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Long-Range Current Mapping using HF backscatter near
4.5 MHz
Michael Kosro
Status: Accepted
COAS/Oregon State University
104 Ocean. Admin. Bldg.
Corvallis , OR USA
97331-5503
Phone: 541-737-3079
Email: kosro@coas.oregonstate.edu
Co-Authors:
B. Walt Waldorf, COAS/OSU, Corvallis, OR 97331-5503
Jeffery D. Paduan, Naval Postgraduate School, Code OC/Pd, Monterey, CA.,
93943
The range of ground-wave propagation for HF radio signals increases
dramatically as frequency is lowered. Standard SeaSonde mapping
systems operating at 12-14 MHz have typical ranges of 40-60 km.
Similar systems operating at 4-5 MHz, by contrast, have yielded typical
ranges of 180 km in recent tests along the Oregon coast. An array of four
such long-range sites at locations from Crescent City, CA to Newport,
OR is providing time-series mapping of the surface circulation between
41.7°N and 45°N. The maximum range shows little day/night modulation.
Increased propagation range introduces the potential for noise from ionospheric
reflection. Indeed, episodes of ionospheric backscatter are evident in
the data, which produce large error vectors in the far range cells. An
algorithm developed by CODAR Ocean Sensors to detect and screen-out such
noise is being tested, with positive preliminary results. The HF-derived
currents (surface flow) are being compared with those from in-situ ADCP
(9m depth) at specific locations. The independent measurements show best
agreement at subtidal frequencies; tidal and higher frequency fluctuations
are more energetic in the HF radar-derived currents. Examples of circulation
fields from this new measurement capability will be shown and discussed.
Submitted on October 16, 2002
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