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August 2017
Development of Combined Transmit-Receive Antenna for Long-Range SeaSonde

SBIR-funded technology development program will bring valuable siting flexibility for Long-Range systems

Long-Range (LR) SeaSonde systems transmitting in the 4-5.5 MHz band, with nominal offshore ranges of 160-220 km and range resolutions of 3 – 6 km, account for approximately one-third of the stations in the U.S. National HF Radar Network, part of the U.S. Integrated Ocean Observing System (IOOS). LR SeaSondes are a crucial component as they provide the largest coverage area and farthest offshore range for applications like search and rescue, spill response, among others. In analyzing data collected during both hurricanes Irene (2011) and Sandy (2012), researchers at Rutgers University were able to show that the two-dimensional surface current data from their LR SeaSonde network can be a key observation tool, along with subsurface gliders and satellite data, that can help better predict the intensity of approaching hurricanes and their associated storm surge before they make landfall [Glenn, et al, 2016].

Sadly, Hurricane Sandy’s storm surge, which devastated entire communities along the Northern New Jersey and New York coasts, also damaged many of the HF radar stations installed in the most vulnerable positions along low-lying areas [Malakoff, 2012]. When rebuilding in the Mid-Atlantic region an additional hardening of the HF radar installations was performed [Roarty, 2013] to try and mitigate damages in future storm events and is an important planning consideration in many operational networks.

LR SeaSondes presently require separate transmit and receive antennas spaced approximately 60 m apart, which precludes mounting them on most structures and platforms leaving only ground-mounted solutions. Although SeaSonde antennas are designed to withstand hurricane force winds, when mounted on the ground, they can be vulnerable to damage from intense storm surges and erosion in lowlying areas as they were during Sandy. By redesigning the LR SeaSonde antenna as a co-located single-mast solution, like the present configuration for SeaSonde antennas above 11 MHz, they can be placed in areas better protected from severe storm surges, providing valuable data on approaching storms.
Earlier this year, CODAR applied for, and was awarded, a FY2017 Phase I Small Business Innovative Research (SBIR) Grant to design a single-mast LR SeaSonde antenna system for placement on hardened, fixed structures like concrete buildings and parking structures or on existing hurricane-resilient stations like NOAA Sentinels. Sentinels are water level observing stations, designed by The Center for Operational Oceanographic Products and Services (CO-OPS), part of NOAA’s National Ocean Service (NOS), that
have been strengthened to deliver real-time storm tide data during severe coastal events. These stations, one of which is shown in the adjacent photo, are single-pile structures designed to withstand category 4 hurricanes. CODAR is partnering with the Texas General Land Office (TGLO) to utilize their Sentinel stations in the design and testing process. The Phase I program runs 6 months and is structured like a feasibility study in which concepts and designs are investigated. Following the phase I program, CODAR will be applying for FY2018 phase II funding in which a prototype will be built and tested.

1. Glenn, S. M. et al. Stratified coastal ocean interactions with tropical cyclones. Nat. Commun. 7:10887 doi: 10.1038/ncomms10887 (2016).

2. Malakoff, D. Scientists Assess Damage From Sandy's Deadly Punch. Science, vol. 338, pp. 728-729 (2012).

3. Roarty, H. Repair and Hardening of Mid Atlantic Ocean Observing Assets After Hurricane Sandy. NOAA Cooperative Agreement Proposal (2013).

Texas Sentinel Station.
Photo provided by TGLO.




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