Tracking Geomagnetic Storms in the Ionosphere
AbstractThe Sun is the ultimate source of the energy that powers weather systems on Earth. Geomagnetic storms are sun-powered storms in the upper atmosphere, arising from energized particles that are periodically ejected by the Sun. Among other effects, geomagnetic storms can wreak havoc with earth-orbiting satellites, and disrupt satellite communications. The global positioning system (GPS) is a network of 24 earth-orbiting satellites that constantly sends radio signals through the earth's atmosphere. GPS receivers use these signals to determine their position on Earth. Can you use errors in GPS signals to identify geomagnetic storm activity?
The goal of this science fair project is to test whether errors in GPS (global positioning system) signals are correlated with geomagnetic storm activity in the ionosphere.
Andrew Olson, PhD, Science Buddies
Edited by Sandra Slutz, PhD, Science Buddies
This project is based on:
- Elder, S.M. (2003). Tracking Storms in the Ionosphere. California State Science Fair Abstract. Retrieved December 7, 2006 from http://cssf.usc.edu/History/2003/Projects/J0607.pdf
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Last edit date: 2017-07-28
Before You Start: The sun has periods of increased, solar maximum, and decreased, solar minimum, sunspot activity. This 11-year cycle has effects on many types of space weather. Before starting this experiment you should read a bit about the sunspot cycle and determine where we currently are in the cycle. You can do this project anytime during the solar cycle, but the frequency and intensity of space weather will be highest during the solar maximum.
A GPS (global positioning system) receiver works by monitoring radio-frequency (RF) signals from Earth-orbiting satellites. There are 24 of these satellites orbiting the globe, with control stations on the ground. The position in space of each of the satellites is known at all times. By measuring the relative time delays between signals from the different satellites, the GPS receiver can calculate its position on earth. If the receiver can lock onto signals from three of the satellites, it can determine its position in two dimensions (latitude and longitude). If the receiver can lock onto signals from four of the satellites, it can determine its position in all three dimensions (latitude, longitude, and altitude). One place you can read more details about how the system works is in the "GPS Guide for Beginners" (Garmin, Ltd., 2000).
When the GPS receiver determines its position, there are many possible sources for error, including:
- Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
- Signal multi-path — This occurs when the GPS signal is reflected off objects, such as tall buildings or large rock surfaces, before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
- Receiver clock errors — A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
- Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
- Number of satellites visible — The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater, or underground.
- Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles, relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
- Intentional degradation of the satellite signal — Selective Availability (SA) was an intentional degradation of the signal that used to be imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers (Garmin, Ltd., 2006a).
The first source of error, ionosphere and troposphere delays, is affected by the level of geomagnetic storm activity. Check out the Space Environment Center links in the Bibliography section to learn more about what causes geomagnetic storms, and to see how these storms are monitored and reported.
Many GPS receivers sold in North America are "WAAS-enabled," meaning that they take advantage of a second set of signals (the Wide Area Augmentation System, or WAAS) to calculate their position more accurately. "WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift, plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal" (Garmin, 2006b).
The WAAS correction feature of the GPS receiver can be turned on or off, allowing you to see the calculated position with or without the WAAS correction. In this science fair project, you will take regular position readings with a GPS receiver using both the uncorrected mode (WAAS off) and the corrected mode (WAAS on). You will keep track of the difference between the two readings—we will refer to this difference as the error signal. How will the error signal vary over time? Will there be a strong correlation between high-error values and ionospheric storms? You'll find out by comparing your readings to daily space weather reports. You'll see if you can use the error signal to identify times when there is increased geomagnetic storm activity.
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:
Space Weather Terms:
- Solar flare
- Solar cycle
- Coronal mass ejection
- Geomagnetic storm
- Planetary K-index
- DOP (dilution of precision)
- WAAS (Wide Area Augmentation System)
- Where is the Sun in the solar cycle, and how might this affect your project?
- What are some of the potential sources for error in receiving GPS signals?
- How many of these are corrected by WAAS?
- What sources of error, besides ionospheric and tropospheric delays, might cause an increase in the difference between the corrected and uncorrected position (the "error signal")?
- The Space Weather Prediction Center (SWPC) is the part of the National Weather Service that is responsible for monitoring and forecasting space weather. The SWPC website has many resources that will be helpful for this project:
- For an introduction to space weather, see: Space Weather Prediction Center. (n.d.). Space Weather Phenomena. Retrieved January 19, 2015 from http://www.swpc.noaa.gov/phenomena/
- For information on how space weather affects GPS systems, see: Space Weather Prediction Center. (n.d.). Space Weather and GPS Systems. Retrieved January 19, 2015 from http://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems
- For a glossary of space weather terms, see: Space Weather Prediction Center. (n.d.). Space Weather Glossary. Retrieved January 19, 2015 from http://www.swpc.noaa.gov/content/space-weather-glossary
- For information on NOAA space weather scales, see: Space Weather Prediction Center. (n.d.). NOAA Space Weather Scales. Retrieved January 19, 2015 from http://www.swpc.noaa.gov/noaa-scales-explanation
- For current space weather, see: Space Weather Prediction Center (n.d.). Space Weather Enthusiasts Dashboard. Retrieved January 19, 2015 from http://www.swpc.noaa.gov/communities/space-weather-enthusiasts
- These web pages from a manufacturer of GPS receivers have information about how the GPS works:
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Materials and Equipment
- WAAS-capable GPS receiver
- Note: You must be able to turn the WAAS correction on and off. Consult your GPS receiver instruction manual to see how to do this.
- Computer with Internet access
- Lab notebook
- Graph paper and pencil (or spreadsheet and graphing software)
- For at least three weeks, collect baseline data with your GPS receiver, twice each day at the same time of day, and in the same location in your house or yard. Record all of the following collected information in your lab notebook.
- First consult your GPS manual and learn how to turn the WAAS correction on and off.
- Pick a position in your home or yard where you can safely stand twice a day for at least three weeks.
- Turn your GPS on, with the WAAS on. Now record the location data (latitude, longitude, altitude) in your lab notebook. Note: If you don't know how to obtain these readings from your GPS, look it up in the manual that comes with the GPS.
- Immediately after taking those readings, turn off the WAAS on your GPS and measure the location data again, recording the data in your lab notebook.
- After you've collected all your data at each reading, you'll need to calculate the error signal. The difference between each pair of readings is the error signal. For example, the difference between the altitude reading from the morning of day 1 with the WAAS ON and the altitude reading from the morning of day 1 with the WAAS OFF is the altitude error signal for day 1. Calculate the error signals for each type of measurement (altitude, longitude, and latitude) every time you take measurements and always record the data in your lab notebook.
- Right after each reading, go to the Space Environment Center website (http://www.swpc.noaa.gov/products/planetary-k-index) and record the value of the planetary K-index (Kp) at the time of your measurement. Remember that the planetary K-index is an indicator of geomagnetic storms.
- At the top right corner of the page, this website will tell you if there are currently any geomagnetic storms. (Look for the green box with the "G" in it). Record whether there are or not in your lab notebook.
- If a geomagnetic storm is happening right now (meaning right after the time you took your reading, hence the importance to get online immediately after each reading), the website will list the "scale" of the storm, which indicates how the storm might affect power systems, spacecraft operations, and other systems. The scale goes from G1 to G5 with G5 being the strongest.
- Record the Kp value in your lab notebook.
- Repeat the GPS readings and NOAA website checking procedure (steps 1-2) every day for at least 3 weeks—longer is better if you have enough time between now and when your project is due.
- Make a graph to see if there is any correlation between GPS error signal and geomagnetic storm activity. Your graph should have Kp Index on the y-axis and GPS Error Signal on the x-axis. Each of your observations will produce one data point on the graph. Make separate graphs for the error signals for each measurement (latitude, longitude, and altitude).
- Is there a correlation between the magnitude of the error and the Kp index?
- How reliable is the error signal as an indicator of geomagnetic storm activity? In other words, are your measured error signals consistently higher or lower than usual when a geomagnetic storm is happening?
- You can use a spreadsheet program (e.g., Excel or QuattroPro) to perform a statistical analysis of the correlation between the error signal and the Kp index to find out. To learn how to calculate and interpret the correlation coefficient, see the Science Buddies project Which Team Batting Statistic Predicts Run Production Best?.
If you like this project, you might enjoy exploring these related careers:
- Can you use the error signal to identify times when there is increased geomagnetic storm activity?
- Make observations with your GPS receiver, as before, and determine the magnitude of the error signal. Record the observations in your lab notebook, including the date, time, and position information both with and without WAAS correction.
- Calculate the magnitude of the error signal.
- Use your graph to identify whether or not geomagnetic storm activity is likely to be occurring.
- Then check the Space Environment Center website to see if your prediction was correct.
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