an atmospheric
correction.
Sokkia recommends that extremely precise instruments be used to monitor the air temperature and
pressure.
• Finding the average temperature and pressure between two points in different atmospheric
conditions
To precisely determine the atmospheric correction factor, the average temperature and air pressure
along the measurement beam route must be taken.
Determine the temperature and pressure as follows.
Flat terrain
:Use the temperature and pressure at the midpoint of the line.
Mountainous terrain :Use the temperature and pressure at the intermediate point (C).
If it is not possible to measure the temperature and pressure at the midpoint, take the temperature
and pressure at the instrument station (A) and the target station (B), then calculate the average
value.
Average air temperature :(t1 + t2)/2
Average air pressure :(p1 + p2)/2
• Calculation of atmospheric correction factor allowing for humidity
30.2 Atmospheric Correction for High Precision Distance
Measurement