Section 4: Soil and Water Conservation Engineering
Surveying and Levelling
Subtopic: Total station, introduction to GPS survey
Question Statement:
Which of the following statements regarding Total Station and Global Positioning System (GPS) surveys are correct?
Options:
(A) A Total Station integrates an electronic transit theodolite, an Electronic Distance Meter (EDM), and an internal microprocessor.
(B) EDM instruments measure distance using the transit time of modulated infrared or laser electromagnetic waves.
(C) A minimum of 4 satellites with clear line-of-sight are required by a GPS receiver to solve for three-dimensional position ($x, y, z$) and receiver clock bias.
(D) Atmospheric refraction causes zero measurement errors in Total Station EDM surveys.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
• A Total Station combines an electronic theodolite, EDM, and on-board computational data logger (A is correct).
• EDMs operate on phase comparison or pulsed time-of-flight of infrared/laser carrier beams (B is correct).
• 4 satellites are mathematically required to solve 4 simultaneous equations for latitude, longitude, elevation, and receiver clock offset (C is correct).
• Atmospheric temperature, pressure, and humidity alter the refractive index and velocity of light, necessitating meteorological ppm corrections (D is incorrect).