Exam 1 Cram Study Guide for SRVY 2331

Condensed Study guide for Major Test

What are the four major GNSS constellations?

GPS, GLONASS, Galileo, and BeiDou

What is trilateration?

Determining a position using measured distances

Why is GNSS called a passive system?

The satellites transmit signals while receivers only receive them

Why are at least four satellites required for a GNSS position?

To solve for X, Y, Z coordinates and receiver clock bias

What is the difference between ephemeris and almanac?

Ephemeris gives precise orbit information for a satellite, almanac gives coarse orbit and status information for the constellation

What is a pseudorange?

A code-based satellite-to-receiver range that still contains clock, atmospheric, and other errors

What is carrier-phase ranging?

High-precision ranging using the phase of the carrier wave

What are the three legacy GPS codes?

C/A code, P(Y) code, and LNAV navigation message

What is the Doppler effect in GNSS?

A change in observed signal frequency caused by relative motion between the satellite and receiver

What is the ellipsoidal height relationship?

h = H + N, where h is ellipsoidal height, H is orthometric height, and N is geoid height

What is a bias in GNSS?

A systematic repeatable error that averaging does not remove

How is expected position error related to DOP and UERE?

Position error is approximately DOP × UERE

Why can dual-frequency GNSS reduce ionospheric error?

The ionosphere is dispersive, so its delay depends on frequency

How does the ionosphere affect code and carrier measurements?

It delays the code and advances the carrier phase

What is TEC?

Total Electron Content, the amount of free electrons along the signal path that determines ionospheric delay

What is the Klobuchar model?

The single-frequency ionospheric correction model broadcast by GPS

Why can't dual-frequency GNSS eliminate tropospheric delay?

The troposphere is non-dispersive

Approximately how large is zenith tropospheric delay?

About 2.3 to 2.5 meters

What is multipath?

Error caused when reflected or diffracted GNSS signals reach the antenna

What is a typical GNSS mask angle?

10° to 15°

What polarization do GNSS satellites transmit?

Right-Hand Circular Polarization, RHCP

What does a between-receiver single difference remove?

Satellite clock error

What does a double difference remove?

Satellite and receiver clock errors

What is the difference between a float and fixed solution?

Float estimates ambiguities as real numbers, fixed resolves the ambiguities to integers for higher precision

What is a cycle slip?

Loss of carrier-phase lock that causes the integer cycle count to change

What does LAMBDA stand for?

Least-squares Ambiguity Decorrelation Adjustment

What is RINEX?

Receiver Independent Exchange Format, a standard format for GNSS observation data

What is a CORS?

A Continuously Operating Reference Station with known coordinates that continuously collects GNSS data

What is OPUS?

NGS Online Positioning User Service for processing GNSS observations using CORS

What are ARP, HI, and PCO?

ARP is the physical antenna reference point, HI is antenna height from the mark to the ARP, and PCO is the offset from ARP to the electrical phase center

What was the primary purpose of TRANSIT and how did it determine position?

Navigation using satellite Doppler shift

What did System 621B contribute to GPS?

PRN ranging codes and the multiple-satellite constellation concept

What did Timation contribute to GPS?

Precise atomic clock technology

What are the major design characteristics of GPS?

Global, continuous, real-time, passive, precise, and secure

How does GPS distinguish satellites transmitting on the same frequencies?

Each satellite uses a unique PRN code

What are the three segments of GPS?

Space segment, control segment, and user segment

What was the baseline GPS constellation design?

24 satellites in 6 orbital planes inclined about 55 degrees

Approximately what is the GPS satellite altitude and orbital period?

About 20,200 km altitude and about 12 sidereal hours

What is Dilution of Precision, DOP?

A measure of how satellite geometry affects positioning accuracy

What DOP and satellite geometry are preferred?

Low DOP with satellites widely spread across the sky

What does the GPS Operational Control System, OCS, do?

Monitors GPS satellites, determines orbit and clock corrections, and uploads updated information

How can a GNSS receiver recover a signal weaker than the background noise?

By correlating the incoming signal with a replica of the known code

What antenna design is most common on survey GNSS receivers?

Microstrip or patch antenna

How does increasing antenna bandwidth affect GNSS reception?

It increases operating range but also increases interference and lowers SNR

What is an isotropic antenna?

A hypothetical lossless antenna that receives equally in all directions

What does +3 dBi mean?

About twice the response of an isotropic antenna in that direction

What are ARP, PCO, and PCV?

ARP is the physical reference point, PCO is the offset to the average phase center, and PCV is movement of the phase center

What do DLL, PLL/FLL, and NCO do?

DLL tracks code delay, PLL/FLL track carrier phase and frequency, and NCO generates the matching replica

What is integer ambiguity?

The unknown whole number of carrier cycles between the satellite and receiver

What is the difference between local and network accuracy?

Local accuracy is point-to-point relative accuracy, network accuracy is point-to-datum or reference-frame accuracy