1. NGS River/Valley Crossing Procedures
Transportation Research Board – AFB80 Meeting
Minneapolis, MN
August 1, 2017 by
Dave Zenk
NGS Northern Plains Regional Advisor
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2. Why NGS Needed a New Method
Traditional leveling across rivers is impossible.
Traditional leveling across highways or bridges is possible, but DANGEROUS.
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3. Why NGS Needed a New Method
Existing River/Valley Crossing procedures do not meet customers needs.
Existing procedures do not include the use of digital leveling systems.
Required specialized instruments (Zeiss River Crossing Equipment) which are no longer commercially available.
The “Instructions for Ordinary Leveling Instruments” (Fischer level) relies upon an instrument which is no longer commercially available.
NGS customers have a need to conduct this activity and are looking to us for guidance.
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4. Team Members (2014) Kendall Fancher, Team Leader,
Instrumentation Branch Chief
Steve Breidenbach, Charles Geoghegan
Instrumentation Branch
John Ellingson, Dave Zenk,
Advisors in Wisconsin and Minnesota
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5. Outline Review of Historical River/Valley Crossing Procedures
Design of New River Crossing Method
Design of New River Crossing Equipment
Initial Test at NGS Instrumentation Branch Corbin Lab
MNDOT Test Results
Cautionary Statement
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6. Historical Review
Chapter 4 of “NOAA Manual NOS NGS 3 GEODETIC LEVELING”, 2001
Chapter 4 discusses the error theory of River/Valley Crossings and outlines several methods by which such crossings may be conducted.
Zeiss River Crossing Method (1970?) Section 4.3
Fischer Method (1929) Section 4.4
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7. Zeiss River Crossing Equipment
2 identical level instruments each equipped with a rotating wedge device and mounted on a single tripod head.
Sighting to a target column with 2 targets and a height stud.
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8. Zeiss River Crossing Equipment
Rotating Wedge Device allowed line of sight to be angled (not shifted) upward or downward by up to 200 arc-seconds with an accuracy of 0.2 arc-seconds.
By carefully measuring the angular deviations to upper and lower targets and accounting for instrument collimations, one could conduct First Order Class 1 River Crossings up to 1 km or more.
TRB – AFB80 Meeting

9. Fischer Method
The Fischer Level was equipped with a precise tilting screw with which the line of sight could be angled (not shifted) upward or downward by up to 200 arc-seconds with an accuracy of 0.5 arc-seconds.
Similar targets as for Zeiss.
Not recommended for First Order.
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10. Good Results, Slow
The Zeiss Method and Fischer Method each produced good results when all procedures were followed.
Complete field observing routines required about 1 day.
Resulted in only 1 measurement of height difference.
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11. Expected Outcomes for New Method
Design river/valley crossing data collection/analysis procedures and forms which enable our customers to conduct this type of activity, achieving 1st order precision, while using commercially available instrumentation along with specialized equipment readily fabricated at the average machine shop.
Field test new procedures, comparing against a standard (Zeiss river crossing procedure) and report on results.
Publish new river/valley crossing procedures in the form of a technical paper and make available to our customers for use as a viable alternative to current river crossing procedures.
In future revision of NOS-NGS 3 incorporate the new river/valley crossing procedure into the document as a replacement to the existing procedures.
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12. Design of New Method
NGS Instrumentation Branch studied the existing methods and adopted the following guiding principles
Dual simultaneous reciprocal observations
Precise vertical angle measurements
Sighting Targets
Readily available or easily constructed equipment
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13. Design of New Method NGS Instrumentation Branch
Adopted the use of modern digital readout theodolites, to replace the leveling tools and their attachments.
Designed a set of sighting targets which could be locally constructed.
Created a set of field observations and computations procedures.
Conducted an initial test at their Corbin Lab Facility.
Conducted additional field testing.
New Method has been Approved for Bluebooking.
