Satellite Sandwich

In the quest to improve severe weather forecasts, researchers look to innovative tools to learn about evolving atmospheric conditions. One of those tools, known as the “sandwich’ satellite product, combines different types of satellite imagery to provide meteorologists new angles to watch storms as they form and intensify.

Recently, scientists at the Space Science and Engineering Center (SSEC) and the Cooperative Institute for Meteorological Satellite Studies (CIMSS) released a GOES-16 sandwich satellite product accessible via SSEC’s visualization and data analysis software package McIDAS-V, as well as the Geostationary Satellite Image Browser.

The sandwich is a composite image created by stacking visible light (0.64µm) and infrared (10.3 µm) channels. The resulting multi-dimensional image gives meteorologists and researchers an efficient way to study severe weather in near real-time with an added texture from the sandwich-like layers.

Combining imagery from the GOES-16 weather satellite, the sandwich animation shows the development and progression of a derecho that blazed its way across the Midwest July 19, 2017. Credit: SSEC/CIMSS

“The combination of the two channels gives more context to a storm as it’s developing,” says Joleen Feltz, CIMSS research scientist who led the development efforts. “The mix of temperature and visible data together can help identify key formations in a storm.”

The sandwich method was pioneered by research scientist Martin Setvák from the Czech Hydrometeorological Institute using data from European Space Agency satellites. Setvák, a skilled photographer, recognized the diagnostic power of combining different visible light and infrared channels. During a science visit to SSEC, Setvák instructed CIMSS scientists and McIDAS-V programmers in the method of creating sandwich imagery using digital processing software.

Building on Setvak’s foundational work, Feltz saw an opportunity to build on it by using the new GOES-16 multi-spectral Advanced Baseline Imager: she was able to take advantage of the ABI’s rapid scans to create fluid animations. With 30-second mesoscale data as well as one-minute imagery, the CIMSS sandwich satellite product automatically combines the infrared and visible light channels for retrieval in the McIDAS-V system.

As with any visible light channel, its effectiveness is limited to daylight hours. In order to provide a 24-hour product, Feltz incorporated a transition algorithm to smoothly navigate the change from a combined daytime visible/IR channel to a nighttime only IR channel. The transition provides continuity for monitoring evening storms into the night, a common time for hazardous weather, especially during spring and summer months.

Using mesoscale imagery from GOES-16, the sandwich product reveals useful details about storm development. Additionally, a day to night transition provides continuity with infrared data, even when the sun sets. Credit: SSEC/CIMSS

For researchers like Kris Bedka with the NASA Langley Research Center, who studies hazardous convective storms, the sandwich product is a useful mechanism for monitoring storm developments.

“The beauty of the sandwich product is the visible light offers extremely high spatial resolution,” he says. “With the infrared you can learn a lot about dynamics and whether the clouds are made of either ice or water.”

According to Bedka, before the launch of the GOES-16 satellite, these types of visualizations were less practical given the limited spatial resolution of previous GOES satellites.

Now that the product is supported within McIDAS-V, Feltz encourages other researchers to use the imagery in combination with other meteorological products and leverage the diagnostic tools of McIDAS-V.

“We hope it will aid researchers and meteorologists to better understand severe storms and improve forecasting,” she says.

by Eric Verbeten