Ask an Expert: Dr. Marnie Sturm

by Dr. Marnie Sturm

Dr. Marnie Sturm is a Geospatial Analysis and Earth Science teacher at South Lakes High School in Reston, VA, where she has taught for the past five years. She holds a PhD in Geochemistry from Duke University and has a passion for maps, geography, and exploring the world.

How does a GPS know where I am when I go geocaching?

A GPS (Global Positioning System) communicates with satellites in space. These satellites send signals to your GPS, and by measuring how long it takes the signals to arrive, it figures out exactly where you are located on Earth. To find your exact location, there needs to be data from three different satellites.

What do you use satellites for when you're studying geography?

Satellites take pictures of Earth from space and help scientists like myself and my students learn about weather, forests, oceans, cities, and how the planet is changing. It’s like having a camera way up high in the sky. Looking at satellite imagery over time allows us to view changes on Earth, such as seeing the extent of melting of glaciers or the rise or fall of sea level in specific places.

Can you find treasure anywhere in the world with geocaching?

Yes, you can. People hide geocaches all over the world including in cities, forests, and on mountaintops. People can use GPS to find these treasures almost anywhere, but some may be in hard-to-reach places. Often, there is a logbook at the cache site where you can leave a journal entry or note.

How do you know where mountains, rivers, and cities are without going there?

Maps and satellite images show us where these places are. You can look at them on a screen to see what the land looks like and where things are without ever leaving home. In my classes, we plan trips all over the world without ever leaving our classroom.

Have you ever found something really cool using your maps or GPS?

Yes, all the time. One of my students this year mapped out vernal pools in Virginia that no one even knew existed using satellite data. Vernal Pools are temporary, isolated water bodies that form in low-lying areas, particularly in woodland depressions or meadows, during the wet seasons and are very important to the biodiversity of local ecology. Now, scientists can use her maps to study these vernal pools.