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14. Geometry and Math Side 1 + 45.5” + 58.5” X - 35.0” Y Total Station
1.580
+ 45.5”
0.659
+ 58.5” X
0.511
- 35.0”
Foresight = Y
Total Station
Total Station
Backsight = 0.566
- 42.5”
0.462
0.000
0.000 C D
Elevation Difference = meters
330 meters
2620 meters
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15. Calculate by proportion what would the rod reading have been with a total station angle of 0⁰-00’-00”
(-35.0”)
(+58.5”) – (-35.0”)
(X)
(0.659 – 0.511) =
(-35.0”)
(93.5”)
(X)
(.148) =
Side 1 – backsight rod
X = (0.148) (-35.0” / 93.5”)
X = m
Rod =
Rod = meters
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16. Geometry and Math
Similarly, compute Side 1 Foresight to opposite bank of river.
Elevation Difference = backsight – foresight
Elevation Difference is affected by Earth’s curvature and atmospheric refraction.
Instrument has collimation errors.
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17. Error Control
Simultaneously observe all angles from both sides of river.
Mitigates (or eliminates) effects of curvature and refraction.
Observe all angles with telescope in direct and reversed positions (face 1 / face 2).
Eliminates instrument collimation errors.
Observe multiple sets of angles
Eliminates small random errors of sighting and reading.
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18. Errors Caused by Angular Resolution Limits
River Crossing Wedge & Total Station
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19. Error caused by 0.2” angular error at varying distancesX
0.2”
Distance to Target (in meters)
Error (in meters)
30 m
m = 0
100 m m
300 m m
500 m m
1000 m m
2000 m m
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20. Error caused by 0.5” angular error at varying distancesX
0.5”
Distance to Target (in meters)
Error (in meters)
30 m
m = 0
100 m m
300 m m
500 m m
1000 m m
2000 m m
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21. Error Budget Side 1 Y X Total Station Total Station C D 0.659 0.511
Backsight = 0.566
Foresight =
0.000 C D
Elevation Difference = meters
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22. Error Budget Assume 0.1 mm error in each target height
Assume 0.5 second vertical angle error
Operator error controlled by rejection limit from mean
C+R will be eliminated by dual-simultaneous observations
Compute 30 meter BS and 300 meter FS
Compute 30 meter BS and 1000 meter FS
Compute 30 meter BS and 2000 meter FS
All quantities are added/subtracted so error propagates as square root of sum of squares
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23. Error Budget at 300 meters Backsight error = sum of 4 errors
= sqrt [( ) + ( ) + (02) + (02)]
= m
Foresight error = sum of 4 errors
= sqrt [( ) + ( ) + ( ) + ( )]
= m
dH Error = sqrt [( ) + ( )]
= m
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24. Error Budget at 1000 meters Backsight error = sum of 4 errors
= sqrt [( ) + ( ) + (02) + (02)]
= m
Foresight error = sum of 4 errors
= sqrt [( ) + ( ) + ( ) + ( )]
= m
dH Error = sqrt [( ) + ( )]
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25. Error Budget at 2000 meters Backsight error = sum of 4 errors
= sqrt [( ) + ( ) + (02) + (02)]
= m
Foresight error = sum of 4 errors
= sqrt [( ) + ( ) + ( ) + ( )]
= m
dH Error = sqrt [( ) + ( )]
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26. Error Budget
Operator error = inability to sight the target, read the instrument, and record the angle.
For digital theodolites the error is in the sighting, since the instrument reads the angle.
Transcription errors are eliminated by recording the angles to a data collector.
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27. Error Budget
If operator can sight target within σ = 2”, then if 16 sets are turned:
σmean = 2” / [sqrt(16)]
σmean = 0.5”
If operator can sight target within σ = 1”, then if 4 sets are turned:
σmean = 1” / [sqrt(4)]
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28. Combined Effect of C+R Assume a 300 meter imbalance of BS and FS
300 meters = km = 984 feet = miles
Combined (c+r) Equations (from textbooks):
c+r = M2
M is distance in miles
c+r = (0.186)2 = feet
c+r = F2
F is distance in thousands of feet
c+r = (0.984)2 = feet
c+r = K2
K is distance in kilometers
c+r = (0.300)2 = meters
c+r = difference between “line of sight” and “level surface”.
