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