Sea of Shadows eBook - Navy Thriller.com

SEA OF SHADOWS 115
The P-3 continued launching sonobuoys at precisely measured
intervals, turning occasionally to begin another row. Buoy after buoy shot
from the launch tubes, each spinning down toward a pre-selected spot in
the ocean, until they formed an integrated field of sonar sensors: a Briar
Patch.
In Shari’s left ear, the TACO’s voice said. “Buoy 12 won’t tune up.
All other buoys are up and operational.”
“Copy,” said Shari. “How big a hole does that make in our coverage?”
“Negligible,” George said in her ear.
Andy keyed his mike. “Do you want to swing back around and re-seed
buoy 12?”
“It’s a tight pattern with a lot of coverage overlap,” George said. “We
can reseed, if it’ll give you a warm-fuzzy, but it’s not really necessary.”
“You’re the USW guru,” Shari said. “I’m just the bus driver.”
“Copilot concurs,” Andy said. “If you’re happy, we’re happy.”
“Roger,” said George. “Looks like we’re getting some LOFAR data
now.”
LOFAR is an acronym for Low Frequency Analysis and Recording.
It’s a method of acoustic processing that takes the noise detected by a
sonar sensor and strips it apart into individual component frequencies. By
comparing those frequencies against a catalogue of known acoustic
sources, it is often possible to classify the source of a particular noise.
A skilled acoustic analyst can read a LOFAR gram the way an average
person reads a newspaper. The process is largely one of elimination.
Three-bladed propellers have different characteristics than four-bladed
propellers. Engines with in-line cylinders generate different frequencies
than V-configured engines. Four-pole electric motors make different
tonals than two-pole motors. Chinese-built ventilation fans are different
from French-built fans, which are different from Russian-built fans.
Different hull designs have different hydrodynamic characteristics, which
create identifiable sounds.
Sometimes, the majority of the contact's frequencies are common to
several possible sources and the resulting classification may be
ambiguous: This is a non–Russian-built Type I diesel submarine—
probably Chinese but possibly Korean. Other times, the classification can
be startlingly exact: This is a Russian-built Akula submarine hull Number
8.
From their display consoles, the two Acoustic Sensor Operators began
the process of classifying the frequencies coming in from the sonobuoys.
After several minutes, George’s voice came over Shari’s headset. “All
buoys are cold.”