USGS' seismic shift
The U.S. Geological Survey upgrades its earthquake monitoring system in Northern California to digital, operating in the newly available upper half of the 1.7 GHz radio frequency band
- By William Jackson
- Dec 15, 2008
THE U.S. GEOLOGICAL SURVEY has moved its seismic network in the
San Francisco Bay area into a new slice of the radio spectrum.
The agency moved to the upper half of the 1.7 GHz band, becoming
one of the first agencies to turn over newly vacated spectrum in
the bottom half of the band to commercial users who bought rights
to those airwaves in 2006.
The new network expands the microwave backhaul capacity of the
earthquake monitoring system from 1.5 megabits/sec to 24
“That comes at just the right time,” said Gray
Jensen, supervising electrical engineer in the USGS office at Menlo
Park, Calif. Although 1.5 megabits/sec has been adequate, the
network was reaching its capacity as the monitoring system
That development also came at just the right time for T-Mobile,
which bought licenses in the vacated spectrum in northern
“We knew the cellular phone operators were eager to move
in,” Jensen said. “We still have things to do,”
such as integrating network management systems into the new
frequencies. However, the network now is operational in its new
home in the radio frequency spectrum. “Our main goal was to
get the basic system installed, and then take care of the other
issues later,” he said.
USGS dodged a bullet in the transition. It was originally
thought that the network would have to be moved out of the 1.7 GHz
band entirely, all the way up to the less-crowded 8 GHz band, which
could have delayed the move for years and substantially increased
the network’s cost as a new physical infrastructure was
engineered and installed. However, when frequencies adjacent to the
original network became available, the Alcatel- Lucent government
service subsidiary LGS was able to provide a new radio system that
would work on the existing infrastructure.
Meanwhile, it wasn’t simple to plan and install a new
system on the existing towers without interrupting network
“Logistics-wise, it was a Herculean task,” said Tony
Boykins, LGS civilian agencies account executive.
But the work was substantially completed four months ahead of
schedule, and digital seismic data now is streaming into Menlo Park
over the new links.
The network links about 450 stations that monitor ground motion
along northern California fault lines, about half of them
connecting with eight mountaintop microwave hubs to aggregate data
and backhaul it to the central office.
“It’s the backbone of the system,” Jensen said
of the microwave backhaul. But satellite links and even DSL lines
for nearby stations are also used where microwave hops are not
practical or necessary. “We use a lot of telemetry
paths” to keep down costs and provide diversity so that a
strong quake will not knock out the entire system.
The stations continuously monitor ground movement in fault areas
to provide real-time warnings about earthquakes and data for
researchers. Many of the stations are located in remote, rugged
areas where communications infrastructure is not easy to come
“We decided in the early 1980s to put together a microwave
system of our own when the cost of telephone lines started to go up
after deregulation,” Jensen said.
USGS built its own system of microwave relay towers for backhaul
south from the Bay Area and connected with an Army Corps of
Engineers network using the same Motorola equipment to the north.
When the corps gave up its network, USGS took it over and now
operates the entire system from north of Eureka south to San Luis
Originally it was an analog system. Stations sent data via FM
radio to the microwave hubs, which passed it along via Motorola
radios operating in the 1.710 GHz to 1.755 GHz band. Data was
gathered at the Menlo Park office and was digitized. The microwave
links provided the equivalent of as many as 120 channels of analog
“It’s an audio tone,” Jensen said of the data.
“If you listen to it, it sounds like a whistle, and it
warbles when the ground moves.”
Several years ago, USGS began changing the configuration,
putting modems into the microwave sites so they could send more
efficient digital signals to the central office. At the same time,
it began upgrading the monitoring stations to send data in digital
“We were living in a dual world,” with digital and
analog signals, Jensen said. “That was the situation we were
in when the transition came along.”
From Sonet to Ethernet
The transition resulted from the Federal Communications
Commission’s Advanced Wireless Services (AWS) Spectrum plan,
intended to accommodate the rapid growth in commercial wireless
services by licensing additional government spectrum for commercial
Originally, it was expected that the entire band from 1.710 GHz
to 1.850 GHz would be sold off, which would have been bad news for
USGS and others in similar positions.
“We had been eyeing the 8 GHz band for some time,”
as an alternative location for the network, because it is less
crowded, Jensen said. “But that was not a very desirable
“The higher you go in the spectrum, the shorter the
distance the signal will go,” Boykins explained.
That meant additional relay towers would be needed for the added
hops. Finding adequate sites, doing environmental impact studies
and constructing the facilities would have been expensive and
Fortunately, when FCC auctioned AWS spectrum in 2006, it sold
only the 1.710 GHz to 1.755 GHz band, leaving the upper end, up to
1.850 GHz, in government hands. Unfortunately, there was no
commercial equipment operating in this band.
“For the past five years, they had been saying that this
spectrum was going away,” Boykins said, so vendors were not
building for it.
But when USGS began asking for help, LGS was able to modify the
Alcatel- Lucent MD-8000 series radio with existing equipment to
operate in the required lower band.
Because the upper 1.755 GHz band is in the same propagation
range as the band originally used by USGS, LGS was able to use the
same infrastructure for the new radio system, allowing a relatively
USGS began talking with LGS about a new radio system in January
2006, before the FCC auction. It took the company about six months
to test prototypes of its new MD 8502 model radio and establish
that it was commercially viable. USGS released a request for
proposals in September 2007, awarded the contract in December and
gave the company 12 months to get the new system in place. It took
about 45 days to design the new system.
Installation on the existing infrastructure began in early 2008
and was completed in August.
William Jackson is a Maryland-based freelance writer.