Prompted by Laurent Jacques's tweet, I went to read the excellent arxiv blog entry featuring a paper purporting to explain how ionospheric disturbances correlated to the Tohoku earthquake in Japan. Here are a few observations. The paper looks at three means of getting some information around the Tokohu region at about the time of the earthquake. The authors first used multispectral (AVHRR) data. This reminded me that we submitted a proposal to the NSF a while back to fly a CASSI hyperspectral sensor on board a cubesat. The proposal did not fare well and it was all my fault but maybe I should have pushed this one again last year. On the other hand, our implementation did not look at long wave IR wavelength and more importantly once you have a satellite with the right sensor, you really only have a point-like coverage of earth and there is chance you might miss some events. The next best thing is to probably to consider what you can get from a sensor network in order to improve coverage. The authors of the paper did just that by looking at ionospheric measurements. If you recall these can be done directly using the GPS constellation as explained in this Wondering Star entry. From the paper:
"...GPS TEC in the form of Global Ionosphere Maps (GIM) maps, ionospheric tomography, using the signal from low-Earth orbiting satellites (COSMOS), and data from the ground based vertical sounding network in Japan. The period of this earthquake was very environmentally noisy for our analysis since two (small and moderate) geomagnetic storms took place on the first and eleventh of March respectively (Fig 4B). There was a short period of quiet geomagnetic activity between March fifth and tenth but it was during a period of increasing solar activity. During period from 26 February through 8 March the solar F10.7 radio flux increased almost two-fold (from 88 to 155). So the identification of the ionospheric precursor was the search a signal in this noise. .."
The Global Ionosphere Maps is updated here every five minutes ( I added a new entry on Wondering Star about this Earth-wide sensor network) but the main problem was delineating the disruption to the ionosphere due to solar storms and that due to the earthquake releasing gases into the atmosphere. Check Ionospheric Precursors of Earthquakes; Recent Advances in Theory and Practical Applications by Sergey Pulinets for an explanation. This use of the ionosphere also reminded me of Lianlin Li's comments a while back on "the ionosphere can be looked as the natural compressive sensing measurement system". Finally, I also note that one of the commenter on the arxiv blog makes the astute comment about Bright Orange Eerie Sunsets. Maybe we ought to have a closer look at using a worldwide outdoor webcam system ? or make sense out of outdoor photos taken by a billion smartphones.
Here is the paper: Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary results by Dimitar Ouzounov, Sergey Pulinets, Alexey Romanov, Alexander Romanov, Konstantin Tsybulya, Dimitri Davidenko, Menas Kafatos, Patrick Taylor. The abstract reads:
The recent M9 Tohoku Japan earthquake of March 11, 2011 was the largest recorded earthquake ever to hit this nation. We retrospectively analyzed the temporal and spatial variations of four different physical parameters - outgoing long wave radiation (OLR), GPS/TEC, Low-Earth orbit tomography and critical frequency foF2. These changes characterize the state of the atmosphere and ionosphere several days before the onset of this earthquake. Our first results show that on March 8th a rapid increase of emitted infrared radiation was observed from the satellite data and an anomaly developed near the epicenter. The GPS/TEC data indicate an increase and variation in electron density reaching a maximum value on March 8. Starting on this day in the lower ionospheric there was also confirmed an abnormal TEC variation over the epicenter. From March 3-11 a large increase in electron concentration was recorded at all four Japanese ground based ionosondes, which return to normal after the main earthquake. We found a positive correlation between the atmospheric and ionospheric anomalies and the Tohoku earthquake. This study may lead to a better understanding of the response of the atmosphere /ionosphere to the Great Tohoku earthquake