Use of GOES-8 Image Data for the Discrimination and Measurement of Volcanic Clouds

David J. Schneider and William I. Rose
Dept. of Geological Engineering and Sciences
Michigan Technological University
1400 Townsend Drive
Houghton, MI, 49931


Image data from the Geostationary Operational Environmental Satellites (GOES-8 and GOES-9) are now useful for determining the eruptive state of volcanoes, to determine temporal trends during eruptions, and to measure the size and location of volcanic ash clouds, which are an aviation hazard. GOES image data are collected in five spectral bands as frequently as every 15 minutes, which makes it useful for aviation purposes, where timely warnings must be given. As a test of the utility of this data, twenty-two GOES-8 images of the March 10-11, 1996 ash emission event at Popocatepetl Volcano, Mexico were analyzed. The volcanic ash cloud was discriminated from meteorological clouds using a brightness temperature difference between GOES thermal-infrared bands 4 and 5, and the position of the volcanic cloud was observed at thirty minute intervals. The mass of fine grained (1-10 micron radius) silicate ash in the cloud was retrieved following the technique of Wen and Rose [1994]. Results demonstrate detection of small ash clouds, with silicate ash burdens of 2-15 kilotonnes. The frequent measurements of airborne ash mass, allows for an estimate of the eruption rate of fine grained volcanic ash, and provide insight into the fallout and dispersion of particles in the atmosphere.


During the past 15 years, there have been more than 80 jet aircraft encounters with volcanic clouds. Seven of these incidents resulted in the in-flight loss of engine power, which could have resulted in the crash of the aircraft, and repair costs through mid-1994 have been estimated at more than $200 million [Casadevall, 1994]. As a result of these encounters, research on the satellite detection and tracking of volcanic clouds has been stimulated. Data from the Advanced Very High Resolution Radiometer (AVHRR), have been used to detect and track volcanic clouds using a dual thermal-IR procedure [Prata, 1989, Schneider and Rose, 1994; Schneider et al., 1995]. Although the AVHRR procedure has been useful, the frequency of available imagery from the polar orbiting satellites (4-6 times per day at the equator) limits its usefulness for aviation purposes, where timely warnings must be given. Geostationary satellites, such as the Geostationary Operational Environmental Satellite (GOES), have higher temporal resolution than AVHRR, but their usefulness has been limited by their limited spectral coverage (just one visible and one thermal channel), and low spatial resolution (7 km at the sub-satellite point for the thermal channel).

The new generation of imagers, currently aboard GOES-8 (centered at 75 W) and GOES-9 (centered at 135 W) have several significant improvements for the detection, tracking and measurement of volcanic clouds. Imager data are now collected simultaneously in five spectral bands (0.52-0.72, 3.78-4.03, 6.47-7.02, 10.2-11.2, 11.5-12.5 microns), at higher spatial resolution (4 km for the thermal channel at the sub-satellite point), and are available as frequently as every 15 minutes. This paper reports on a test of GOES imager data to detect and discriminate volcanic clouds. Twenty-two GOES-8 images of a minor ash emission event from Popocatepetl Volcano, Mexico (March 10-11, 1996) were analyzed using a two band technique, and the results show that it is possible to detect small volcanic clouds using GOES. The mass of airborne volcanic ash was retrieved from the GOES data using a slight modification of the technique developed by Wen and Rose [1994] for use with AVHRR. The frequency of the available imagery allow for detailed observations of the eruptive activity of the volcano.

Volcanic Activity at Popocatepetl Volcano

Popocatepetl volcano (19.02 N, 98.62 W; summit elevation: 5465 m), located 55 km east of Mexico City, started a new episode of explosive activity on December 21, 1994 with a series of small earthquakes and phreatic explosions. Although documentation is poor, there have been about 30 eruptions in historical time, with most of them being mild to moderate Vulcanian steam and ash emissions. (Smithsonian Institution, 1994). For the following two years, the activity consisted mainly of fumarolic activity with occasional small ash emission events.

On March 5, 1996, a small explosion cleared the vent, and between that time, and the period covered by the satellite observations presented herein, the activity was characterized by a number of small, continuous ash emission events. These ash emission events typically lasted for several hours to tens of hours, and were accompanied by continuous tremor, which has been interpreted as high-speed exhaust of volcanic gases that remobilize non-juvenile ash (Smithsonian Institution, 1996). On March 7, 1996, the tremor amplitude and duration increased to levels exceeding those of December 1994, and persisted until 2000 UT on March 10, when it slowly decreased until its end at 2110 UT. (Smithsonian Institution, 1996). The seismic activity continued at low levels until 0000 UT on March 12, when continuous tremor resumed. The satellite observations in this paper are of the end of continuous tremor, and the subsequent low-level seismic activity.

