Volcanic emissions from Popocatépetl volcano, Mexico, quantified using Moderate Resolution Imaging Spectroradiometer (MODIS) infrared data: A case study of the December 2000–January 2001 emissions

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During December 2000 and January 2001, an increase in activity at Popocatépetl volcano, Mexico, was observed in both ground-based correlation spectrometer (COSPEC) data and in imagery from various satellite sensors, including the Moderate Resolution Imaging Spectroradiometer (MODIS), Total Ozone Mapping Spectrometer (TOMS), Advanced Very High Resolution Radiometer (AVHRR), and Geostationary Satellite 8 (GOES-8). Fine ash abundances detected by MODIS ranged between 6000 and 255,000 metric tons, and fine ash abundances detected by AVHRR, measured at different times, ranged between 4000 and 76,000 metric tons. The difference in ranges of ash mass detected by these two sensors depends largely on the difference in data acquisition time between the two sensors in detecting Popocatépetl's ash clouds. However, the difference could also be partly attributed to differences in spatial resolution and band sensitivity, which are believed to be significantly more favorable for MODIS. Mean effective radii for the two sensors images were typically within 10% of each other; values ranged from 5 to 8 μm and were strongly a function of residence time.

Two types of infrared retrieval were used for the detection and quantification of SO2masses — one based on the 7.3 μm SO2 absorption feature and the other on the 8.6 μm absorption feature. SO2 values were attainable using the 8.6 μm retrieval for most images, but were problematic using the 7.3 μm retrieval. Only one SO2 cloud was successfully measured by the 7.3 μm retrieval (January 23rd 2001 04:50 UTC). This cloud was at an altitude of approximately 12 km, the highest cloud in the suite of images analyzed, and yielded an SO2 mass of 16,500 metric tons. This suggests that elevated heights – above ∼ 10 km – are required to negate the effects of atmospheric water vapor upon the 7.3 μm retrieval at tropical latitudes. SO2 clouds for which the 8.6 μm retrieval was successful but 7.3 μm was not were at heights between 6 and 10 km.

Comparison of SO2 retrievals obtained from MODIS images directly to COSPEC measurements was achieved by taking cross sections of the plume in the MODIS SO2maps. Wind data at the appropriate altitude can then be used to calculate fluxes comparable to those measured by COSPEC in units of tons day− 1. The fluxes calculated from the plume transects fell within the range of fluxes measured by the COSPEC, at 5–32 kT day− 1, and suggest more emissions in mid to late December, and lower emission rates throughout January. The MODIS data also complement a ground-based study on magnetic anomalies in which it was observed that more magma was extruded in the January 23, 2001 eruption than in the eruptions in December of 2000. Ash quantification from MODIS imagery suggests that the majority of fine ash was erupted in January of 2001.

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© 2007 Elsevier B.V. Publisher's version of record: https://doi.org/10.1016/j.jvolgeores.2007.09.010

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Journal of Volconology and Geothermal Research