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Unique and Patented CODAR Features
Give SeaSondes® the Distinction of Being the Only HF Radar
Commercially Available Today as a Truly Complete Operational
Ocean Monitoring System.
All Required Radar Hardware & Software Are Designed and
Implemented by CODAR
-- No Dependence on Third Parties for Any Elements.
• CODAR Invents Radar
Direction Finding to Replace Conventional Phased-Array Antenna Beam Forming:
[Barrick, D.E. and M.W. Evans (1979), CODAR: A coastal HF radar
for real-time current mapping, U. S. Patent 4 172 255]
This
breakthrough got rid of the large, cumbersome, expensive, conventional phased-array
antennas that had hindered widespread HF radar acceptance.
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Document << (approx. 720K)
• CODAR Creates Even Smaller Crossed-Loop/Monopole Antenna
System:
[Carr, A.C. (1984), Three-element antenna, U.S. Patent 4 433
336]
[Barrick, D.E., B.J. Lipa, P.M. Lilleboe, and J. Isaacson (1994),
Gated FMCW DF radar and signal processing for range/Doppler/angle
determination, U. S. Patent 5 361 072]
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Document << (approx.
1.6M)
Three antennas are combined inside a tiny box, mounted on single
pole out of reach, on offshore rig, or building roof. Has demonstrated
optimal efficiency and better accuracy for current mapping
than phased-array beam-forming or older square NOAA direction-finding
array of preceding patent.
• CODAR Staff Invents Highly Efficient
Radar FMCW Waveform for Low-Data-Rate PC Digital Processing with High-Bandwidth Signals:
[Barrick, D.E. (1973), FM/CW radar signals and
digital processing, NOAA Tech. Report ERL 283-WPL 26]
Until
this invention, high pulse power and high data rate processors were required for
radars to achieve great ranges and good spatial resolution. The FMCW (frequency-modulated
continuous wave) signal with receiver demodulation and low-rate PC digital processing
was the breakthrough that leap-frogged ahead two generations to the present robust,
low-cost, efficient SeaSondes.
•
CODAR Invents Pulsing Format with FMCW Waveform That Allows Its Use with Backscatter Radars:
[D.E. Barrick, B.J. Lipa, P.M. Lilleboe, and J.
Isaacson (1994), Gated FMCW DF radar and signal processing for range/Doppler/angle
determination, U. S. Patent 5 361 072]
When radar transmitter
and receiver are co-located (i.e., backscatter), pulsing must be applied to prevent
destruction of dynamic range or damage to receiver. CODAR invented a pulsing format
that accomplishes this, while not introducing aliasing or blind zones encountered
with all prior waveforms and retaining the highly efficient, low-data-rate advantages
of the original FMCW signal.
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Document << (approx. 1.6M)
•
CODAR Develops and Tests Objective Least-Squares Algorithm for Current Mapping:
[Lipa, B.J. and D.E. Barrick (1983), Least-squares methods for
the extraction of surface currents from CODAR crossed-loop data: Application at
ARSLOE, IEEE J. Oceanic Engr., vol. OE-8, pp. 226-253]
This robust,
objective algorithm overcomes the arbitrary, ambiguous "closed-form"
algorithms developed at NOAA for direction finding. It allows objective statistical
testing that selects among signal hypotheses. The result is increased accuracy
while eliminating ambiguities, so as to map complex current features better than
the older, more cumbersome phased array antenna systems.
• CODAR Discovers and Implements MUSIC Direction-Finding Algorithm
That Replaces Least Squares:
[D. E. Barrick, and B. J.
Lipa (1999), Radar angle determination with MUSIC direction finding, U. S. Patent
5 990 834]
As much as the CODAR least-squares direction-finding
algorithm revolutionized HF radar current mapping, it had a drawback due to the
linear dependence among multiple signals from different directions. This was eliminated
by application of a specially designed MUSIC (MUltiple SIgnal Classification)
algorithm that actually capitalizes on this linear dependence, thereby providing
totally robust performance in complex signal environments.
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Document << (approx. 980K)
• CODAR Invents GPS Modulation Synchronization So Multiple Radars
Operate Simultaneously on Same Frequency:
[D.E. Barrick,
P.M. Lilleboe, and C.C. Teague (2001), Multi-station HF FMCW radar frequency sharing
with GPS time modulation multiplexing, U. S. Patent SN 10/109,769]
Proliferation
of HF radars worldwide means that multiple stations can no longer obtain approvals
for separate operating frequencies. CODAR solved this problem by employing worldwide
satellite GPS (global positioning system) time signals to synchronize the modulation
timing of multiple HF FMCW radars. This minimizes HF radar spectral occupancy
with no interference penalty among SeaSondes simulataneously sharing the same channel.
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Document << (approx. 712K)
• CODAR Invents and Applies Bistatic
Augmentation to SeaSonde Current-Mapping Radars:
[D.E.
Barrick, P.M. Lilleboe, B.J. Lipa and J. Isaacson (2001), Ocean surface current
mapping with bistatic HF radar, U. S. Patent SN 10/027,161]
This
breakthrough invented at CODAR allows simple, tiny, low-cost, transmitter units
to be added to existing SeaSonde backscatter radars, converting a single radar
into many. Operating simultaneously with the GPS synchronization described above,
the same point on the sea is illuminated by multiple transmissions, the echoes
from which are all processed in the same PC-based receiver unit. This extends
the coverage distance and improves the accuracy and robustness of standard backscatter
SeaSonde networks.
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Document << (approx. 1M)
• CODAR Pioneers in Estimating Total Vectors when
Two-Site Data Are Unavailable: Normal Modes:
[ Barrick, D.E. (2003), Synthesis of total surface current
vector maps by fitting normal modes to single-site HF radar
data, U.S. Patent 6,590,523. ]
Large area sectors of the sea can usually be seen by only one
radar. Often, land protrusions block visibility to even a single
radar. By conventional wisdom, such situations imply no total
vectors. When this happens within nearly enclosed bays, CODAR
has adapted Normal Mode Analysis, a hydrodynamics-based method,
to fit directly to all available radial velocities, so as to
produce continuous total vector fields within the bay.
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Document << (approx.
1.1M)
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