Volcano Watch — Santa is not the only eye in the sky on Christmas

While Santa may know if you've been bad or good, other observational systems also travel far above us, collecting additional information. Since 2004, Santa has shared the heavens with a satellite-based imaging instrument known as OMI.

While Santa travels by sleigh, the Ozone Monitoring Instrument (OMI) rides on NASA's Earth Observing System (EOS) Aura research satellite. Aura, which is Latin for "breeze," researches the composition, chemistry, and dynamics of the Earth's atmosphere. Instruments aboard Aura measure environmental conditions such as stratospheric ozone, air quality, and climate. Santa flies but once a year, but Aura has daily global coverage.

As the Aura spacecraft orbits the earth, OMI takes a sequence of downward-looking images along a strip of the earth's surface. Each image represents the amount of sunlight energy at precise wavelengths (or frequencies) within the ultraviolet and visible range that is reflected by Earth and its atmosphere. Just as a color photo can be represented by separate red, green, and blue images, OMI images are made up of light intensities at hundreds of different frequencies. Ultraviolet light energy, visible to OMI, is beyond the violet end of visible light and is therefore invisible to the human eye. We know that this type of energy is strongly absorbed by some atmospheric pollutants and OMI uses this fact to measure the distribution of many pollutants worldwide.

For example, OMI can map atmospheric pollution products such as nitrogen dioxide (NO₂), sulfur dioxide (SO₂), bromine monoxide (BrO), chlorine dioxide (OClO), and tiny suspended particles known as aerosols. OMI can distinguish between smoke, dust, and sulfur containing aerosols. It also measures cloud pressure and coverage, which provides data to determine the amount of ozone pollution in the troposphere, the lowest layer of atmosphere, where we live and breathe.

OMI data is also being used to track the size and distribution of the hole in the stratospheric ozone above Antarctica. And this past fall, it produced remarkable images showing the smoke aerosol layer generated by the fires in Southern California as it drifted over the Pacific.

In spite of the numerous shopping mall spin-offs, Santa is a unique character. OMI, on the other hand, comes from a long line of remote sensing instruments which include NASA's retired Total Ozone Mapping Spectrometer (TOMS) and the European Space Agency's Global Ozone Mapping Experiment (GOME). But OMI excels beyond its older siblings' capabilities. Compared to TOMS, OMI can resolve details on the ground that are 8-times smaller and can detect 10-times lower concentrations of SO₂.

Since OMI detects SO₂ and ash, it is also useful for monitoring volcanic eruptions. With the increased sensitivity of OMI over its predecessors, it detects low-level passive volcanic degassing in addition to the dramatic explosive plumes measured in the past by TOMS.

While TOMS easily detected the 19 megaton eruptive plume from Mount Pinatubo, and could even detect the 0.13-0.19 megaton plume from the Mauna Loa 1984 eruption, OMI is able to see the eruptive plume from Kīlauea, which ranges between 0.001 and 0.004 megatons per day. A rich collaboration between scientists studying space-based measurements and those studying ground-based data is evolving, so that reliable daily measurements of volcanic degassing can be provided by OMI. OMI's measurements of volcanic clouds are already helping to identify volcanic emergencies and can be used to help divert aircraft from potentially dangerous volcanic ash and gas plumes.

As Santa makes his historic flight, OMI will also cruise the skies, showering us with information that helps track volcanic eruptions, trace pollution sources, and monitor effects of climate change. For more information on OMI and other space-based instruments visit NASA's website.

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Volcano Activity Update

Kīlauea summit and Pu`u `O`o continued to deflate. Seismic tremor levels at the summit increased for the last few weeks but are still at low levels. Earthquakes were located mostly beneath Halema`uma`u Crater and the south flank faults.

On July 21, 2007, lava began erupting from a set of fissures on the east flank of Pu`u `O`o. Eruptive activity soon stabilized at fissure D, 2.3 km (1.4 mi) northeast of Pu`u `O`o. For the last several months this lava was directed entirely into a perched channel, consisting of separate pools often separated by bridges of cooled lava. At dawn on November 21, lava began to erupt directly from fissure D, outside of the perched channel, creating the Thanksgiving Eve breakout (TEB) flow. Lava supply to the original perched channel has been, in part, redirected through this new outlet, cutting off supply to the eastward tube which had been feeding flows in the vicinity of Pu`u Kia`i through much of November.

The TEB flow has built itself vertically and laterally over the last several weeks, and has not surpassed the maximum along-flow distance of 2 km (1.2 mi) which it reached in the first few days of its emplacement. During the last week TEB flows have been breaking out of the south base of the TEB shield, from a point approximately 500 m (0.3 mi) south of fissure D, and traveling another 500 m (0.3 mi). Just north of the TEB flows, the original perched channel has been highly active over the last week. Lava has been at or near the rim of Ponds 1 and 3, though has not yet reoccupied Pond 4. Extensive seeps have developed on the east and west sides of Pond 3, with the east seeps most active. These east seeps have grown vertically, developing a wide terrace, and host a large area of ponded lava.

Minor incandescence in Pu`u `O`o was observed for two nights in early December, but has otherwise been absent since August 31. As in years past, Pu`u `O`o likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially enroute to the erupting fissure. Sloughing of Pu`u `O`o into its own crater since late August has left numerous fresh cracks on the north rim and south flank of the cone.

Vent areas are hazardous. Access to the eruption site, in the Pu`u Kahauale`a Natural Area Reserve, is closed (http://www.state.hi.us/dlnr/chair/pio/HtmlNR/07-N076.htm).

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.2 earthquake occurred at 7:53 a.m. H.s.t. on Thursday, December 20, 2007, and was located 7 km (4 miles) northwest of Waiki`i at a depth of 34 km (21 miles).

Mauna Loa is not erupting. Three earthquakes were located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates.