Geostationary Lightning Mapper (GLM)

The Geostationary Lightning Mapper (GLM) is a single-channel, near-infrared optical detector on the GOES-R Series satellites. It is the first instrument of its kind to continuously map lightning from geostationary orbit, detecting quick flashes in the atmosphere that indicate in-cloud, cloud-to-cloud, and cloud-to-ground strikes. Because of its vantage point, GLM can monitor large areas over time, even over oceans and regions with limited radar coverage.  

GLM also offers insights beyond the presence of a lightning strike, revealing the extent of lightning flashes and the distance they travel. Its data helps produce a long-term database to track lightning activity over decades, which can give insight into the Earth-atmosphere electrical balance.

Tracking Lightning to Improve Safety and Forecasting

Rapid increases in lightning activity can indicate that a thunderstorm is intensifying. Since storms can intensify very quickly, it’s important to get that data as fast as possible. While radar updates roughly every 5 minutes, the lightning mapper updates every 20-60 seconds, making it a valuable tool in forecasting severe weather. Lightning activity detected by the GLM alerts forecasters to possible tornadoes, large hail, damaging winds, and even hurricane intensification before severe weather strikes.It’s also used to inform lightning hazard warnings, estimate precipitation, identify lightning flashes most likely to ignite wildfires, and mitigate aviation hazards. This technology is especially beneficial in rural or mountainous areas, as well as over open oceans, where other data resources such as radar and surface observations may be limited.

Severe Thunderstorm and Tornado Warnings

Storms that go on to produce damaging winds, hail, and even tornadoes often show a significant jump in lightning activity. With the GLM, the increase in lightning can be seen minutes before radar detects signs of severe weather. Combined with radar, other satellite data, and surface observations, total lightning data from the GLM can help get severe thunderstorm and tornado warnings out sooner and reduce false alarms.

Precipitation Estimates

Lightning activity is closely tied to strong convection currents, such as updrafts– the warm, moist rising air that fuels storms. The more lightning detected usually means the stronger the storm and increasing potential for heavy rain or hail is likely. By combining GLM lightning data with radar and satellite images, meteorologists can put together faster and more accurate precipitation forecasts.

Hurricane Forecasting

For hurricanes, the GLM reveals lightning patterns within the storm that reveal changes in structure and intensity. These insights help forecasters understand how a storm is evolving, which leads to more accurate predictions for where the storm will track and how strong it will be.

Improving Lightning Safety

Lightning can strike ground as far as 100 miles from a thunderstorm, so knowing its prevalence and spatial distribution helps forecasters warn the public when it’s unsafe.

This is vital during outdoor activities, such as fishing, enjoying the beach, boating, camping, playing soccer, mowing the lawn, and farming. Watersports are especially risky. For example, lightning over the ocean is especially hazardous since boats travel far from shelter, a boat’s engine makes it more difficult to hear thunder, and it takes longer to find a safe location. 

The GLM data can be minutes ahead of radar, giving the public more time to get out of harm's way, whether that’s on the water or on land. It’s also free, publicly available, and easy to interpret, allowing those responsible for others in outdoor activities to make quick, informed lightning safety decisions.

Aviation and Airport Weather Warnings

To protect ground crews at airports, alerts typically are issued when lightning strikes within five miles of the airport, and operations are halted when it strikes within three miles. The GLM provides tremendous benefit for these situations, helping to alert airport operators of potential danger. The airline industry also benefits from using lightning mapping data to reduce weather-related costs. The lightning data contributes to cost savings through reduced fuel use and fewer delays and diversions. GLM data support the efficiency of both ramp operations and airplanes in the sky, on approach, and on the taxiway.

For pilots, GLM data warns of dangerous thunderstorms before and during flight, allowing them to plan routes to avoid lightning strikes to their aircraft and turbulence from severe weather. This is especially valuable when there are storms over the open ocean because there are fewer sources of storm detection.

Wildfire Response

Lightning strikes ignite more than half of the acreage burned by wildfires in the U.S., routinely sparking the costliest and deadliest fire complexes. Many of these fires begin in remote areas and go undetected for hours after they start. That’s because lightning can strike in less populated areas where ground detection sources are limited and response resources have to be brought in, delaying both detection and firefighting efforts. 

GLM is uniquely able to monitor vast areas and identify lightning flashes most likely to ignite fires. This information can help emergency personnel respond sooner, reducing property damage and firefighting costs and potentially saving lives. 

GLM can also help identify dangerous pyrocumulonimbus clouds, or thunderstorms formed by wildfire heat and smoke. These can threaten firefighters with erratic winds that can spread fires quickly along cloud-to-ground lightning strikes and severe weather. 

Meteor Detection

Although designed for lighting mapping, GLM can also detect bright meteors (bolides), which flash similarly to lightning. The instrument takes 500 images of Earth every second, allowing it to measure the shape of a meteor’s light curve, or the change in brightness of a meteor with time, with millisecond precision. 

The loud “booms” that accompany meteors entering Earth’s atmosphere with no visible source can cause a lot of anxiety, especially in populated areas. The National Weather Service (NWS) and broadcast meteorologists use GLM data to quickly confirm the source and notify citizens. 

Meteor detections also support national defense. GLM data helps NASA’s Planetary Defense Coordination Office and the Department of Defense better understand and mitigate the threat posed by potentially dangerous larger asteroids hitting Earth. GLM data helps improve impact prediction warnings by studying how asteroids fragment as they travel through the atmosphere. 

GLM Characteristics

• Staring CCD imager (1372x1300 pixels)
• Near uniform spatial resolution 8 km nadir, 14 km edge fov
• Coverage up to 52 deg N lat
• 70-90% flash detection day and night
• Single band 777.4 nm
• 2 ms frame rate
• 7.7 Mbps downlink data rate (for comparison- TRMM LIS 8 kbps)
• 20 second product latency