Global Positioning System (GPS)

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Questions and Answers

What is the primary advantage of using very low frequency (VLF) transmission waves in ground-based radio navigation systems?

They can be modulated with a large amount of useful information.
They achieve wave-form ducting by reflecting off the ionosphere, broadening the coverage area. (correct)
They offer line-of-sight coverage, ensuring signals aren't bent by the ionosphere.
They provide more accurate navigation solutions due to minimal ionospheric refraction.

What limitation is associated with ground-based, high-frequency carrier waves in radio navigation systems?

High-frequency waves are unable to travel long distances due to atmospheric interference.
High-frequency waves are prone to refraction, making navigation solutions inaccurate.
High-frequency waves cannot be effectively modulated, reducing the amount of transmittable data.
High-frequency waves 'punch' through the ionosphere, resulting in limited line-of-sight coverage. (correct)

What altitude do NAVSTAR GPS satellites orbit at?

10,898 nautical miles (correct)
20,000 nautical miles
5,000 nautical miles
15,000 nautical miles

How many satellites form the GPS constellation?

24 (A) Signup and view all the answers

What is the primary function of trilateration in GPS operation?

To deduce the location of the GPS receiver by measuring distances from multiple satellites (A) Signup and view all the answers

What is the result of knowing your distance from two satellites?

You must be at one of two intersection points. (C) Signup and view all the answers

From the text, what does knowing your distance from three satellites allow?

The narrowing down of your location to just two points in space. (D) Signup and view all the answers

What is the fundamental principle behind GPS position fixing?

Measuring the time taken for a radio signal to travel from a satellite to the receiver. (B) Signup and view all the answers

What information does each satellite emit within its coded signal?

Its position and the exact timing of the signal emission (C) Signup and view all the answers

The GPS system achieves accurate timing with...

Extremely accurate atomic clocks on the satellites. (D) Signup and view all the answers

Why do GPS systems require data from at least four satellites?

To calculate and correct for timing errors of the receiver's clock (C) Signup and view all the answers

What are 'pseudo-random' codes used for in GPS technology?

To enable easy and unambiguous signal comparison between satellites and receivers. (C) Signup and view all the answers

What is a 'multipath error' in GPS?

Errors caused by GPS signals being reflected off of terrain and structures before reaching the receiver (D) Signup and view all the answers

What is the 'mask angle' in the context of GPS?

The minimum angle above the horizon at which a GPS satellite is considered usable. (B) Signup and view all the answers

What is the effect of ionospheric attenuation on GPS signals for civilian users, and how is it managed?

It delays the signal, for which a fixed correction is applied based on averaged induced errors. (A) Signup and view all the answers

What is 'Geometric Dilution of Precision' (GDOP)?

A measure of how satellite geometry affects the accuracy of position measurements (D) Signup and view all the answers

What is Differential GPS (DGPS), and how does it enhance accuracy?

A refinement of standard GPS that uses ground-based transmitters to eliminate most errors. (B) Signup and view all the answers

What are pseudo-satellites (or pseudo-lites), and what is their primary purpose?

Ground-based transmitters that mimic GPS satellite signals. (A) Signup and view all the answers

According to Dr. Brad Parkinson's research, where is the most effective location for a ground-based pseudo-satellite near an airport runway, and why?

30 miles south of the runway, to provide improved viewing geometry due to GPS satellite orbit planes. (B) Signup and view all the answers

What is the Wide Area Augmentation System (WAAS), and what is its purpose?

A satellite-based system for improved accuracy and integrity. (B) Signup and view all the answers

Which errors does WAAS correct for?

Ionospheric disturbances, timing, and satellite orbit errors. (D) Signup and view all the answers

Which area has WAAS satellite coverage?

North America (B) Signup and view all the answers

What is the name of a similar system to WAAS that is being developed for the Australasian region, anticipated to be fully operational by 2023?

Southern Positioning Augmentation Network (A) Signup and view all the answers

Why is 'System Integrity' important in GPS?

It refers to the ability to provide timely warnings if the system is unsuitable for navigation. (D) Signup and view all the answers

According to the material, what makes GPS more complicated than 2D systems like VOR/DME in terms of integrity?

GPS is a 4D system, and signal-in-space error reflects into horizontal position error via a relatively complex function of satellite geometry. (D) Signup and view all the answers

What is RAIM, and what is its primary function?

A method where GPS tells user about when GPS should not be used for navigation. (B) Signup and view all the answers

What is necessary for all RAIM schemes?

Self-consistency checking of the sensor data, requiring redundant measurements. (C) Signup and view all the answers

What are the two types of RAIM?

Detection and Isolation (B) Signup and view all the answers

What is the key distinction between the RAIM detection function and the isolation function?

The detection function can detect a faulty satellite, but the Isolation function can determine the faulty one and ignore it. (D) Signup and view all the answers

What is the main purpose of a moving map display in a GPS receiver?

