Surveying a Level Loop Level Loop or Closed

Surveying a Level Loop

Level Loop (or Closed Circuit) Instrument location (TYP) FS 4. 26 ft t f 3 1 7. S = 1 B Elev. 100. 00 ft Turning Point (TYP)

Closed Circuit or Level Loop (+) BS PT AUTO LEVEL READINGS (-) FS HI 7. 13 BM STADIA TP-1 TOP/BOT DIST STADIA /Angle ELEV 107. 13 X 100. 00 4. 26 102. 87 �

Level Loop (or Closed Circuit) ft 5 7 1. = BS Elev. 100. 00 ft FS = 2. 99 f t 2 Turning Point Elev. 102. 87

Closed Circuit or Level Loop (+) BS PT AUTO LEVEL READINGS (-) FS HI STADIA TOP/BOT DIST STADIA /Angle ELEV 7. 13 107. 13 X 100. 00 TP-1 1. 75 104. 62 4. 26 102. 87 TBM 2. 99 101. 63 � BM

Level Loop BS = 5. 62 ft (or Closed Circuit) 3 5 . 12 ft = FS BS = 0. 94 ft 4 6. 0 8 ft 9. 7 = BS = 9 FS t 4 f 3. 3 = FS 1 f t Elev. 100. 00 ft Elev. 101. 63 ft

Closed Circuit or Level Loop (+) BS PT AUTO LEVEL READINGS HI (-) FS STADIA TOP/BOT DIST STADIA /Angle ELEV 7. 13 107. 13 X 100. 00 TP-1 1. 75 104. 62 4. 26 102. 87 TBM 5. 62 107. 25 2. 99 101. 63 � TP-2 0. 94 102. 18 6. 01 TP-3 9. 12 103. 32 7. 98 POR BM 3. 34 101. 24 94. 20 99. 98

Closure Error The difference between a measured or calculated elevation and the true or established elevation. Closure Error = Final Elev. – Initial Elev.

Closed Circuit or Level Loop (+) BS PT AUTO LEVEL READINGS HI (-) FS STADIA TOP/BOT DIST STADIA /Angle ELEV 7. 13 107. 13 X 100. 00 TP-1 1. 75 104. 62 4. 26 102. 87 TBM 5. 62 107. 25 2. 99 101. 63 � TP-2 0. 94 102. 18 6. 01 TP-3 9. 12 103. 32 7. 98 BM POR 101. 24 94. 20 3. 34 99. 98 - 100. 00 CLOSURE ERROR = - 0. 02 ft

Allowable Error • The allowable error depends on the type and purpose of the surveying. • In this class, we will use

Closed Circuit or Level Loop (+) BS PT AUTO LEVEL READINGS (-) FS HI BM 7. 13 107. 13 X TP-1 1. 75 104. 62 4. 26 107. 25 2. 99 TBM TP-2 TP-3 POR 5. 62 0. 94 9. 12 102. 18 103. 32 6. 01 7. 98 STADIA TOP/BOT DIST STADIA /Angle ELEV 100. 00 BS 8. 63 / 5. 63 102. 87 FS 5. 69 / 2. 83 BS 3. 15 / 0. 25 101. 63 FS 4. 44 / 1. 54 BS 6. 67 /4. 57 101. 24 FS 7. 08 / 4. 94 BS 1. 84 / 0. 04 94. 20 FS 8. 94 / 7. 02 BS 10. 42 / 7. 82 300 ft 286 ft 290 ft 210 ft 214 ft 180 ft 192 ft 260 ft 3. 34 99. 98 FS 4. 58 / 2. 10 248 ft - 100. 00 TOTAL = 2470 ft CLOSURE ERROR = - 0. 02 ft

Level Loop (or Closed Circuit) Instrument location (TYP) ft 0 29 3 f 00 210 ft 286 ft 290 ft t 3 5 19 2 ft 180 ft 4 21 4 t 8 f 24 ft Elev. 100. 00 ft 260 ft Elev. 101. 63 ft

Allowable Error Survey data is acceptable

Reducing Errors • Check that bubble is centered for EVERY rod reading. • Keep the rod plumb during each reading. • Establish equal BS and FS reading distances. – Equal reading distances will cancel out any error caused by the line of sight not being parallel with the axis of the bubble tube. – This is not always possible due to terrain.

Common Errors • • Faulty rod reading (verify reading) Rod not fully extended (high reading) Tripod movement during reading Confusion between recording BS and FS entries in the field book

Can You Top That? Courtesy NOAA Photo Library http: //www. photolib. noaa. gov/htmls/theb 1809. htm According to NOAA, this survey party made 329 setups in 7 hours and 55 minutes working in an area of extreme grades in the Western United States in 1934.

Image Sources National Oceanographic and Atmospheric Administration Photo Library http: //www. photolib. noaa. gov/cgs/marks 1. html