Navigation and Bathymetry
Adapted by Carrie Jones for 9-12 Marine Science
A. Standards (Ocean Literacy standards)
1. The ocean has one big ocean with many features
2. The ocean and life in the ocean shape the features of the Earth
4. The ocean makes Earth habitable
5. The ocean supports a great diversity of life and ecosystems
6. The ocean and humans are inextricably connected
B. Performance objectives
Following completion of this lesson, students will be able to:
· Understand and locate latitude, longitude, any location at given coordinates
· Demonstrate the difference between magnetic and true north
· Determine the distance between 2 locations, speed and depths at certain locations
· Draw a bathymetric profile
C. Lesson Plan
1. Concept Exploration
Have the students look at a local nautical map and try to find their location. Ask the students why it is important to be able to read maps and navigate, when technology like GPS are now available. On the water GPS is heavily unreliable as they rely on power and satellites, salt water and batteries don’t mix, and sun spot activity breaks down radio transmissions.
2. Concept Introduction
Since the Earth is spherical, we use a system of large circles- latitude and longitude. Latitude lines run from East to West, parallel to the equator and each other, so are also called parallels. Latitude is measured in degrees north and south of the equator. There is also always the same distance between each latitude line, which is why we use latitude in order to measure distance: 1 minute of latitude=1 nautical mile. Longitude lines run from North to South, connecting the poles, expressed in degrees east or west of the Prime Meridian (0 degrees). The International Date Line is located at 180 degrees from the Prime Meridian or halfway around the Earth. Latitude and longitude are written as degrees (°), minutes (‘), seconds (“). Each degree of latitude is divided into 60 minutes and each minute is divided into 60 seconds. Point out on the maps what hemisphere’s we’re in and because it’s on a small scale, the lines are straight.
Explain how to find speed and distance and that when you’re subtracting lat and long we’re subtracting time so it is not normal subtraction rules. Speed is measured in knots (1 nautical mile per hour). In the olden days, actual lines with knots on it were used. A boat reads course headings as 0-360 degrees, not North, South, East, or West. There are two North Poles: Geographic North Pole and Magnetic north Pole. Geographic North Pole is also called “true” north because it is what you normally think of as the North Pole, the top point on the Earth. Because the materials in the center of the Earth are liquid, the magnetism of the Earth moves around and sometimes flips, which is considered the geographic North Pole. Therefore, we need to make corrections for this, since our compasses point to the magnetic north pole and our maps read to the geographic North Pole. Nautical maps have a tool on the maps to correct for this called a compass rose.
Marine Scientists also need to know the bathymetry, which are the structure, topography and depth of the ocean floor. On the maps, they show the depths as soundings (depth at specific points) and contour lines (lines that connect equal depths). Soundings are given as fathoms (1 fathom=6 feet). A bathymetric profile can be drawn on an X-Y graph to determine the shape of the seafloor in a given line. We currently measure the depth through sonar and echosounding technology.
3. Concept Application
Purchase nautical maps of your area. I purchased them online from www.nauticalchartsonline.com. Students should work in groups of 3-4. Develop a worksheet using locations from your area. Questions could include but are not limited to, finding latitude and longitude, distance and speed, plotting a course and bathymetry. Let the students try to find locations and explore the maps themselves before helping them.
Examples:
What are the latitude and longitude of Ocracoke, NC?
What is the difference in latitude and longitude between Ocracoke and Georgetown?
What is the distance in nautical miles from Tubbs Inlet to Pawleys Inlet, SC?
If you were traveling at 8 knots how long would it take?
If you leave Hatteras Inlet, NC at 0900 and assume a speed of 10 kt, what time will you arrive at Drum Inlet, NC?
How to calculate your true course.
Determine the depth of the sea floor at 10 nmi offshore of Myrtle Beach.
If the latitude is 33°30’N, and the ocean depth is 10fm, what is the longitude?
Construct a bathymetric profile traveling from Myrtle Beach in a straight line due East, determining the depth at 5nmi intervals.
D. Review/Evaluation
Review their understanding from the worksheet and bathymetric profile. Discuss that knowing how to read a map, even if you are not an avid boater is a useful skill to have!
Sources:
Adapted from Coastal Carolina University Marine Science 101 Lab compiled by Erin Wolfe