Fundamentals of Surveying Flashcards

Multi-path errors are most likely to occur in a receiver in which of the following locations?

Answer: Urban area with numerous tall buildings

Explanation: Multi-path errors in GPS occur when satellite signals are reflected off surfaces such as buildings, terrain, or other obstacles before reaching the receiver antenna. In urban areas with tall buildings, there are many surfaces from which signals can reflect, causing the receiver to receive multiple versions of the same signal with slight delays. This can lead to inaccuracies in determining the receiver's position.

Assuming the speed of light to be 186,000 mi/sec and a signal transit time of 92ms, what is the approximate distance from the GPS satellite to the receiver?

Answer: 17k mi

Explanation: To determine the distance 𝑑 from the GPS satellite to the receiver, we use the formula: 𝑑 = Speed of light × Signal transit time Given: *Speed of light = 186,000 miles per second *Signal transit time = 92 milliseconds = 0.092 seconds (since 1 millisecond = 0.001 seconds) Calculate the distance: 𝑑 = 186,000mi/sec × 0.092sec 𝑑 ≈ 17,112 miles Rounded to the nearest thousand miles, the approximate distance from the GPS satellite to the receiver is 17,000 miles. This calculation illustrates how GPS determines distances based on the time it takes for signals to travel from satellites to receivers, using the speed of light as a constant factor.

Using GPS, a point's ellipsoidal elevation is determined to be 592.8 ft. From the GEOID03 model, the geoid separation for that point is -139.4 ft. What is the Orthometric height above the geoid at that point?

Answer: 732 ft

Explanation: To find the Orthometric height (H) above the geoid at a given point, we use the formula: H = Ellipsoidal height − Geoid separation Given: *Ellipsoidal elevation = 592.8 ft *Geoid separation = -139.4 ft (negative indicates below the ellipsoid) Calculate the Orthometric height: H = 592.8 ft − (−139.4 ft) H = 592.8 ft + 139.4 ft H = 732.2 ft Rounding to the nearest whole number, the Orthometric height above the geoid at that point is approximately 732 ft.

Which of the following conditions would be expected with an increasing value for PDOP?

Answer: A decrease in positional accuracy

Explanation: Position Dilution of Precision (PDOP) is a measure of the geometric strength of satellite configurations used to determine a GPS receiver's position. A higher PDOP value indicates poorer satellite geometry, which leads to decreased positional accuracy. Therefore, A decrease in positional accuracy is correct because higher PDOP values result in poorer satellite geometry, leading to decreased accuracy in determining the receiver's position.

The most suitable elevation masks for differential GPS surveys are:

Answer: 10 degrees at the base and 15 at the subordinate station

Explanation: Elevation masks in GPS refer to the minimum angle above the horizon at which satellites are considered for use in position calculations. Differential GPS (DGPS) surveys typically require higher elevation masks to ensure accuracy and reliability of positioning. The base station and the subordinate station (or rover) may have different elevation mask settings depending on their roles and the survey conditions. Therefore, the correct answer is 10 degrees at the base and 15 degrees at the subordinate station, providing adequate satellite visibility and geometric strength for differential GPS surveys, thereby enhancing the accuracy and reliability of survey measurements.

With a base station data collection interval of 2 sec, which of the following would be an acceptable collection rate for a GPS receiver at a subordinate station?

Answer: 4 sec

Explanation: In GPS surveying, especially in differential GPS (DGPS) operations, the subordinate station (or rover) typically needs to collect data at a rate that allows it to synchronize with the base station's data collection interval. The base station collects data at regular intervals to calculate corrections that the subordinate station can use to improve its positional accuracy. 4 sec allows the subordinate station to collect data slightly less frequently than every 2 seconds but still ensures that it captures enough data points to effectively use differential corrections from the base station.

Meridians, or lines of longitude, measure the arc distance (in degrees):

Answer: East and west of the prime meridian

Explanation: Meridians are imaginary lines on the Earth's surface that run from the North Pole to the South Pole and are used to measure longitudinal distances. East and west of the prime meridian correctly describes how meridians measure arc distances on Earth's surface.

A Mercator projection uses which of the following?

Answer: Cylinder

Explanation: The Mercator projection is a cylindrical map projection. The Mercator projection uses a cylindrical surface onto which the Earth's surface is projected. This projection is particularly useful for navigation because it preserves angles, making it suitable for nautical charts, but it distorts size and distance at higher latitudes.

A Lambert projection uses which of the following?

Answer: Cone

Explanation: The Lambert projection is a type of map projection named after Johann Heinrich Lambert, which is used primarily for mapping large regions that are in the middle latitudes. A conic projection is a map projection that projects the Earth's surface onto a cone. While some conic projections exist, the Lambert projection is not specifically based on a cone.

A Lambert conic secant projection uses which of the following?

Answer: One cone that slices the earth at two parallels

Explanation: A Lambert conic secant projection is a specific type of conic projection used in cartography. The Lambert conic secant projection uses a cone that intersects the Earth's surface at two standard parallels (or secant lines). These secant lines are chosen so that the cone touches the Earth's surface at two points along those parallels, minimizing distortion within the region bounded by those parallels.

The mapping angle in a Lambert projection varies with which of the following?

Answer: Latitude

Explanation: The mapping angle in a map projection refers to how angles are preserved or distorted in the process of projecting the Earth's curved surface onto a flat map. The mapping angle in a Lambert projection varies with latitude. The projection is designed such that angles are preserved along lines of latitude (parallels), but the distortion increases as you move away from the standard parallels (secant lines).