FUNDAMENTAL SURVEYING Leveling & Differential Leveling 2

Question 1

What is the allowable closure for third-order leveling per NGS specifications (in feet, where M = miles)?

Accepted Answer

0.035 sqrt M

Answer

NGS third-order leveling allows a closure of 0.035 sqrt(M) feet, where M is the total distance leveled in miles.

Question 2

Curvature and refraction combined correction (C&R) in leveling is approximately how many feet per 1,000 ft of sight distance?

Accepted Answer

0.0239 ft

Answer

The combined curvature and refraction correction is approximately 0.0239F squared feet where F is sight distance in thousands of feet, about 0.024 ft per 1,000 ft.

Question 3

What is the purpose of balancing backsight and foresight distances in differential leveling?

Accepted Answer

To cancel out errors from instrument mis-leveling and curvature/refraction

Answer

Equal BS and FS distances ensure that any small collimation error and curvature/refraction effects cancel out, as they affect both readings equally.

Question 4

A level loop starts and ends at BM-A (elevation 100.000 ft). The computed closing elevation is 100.042 ft. What is the closure error?

Accepted Answer

+0.042 ft

Answer

Closure error = computed final elevation minus known starting elevation = 100.042 minus 100.000 = +0.042 ft.

Question 5

What is 'reciprocal leveling' used for?

Accepted Answer

Accurately determining elevation differences across wide obstacles like rivers

Answer

Reciprocal leveling averages observations taken from both sides of an obstacle (e.g., a river) to eliminate curvature, refraction, and instrument errors.

FUNDAMENTAL SURVEYING Practice Test

FUNDAMENTAL SURVEYING Practice Test

FUNDAMENTAL SURVEYING Leveling & Differential Leveling 2