HVO/RVTS-1, a prototype Remote Video Telemetry System, is currently in use at the U.S. Geological Survey's Hawaiian Volcano Observatory (HVO). Recording of video images transmitted at near real-time from the currently active Pu`u `O`o vent on the east rift zone of Kilauea Volcano, began in early April 1997. Since that time, the RVTS-1 has proven its value and reliability as an eruption monitoring device and promises to be a long-lived addition to HVO's real-time instrumental array.
The system comprises a unique configuration of mostly "off-the-shelf" products. The key components are a HyperScanTM digital transmitter module and a desktop computer with HyperScanTM receiver software (Sensormatic, Inc.). The high-speed broad-band radio communication link is achieved using FreeWaveTM Wireless Data Transceivers (FreeWave Technologies, Inc.). The receiver software package allows for near-real-time, high-resolution image display along with storage and review of digital images in a moving picture mode.
This report provides a technical overview of the first remote video telemetry system of its type. The HVO-RVTS-1 is significantly more advanced than slow-scan video telemetry developed by USGS for monitoring Mount St. Helens in 1987 (Furukawa, et al. 1992). Also, this system provides a more robust, portable and low-cost alternative to the closed-circuit, microwave TV system that was successfully used by the USGS at Mount St. Helens in 1980 (Miller and Hoblitt, 1981). There is sufficient information provided herein to reproduce the new system. Detailed instructions on the installation and operation of system components is beyond the scope of this report and the reader is referred to well-written equipment manuals supplied by respective manufacturers. A brief summary of recorded eruptive activity from April through September 1997 is presented to demonstrate the utility and value of the system as an eruption monitoring tool. Finally, suggestions are made for improvements which could lend greater versatility to this prototype system for live volcano monitoring.
For the purpose of programming transmission/reception parameters, the FreeWaveTM Transceivers are uniquely identified by call numbers (unit serial numbers) and assigned as "Master", "Repeater" and "Slave" modems in a "point-to-point" array. In order to avoid interference with other FreeWaveTM arrays, a single and unique frequency-hopping interval is programmed into all three in-line Transceivers. The RVTS array has all in-line modems configured with a 19,200-baud data transmission rate, which is compatible with the computer communication port at the receiver hub and sufficient for continuous image transmission.
The ~34-km-long link between transmitter and repeater is accomplished using a 6 element directional Yagi antenna (896-960 MHz, 12 dB gain). The Mauna Loa repeater and HVO receiver modems, which are ~16 km apart, each use a 33-inch omnidirectional whip antennae (896-940 MHz, 5 dB gain).
A precise discussion of similar telemetry system capabilities and equipment options is provided on the Internet website of the University NAVSTAR Consortium (UNAVCO) for GPS research (http://www.unvavco.ucal.edu). Details of HVO/RVTS-1 telemetry equipment specifications and installation instructions are provided by the FreeWave manual and information can be obtained at the FreeWave Internet Website (http//www.freewave.com).
2a) Transmitter Hub (September 11, 1997): 1) Transmitter Hub Container: an environment-proof fiberglass box with hinged lid housing four 12V deep cycle batteries (in base) and a charge regular and transmitter instrument package in separate sealed cases;
2) Solar Panel Array: 200 watt, wired to charge regulator in the transmitter hub container.
3) 6 Element Directional Yagi Antenna with 896-960MHz transmission band and 12db elevated feed gain, connected to the FreeWaveTM data transceiver in the transmitter hub container; 4) Remote Camera Site (C3)
2b) Transmitter Instrument Package (September 11, 1997): 1) HyperScanTM TX50H Digital Transmitter Module; 2) Camera Event Timer (FB Engineering); 3) FreeWaveTM DGR-115H 115kbaud Wireless Data Transceiver 4) Battery Charge Regulator (24V,16amp) connecting the Solar Array to the four 12V battery bank and with a terminal strip for 12V power lines to all transmitter hub devices. 5) Dessicants and Acid Absorbers contained in air-permeable bags are placed in all sealed equipment boxes to further prevent equipment deterioration in noxious environmental conditions
The HyperScanTM TX50H Digital Transmitter Module converts the analog camera video signal inputs from up to four on-site cameras into digital signals. The digital video image data from each camera is stored in memory, along with date, time and alarm information. Stored digital images are processed by a proprietary image compression routine (HyperScanTM) and sent via RS232 output to the radio transceiver module. Primary HyperScanTM image files, referred to as "training images," are sent in their entirety. In subsequent images, called "delta images," only changes in training image files are sent, thus enhancing efficiency of transmission. The desired frequency of training image collection and processing is programmable from the receiver hub using HyperScanTM RX-50S software and is set at 5-minute intervals in the current system. Additional details on HyperScanTM equipment can be obtained by consulting the HyperScanTM system operating and instruction manuals and general product specifications are posted by Sensormatic Inc., Video Products Division on the Internet at http://www.sensormatic-vpd.com.
The FB Engineering "Camera Event Timer" sends a timed electronic pulse to the HyperScanTM Digital Transmitter Module. The transmitter responds to this pulse by signaling the receiver hub to save a series of incoming images. This image-recording condition is referred to by HyperScanTM as an "alarm condition". The timing device has a 10 position DIP switch that can be configured to trigger alarm conditions every 1 minute for up to 9 minutes or at 10 minute intervals for up to 90 minutes. A 5-minute alarm trigger interval is used by the current system, thus enabling the receiver hub to save several images from each camera every 5 minutes.
The Polaris VT80C and Cohu 2222 security cameras both suffered non-warranty damage under adverse field conditions. The Panasonic "TV camera" images are hampered by inaccurate auto white balance corrections and by the restricted auto iris range set by an optimal day/night filter. Among the cameras tried, the Canon VCC1 MKII is recommended for durability, simplicity and image quality. This unit also has built-in capabilities for remote control of Pan-Tilt-Zoom (PTZ). The possibilities for configuring PTZ control via a simple radio communication link are being explored.
The transmission of video between remote cameras and the communication hub at Pu`u `O`o is accomplished in two ways. Most camera sites have been placed at the end of 50 to 75 m of heavily insulated coaxial cable. For longer distances a fiber optic connection is desirable. A fiber optic cord is less prone to environmental deterioration than coaxial cable and it will not attract lightning. A ~100 m-long fiber optic connection has been used at two remote camera sites. The fiber optic line requires a powered signal converter at each end and may necessitate deployment of a camera-site power station. The signal converter at the camera end (fiber optic transmitter) converts the analog video signal from the camera into a pulse frequency modulated signal for optical transmission. This process is reversed by the fiber optic receiver at the remote transmitter hub, where the reconstructed analog signal is digitized, encoded and sent to HVO via the Mauna Loa repeater. There is no discernible difference in the quality of images received from the system that can be attributed to the use of either coaxial cable or expensive fiber optics at the remote camera sites.