Volcanic Cloud Detection: Thermal Band Difference Method

Thermal image data from two channels (band 4: 10.2 to 11.2 microns ; band 5: 11.5 to 12.5 microns) of the GOES-8 imager were used in this study. Raw sensor counts (10-bit data) were converted to radiance values using the standard calibration techniques, and the radiance values were converted to brightness temperature by inverting the Plank function. The image data were rectified to an equal area projection (Lambert Azimuthal) from the standard GOES image format, and resampled to 4 km spatial resolution. Following work conducted on AVHRR data, band 4 minus band 5 brightness temperature difference images were used to detect the volcanic cloud, and distinguish it from meteorological clouds. Many volcanic clouds have negative AVHRR band 4 minus 5 brightness temperature differences (Prata, 1989; Schneider et al., 1995), while meteorological clouds generally have positive brightness temperature differences (Yamanouchi et al, 1987). Twenty-two GOES-8 images were analyzed using a thermal band difference technique, and the volcanic cloud was detected and observed in all of them. These images cover 10.5 hours of activity, from 1715 UT on March 10, 1996 to 0345 UT on March 11, 1996, at 30 minute intervals.

The band subtraction technique is demonstrated in Figure 1, an image from a small ash emission event of Popocatepetl Volcano, collected at 1945 UT (local time=UT-6) on March 10, 1996. Figure 1a is a band 4 image, and Figure 1b is the corresponding band 4-5 image. In the band 4 image (Fig. 1A) bright features, such as high clouds, are cold (~-20 C.), and dark features, such as land, are warm (~25-30 C). Note that although a small bright feature exists near the volcano, it looks very similar to other features in the image. By comparison, in the band 4-5 image (Fig. 1B), bright features have a negative brightness temperature difference (maximum value: -4 C), while dark features have positive differences (maximum value: 2 C). In this image, the detected volcanic cloud is indicated by its characteristic negative temperature difference (bright feature), and clearly discriminated from meteorological clouds (dark features).

Figure 1

Volcanic Ash Mass Retrieval

The mass of fine-grained (1-10 micron radius) volcanic ash was retrieved from the GOES image data, following the technique developed by Wen and Rose (1994) for use with AVHRR. The retrievals assume a single layer, partially transparent cloud, which is parallel to a homogeneous underlying surface, and composed entirely of spherical andesitic particles having a lognormal size distribution. The retrieval model was modified to account for the slight difference in position of the GOES band 4 (10.2 to 11.2 microns) versus AVHRR band 4 (10.3 to 11.3 microns). The volcanic cloud height was estimated at 400 mb (6.5 km), by comparing the cloud trajectory to radiosonde wind data from Mexico City, which yields a corresponding radiosonde temperature of -23 C.

The results of the mass retrievals are shown in Figure 2, and demonstrate that GOES image data can be used to detect and measure the volcanic ash from small explosive eruptions. The retrieved mass ranges from 2-15 kT of volcanic ash, which compares very well with a mass retrieval conducted on an AVHRR (4km spatial resolution) image collected at 2000 UT on March 10. Based on cloud height, the event described in this paper had a Volcanic Explosivity Index (VEI) (Self and Newhall, 1982) of 1 or possibly 2. The temporal resolution of the GOES imager, should allow for more observations of the highly ephemeral ash clouds from small to moderate explosive eruptions (VEI 1-2), which occur much more frequently than moderate to large eruptions (VEI 3-4) (Simpkin and Siebert, 1994).

Figure 2

GOES-8 Observations

Maps of the retrieved volcanic ash mass are shown in Figure 3, and document the extent of the ash plume, and the eruptive state of the volcano, from 1715 UT on March 10 to 0215 UT on March 11 at one hour intervals. In the first image analyzed (Fig. 3A), the detected volcanic cloud extended approximately 140 km south of the vent, was about 15 km wide, and covered 1300 km2. By 1915 UT (Fig. 3C), the cloud started to fan out and form a v-shaped plume, with its vertex at the vent. The detected cloud had a maximum width of 45 km, at a point 75 km south of the vent, and covered 2450 km2. The area of cloud continued to increase, and by 2115 UT (Fig. 3E) the cloud covered 5350 km2, and was 75 km wide at a point 100 km south of the vent. By 2245 UT, the v-shape of the cloud starts to diminish, and the cloud starts a transition to an elongated plume. By 0015 UT on March 11 (Fig. 3H), the plume appears to detach from the vent, and drift to the south. Ash in the drifting cloud is visible in the imagery for about 3 hours, until 0245 UT. At 0115 UT (Fig. 3I), a new, much smaller plume is visible, extending 25 km from the vent. This plume was the result of an ash emission event which started at 0045 UT, and was accompanied by a small 2-minute duration volcanic earthquake (Smithsonian Institution, 1996). By 0215, the plume extends about 75 km to the south, and covers 2125 km2. The small plume detaches from vent at 0315 UT and is seen drifting to the south until the end of studied imagery at 0345 UT on March 11, 1996.