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29. Combined Effect of C+R
So, for a 300 meters imbalance in BS and FS distances, we should expect a measured difference in height to be affected by meters in each direction. Example – consider known BM “A” is meters, and known BM “B” is meters.
FS = 2.006
c+r = 0.006
c+r = difference between “line of sight” and “level surface”.
BS =1.000
c+r = 0 A B
99.000
97.994
Level surface
measured dH = meters
BS = 2.000
c+r = 0
FS =1.006
c+r = 0.006 A B
98.994
98.000
measured dH = meters
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30. Overall Leveling / River Crossing Diagram
River bank
River bank J A H G D B C I
300 m
40 m
40 m E F
All lines are double-run leveling
River
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31. Limits and Tolerances Limits and Tolerances Examination of:
“FGCS Specifications and Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems” and
“Standards and Specifications for Geodetic Control Networks”
shows several limits and tolerances that could be applied to the new procedure, including:
Least count of theodolite
Number of repeat measurements
Rejection limits from mean
Loop closure
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32. Limits and Tolerances
Rejection Limits from Mean by Order/Class of Leveling mm
Order/Class
Limit (mm)
1/1
(3mm ) * sqrt (km)
1/2
(4mm ) * sqrt (km)
2/1
(6mm ) * sqrt (km)
2/2
(8mm ) * sqrt (km) 3
(12mm ) * sqrt (km) KM
Note: at least 2mm will be tolerated for shorter lines
See Table 3.1 on page 3-7 of NOAA Manual NOS NGS 3 Geodetic Leveling
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33. Limits and Tolerances Loop Closures by Order/Class of Leveling
Closure (mm)
1/1
(4mm ) * sqrt (km)
1/2
(5mm ) * sqrt (km)
2/1
(6mm ) * sqrt (km)
2/2
(8mm ) * sqrt (km) 3
(12mm ) * sqrt (km)
Note: at least 4mm will be tolerated for shorter loops
See Table 3.1 on page 3-7 of NOAA Manual NOS NGS 3 Geodetic Leveling
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34. Limits and Tolerances
The least count (L.C.) and standard deviation (S.D.) of the optical total station must be capable of delivering the tolerances as specified for the Order and Class of the leveling in which the crossing will be included (see Table 3-1).
Example:
What least count and standard deviation would be needed for a 290 meter crossing in a second order, class 1 leveling survey?
Table 3-1 requires 6mm x √K
The total tolerance for error would be 6 x √.290 = 3.23 mm
The error occurs due to angles to bottom and top targets, so each error can be ½ of the total error. Therefore, each angle must be measured to achieve 1.6 mm of error.
The angular error β = tan­-1(0.0016/290) = 1.1 seconds
Because each angle is to be measured 8 times, then the instrumental precision may be estimated from the following equation: σmean = σo /√n
1.1 seconds = σ0/√8
σo = 1.1 x √8
σo = 3.1 seconds
The required standard deviation of the measured angles should therefore be +/- 3.1 seconds.
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35. Limits and Tolerances
Required Standard Deviation (S.D.) by Order/Class and Width
Crossing Width (meters)
Item
1/1
1/2
2/1
2/2 3
S.D. seconds
1.4
2.2
3.1
3.9
6.2
1.1
2.3
2.8
4.2
0.8
1.7
3.4
0.7
2.0
0.6
2.5
Recommended Least Count (L.C.) by Order/Class and Width
Crossing Width (meters)
Item
1/1
1/2
2/1
2/2 3
L.C. seconds
0.1
0.5
1.0
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36. Corbin Baseline Test Setup 2 marks 300 meters apart
OBSERVATORY and MITCHELL
Ran levels between them
elevation difference = m
Setup theodolites and observed 20 sets of D+R angles on target sets.
