ES 351 Lab Exercise
Ross Reservation

This exercise is based on the class field trip to Ross Natural History Reservation. On this trip we undertook various kinds of survey measurements and used GPS units to acquire UTM coordinates for selected locations. All students who participated in the field trip are expected to complete both parts of the exercise. Out-of-state students may skip part A and go directly to part B. Each part is worth 10 points.

Part A

During the trip, we observed features at several sites in and around Ross Reservation. On your topographic map (large version), plot the sites listed below, as you noted their locations in the field. Mark each feature by number. Note: the original topographic map has a scale of 1 inch = 2000 feet; the large-version scale is 1 inch = 1300 feet.

  1. Entrance gate to Ross Reservation.
  2. Water well in front of main building.
  3. Southwestern corner of reservation boundary.
  4. Northwestern corner of reservation boundary.
  5. Dock at Gladfelter Pond.
  6. Spring near abandoned county road.
  7. Old limestone bridge on abandoned county road.
  8. Northeastern corner of reservation boundary.
  9. Dock at small pond in southeastern part of reservation.

Make a table of GPS readings for these nine sites in UTM coordinates. Now prepare a plot of the GPS values that we acquired for each of these sites. Use cm/mm graph paper to lay out a UTM grid: the x axis represents east values, and the y axis gives north values. Use a scale of 1 cm on the graph = 100 meters UTM. Plot the position for each point (1-9) on your graph, and compare with the topographic map.

1. What scale is your UTM graph? What is the scale of the topographic maps? Note: give ratio or fractional scale values (such as 1:20,000 or 1/20,000).

2. How does the size of your graph compare to the size of the topographic maps?

3. How do the positions of features on the graph compare with the topographic maps? Explain any similarities and differences in the relative pattern of survey points.

Now turn your attention to the northeastern portion of the reservation where the study plots are located. The following plan is based on a DOQ base map. Study plots are identified by number (72 total); each plot is 30 x 30 m square, and plots are separated by mowed paths 2 m wide. The mowed paths were created in the fall of 2007 using a GPS-guided tractor.

Plan of biology study plots at Ross Reservation.
Red squares show GPS survey control points.

The plan above represents an idealized scheme for the study plots. In the field, we collected UTM values for each of the ten ground control points (shown in pink-red). The following color-visible airphotos were collected by students on a class field trip in mid-October 2008; the color-infrared pictures were acquired by your instructor in early October of the same year. No treatment (mowing or burning) of study plots had been conducted at this time.

Oblique color-visible views

View southwest

View southeast

View northeast

Oblique color-infrared views

View southwest

View southeast

View northeast

Vertical color-visible views
 North to upper right corner

Southeast corner

Central portion

Southwest corner

Vertical color-infrared views
 North toward right side

Eastern margin

Western margin

Southwest corner

Your task is to compare the geospatial data (GPS & airphotos) collected in the field with the idealized plan. Make a second table of control-point UTM values collected with GPS in comparison to the idealized UTM values shown on the plan above. On this table note the differences between actual and idealized UTM values.

4. What is the overall variation of UTM values collected with GPS units compared with idealized UTM values?

5. In what ways does the actual grid of study plots deviate from the idealized plan? Explain why you think this happened; consider all potential sources for error.

6. On the basis of your experience at Ross Reservation, discuss realistic accuracy for GPS applied for various survey purposes.

Turn in part A

Part B

This portion of the exercise is based on a low-height aerial photograph of the Gladfelter Pond vicinity. The image was acquired by students on a course field trip in October, 2006, during drought conditions. Water storage was low, and the dock stood well above water level. This view is near-vertical, which means it can be used for accurate scale, size and height measurements.

Kite aerial photograph of Gladfelter Pond. Click on the small image to see a full-sized version. Margins of the pond are covered by American lotus (Nelumbo lutea), which appears bright green. North is toward the top of view. Photo date 10/06; © J.S. Aber.

To begin this exercise, you need to import the image, named ross_1200.jpg, into Idrisi Andes format. The original six-megapixel digital image was reduced considerably for purpose of this exercise. Download the image file via FTP into your student folder.

To import the file into Idrisi, go to the File menu and select Import. Next select Desktop Publishing Formats, and JPGIDRIS. Enter ross_1200 as the input file name and use the same name for the output file. Leave "output reference information" and "output documentation" as is. Click OK; Idrisi will generate a raster image file (rst) and a documentation file (rdc)--both named ross_1200. A display of the image should appear immediately after importing it.

A special palette (ross_1200.smp) was also created automatically for the image. Hit the "End" key to maximize the display frame.

Use the Idrisi Explorer (bar on left) to examine the metadata. Most of the entries are simply default values or listed as "unknown." In fact the only thing we know definitely is the number of rows and columns.

1. How many rows and columns does the image have?

At this point, the image is simply a raster grid of unknown resolution and value units (these are default values). The reference system/units and x/y values are default entries based on the number of rows and columns. The most important geometric attribute to establish is the resolution--linear dimension of each cell (pixel) in the image. For this, refer to the dock at Gladfelter Pond. Field measurement gave an average length of 51¼ feet (15.6 m) for the dock. Use the ZOOM WINDOW function to enlarge the dock. Locate center pixels at each end of the dock and check their column/row positions. Note: the land end of the dock ends over loose rocks on the ground. Locate the square end of the dock based on shadows.

2. What are the column and row positions for the ends of the dock?

The dock is oriented diagonally to the row/column grid. To determine the size of individual cells is a simple right-triangle geometric problem, in which the dock represents the triangle hypotenuse. Rows and columns represent the other sides of the triangle. The relationship of the sides is given by the Pythagorean theorem, as modified below.

R² + C² = H²

Where:
R = difference in rows between ends of dock.
C = difference in columns between ends of dock.
H = hypotenuse or the length of the dock.

Solve this relationship for length of the dock. Round your answer to the nearest tenth unit. The units of measurement are simply cells in the raster grid. To determine the size of each cell, divide the dock length (15.6 m) by your result (H) from above. Round your answer to the nearest centimeter (0.01 meter).

3. What is the cell resolution for the ross_1200 image? What are the reference units?

You are now ready to revise the documentation file with appropriate spatial information. Update the following information.

Note: first enter new values for max x and max y, then under resolution select "calculate resolution" option. The result should be the same as your value for resolution.

After updating the metadata information, click in the "Files" frame, and you will be prompted to save changes, which you should do. Then "close all windows" and redisplay ross_1200.

4. What values did you enter for max x and max y coordinates?

5. How much ground area does the image cover? Give your answer in hectares (one ha = 10,000 m²). Hint: rows x columns x resolution squared, or max x times max y, which should give the same result.

6. What are the smallest discrete objects that you can positively identify, and how big are these objects?

As your final task, construct a map composition of the aerial photograph that includes a suitable title, subtitle (your name/date), and scale bar. Name your composition GLAD, and make a digital image file (jpg) to turn in. Note: check that your scale bar is visually correct in relation to known length of the dock.

This image could be used for accurate measurements of lengths, areas, perimeters and heights of various objects. For example, it would be possible to determine the area of water within the pond and to measure other features of interest.

Turn in part B

Return to course schedule.
EB/ES/GE 351 © J.S. Aber (2008).