Editorial Type:
Article
Article Type:
Research Article

Measuring Antenna Patterns for Ocean Surface Current HF Radars with Ships of Opportunity

Brian M. Emery Marine Science Institute, and Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, California

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Libe Washburn Department of Geography, University of California, Santa Barbara, Santa Barbara, California

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Chad Whelan CODAR Ocean Sensors, Ltd., Mountain View, California

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Don Barrick CODAR Ocean Sensors, Ltd., Mountain View, California

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Jack Harlan National Oceanic and Atmospheric Administration, Silver Spring, Maryland

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Print Publication:
01 Jul 2014
DOI:
https://doi.org/10.1175/JTECH-D-13-00181.1
Page(s):
1564–1582
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Abstract

HF radars measure ocean surface currents near coastlines with a spatial and temporal resolution that remains unmatched by other approaches. Most HF radars employ direction-finding techniques, which obtain the most accurate ocean surface current data when using measured, rather than idealized, antenna patterns. Simplifying and automating the antenna pattern measurement (APM) process would improve the utility of HF radar data, since idealized patterns are widely used. A method is presented for obtaining antenna pattern measurements for direction-finding HF radars from ships of opportunity. Positions obtained from the Automatic Identification System (AIS) are used to identify signals backscattered from ships in ocean current radar data. These signals and ship position data are then combined to determine the HF radar APM. Data screening methods are developed and shown to produce APMs with low error when compared with APMs obtained with shipboard transponder-based approaches. The analysis indicates that APMs can be reproduced when the signal-to-noise ratio (SNR) of the backscattered signal is greater than 11 dB. Large angular sectors of the APM can be obtained on time scales of days, with as few as 50 ships.

Denotes Open Access content.

Corresponding author address: Brian Emery, Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106-6150. E-mail: brian.emery@ucsb.edu

Abstract

HF radars measure ocean surface currents near coastlines with a spatial and temporal resolution that remains unmatched by other approaches. Most HF radars employ direction-finding techniques, which obtain the most accurate ocean surface current data when using measured, rather than idealized, antenna patterns. Simplifying and automating the antenna pattern measurement (APM) process would improve the utility of HF radar data, since idealized patterns are widely used. A method is presented for obtaining antenna pattern measurements for direction-finding HF radars from ships of opportunity. Positions obtained from the Automatic Identification System (AIS) are used to identify signals backscattered from ships in ocean current radar data. These signals and ship position data are then combined to determine the HF radar APM. Data screening methods are developed and shown to produce APMs with low error when compared with APMs obtained with shipboard transponder-based approaches. The analysis indicates that APMs can be reproduced when the signal-to-noise ratio (SNR) of the backscattered signal is greater than 11 dB. Large angular sectors of the APM can be obtained on time scales of days, with as few as 50 ships.

Denotes Open Access content.

Corresponding author address: Brian Emery, Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106-6150. E-mail: brian.emery@ucsb.edu
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Journal of Atmospheric and Oceanic Technology

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