Bathymetry is the process of measuring underwater depths. This hands-on lesson for students in a Marine Biology class is designed to both teach them to recognize various sea floor formations as well as experience how underwater mapping is done. It involves digitally sculpting and creating (with a 3D printer or CNC router) a model of the sea floor with various formations, and a box with holes in it that represents the ocean's surface. Marked rods are inserted into the holes to measure the depth to the sea floor. The results are recorded in a spreadsheet and a 3D graph is produced and compared to the original sea floor.
Step 1: Create Your Digital Sea Floor Model
Using the free program Sculptris import the Sea Floor Block Template .obj file. Use the tools to sculpt the surface of the block into whatever features are required. The crease, grab, inflate and smooth tools are particularly useful. It is important for students to focus on lowering the top level of the block, particularly if you are using a CNC machine to mill the shape. The block template measures 2 inches high, which works for 2 inch insulation foam. If you are 3D printing your sea floor, it can be taller.
Step 2: Turn Your Digital Sea Floor Into a Physical Model
When your design in Sculptris is complete, export it as an .obj file. This file can be put into a slicer program for a 3D printer or a program like Vcarve for making toolpaths for a CNC router. If you use a router you can carve the model out of 2 inch insulation foam very quickly.
You could, of course, make your sea floor by carving the foam by hand, sculpting in modeling clay or doing papier mache. This would be faster than 3D printing in most cases, but not as fast as the CNC router. Making sure the carving or sculpture fits the box is the most important part. The box measures 4 x 8 inches and is 4 inches tall.
Step 3: Create the Box
Using the Box Design.svg file, create the box that fits over your sea floor model. The top of this box represents sea level, and by dropping a marked rod into the holes and recording how far down they go, you can mimic the process of depth sounding.
The .svg file can be laser cut out of cardboard or corrugated plastic. It could also be printed onto paper and then cut out of the cardboard by hand. It would take a few sheets of paper to get the entire design without shrinking it. The holes on the top could be poked in with a pencil or small screwdriver.
The Box Design file is designed to be folded up as one piece. Adjusting the power and speed settings of the laser cutter allowed met to cut some lines all the way through the corrugated plastic (black lines; highest power), fold against the grain of the corrugation (green lines;medium power) and fold with the grain of the corrugation (red lines;lowest power).
When the box is cut, put a little double sided tape in the tabs and fold everything up.
Step 4: Measure the Depth - Bathymetry
Mark some small dowels (we used grilling skewers) at .25 centimeter or 1 mm intervals and poke them into the holes of the box to measure the depth. Enter each measurement as a negative number in the corresponding box in a spreadsheet. When all of the data is entered, highlight it and click on "All Charts" on the Insert menu. Look for the "Surface" option and select the 3D Surface chart. Compare the resulting chart with your original digital design or sculpted sea floor model.