lab 1: basic surveying techniques model answersweb.unbc.ca/~cjackson/geog_210/field...

Lab 1: Breaking Tape Surveying Method Model Answers GEOG 210, 2017

1

Lab 1: BASIC SURVEYING TECHNIQUES MODEL ANSWERS Total Marks: (40) Use this marking scheme to evaluate your own answers if you wish.

Answer Components based on Lab Instructions, Questions & Assignment Requirements

Lab instructions 1 to 7 indicate how to record Table 1 data and construct your graph. Below are comments that should help you determine if your answers are correct. The numbers below match those used in the lab instructions.

5. Each person is required to turn in a complete Table 1 data sheet. (10 marks)

See Table 1, (following). On Table 1 we expect you to report the:

Location you started from - either University Parking Lot B (for those working top-down), or University Way (for those working bottom-up)

Each team member’s names - first and last

Date including year, start & end times, weather, and light /visibility conditions

Recorded A, B, and C values for each measurement in meters

Comments reporting the locations of specific errors, changes in conditions, or equipment issues. Errors include human, method, and/or instrument errors. Your comments should clearly describe any relevant observations as they happened. (If you forgot to record comments, rather than making them up afterwards or copying those in this answer key, indicate on Table 1 that you forgot to do this. If there were no comments, indicate this instead. This clarifies omission from instances of not having any comments. Never recreate data after completing measurements. )

Use Model Answers to determine if your methods and thinking processes are correct.

Do not expect your values to match the measurements in this answer key. If you have an error, DO NOT REPLACE YOUR MEASURMENTS WITH ANSWER KEY VALUES. Instead, correct your mistake by re-doing calculations using your own measurements, or rethinking your answers so they incorporate corrections. If you do not understand something in this answer key, clarify the issue with your lab instructor.

Yellow highlighted information is required in your work, non-highlighted text should be read; generally it adds deeper explanation or detail but it is not required in your answer. Measurements vary widely between survey groups, but within each group, the data and profile plots should be identical.

Assignment Format: Follow the question order. Table 1 should be the first page, followed by your longitudinal profile (graph), and then your answer to question 8.

To enter the bonus mark contest: Before turning in your assignment for the second time, ensure your group’s total distance, total elevation change, and lowest elevation value are the same.


2

6. Your topographic profile is based on instructions from lab instruction 6. (10 marks) The following graphs show the required information but for clarity, we have split the

answers over two graphs (both with the same scale, but one for slope change points and their elevations; one for maximum and minimum slopes). The red line is the plotted model answer data. We have also plotted the professional survey as a green line on each graph. This will allow you to compare a student profile with the professional one. Your answers will not have the professional survey nor be they be presented as two graphs.

Evaluate your graph for having all the required information

slope change points with their elevations identified;

maximum and minimum slopes

a title,

axis labels: names, units, symbols (if any) and divisions,

labels identifying specific required features, or a legend if ;

points plotted correctly

a profile similar to the professional survey – similar steep and flat sections

7. Report the total path length and total elevation change in the provided space below Table 1. All are measured must be in meters. (4 marks) [Professional Survey Values: Total Distance (P): 174.00 m1

Total Elevation Change: 15.55 m]

8. Compare your total distance and elevation change to the professional values and account for the differences / errors. The model answers show how to organize a good answer. (8 marks) The best answers:

Indicate whether your results are greater or smaller than the professional result

Explain how your errors affected or contributed to your results

Organize errors by their type (method, human, or instrument) and severity (most to least impact)

9. On your graph, identify the points of slope change with an arrow and the value of the elevation

at that point. The arrows identify sections of different slope along your transect. (4 marks)

See the first graph (following). The arrows point to positions along the red (My Survey) line; these indicate changes in slope and their elevations. Your measurements will differ so your slope change points will also differ. However, the path’s profile will change in roughly the same locations, so you should see a similar pattern in your data’s profile. In your survey groups, breaks in slope and elevation values should be identical (as you are all using the same data to create your graphs).

Generally, slope changes do not occur at every measurement point and there are segments where multiple measurements follow the same slope (or given the precision of our graph, essentially the same slope). Typically along the length of the path, there are three main slope changes (best seen on the professional graph -- flatter at the top, steeper in the middle, and


3

flatter again near the bottom), and several minor slope changes. The path is always descending; as seen on the professional survey plot, at no point does the slope rise as you go from the parking lot to University Way.

