GPS & GNSS Surveying Technologies Flashcards
7 cards from real CST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 GPS & GNSS Surveying Technologies flashcards as text
In RTK GPS surveying, what must be successfully completed before the receiver can deliver centimeter-level accuracy?
Answer: Integer ambiguity resolution (initialization)
RTK GPS requires integer ambiguity resolution — determining the exact whole number of carrier wave cycles between each satellite and the antenna — before centimeter-level accuracy is achievable; until then, only a less accurate 'float' solution is available.
What is a CORS station in the context of GPS surveying infrastructure?
Answer: A Continuously Operating Reference Station providing permanent GPS data
CORS (Continuously Operating Reference Station) are permanently installed GPS receivers that collect data 24/7, forming networks that support post-processing, real-time corrections, and national spatial reference infrastructure.
When converting GPS ellipsoidal heights to orthometric (mean sea level) heights, what resource does a surveyor use?
Answer: A geoid undulation model such as GEOID18
GPS measures heights above the WGS 84 ellipsoid, while engineering and construction require orthometric heights above the geoid (mean sea level); NGS geoid models like GEOID18 provide the geoid-ellipsoid separation (N) needed for conversion.
Which primary operational advantage does GNSS offer over traditional total station traversing on large-scale projects?
Answer: GNSS allows positions to be determined without intervisibility between stations
Unlike total station surveys that require unobstructed sightlines between consecutive points, GNSS receivers determine positions independently anywhere with a clear view of the sky, greatly increasing efficiency on large or obstructed sites.
During an RTK GPS survey, the PDOP value rises to 9.2. What is the appropriate course of action?
Answer: Suspend observations and wait for satellite geometry to improve
A PDOP above 6 indicates poor satellite geometry that significantly degrades positional accuracy; observations should be suspended until PDOP drops to an acceptable level (typically below 4) to ensure reliable results.
In RTK GPS processing output, what does a 'fixed solution' signify compared to a 'float solution'?
Answer: Carrier phase integer ambiguities have been resolved, yielding centimeter-level accuracy
A 'fixed solution' means the receiver has successfully resolved the carrier phase integer ambiguities to exact whole numbers, enabling centimeter-level RTK accuracy; a 'float solution' carries unresolved fractional ambiguities and is considerably less accurate.
What is the primary limiting factor that determines the maximum practical baseline length for reliable RTK GPS surveys?
Answer: Ionospheric conditions and the distance-dependent difference between base and rover
As baseline length increases, ionospheric conditions at the base and rover diverge, making it progressively harder to resolve integer ambiguities and maintain a fixed solution; practical RTK baselines are typically limited to 10–20 km for this reason.