Appendix D—Example of Grid Setup Instructions
The data collection grid has 800 points (see grid map), arranged in 20 columns and 40 rows. Columns refer to the downrange component of the grid (its length) and rows refer to the crossrange component of the grid (its width). The grid should be oriented downrange, parallel to the prevailing winds.
Start by setting up the two outside columns (columns 1 and 20) as accurately as possible using a sighting device (transit or theodolite) and the marked cable (rolled up on a wooden spool, included with the stakes). The marked cable is 250 feet long (the width of the grid). Copper clasps, crimped along the cable, mark positions where stakes should be placed. Use the cable to determine the distance between the two outside columns of the grid. Use the sighting device to make sure the first row of the grid is perpendicular to the outside columns.
Once the outside columns have been staked, use the 100- foot tapes to place stakes at 15-foot intervals along the columns. Stakes should be driven carefully into the ground to the depth of the square washer. These stakes will mark the location of the 40 rows. Use the cable stretched between the two outside stakes of each row to position the stakes within each row.
I've divided this part of grid setup into three steps:
Grid map of the Kingman, AZ, drop test showing placement of stakes. To set up: 1—Place stakes at
the
four corners; 2—Place stakes along the two outer columns (columns 1 and 20); 3—Place
stakes
along each row between the two outer columns.
Step 1—Establish Four Corners of the Grid
Referring to the grid map below, mark the position of column 1, row 1 on the ground.
Place a theodolite at the point you just marked (column 1, row 1) and aim it in the directions where column 1, row 40 will be. Using the 100-foot tapes, place a marker every 100 feet out to 600 feet. The sighting device helps keep the markers in a straight line. The last marker, at 600 feet downrange, represents column 1, row 40.
Rotate the theodolite 90 degrees counterclockwise and stretch the 250-foot cable along this line. Mark the last point on the cable on the ground. This point represents column 20, row 1.
Relocate the theodolite to column 1, row 40 and aim it at column 1, row 1.
Rotate the theodolite 90 degrees clockwise and stretch the 250-foot cable along this line. Mark the last point on the cable on the ground. This point represents column 20, row 40.
There are other ways to establish the four corners of the grid, but I believe this process will provide the most accurate layout.
Step 2—Install Stakes Along Columns 1 and 20
Locate the theodolite over one of the grid corners. If you are following these directions exactly, the theodolite is still over column 1, row 40. Aim the theodolite at column 1, row 1. Using the 100-foot tape, insert stakes at intervals as indicated on the map. Use the theodolite to keep the stakes in a straight line.
Locate the theodolite over column 20, row 40 and aim it at column 20, row 1. Insert stakes as described above.
Step 3—Install the Rest of the Stakes
Load the rest of the stakes in the back of a truck. Drop 18 stakes next to each of the stakes in column 1.
Starting with row 1, have two people stretch and hold the 250-foot cable while two or more people insert the 18 remaining stakes for that row. Use the marks on the cable to guide stake placement. Continue with the next rows.
After the stakes are installed, install sample cup holders on the top of each stake. The sample cup holders are sample cups that have been drilled with two ¼-inch holes, one in the center to attach the cup to the stake and one near the edge for a drain hole. The shortest of the shrink-wrapped pallets contains three boxes of cup holders. Nylon nuts and bolts attach the cup holders to the stakes. Each cup holder requires a washer on both sides of the cup. The curve of the washer is oriented to support the bottom of the cup, which is slightly raised. A stake with an attached cup holder is included for an example. It is important that the washers are placed as described as in the example.
A system that has worked for us is to have several people inserting bolts and washers into the cups, several others placing one of these assemblies on the ground next to each stake, and several others armed with 7⁄16-inch nut drivers (supplied) and a pocket full of nuts attaching the cups to the stakes.