Making a Bathymetric Map
The students will use a probe to measure the bottom of the "ocean" that the teacher creates. They will plot their measurements and draw isolines to depict the bottom. More advanced students will correct the measurements for tidal changes and horizontal positioning.
- A large, deep, lightweight cardboard box with a lid. A department store gift box would be ideal.
- Various objects of unequal height and shape to glue in the bottom of the box (half a tennis ball, a rock, a wedge, a cone, a wooden rectangle block, etc). Alternately, a piece of Styrofoam cut to the size of the box that will be carved to make measurable relief.
- Straws, or narrow diameter wooden dowels, or shish-kabob sticks longer than the box is deep
- Glue and markers
- Depending on what you will use for a depth finder (a straw, dowel, or stick), punch holes with an adequate diameter to insert the probe in the box lid. The holes should be aligned in a grid pattern. The distance between points should not be greater than 1 inch in any direction. Too close a grid will cause your box to fall apart!
- Glue the various objects on the bottom of the box, keeping in mind the grid that you have prepared for "remote sensing" of the bottom.
- Tape the box lid to the box bottom, so that students won't be tempted to peek at the "ocean" floor.
- Depending on the age and ability of the students, you may pre-mark your measuring sticks or have students calibrate them as part of the exercise. Each unit will equal 1 foot, but there should be interim hash marks for fractional parts … at least 0.25, 0.5, and 0.75 feet.
- Preparation of the Ocean Bottom
Hints: When preparing the bottom, you might consider placing a small narrow object that could easily be missed, or two objects near but not touching each other, that would give the illusion of a continuous surface if the space between is missed. This will illustrate the necessity of a closely spaced grid when many features are likely.
Gradual surface changes are easier to plot and draw isolines.
Webdate: April 23, 2002
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