No turn's too tight for Guard
- By William Jackson
- Aug 10, 1998
Every day about 350 vessels visit the Port of Houston, one of the nations busiest
They have a lot of dangerous traffic, said Lt. Mike Johnston, an engineer
for the Coast Guards Shore-based Systems Engineering Branch.
The ports service area includes not only Houston and Galveston, Texas, but also
Texas City, the nations busiest petrochemical port for container loads of hazardous
chemicals. The 54 nautical miles of channel are narrow and winding, making travel risky.
Houston is one of a handful of U.S. ports using the Vessel Traffic Service (VTS)
system. Its system uses a network of radar, video and radio links to direct ships much as
air traffic controllers do at the nations airports.
The Houston service recently replaced its analog microwave video links with compressed
digital transmission and installed fiber-optic cable to carry radar signals.
The old radar had been in place since 1975, and the analog video dated back to the late
1980s, said Lt. Mark Gill, the operations officer in Houston. Not only were the old
devices unreliable and expensive to maintain, but spare parts were hard to find.
The new radar and communications upgrade is a welcome addition, Gill said,
in spite of the usual headaches involved in switching systems.
Large ships, towing vessels and ferries are required to use the VTS, Gill said. They
must report by radio at 13 checkpoints through the channels from Galveston to Houston. VTS
controllers return information about traffic, weather advisories and dangerous conditions.
In addition to the radio contact, controllers also keep tabs on traffic via radar in
lower Galveston Bay. But for about 35 miles, the channel is too narrow and twisting for
effective radar coverage. Video picks up where the radar leaves off.
There are 11 video sites along the channel with two cameras at each site, one facing
upbound and one downbound. Until June, live analog video signals arrived at the VTS Center
over microwave, which was expensive to maintain and unreliable in bad weather.
The new system uses 11 LiveSystem encoders and transceivers from Optivision Inc. of
Palo Alto, Calif. They compress Motion Picture Experts Group 1 video streams, which are
fed to a 7206 router from Cisco Systems Inc. of San Jose, Calif.
The signals go over a T1 Ethernet link to the VTS Center, where another Cisco router
distributes them to five LiveSystem decoders. Controllers view the images on 15-inch
monitors at PCs running Optivisions LiveWare client software.
Radar data goes through a radar processor and over a fiber-optic link to the center,
where it is combined with map data and displayed on 21-inch Hewlett-Packard Co. monitors.
The center records video and radar data on a Hewlett-Packard AutoRAID disk array and
periodically dumps data to tape for storage.
The system will not be complete until all ships entering the port have Global
Positioning System transponders that integrate with a VTS computer system to track their
Ship positions now are logged manually on what Gill called a card-on-a-board system. He
said the shore-based computer system will replace the board system late this year. But
until transponders become more common on ships, location data must be entered manually.
The Coast Guard does not have the authority to require the worlds shipping fleet
to use GPS transponders. Tests are under way, however, of a portable unit that a pilot can
carry aboard when a ship enters port. Gill said GPS transponders on ships would not be
common until 2000 or later.
William Jackson is a Maryland-based freelance writer.