DESCRIPTION:
Video and Television Surveillance Monitoring Systems

Visual monitoring of Mount St. Helens volcano by closed-circuit television allows eruptive events to be observed as they occur and an immediate evaluation of potential hazards to be made. Use of the remotely controlled TV system also reduces risks to personnel during eruptions by eliminating the need for close-in observers on the north side of the volcano, and reduces to need for continuous observation from aircraft.

Visual monitoring of Mount St. Helens volcano by closed-circuit television was started in July 1980. The TV system consists of a remotely controlled video camera situated on a ridge 9 kilometers north of Mount St. Helens, a microwave repeater station west of the volcano, and viewing and recording equipment at the Emergency Coordination Center (ECC) in Vancouver, Washington. There, the picture is monitored during daylight hours by personnel of the U.S.Geological Survey and the U.S.Forest Service. The TV surveillance system was installed to allow direct visual monitoring of the volcano by personnel in Vancouver, to reduce or eliminate hazards to ground observers during eruptions, and to reduce the need for, and thereby the cost of, continuous observation from aircraft. A system was selected, assembled, and installed near the volcano by July 15, and became fully operational on July 20.

Advantages of the TV surveillance system, in addition to those mentioned above are as follows:

• Eruptive events can be observed as they occur and their potential dangers can be immediately assessed.

• The volcano can be examined at any time during daylight hours except during periods of cloudy weather (at night, incandescent events can be observed).

• The video system permits events at the volcano (for example, eruption plumes, avalanches) to be correlated with other monitoring data received by telemetry at the Emergency Coordination Center in Vancouver.

• Weather conditions can be viewed each morning prior to planning the day's activities at and near the volcano.

• The video signal can be recorded on magnetic tape to provide a record of events for subsequent scientific studies.

The video system provides a sharp, live color picture of the mountain and has proven to ba a valuable monitoring tool for hazards response and in planning daily operations. During periods of good weather in July and August, the system was operated for as much as 13 hours per day. Electrical power is adequate for about 65 minutes of pan, tilt, and zoom functions per day, which permits viewers in Vancouver to investigate the state of the volcano each morning and to look for changes that may have occurred overnight. ...

The system is used regularly to examine fluctuations in gas emission, avalanche frequency, local wind conditions, blowing ash in potential work areas, and eruptive events. The system is also useful for briefing scientists and public officials without visiting the volcano.

Video monitoring using slow-scan television has proved to be a valuable monitoring tool at Mount St. Helens. The system provides a permanent video record of events at the volcano and is also an important aid in planning field logistics and operations. Such a system is particularly valuable at remote volcanoes, where continuous observations are otherwise no feasible.

Video monitoring of Mount St. Helens volcano using slow-scan television (SSTV) began on September 4, 1987. The system consisted of a video camera, a scan converter, a radio transmitter, and a power system, all located on a ridge 8.5 kilometers (5 miles) north of Mount St. Helens; a radio repeater on a high point west of the volcano; and a scan converter, video monitor, and recording equipment at the Cascades Volcano Observatory (CVO) in Vancouver, Washington. After several months of operation, the system was modified to turn off a night and back on again in the morning in order to conserve power. A later enhancement included the capability to remotely control various other functions, such as zoom and pan.

Video monitoring of active volcanoes has several attractive benefits.

• First, there is the potential to significantly reduce the cost of monitoring a volcano. Adverse weather conditions as well as steam and dust conditions can be observed and considered before planning daily field activities.

• Second, the need for aircraft observation flights is reduced.

• Third, a reliable video system can significantly reduce hazards to field personnel during periods prior to and during eruptive activity, by supplementing on-site observations of field personnel. Remote variable-power zoom can allow observers to remain a safe distance from the activity.

• Fourth, video information available during daylight hours is easily correlated with other telemetered monitoring data to assess current conditions.

At night, an SSTV monitoring system could utilize an infrared camera for monitoring hot spots. Or a video cassette recorder (VCR) could be connected at the output of the video camera in parallel with the output of the scan converter and triggered to turn on in response to either a control signal from a base station or a signal from a monitoring device in the field such as a seismometer or a trip wire, in order to continuously record events such as eruption plumes, debris avalanches, or lahars for subsequent detailed analysis. It is even possible to design a transportable SSTV system that could be rapidly deployed at volcanoes threatening to erupt. Finally, video information can be stored on magnetic tape for future analysis.

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