Tag Archives: Remote Sensing

Big Ben Eruption Update 2017-02-27

Mawson Peak's summit crater glows orange in this false-color infrared image (bands 7-6-5) taken February 27, 2017.  Image credit: Bill Mitchell (CC-BY) using data from USGS LANDSAT 8 (public domain).
Mawson Peak’s summit crater glows orange in this false-color infrared image (bands 7-6-5) taken February 27, 2017. Image credit: Bill Mitchell (CC-BY) using data from USGS LANDSAT 8 (public domain).

It has been three weeks since I reported on an active eruption on Heard Island seen by Landsat 8. Since then, the presence of lava at or near the surface in the summit crater of Mawson Peak has continued, and a thermal anomaly is present both in the February 27 Landsat 8 image shown above and in February 20 imagery. It is difficult to discern in the true-color imagery from February 27 whether there are any new lava/debris flows present. The two MODIS instruments (one on Aqua, one on Terra) have not picked up any thermal anomalies since early February.

Unfortunately, one of the best tools I’ve had at my disposal for keeping an eye on Mawson Peak is no longer available: NASA/USGS satellite EO-1 was decomissioned last week. EO-1 provided 10 m/pixel true-color imagery, which is significantly higher resolution than 15 m/pixel of Landsat. Archival data for both satellites remains available, but no new EO-1 data will be taken. New data from Landsat 8 typically comes in a few times each month (every 7-16 days), and I’ll be keeping an eye on it.

Mawson Peak in true color, February 27, 2017.  Image processing: Bill Mitchell (CC-BY) using USGS Landsat 8 data (public domain).
Mawson Peak in true color, February 27, 2017. Image processing: Bill Mitchell (CC-BY) using USGS Landsat 8 data (public domain).

Show Me the Data: Satellite Observations

Heard Island, March 27, 2013.  Elephant Spit imagery (at right) is from March 3, 2013.  Image has been adjusted to increase bring out detail in exposed land.  Image credit: processed by Bill Mitchell (CC-BY) using data from NASA/EO-1 (public domain).
Heard Island, March 27, 2013. Elephant Spit imagery (at right) is from March 3, 2013. Image has been adjusted to increase bring out detail in exposed land. Image credit: processed by Bill Mitchell (CC-BY) using data from NASA/USGS/EO-1 ALI (public domain).

With Heard Island being remote and uninhabited, studying it can be a bit difficult. However, as readers of this blog (and my Twitter followers) are aware, one of the ways I have been preparing for the expedition is by keeping an eye on it using various satellites and their remote sensing capabilities. Sure, there is often cloudcover at Heard, but some days it’s clearer and on a few of those days, the satellites pass over.

Most of my information comes from NASA’s MODIS instruments, aboard the Terra and Aqua satellites. These have at least every-other-day coverage of everywhere on Earth, although with a moderate resolution of 250 m/pixel. In the morning when I’m catching up on email and comics, I’ll check the near-real-time MODIS image page to see whether there are clear images of Heard Island from either instrument. Finding Heard Island can be difficult: I still usually find the Kerguelen Islands first, then look to the south-southeast. Many times there are indications such as vortices or gravity waves (not gravitational waves, those are different).

A related page is MODVOLC, which uses MODIS for volcano monitoring. In addition to visible light, MODIS can detect several wavelengths of infrared, and the signature from those wavelengths can be used to determine whether there is a likely volcanic eruption occurring at a given place.

MODIS is a great instrument in that it has daily or every-other-day coverage. However, the 250 m/pixel resolution can be quite limiting. For higher-resolution imagery, I look to the ALI instrument on NASA’s EO-1 satellite. These images are available (free registration required) from EarthExplorer, a data search portal from the USGS. ALI has a 30 m/pixel resolution on its color imagery, and 10 m/pixel resolution on the panchromatic image (total light intensity). These can be combined using QGIS into 10 m/pixel color images. By exploring the EO-1 page I found that members of the public can make requests for image targets! Imaging requests are subject to a bunch of conditions (availability of satellite, >30-day lead time, recommended >3 month window for imaging), but the request and any data generated from fulfillment of the request are free.

How did I come to know about these great resources? It takes time, searching, and some attention to detail. MODIS I learned about as a graduate student, from friends who used data products (not the true-color imagery) in their doctoral research on atmospheric chemistry. I came across EO-1 ALI from searching for images of Heard Island: I found some higher-than-MODIS resolution images from NASA which were good about indicating the source satellite/instrument. Citing image sources is incredibly useful, and I’m always disappointed when images (at least, non-screenshot images) are given without any sort of source information.

MODVOLC I learned about from the Smithsonian’s Global Volcanism Program, which cites the sources of their eruption reports. Information about the source plus a little searching yielded an interesting and useful data source.