Profile and Differential Leveling
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Transcript of Profile and Differential Leveling
Profile and Differential Leveling
AGME 1613Fundamentals of AST
Objectives
• Define differential and profile leveling, and explain the purpose(s) and agricultural applications of each.
• Identify and correctly set-up and use leveling equipment.
• Properly record leveling field notes and perform error checks for differential and profile leveling surveys.
• Complete differential and profile leveling surveys.
Leveling Definition and Types
• A surveying procedure used to determine the elevation of points on the Earth’s surface.
– Differential Leveling
– Profile Leveling
Differential LevelingPurpose is to determine the difference in elevation between two (or more) points on the Earth’s surface.
A
B
Difference?
Where is Differential Leveling Used?
• Determining field slope (conservation plans, soil loss prediction, etc.).
• Laying out and checking drainage ditches, waterways, tile drainage systems, etc.
• “Cut-and-fill” requirements for building foundations.
• Establish new “benchmarks” that have elevations tied in with existing benchmarks.
Profile Leveling
A
B
Purpose is to describe the elevation at selected points on the Earth’s surface.
X
XX
X
X
X X X
X X
Where is Profile Leveling Used?
• Developing field “contour maps.”
• Designing and checking grade for drainage ditches and waterways.
• Laying out farm ponds.
• Road and highway construction.
Leveling Equipment:The Engineer’s Level
• Telescope with “crosshairs.”• Base plate – attaches level to
tripod.• Leveling screws – allows
user to establish a “level line of sight.”
• Level bubble – Instrument is level when bubble is inside target.
• Focusing knob
Leveling Equipment: Tripod and Leveling Rod
Reading the Leveling Rod
Feet
Tenths (.10) of a foot
Hundredths (.01) of a foot
6
1
.01.02
.03.04
.05.06
.07.08
.09.10
6.00-ft.
Reading the Leveling Rod
Crosshair
Feet = 6
Tenths = .0
Hundredths = .09
Reading = 6.09 ft.
Reading the Leveling Rod
3
Direct Differential Leveling
A
B
6.45
“What is the difference in elevation between two points,
Where both points can be “shot” from the same location?”
Direct Differential Leveling
A
B
3.21
Direct Differential Leveling
• Difference in Elevation – Rod reading at A = 6.45– Rod reading at B = 3.21
Difference in elevation = 3.24-ft
A
B
-
Which point is higher, A or B?
Leveling Terms
• Station (STA)
• Benchmark (BM)
• Backsight (BS)
• Height of Instrument (HI)
• Foresight (FS)
• Elevation (ELEV)
Leveling Terms
• Station (STA)– Point where the rod is placed for a
reading – Stations typically use a “distance-
numbering” identification system:• STA 0 + 00 = 0 hundred feet + 0 feet• STA 2 +75 = two hundred feet + 75 feet• STA 5 + 05 =?????????
Leveling Terms
• Backsight– A rod reading taken on a point of
known elevation:• BM• TBM• Turning Point (TP)
Leveling Terms• Benchmark (BM)
– A point of known elevation used as a reference point in a leveling survey.
– A BM has a precisely known elevation above “mean sea level.”
– Established by a variety of government agencies.
• Temporary Benchmark (TBM) – Point of “assumed” elevation. Commonly used in “on-farm,” local surveys.
Leveling Terms
• Height of Instrument (HI)– Height (elevation) of the level’s line of
sight.
• HI = BS + Known Elevation
Determining HI
BM-1
Elev = 100.00 ft.
4.35
HI = Elev + BS
HI = 100.00 ft + 4.35 ft = 104.35 ft
Leveling Terms
• Foresight (FS)– Rod reading taken on a point of unknown
elevation
• HI – FS = Elev
Determining Elevation
HI = 104.35 ft 6.35
Elev = HI - FS
Elev = 104.35 ft. – 6.35 ft. = 98.00 ft.
Leveling Terms
• Elevation (ELEV)– Vertical distance above “mean sea level”
of a point on the earth’s surface.– Depending on purpose of survey, may be
determined to nearest:.1 –ft.01 – ft..001 –ft.
Differential Leveling Field Notes
STA BS HI FS ELEV Dist.
Differential Leveling
BM-1
TBM-1
3.21
Elev = 1225.50 ft.
Differential Leveling
BM-1
TBM-1
3.01
TP-1
Differential Leveling
BM-1
TBM-1
6.04
TP-1
Differential Leveling
BM-1
TBM-1
0.28
Differential Leveling
BM-1
TBM-1
6.45
Differential Leveling
BM-1
TBM-1
TP-2
10.98
Differential Leveling
BM-1
TBM-1
TP-2
3.95
Differential Leveling
BM-1
TBM-1
TP-2
5.36
Error of Closure
• Difference in the “beginning” and “ending” elevation of a known point.
• All surveys will have error.
• The question is, “How much error can we tolerate in our survey?”
Error Check
• Mathematical Error CheckError of closure = |SBS - SFS|
• Allowable Error Check– Depends on purpose of the survey– Maximum feet of error based on distance
AE = 0.10 √ M
Profile Leveling Field Notes
STA BS HI FS ELEV
Simulated Profile Survey
TBM-A
4
3
5
(Elev = 100.00)
2
1
3
STA. 0+00
9
5
STA. 1+00
STA. 1+35
3
46
STA. 2+00
3
2
2
STA. 2+00
9
8
7
STA. 2+75
3
40
STA. 2+95
1
20
2
1
STA. 2+95
8
912