(BIVN) - From this week's U.S. Geological Survey Hawaiian Volcano Observatory Volcano Watch article by Tyler Paladino, a Postdoctoral Fellow with the USGS:
Interferograms are images created by radar satellites that show how the ground has changed shape, or deformed, over time. Today, we'll dive into one of the trickiest parts of interpreting interferograms: the perspective of satellites.
Volcanologists use interferograms to detect unrest by observing how the surface of a volcano is deforming in response to migrating magma beneath the ground. We can see changing subsurface magma reservoirs, their connections, and new paths magma creates as it travels closer to the surface. While interferograms can be beautiful and informative, they are also difficult to interpret.
A "Volcano Watch" article from June 2019 discussed how to read the repeating cycles of color, called fringes (which often make bullseye or butterfly wing patterns), to figure out how much ground movement is occurring. To summarize quickly: count the fringes, starting from the outside of the feature towards the inside. Keep track of the sequence the color is cycling: is it red-yellow-blue or blue-yellow-red? Use the figure key to work out which direction the ground is moving, either towards or away from the satellite. The change in distance between the ground and satellite is called "range change". Multiply the number of fringes by the range change value of a single fringe (also given in the figure key) and you've calculated displacement and its direction. Or have you? In reality, it's a bit more complicated.