Figure 3

MPEG of March 10-11 1996 volcanic cloud from Popocatepetl. 1715UT March 10 to 0245UT March 11 at 30 minute intervals. GOES-8, band4-band5.


The frequent measurements of ash masses in volcanic clouds, available with the GOES imager, allows for a new type of monitoring of activity. The fall rate for simple particles with an effective radii of 5 microns (as determined from the mass retrieval model) and an initial height of 7 km, is 300-400 m/hr. Thus, the ash would be expected to be removed in about 10 hours with no replenishment. The rate of mass increase measured from 1700 UT until 2300 UT on March 10 show that the volcano was erupting continually at a rate which is faster than the rate of fallout, which resulted in the increase in the total retrieved mass shown in Figure 2. The decreasing mass observed after 2315 UT show that eruption rate declined, and this was followed by the observation of detachment at 2345 UT. The half life of the mass of the drifting cloud is about 2 hrs, suggesting that the ash may be falling out faster that could be explained by the fall of simple particles, perhaps reflecting agglomeration.

Figure 4

An estimate the eruption rate of fine ash (1-10 micron radius) was made and is shown in Figure 4. The estimate was made by subtracting the cloud mass at t0 from the subsequent cloud mass, t1, and adding a constant fallout rate [(mass t1 - mass t0) + fallout rate)]. A three- point moving average was applied to individual mass retrieval values to reduce the noise level, and the fallout rate was determined from the mass retrievals of the detached cloud (from 0015 UT to 0215 UT on March 11.) Two main pulses of activity are indicated in figure 4; one which ends at 1915 UT, and the other from 1915 UT to 2315 UT. A minor pulse from 0045 to 0315 UT on March 11 is also observed. Because the eruption rate estimate is based on the satellite retrievals of airborne ash, which is typically several percent of the total mass of an eruption, the actual rate may be up to 100 times greater.

A primary factor in the successful discrimination of the volcanic cloud from this small explosive event was the high thermal contrast (as great as 50 C) between the volcanic cloud and the underlying surface. Due to the height of the volcano (5465 m), small ash clouds that rise several kilometers above the vent, cool to the ambient atmospheric temperature of -20 to -30 C. This combined with warm ground temperatures (20 to 25 C), produce adequate thermal contrast. It is important to note that the discrimination was done under clear meteorological conditions, and it is doubtful that the volcanic cloud would have been detected if it was overlying cold, meteorological clouds, because the thermal contrast would be much lower.

The mass of airborne ash, and the areal extent of the detected volcanic cloud, increased after the end of continuous tremor, at 2110 UT on March 10. AVHRR data from the period of continuous tremor was analyzed to determine if the GOES analysis post-dated a larger ash emission event. The area of the volcanic cloud detected by the AVHRR at March 10 at 0845 UT, was only 1000 km2. Thus, it seems that the GOES imagery did record an actual increase in the ash emission, after the end of continuous tremor. It is unknown why the eruption rate of volcanic ash increased after the volcanic tremor stopped, but these observations reinforce the usefulness of the satellite imagery in determining the eruptive state of the volcano.


The thermal band difference technique was successful in discriminating the very small volcanic clouds from Popocatepetl volcano, under favorable atmospheric conditions. The frequency of available imagery provides much greater detail on eruptive events than could be observed using AVHRR. Twenty-two GOES images were analyzed for this study, for a time period that was covered by just two AVHRR images. For this study the GOES imager data was analyzed at 30 minute intervals, but imagery was available for analysis at 15 minute intervals. The high temporal resolution enables observation of many details of the eruption, especially time trends. Mass retrievals document an increase in ash emission over a six hour period, and the fallout of ash that followed. Analysis of the imagery was able to determine when the volcanic cloud detached from the vent and drifted away, and was able to detect the onset of a new, small, eruptive pulse.

The high temporal resolution of the GOES imager data make it possible to provide frequent observations of the status of volcanic activity, which is vital to the reduction of aviation hazard, and to estimate the eruption rate of fine volcanic ash. In addition, cloud mass retrievals can be used to verify cloud trajectory and fallout models, which are used to forecast the movement of volcanic ash [Heffter and Stunder, 1993; D'Amours, 1994] for aviation purposes. It might be possible to improve the forecasts by providing frequent updates to the models.


We would like to thank Mellisa Seymour of the Earth Scan Laboratory, Coastal Studies Institute at Louisiana State University for providing the GOES data. Funding was provided by the NASA Earth System Science Fellowship Program.


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