GPS Quiz1: Understanding GPS Precision and Accuracy, Quizzes of Earth Sciences

Download GPS Quiz1: Understanding GPS Precision and Accuracy and more Quizzes Earth Sciences in PDF only on Docsity! SUR 3501 QUIZ1 Answer all questions on a separate sheet of paper.1 1. What does the above situation indicate about the precision and accuracy of the GPS observations? Precision is low because points are scattered. Accuracy in Fig 1b indicates a possible bias/systematic error [2] 2. Provide two possible reasons why Figure 1b is not similar to Figure 1a. Fig 1a is centered on the mean therefore points will always surround it on all sides. Fig 1b is centered on an independently determined and more accurate coordinate value and points will not surround the point if there is a systematic error. [4] 3. Why would you expect GPS point positioning to be less accurate than a differentially corrected position? Point positioning is affected by clock, orbital and atmospheric errors. [2] 4. Why is it important to use the same prism in an EDM calibration? Because every prism has potentially a different error due to the optical center of the prism nor being coincident with the plumb line. [2] 5. Why is the first velocity correction necessary in EDM measurements? EDM is standardized at a specific reference refractive index. Because this RI is a function of temperature, atmospheric pressure and humidity, it will cause errors when these atmospheric factors vary. [3] 6. If an EDM accuracy is stated as 5mm + 10ppm, what error would you expect over a distance of 1,000 meters? Error (1,000) = 5mm + 10 (1,000/1,000,000) = 5.01 mm [2] 7. What is a Nomogram? A chart that show atmospheric corrections in ppm as a function of temperature and pressure. [2] 8. Explain why (purpose) a RINEX format was developed in GPS. To allow data to be used from different makes of GPS. Since each of the major GPS’ have their own native format RINEX allows users to mix different rover and base stations (incl. CORS) receivers. (e.g. Trimble and Leica) [2] 1 S = SQRT[ Σ (vi2 ) / (n-1)] Figure 1a. GPS positions compared to mean (shown at intersection of graph) Figure 1b. GPS positions compared to known value (shown at intersection of graph)