To display the aircrafts current location and to keep the aircraft positioned in the center of the display. (D) Signup and view all the answers

In modern aircraft, how is GPS data typically integrated into the flight deck systems?

Integrated into a flight management system (FMS) and shared with other systems. (A) Signup and view all the answers

Why must GPS antennas be mounted on the top of the aircraft fuselage?

To ensure clear reception with line-of-sight access to the satellites (D) Signup and view all the answers

What functions does a typical Multifunction Control Display Unit (MCDU) perform related to GPS?

Turn the GPS on, access navigation data, create or edit flight plans, and warn pilots of GPS malfunctions. (A) Signup and view all the answers

Which of the following is a primary function of the Data Loader Unit in a GPS system?

To load updated navigation information into the GPS memory. (D) Signup and view all the answers

In order to completely integrate a GPS installation, to what onboard systems should the GPS be connected?

Remote GPS annunciators, the aircrafts attitude and heading system, the GPS/NAV transfer relay, and the autopilot system, along with other systems. (C) Signup and view all the answers

What are the primary systems that feed data to a typical GPS system?

Attitude and heading (C) Signup and view all the answers

Within a GPS system, what is the purpose of tracking loops and, specifically, what do the 'code tracking loop' and 'carrier tracking loop' do?

Tracking loops process the different signals. The code tracking loop tracks C/A and P codes, the carrier tracking loop determines the doppler shift. (B) Signup and view all the answers

Why are efficient transmission lines needed to connect the antenna to the receiver?

Because the L-band transmissions from Navstar satellites arrive with very low power densities. (B) Signup and view all the answers

Which GPS cable characteristic is critical?

impedance of the transmission line is 50 ohms (B) Signup and view all the answers

What is the purpose of the 'MSG' annunciator light on a GPS unit, such as the Trimble 2101?

Indicates a message is in the message queue (C) Signup and view all the answers

What happens in a Trimble 2101 GPS if there is no external source or manual entry for altitude?

It prompts the pilot to manually enter altitude. (C) Signup and view all the answers

Why are various test frequencies performed? During a communications test using VHF radio transmissions, what should be observed to determine if there is interference with the GPS?

Observe a drop in the number of satellites being tracked. (B) Signup and view all the answers

What is the function of the ENT (Enter) key on many GPS units?

It is used to enter data or select settings, and is mainly used to scroll between the selector knobs. (B) Signup and view all the answers

What does selecting VNAV provides access to?

E6B functions (B) Signup and view all the answers

Other than having various tests and checks within the GPS itself (as well as with external systems), how can user confirm correct GPS operation?

Selecting a display test. (D) Signup and view all the answers

Why were space-based navigation transmitters developed, despite the long-standing reliability of ground-based systems?

To overcome the limited coverage and accuracy issues associated with ground-based radio navigation systems. (B) Signup and view all the answers

How does the NAVSTAR GPS constellation achieve substantial global coverage?

By positioning satellites at a high altitude, allowing each satellite to have direct line-of-sight access to a large portion of the Earth. (B) Signup and view all the answers

What is the primary reason the C/A code is the only GPS signal available for civilian applications?

It is not encrypted, allowing unrestricted access. (D) Signup and view all the answers

What is the consequence of even small errors in time measurement within a GPS system?

Significant inaccuracies in position calculation. (A) Signup and view all the answers

What makes the codes used in GPS 'pseudo-random'?

They are complex digital codes designed to be easily compared and unambiguously identified, repeating every millisecond. (A) Signup and view all the answers

What is the primary approach used by differential GPS (DGPS) to enhance accuracy?

Utilizing ground-based transmitters at precisely known locations to correct satellite signal errors. (B) Signup and view all the answers

Why do pseudo-satellites placed adjacent to an airport runway negatively impact GPS accuracy?

They jam the signals coming from the GPS satellites circling overhead. (B) Signup and view all the answers

How does the Integrity Beacon Landing System (IBLS) augment GPS to achieve Category III specifications for aircraft landings?

By using Integrity Beacons (compact, low-power ground-based marker beacon 'pseudolites') and a conventional differential GPS reference station. (E) Signup and view all the answers

On a Trimble 2101 GPS, what is the result of the GPS annunciator lamp flashing?

There is degraded satellite coverage, to the point that the system is operating in 2D mode. (B) Signup and view all the answers

How is vertical dilution of precision (VDOP) specifically affected by satellite position, and what implications does this have for aviation?

High VDOP values create large vertical (altitude) navigation errors; this becomes especially problematic near airports, impacting landing operations. (D) Signup and view all the answers

Flashcards

Space-Based vs. Ground?

Ground-based radio navigation systems have provided coverage for over 50 years.

Low Frequency Transmitters

VLF waves reflect off the ionosphere, broadening coverage.