Computed elevation differences from angular measurements
OBSERVATORY to MITCHELL = m
compared to leveling difference = meters
See diagram and tables to follow
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37. Forward Run from Side A to Side B
Total Station K
OBSERVATORY
MITCHELL
T1 =
T2 = J M N n k j m
Height Diff = ?
SIDE B
SIDE A
Forward Run from Side A to Side B
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38. Backward Run from Side B to Side A
Total Station K
OBSERVATORY
MITCHELL
T1 =
T2 = J M N n k j m
Height Diff = ?
SIDE B
SIDE A
Backward Run from Side B to Side A
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39. Average Height Difference from OBSERVATORY to MITCHELL = 1.01298 m
Forward Run from Side A to Side B
OBSERVATORY to MITCHELL
Compute vertical angles j, k , m ,n
from the zenith angles.
Compute distances J, K, M, N
by proportion.
Angles (for Set 15)
j = 0°-52’-48.2”
k = 4°-17’-46.0”
m = 0°-05’-05.8”
n = 0°-01’-21.4”
Distances (for Set 15)
J = (j ) / (j + k) = m
K = (k) / (j + k) = m
M = (m) / (m + n) = m
N = (n) / (m + n) = m
Plate-to-Plate = J – N = m
Height Diff = T1 + J – N – T2 = m
Backward Run from Side B to Side A
MITCHELL to OBSERVATORY
Compute vertical angles j, k , m ,n
from the zenith angles.
Compute distances J, K, M, N
by proportion.
Angles (for Set 15)
j = 0°-05’-10.8”
k = 0°-01’-14.0”
m = 0°-54’-40.0”
n = 4°-09’-01.6”
Distances (for Set 15)
J = (j ) / (j + k) = m
K = (k) / (j + k) = m
M = (m) / (m + n) = m
N = (n) / (m + n) = m
Plate-to-Plate = N – J = m
Height Diff = T2 + N – J – T1 = m
Average Height Difference from OBSERVATORY to MITCHELL = m
Leveled Height Difference = m
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40. General Recon Recommendations
Careful Recon and Setup will make the River Crossing easier.
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41. River Crossing Diagram
River bank
River bank
1002
1003
1005
1000
1001
1004
300 m
All lines are double-run leveling
River
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42. General Recon / Setup Pointers
SIDE A
SIDE B
General Recon / Setup Pointers
Lines of Sight as high as practical
Total Station
LOWER TARGET A to LOWER TARGET B should be about cm
Total Station
Height Diff = ?
MITCHELL
OBSERVATORY
Height Diff should be about cm
River
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43. Target Construction NGS has adopted a recommended target
MNDOT has modified it for local construction and materials
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44. NGS Adopted Targets
12” 6”
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45. MNDOT Adopted Targets Cut at 3” width
Available for $12 each at FastSigns in Minnetonka, MN or nationwide
Dibond material – metal faces sandwiched on 1/16” plastic center. Durable in outdoor exposure. Available in any color combinations.
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46. MNDOT Adopted Targets Mount 2 Targets per column
Permanently mount the 3” piece
80/20 Inc. T-Slotted Extrusions Clear Anodized Aluminum Alloy Framing
1530-LITE-97
1.5” x 3.0” x 72” $125
Add angle clip to back of 9” piece
and clamp on if needed
Also available from Graingers, Inc.
catalog pages
1.5” x 3” Mfg #1530
Grainger # 5JTC1 72” $123.40
Mount 2 Targets per column
TRB – AFB80 Meeting

47. MNDOT Adopted Targets Hilman #11356 48” length $6.50 at Lowe’s
T-Nut & Flanged Button Head Socket Cap Screw, Pkg. of 15. $15.98 at Grainger.
Grainger #2RCT7
80/20 Inc #
Angle Clip – 1.5” x 1.5” x 5.5” with 2 holes 0.375” diameter. Corners to be radiused and edges smoothed for safe handling.
