Navigation means finding our way from one place to another. Drivers use street maps to navigate on roadways. Anyone who uses a boat or a ship needs to use nautical charts to navigate. Nautical charts are like street maps for boats. They give the names of waterways and show how deep they are. They also show things near the water, called landmarks, to help boaters navigate safely. Nautical charts also help boaters avoid running into dangerous objects under the water.

The National Oceanic and Atmospheric Administration (NOAA) makes charts for millions of miles of water, called nautical miles, around the United States.

How Do We Map the Sea Floor? It is easy to see what is on land. It is much harder to look at the bottoms of lakes, rivers, canals, and oceans. To make a map of the sea floor, a ship goes out and does a special survey called a hydrographic survey.

Today, scientists survey the sea floor with SONAR. SONAR stands for SOund NAvigation and Ranging. Sonar systems send sound waves from the bottom of a ship to the bottom of the sea. These sound waves bounce off the sea floor and back up to the ship. Sonar works a little bit like dribbling a basketball. The basketball leaves your hands, hits the ground, and bounces back up to you.

Another tool that surveyors use to map the sea floor is LIDAR. LIDAR stands for Light Detection and Ranging. LIDAR sends laser light from the bottom of an airplane to the sea floor. The light reflects back to the airplane.



What do the last two sections add to this text?
A) They both describe systems or processes that help to map out the sea floor.
B) They both describe systems that ensure sounds can be heard and sights can be seen on the sea floor.
C) One describes a sonar system that gives names to waterways and the other focuses on light detection to show water depth.
D) One describes a sonar system that is similar to basketball and the other focuses on similarities of LIDAR to airplanes.