Our second Earth Day post is contributed by guest author Drew LePage, Senior Project Scientist in the Applied Physics Group at Visidyne.
Earth Day is a good time to step back for a big-picture view of our home planet. Crew members on the International Space Station (ISS) get to see Earth this way all the time! They enjoy photographing large-scale phenomena on Earth such as hurricanes and other tropical cyclones. A project called CyMISS (tropical Cyclone intensity Measurements from the ISS) is using photos taken from the ISS to study these types of storms.
When Hurricane Harvey struck last August, news reports frequently showed animations of the storm moving across the map. Those animations used images acquired by satellites orbiting more than 20,000 miles above Earth’s surface. From that immense distance, satellites with infrared sensors can measure the temperatures at the tops of clouds, but they can’t measure the heights of the cloud tops. Meteorologists need both the temperatures and the heights of the cloud tops to describe storms accurately and make reliable forecasts.
There aren’t any satellites that specialize in measuring the heights of cloud tops, so scientists have tried several ways to extract this information indirectly from satellite images. The CyMISS project takes advantage of the fact that the ISS orbits very close to Earth—only about 250 miles above the surface—and travels at about five miles per second. If an ISS crew member snaps a rapid-fire series of pictures of a hurricane, each picture will show the storm from a slightly different angle. To calculate the heights of cloud tops from these image sequences, scientists apply the same principles used to make 3D movies!
To create the appearance of a 3D scene, you would choose two images from the sequence and send a different image to each eye. Your brain would combine the input from the right eye and left eye to perceive depth and distance. To control which eye sees which image, you could place the two images side by side and view them through a stereoscope or virtual reality headset. You could superimpose the images on top of each other while displaying each image in differently polarized light and wear 3D glasses with polarized lenses; that’s how 3D works in movie theaters. Or you could superimpose the images while displaying each one in a different color and wear 3D glasses with colored filters. This last approach applies to the 3D images shown here. These images are called anaglyphs. View them with red-blue 3D glasses (the red filter goes over the left eye).
To calculate the heights of cloud tops, the CyMISS team chooses images from the sequence and re-map them to a uniform grid. This step is important because the astronauts took the original photos at oblique (partly sideways) angles, but the height calculations work better if the images are in a top-down view. To get every part of the storm in focus, many images are re-mapped and stitched together using custom computer algorithms. After this image processing step, the CyMISS team calculates the heights of the cloud tops based on the location of the camera when it took each image. Meteorologists combine these calculations with temperature measurements to estimate the intensity of the storm.
Grab your red-blue 3D glasses and enjoy these anaglyphs of major storms from the past year. These images were acquired by the Earth Science and Remote Sensing Unit at NASA Johnson Space Center (Houston, TX) and processed by CyMISS scientists at Visidyne, Inc. (Burlington, MA). 2D versions are also shown for viewers who don’t have 3D glasses on hand.