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48. MNDOT Adopted Targets Measured Separation
2” x 3.5” steel top cap (with 5/8” x 11 threaded hole for all target columns)
Measured Separation
2 permanently mounted retro-reflectors on reverse side of target columns (needed only if researching robotic operation)
Measured Separation
2” x 3.5” steel bottom cap
(with 5/8” x 11 threaded hole for short target columns)
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49. MNDOT Adopted Targets
Make a hole or a slot in target column. Insert thermometer probe cable within center hollow. Protect thermometer probe cable from abrasion with foam wrap.
Springfield 90817
$9.45 at Amazon
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50. MNDOT Adopted Targets
Leveling Rod Level
SECO #
Heads-Up Rod Level
SECO #
Standard Rod Level
SECO #
Need to have one well-adjusted rod leveling device per target column
Post Level
JOHNSON #175-O
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51. MNDOT Adopted Targets Need 2 Tall Target Sets and 2 Short Target Sets
Short Target mounts on Tripod
Tall Target rests directly on benchmark
Need 2 Tall Target Sets and 2 Short Target Sets
Total Cost about $1750
Target Columns $450
Arrow Targets $100
Retro Prisms $1200
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52. Bottom of Short Target Rod
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53. Bottom of Tall Target Rod
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54. Top of Target Rod
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55. Prism Attachment
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56. Thermometer Attachment
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57. Measuring Target Separations
Zero-in on target by carefully raising and lowering the level instrument. Read adjacent bar code rod. Repeat several times to get average. Measure both targets and bottom plate. Subtract to get target separations.
Bar-code level and rod ?
Note: For this method, the optical line-of-sight need not be adjusted to exactly match the digital line of sight.
Example Readings Upper Target: m m m
Average = m
Example Readings Lower Target: m m m
Average = m
Target Separation = m
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58. Measuring Target Separations
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59. Adjust Optical/Digital Line of Sight
Setup 1 – Optically sight an exact bottom or top edge of a specific stripe or block on the digital bar-code rod. Obtain digital reading.
Setup 2 – Invert the rod. Optically sight the same exact edge of the specific stripe or block on the digital bar-code rod. Obtain a second digital reading.
Calculate the discrepancy by subtracting the digital rod readings. Any discrepancy should be adjusted by moving the crosshair reticle up or down slightly and repeating the test.
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60. Correct for Temperature
DL = L (α) (T2 – T1)
L = length
Aluminum α = m/m C
T1 = standard temperature (C)
T2 = actual temperature (C)
DL = change in length (m)
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61. Correct for Temperature
Example:
Length = m at 80⁰F (27⁰C)
Correct to length at 68⁰F (20⁰C)
DL = ( ) ( )
DL = m
Length = m at 68⁰F (20⁰C)
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62. Detailed Notes for MNDOT Rods
TALL WHITE ROD
UPPER TARGET
LOWER TARGET
BOTTOM PLATE
AVERAGE
UPPER TO LOWER =
LOWER TO BOTTOM =
Corrected to 68F
NOTE:
Rods measured at 80 degrees F (27C)
Corrected to 68 degrees F (20C)
Coeff of Expansion for Aluminum = m/m C
TALL WHITE ROD
UPPER PRISM
LOWER PRISM
BOTTOM PLATE
1.7056
AVERAGE
UPPER TO LOWER =
LOWER TO BOTTOM =
Corrected to 68F
NOTE:
Rods measured at 80 degrees F (27C)
Corrected to 68 degrees F (20C)
Coeff of Expansion for Aluminum = m/m C
