Fundamentals of Surveying (FS) Practice Exam

Which elevation masks are considered most suitable for differential GPS surveys?

1. 5° at the base and subordinate station

2. 10° at the base and subordinate station

3. 10° at the base and 15° at the subordinate station

4. 15° at the base and 10° at the subordinate station

The correct answer is: 10° at the base and 15° at the subordinate station

In differential GPS (DGPS) surveys, elevation masks play a crucial role in ensuring accurate positioning by determining the minimum angle at which satellites should be used to calculate positions. Elevation masks are designed to avoid signals from low-elevation satellites that may be affected by atmospheric conditions, obstacles, or multi-path effects, which can degrade the quality of the GPS signal. The choice of having a 10° elevation mask at the base station and a 15° mask at the subordinate station is particularly effective. A lower mask angle at the base station allows for more satellites to be utilized, enhancing satellite geometry and providing a more robust solution. The 15° mask at the subordinate station filters out even more low-elevation signals, further refining accuracy and reducing potential errors. This combination helps balance the need for high-quality signal reception while protecting the survey from the interference or inaccuracies that can be introduced by lower elevation satellites. Therefore, this response is considered most suitable for ensuring optimal conditions in differential GPS surveying.