10. Identify your profile’s maximum (steepest) and minimum (shallowest) slope sections and show them on your graph. (Do this visually before calculating any slopes to reduce the number of slope calculations needed.) Report the maximum and minimum slope values in the space following Table 1. Indicate where these slopes occur by marking and clearly labeling these sections on your graph. (4 marks - 2 marks for each value)

See the second graph: The red line is the plotted model answer. Values for all members of your group should be the same and should occur in the same locations on your graphs.

To find maximum and minimum slopes put a straight edge/ruler along the slope of your profile and find the steepest and flattest segments. In some cases you may need to calculate the slope in order to determine which is steeper (or shallower). Similar slopes for the model answers are reported in the table embedded in this answer. The Minimum and Maximum slopes are shown in bold. The “slope number” refers to the label on the red slope segment on the second graph.

For these model answers, slope 7 is the maximum (i.e. most vertical) slope, and slope 1 is the minimum (i.e. most horizontal) slope. Your group’s maximum and minimum slopes will likely differ from slopes shown here. However, if your measurements are realistic, they will be similar to the steepest and flattest sections of the professional survey (green plotted line).

The green (professional survey) line shows the minimum slope should be at the base of the profile (green slope 5 on the professional plot - nearest University Way), while the maximum slope occurs just above the base (at green slope 4).

Model Answers without explanation start on the next page.

Graph 2 Slope Number Slope (%)

1 – Minimum Slope 4.24

2

3

4 – possible minimum slope 4.5

5 – possible maximum slope 11.2

6

7 – Maximum Slope 13.1

8


4

Table 1: Breaking Tape Survey Data Recording Sheet (record your units where needed)

Weather: Cloudy & wet ground, but not raining Date: Mar. 28 2005 Light conditions: good but decreasing

Location: Pathway between University Way & UNBC East Parking Lot (B) Start Time: 5:04 pm End Time: 6:23 pm Group Members: Anita Abney, Bob Stadia, Carmen Level (recorder)

Meter Stick Height (A)

(m)

Survey Rod Height (B)

(m)

Distance (C) (m)

Position (P) in meters

Height (H) in meters

Elevation (E) in meters

Comments: note possible errors,

their type, and why they may have occurred.

0 753 (for

groups starting

at the top)

0.95 1.80 20.05 20.05 0.85 752.15 Survey rod may have been tilted

outwards.

0.95 2.70 27.7 47.75 1.75 750.4 Measuring tape difficult to make

horizontal.

0.95 1.80 13.2 60.95 0.85 749.55

0.95 2.30 18.6 79.55 1.35 748.2

0.95 2.05 24.4 103.95

1.1 747.1

Measuring tape difficult to make

horizontal.

0.95 2.60 14.7 118.65 1.65 745.45

0.95 2.40 17.1 135.75 1.45 744

0.95 4.00 23.2 158.95 3.05 740.95

Survey rod reading error here as

I don’t think any in our group

could reach 4 meters in height.

Poles likely were not level and

dipped outwards

0.95 2.40 21.3 180.25 1.45 739.5 Measuring tape difficult to make

horizontal.

First page of Data

Make sure to include start position (0 m) and elevation (753 m) in your table. If you worked from the bottom of the slope (University Way) up to Parking Lot B, your column values will be reversed from those shown here and the 0 m and 753 m values will be at the bottom of your columns. Ask if you aren’t sure your values are correct.


5

Meter Stick Height (A)

(m)

Survey Rod Height (B)

(m)

Distance (C) (m)

Position (P) in meters

Height (H) in meters

Elevation (E) in meters

Comments: note possible errors,

their type, and why they may have occurred.

Second Page of Data (use as needed)

Report answers for the lab here and on a separate sheet of paper (i.e. for your error discussion

lab point #8). Don’t forget to include units and use the lab instruction / questions number to

identify which answer you are reporting (as shown below).

7. The total length of the path is: 180.25 m (Total Distance (P) last Distance value in Table 1)

The total path elevation change is: 13.50 m (from my elevation values 753.00 m – 739.50 m = 13.50 m)

10. The maximum slope is: 13.1 % -- based on red slope #7 (see graph 2 below)

The minimum slope is: 4.24 % -- based on red slope #1 (see graph 2 below)

Note: By convention, unitless slopes are reported as percentages.


6

752.1 m

749.5 m

748.2 m

747 m

745.4 m

744 m

740.9 m

739.5 m

#9 Graph Showing the Elevations where the Slope Changes

Note: Your graph is not expected to contain the profesional survey. It is plotted here only so you can see the comparison.