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63. Detailed Notes for MNDOT Rods
TALL YELLOW ROD
UPPER TARGET
LOWER TARGET
BOTTOM PLATE
AVERAGE
UPPER TO LOWER =
LOWER TO BOTTOM =
Corrected to 68F
NOTE:
Rods measured at 80 degrees F (27C)
Corrected to 68 degrees F (20C)
Coeff of Expansion for Aluminum = m/m C
TALL YELLOW ROD
UPPER PRISM
LOWER PRISM
BOTTOM PLATE
0.6622
0.6623
AVERAGE
UPPER TO LOWER =
LOWER TO BOTTOM =
Corrected to 68F
NOTE:
Rods measured at 80 degrees F (27C)
Corrected to 68 degrees F (20C)
Coeff of Expansion for Aluminum = m/m C
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64. Target Separations @68F Arrow Targets Tall White Rod Yellow Rod Short
Upper Target m m
n/a
Lower Target m m
Bottom Plate
Prism Targets
Tall
White Rod
Yellow Rod
Short
Upper Prism m m
n/a
Lower Prism m m
Bottom Plate
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65. MNDOT River Crossing Validation
Hastings Bridge Area
Plan for new BM’s (July 2014)
Conduct leveling (July 2014)
Conduct 3 River Crossings (July- August 2014)
2 across the Mississippi River
1 along the south shore (verify w/ double-run leveling)
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66. Hastings Bridge Area Leveling
River bank
River bank
Control Leveling Plan
1001 to 1003 double-run leveling on same bank of river
1003 to 1007 double-run leveling across bridge
1002
River Crossings Plan
1002 to 1008 use new River Crossing Procedure
1008 to 1004 use new River Crossing Procedure
1004 to 1002 use new River Crossing Procedure
1001
300 m
1008
1007
Verification Plan
Summation of 3 River Crossings should = m
Comparison of River Crossings to 2/1 Leveling
1004
1003
River
1006
1005
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67. Hastings Bridge Crossings
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68. Hastings Bridge Crossings
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69. River Crossing Point Naming
There are measurements on 2 benchmarks, 2 instruments, 2 rods, 2 setups, 4 targets, and 4 prisms to manage.
Need to create a reasonable method to keep all the data correct.
A sketch with filenames and point numbers is needed.
Avoid 1000-series numbers (reserved for regular level line bench marks).
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70. River Crossing Point Naming
Yellow Rod
White Rod
Setup # 1 – Triangle Targets
2000 low series
3000 low series
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71. River Crossing Point Naming
Setup # 2 – Triangle Targets
2000 high series
3000 high series
Yellow Rod
White Rod
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72. River Crossing Observations
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73. Effectiveness of Dual-Simultaneous Observations
If the air refracts the forward sight down by m, it also refracts the backward sight down by m.
The effect on the height differences is equal, but opposite.
Therefore, the average eliminates the error.
A plot of the individual results should show the effect >
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74. Effectiveness of Dual-Simultaneous Observations
This plot is messy, but it shows that when the forward sight (red) increases, the backward sight (blue) decreases a similar amount. The average (green) line is shown.
Ideally, these plots should be mirror-flipped images like the faces.
But not every sighting is perfect.
(this is actual data from Hastings River Crossing August 13, 2014)
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75. Example Data from Hastings River Crossing
YELLOW Setup 1
WHITE Setup 1
Diff = 2x(c+r)
Average Ht Diff
Averages
Note: C+R formula predicts meters,
Therefore expect 2 x = meters
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76. Example Data from Hastings River Crossing
YELLOW Setup 1
WHITE Setup 1
Check for Outliers
