CST GPS & GNSS Surveying Technologies 2

Question 1

Which GPS error source is caused by satellite signals reflecting off buildings or other surfaces before reaching the receiver antenna?

Accepted Answer

Multipath error

Answer

Multipath error occurs when GPS signals travel indirect paths by bouncing off nearby surfaces before arriving at the antenna, causing the receiver to compute an artificially long signal travel distance.

Question 2

How does the ionosphere primarily affect GPS signal accuracy?

Accepted Answer

It slows the signal and introduces ranging errors proportional to electron content

Answer

The ionosphere, a layer of charged particles in the upper atmosphere, slows GPS signals as they pass through it, introducing a range error that varies with solar activity and the amount of ionized particles along the signal path.

Question 3

Which receiver capability most effectively eliminates ionospheric delay errors in GPS surveys?

Accepted Answer

Dual-frequency capability measuring L1 and L2 simultaneously

Answer

Because ionospheric delay is frequency-dependent, dual-frequency receivers measuring on both L1 (1575.42 MHz) and L2 (1227.60 MHz) can compute and remove the ionospheric delay from the position solution.

Question 4

Why do GPS surveyors set an elevation mask angle, typically between 10 and 15 degrees?

Accepted Answer

To exclude low-angle satellites whose signals traverse more atmosphere and are prone to multipath

Answer

Satellites near the horizon have signals that pass through a much greater thickness of atmosphere and are more susceptible to multipath from the ground; excluding them with an elevation mask angle improves solution quality.

Question 5

What is ephemeris error in GPS, and what causes it?

Accepted Answer

Inaccuracy in the broadcast satellite orbital position and velocity data

Answer

Ephemeris error arises when the orbital parameters (predicted position and velocity) broadcast by a GPS satellite in its navigation message differ from the satellite's true orbital position, causing small but systematic ranging errors.

CST - Certified Survey Technician Practice Test

CST - Certified Survey Technician Practice Test

CST GPS & GNSS Surveying Technologies 2