Skip navigation

RAMMB: Regional and Mesoscale Meteorology Branch logo CIRA: Cooperative Institute for Research in the Atmosphere logo NESDIS: NOAA Environmental Satellite, Data, and Information Service logo

Announcement: Please visit out new web application, SLIDER, for every pixel of real-time GOES-16 and Himawari-8 imagery.

Volcanic Ash Principal Component Imagery - Basic Information

Go to detailed information...

Click above for full resolution, click here for animated loop.

Figure 1. Example of Volcanic Ash Principal Component Imagery product over the Okmok volcano in the Aleutian Islands, which erupted in 2008. The product depicts airborne volcanic ash (when present), as dark shades in the lower-right panel. Other panels depict various cloud features as noted, such as the lower-level water cloud, the white shades in the lower-left panel.

Watch a video from the VISIT group explaining the Volcanic Ash PCI product in Windows Media Video (.wmv) or Flash (.swf) format.


1) Product Information:

Who is developing and distributing this product?

The Cooperative Institute for Research in the Atmosphere (CIRA) in Fort Collins, Colorado, together with the NOAA/NESDIS RAMM Branch is developing and distributing the Volcanic Ash Principal Component Image Product.

Who is receiving this product, and how?

The Volcanic Ash Principal Component Image product is created at CIRA and made available online. It will be implemented at the NWS Alaska Region Headquarters in Anchorage.

What is the product size?

The size of one Volcanic Ash Principal Component Image product is less than 0.5 MB, with updates available every 30 minutes. Plans are to improve the temporal resolution, by generating image products every 15 minutes.


2) Product Description:

Purpose of this product:

The Volcanic Ash Principal Component Image product, developed at CIRA, is demonstrated on the RAMSDIS Online web page for GOES-West, because the "split-window" bands are not available on GOES-East.

Why is this a GOES-R Proving Ground Product?

The Volcanic Ash Principal Component Image product demonstrates a unique kind of imagery that is primarily available from older GOES Imager instruments (through GOES-11) and all GOES Sounder instruments (although at lower, 10 km, spatial resolution). The "split-window" bands, that are the best inputs for this product, will reappear in the GOES-R era. GOES-R will feature the Advanced Baseline Imager (ABI) sensor which will be able to produce both higher spatial resolution (2 km) and higher temporal resolution (5 min) version of the Volcanic Ash Principal Component Image product.

How is the product created now?

The Volcanic Ash Principal Component Image product is computed from all 5 bands of GOES imagery, but is heavily weighted by the two longwave infrared window bands available on older operational geostationary satellites (up through GOES-11). (On GOES-12 and beyond, the less-transparent longwave band was replaced by a 13.3 um band used to better detect the levels of clouds. This does not prevent the product from being generated, but results in an altered interpretation).

Click above for full resolution, click here for animated loop.

Figure 2. Example of the Volcanic Ash Principal Component Imagery product over the Redoubt volcano on the Cook Inlet in Southern Alaska, which erupted repeatedly in 2009. The 4 panels show 4 selected PCIs (1, 2, 3, and 5), with PCI-4 not shown. The interpretation of the components is provided on the panels. Volcanic ash appears dark in the lower right panel, whereas cloud features appear in the rest of the panels.

The Volcanic Ash Principal Component Image product is generated day or night, whether or not visible imagery is available. However, at night the components will change due to the absence of reflected solar radiation.

3) Product Examples and Interpretation:

The Volcanic Ash Principal Component Image product is even beter when viewed as an image loop. A real-time example of this 4-panel product as a loop is available on the RAMSDIS Online web page for GOES-West. The center point for analysis can be changed as needed to focus on volcanic events of interest.

An additional step that can be applied to the Volcanic Ash Principal Component Image product is to combine some of the components using RGB (Red, Green, and Blue) color combinations. An example of this is shown in Figure 3, where three of the PCIs are given colors and combined.

Click above for full resolution, click here for animated loop.

Figure 3. Example of the Volcanic Ash Principal Component Imagery product that has been colorized using RGB image techniques. This image over the Redoubt volcano on the Cook Inlet in Southern Alaska is the same time as the image in Figure 2. In this image the volcanic ash plume appears the brightest red, and other clouds features occupy other colors.

4) Advantages and Limitations:

The Volcanic Ash Principal Component Image product provides a visually powerful display of areas of volcanic ash, and other associated cloud features that might interfere with the detection of volcanic ash. The components show volcanic ash as dark in the split-window difference in PCI-5. Other cloud features are seen in other components. The user can learn to distinguish between image features with minimal training, and through the use of examples of this product produced during past volcanic eruptions.

The main disadvantage of the product is that the Volcanic Ash Principal Component Image product, when generated to include visible imagery, will change at night due to the absence of reflected solar radiation. One option is to generate the product on infrared spectral bands only, so that the product will not change from day to night. Alternately, the user can be trained to alter the PCI interpretation caused by changes in solar radiation from day to night. This is aided by observing the Volcanic Ash Principal Component Image product over time. Also, with new images available, potentially every 15 minutes, a relatively rapid evolution of the volcanic ash plume is possible.