Also only 1 graph is required for your answer. Two graphs are shown in order to clearly show the slope changes and their elevations on one, and then show how the max & min slopes compare with the professional slope on the other.


7

Possible max slope

My minimum slope - 4.2% (see lab

instruction #9 for discussion of slope values)

Maximum slope – 13.1% (see lab

instruction #9 for discussion of slope values)

Possible min slope

#10. Graph showing Minimum and Maximum Slopes Note: For your answers you are not required to show the plotted professional survey or this method of indicating slopes on a graph.

Only 1 graph is required for your answer; two are shown in the Model Answers so we can demonstrate the method used for determining maximum and minimum slopes more clearly.


8

8. Compare your total path length and elevation change values with the professionally surveyed values for total path distance and elevation change. … In your answer and using your recorded comments, account for your errors. Ensure that you state how your specific errors affected your results by indicating how these errors account for the values you obtained. Group different sources of error by their type – human, method, or instrument / measurement. (8 marks)

Q 8 - Example answer:

The following error types can affect this method’s survey results. They can also act in combination.

Human Errors: The poles were not vertical (i.e. plumb). This will make distance readings closer together

or farther apart depending on which way the pole(s) are leaning. It can affect distance results, and elevation change results.

Misreading the survey rod or not sighting at a horizontal line (i.e. Abney level not at a zero angle). This will affect the height values up or down depending on how the instrument is misaligned,

Tape not tight or wind blowing the tape, which causes a lengthening of the distance measurements.

Not matching the poles to their correct spot when moving to the next measuring spot; this changes shortens or lengthens distances.

Method Errors:

The tape sags, it can never be held as tightly as needed which makes distances longer. This is why more sophisticated equipment (theodolites, total stations, automatic levels, laser levels) can produce more accurate results.

The short meter sticks are very difficult to hold vertically plumb on uneven ground. Eye height measurements are very difficult to maintain at 1 m heights.

Poor visibility (i.e. darkness, fog, poor weather conditions) hinders pole sighting and reading (increases reading errors for both distance and height change)

The path has multiple cracks crossing it as you follow its length. This may indicate stretching of the path over time. Since the professional survey was done after the path was completed (~ 2004), the path may actually be slightly longer than indicated by the professional survey.

Instrument Errors:

Instrument error – the precision of each instrument is limited by how it is constructed; usually precision is limited to half of the smallest measurement division on each instrument). Engineering survey rods can measure to 0.5 cm accuracy ( 3 decimal accuracy for

heights in meters).


9

Measuring tapes and meter sticks and the measuring tape can be read to a half a millimeter (4 decimal accuracy if in meters)

Abney levels can measure angles to a quarter of a degree. (but for novice users to the nearest degree is more likely).

Model Answer specific errors:

The values obtained from my survey of the path are 6.25 meters longer than the professional survey results, and have 2.05 meters less elevation change. Our group attributed these errors mainly to:

A sagging measuring tape which results in increased distance measurements. It was particularly difficult to hold the measuring tape tight over longer distances.

This is a combined method and human error. The method error occurs as the measuring tape can never be horizontal, and over longer distances the problem is exacerbated. (Prior to the introduction of fiberglass reinforced measuring tapes, efforts to pull tapes horizontally level snapped the tapes – thus this technique’s name “breaking tape”.) The human error occurs as the tighter we tried to hold the measuring tape, the more likely we were to tilt the survey pole and meter stick inward.

Survey rods and meter sticks not being vertically level (or plumb). This is mostly a human error (see explanation below). If these poles are not vertical, but extend outwards, two types of errors that could account for our results would occur:

o Distances would lengthen o Height measurements would be shorter.

We know this is likely as we weren’t able to use bubble levels to see if either of our poles was vertical as we did our survey measurements (bubble levels weren’t available).

But, because our distance measurements aren’t hugely different from the professional survey, we feel that this problem isn’t the only reason for our shorter elevation change value, and that we may have be reading our vertical measurements poorly. Our logic is based on the fact that 6.25 meters for 174 meters is ~ 4 % error for distance, while 2.05 m for 15.55 meters is ~13% error for the elevation change.

Mathematically this is: %6.3%10000.174

25.6

m

m & %2.13%100

55.15

05.2

m

m

Note: reporting mathematical errors isn’t required but for my explanation helps explain my logic.

Difficulty reading the survey rod height when the Abney level was horizontal. We made our measurements later in the day when light levels were lower and we know that in the shadows we had more difficulty reading the survey pole heights.

lab 1: basic surveying techniques model answersweb.unbc.ca/~cjackson/geog_210/field...

Documents