Average Ht Diff
Diff = 2x(c+r)
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77. Example Data from Hastings River Crossing
Lower Target to Lower Target
Forward
Backward
Ave
Run 1
Run 2
diff
Bench Mark to Bench Mark
Allowable 1/1
3mm (sqrt KM) =
DISTANCES (m)
Setup 1
Setup 2
Yellow BS
12.880
Yellow FS
White BS
20.728
20.745
White FS
RUNNING LENGTHS
Yellow
White
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78. Hastings Bridge Crossing Results
River Crossing 3 ( )
Forward
Backward
Average
Run 1
Run 2
diff
Using Arrow Targets
Manual pointings
TBM 2
454 meters
BRENNA 2014
River Crossing 2 ( )
River
River Crossing 1 ( )
408 meters
Forward
Backward
Average
Run 1
Run 2
diff
Forward
Backward
Average
Run 1
Run 2
diff
450 meters
2/1 Leveling
TBM 1
2/1 Leveling
Forward
Backward
Average
Run 1
Run 2
Forward
Backward
Average
Run 1 *
Run 2
0.4460
Loop Closure
Allowable 1/1 = 3mm(√1.312 km) = m
Actual = m OK
Allowable 1/1 = 3mm(√.450km) = m
Actual = m OK
Allowable 1/1 = 3mm(√2.572 km) = m
Actual = m OK
Note: * = suspect data
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79. Hastings Bridge Crossing Results
Single prism on
FIXED Height Tripods and
automated rounds
Using Prism Targets
Autolock pointings
TBM 2
River
River Crossing 1 ( )
River Crossing 1 ( )
Forward
Backward
Average
Run 1
0.4298
0.4474
Run 2
Forward
Backward
Average
Run 1
0.4301
0.4465
Run 2
450 meters
TBM 1
2/1 Leveling
2/1 Leveling
Forward
Backward
Average
Run 1 * *
Run 2
0.4460
Forward
Backward
Average
Run 1 * *
Run 2
0.4460
Allowable 1/1 = 3mm(√.450km) = m
Actual = m OK
Allowable 1/1 = 3mm(√.450km) = m
Actual = m OK
Note: * = suspect data
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80. Buffalo Water Crossing
Buffalo Lake
ROCK
Distance = 2308 meters (1.43 miles)
All data were measured on January 22, 2015
ROD
Method
Run
DELTA HT
DIFF
AVERAGE
Diff from Leveling
Time
LEVELING F R m m m m m
8 hours
ARROWS m m m m m
1 hour
PRISMS m m m m m
ROUNDS m m m m
15 minutes
ALLOWABLE (1/1)
+/ m

81. Lake Calhoun Water Crossing
Distance = 1497 meters (0.93 miles)
All data were measured on April 29, 2015
Method
Forward
Reverse
Difference
Allowable (1/1)
Average
Arrows m m m m m
Prisms m m m m
Rounds m
---
Levelling m m m m

82. Dresbach Bridge I-90 Crossing
Distance = 480 meters (0.30 miles)
All data were measured on June 28, 2015
Method
Forward
Reverse
Difference
Allowable (1/1)
Average
Arrows
0.9477m m m m m
Prisms m m m m
Rounds m m m
Levelling
- - -

83. Mendota HWY 55 Crossing Method Forward Reverse Difference
Distance = 1832 meters (1.14 miles)
All data were measured on April 18, 2016
Method
Forward
Reverse
Difference
Allowable (1/1)
Average
Arrows
0.2294m
0.2252m
0.0041m
0.2273m
Prisms
---
Rounds
0.226 m
0.219 m *
Levelling
* - noted as incorrect due to field error

84. St Paul HWY 52 Crossing Method Forward Reverse Difference
All data were measured on June 22, 2016
Distance = 476 meters (0.30 miles)
Method
Forward
Reverse
Difference
Allowable (1/1)
Average
Arrows m m
0.0001m
0.0021m
Prisms
---
Rounds m
Levelling

85. The Automated Rounds Method
Measure zenith angles and slope distances to single prism on FIXED Height Tripods or Rods and automated rounds
TBM 1
Need flat-bottomed shoe
River
TBM 2
TRB – AFB80 Meeting

86. Recent Results – Automated Rounds
+ 2 σ
- 2 σ
Count = 48
AVERAGE =
meters
SDEV (1 σ) =
meters
June 21, 2017
St. Paul, MN
Hwy 52 Crossing
“known” dH = meters
48 height differences measured in 2 hours
TRB – AFB80 Meeting

87. Cautionary Statements
The new total station-based procedure (ARROWS) has been officially adopted and approved by NGS.
Users may submit results of surveys using these (ARROWS) procedures to NGS as part of Bluebook surveys.
Automated Rounds NOT yet approved by NGS for submission as part of Bluebook surveys.
TRB – AFB80 Meeting

88. The End
Questions
TRB – AFB80 Meeting