Application of Radial and Elliptical Surface Current Measurements to Better Resolve Coastal Features  Robert K. Forney, Hugh Roarty, Scott Glenn   Coastal Ocean Observation Lab  Institute of Marine & Coastal Sciences  Rutgers University ABSTRACT In Forney (2012) it was shown that monostatic and bistatic High-Frequency 13-MHz coastal radar systems produce different measurements of sea surface velocity. Based on a geometrical argument concerning accuracy of zonal and meridional component resolution, elliptical measurements can better resolve summer coastal upwelling, sea breeze, and storm related surface current phenomena off the coast of New Jersey. To demonstrate this, radial, elliptical, and composite data from August 1 st to September 30 th 2012 were processed using MATLAB to remove tidal components of surface currents in an attempt to isolate meridional and zonal surface phenomena. This processed data was compared across the three data types using statistical and analytical methods. It was found that ellipticals did not resolve meridional phenomena better than radials because the differences between them can be accounted for by noise. SEA BREEZE THREE WEEK OVERLAY: TIDES STORM EVENT CONCLUSION Neither the monostatic nor the bistatic systems resolved the sea breeze front well. This could be owed to the fact that the sea breeze is slight compared to the other signals even without the tides and only lasts a few hours. However, during the storm on September 18 th there was a large wind event that was reflected in the detided surface current for the single point analysis. Monostatic and bistatic did not produce similar tide measurements over all observed space and time, which could not be explained by poor coverage; this could be explained by a difference in measurement of the O1 and S2 tidal constituents between the radials and ellipticals (the M2 and K1 measurements were in agreement). However, ellipticals and radials are not statistically different from one another, according to the three week overlay. Differences in this study can be accounted for by the short time frame. Radial and elliptical measurement spatial averages produce different results. Total measurements along the same direction produce low- quality results. The optimal angle is 90 degrees. Map of the study area. Triangles represent locations of SeaSonde CODAR sites; the dot represents the location of the single point analysis; an elliptical file is plotted in blue, and a radial file in red. THREE WEEK OVERLAY: NO TIDES Radial Geometry Elliptical Geometry Composite Geometry (month/day) (cm/s) The peak meridional current measured using CODAR ocean sensors was 73 cm/s by radials, 60 cm/s by ellipticals, and 61 cm/s by the composites; the peak zonal current was 71 cm/s by radials, 53 cm/s by ellipticals, and 68 cm/s by composites. The wind record indicated a peak meridional (BLUE) wind speed of 17 m/s and a peak zonal (RED) wind speed of 6 m/s. The surface current speeds associated with those speeds are cm/s and cm/s, respectively. Single-point combined time series: radials are red, ellipticals are blue, composites are green. The tides extracted are mixed, and the radials and ellipticals are far from being in agreement; this is not due to poor coverage by ellipticals as evidenced by their dominance in the composites. Radials have been validated for measuring surface current in multiple studies and serve as a good standard measure. At other single points the radials and ellipticals seem to be in good agreement but not across all time. BAD GOOD A potential case of sea breeze from a 25-hour hourly analysis. Top left, top right, bottom left: radials-only, ellipticals-only, and composite radial and elliptical plots. These maps were plotted for 19:00 GMT, 15:00 local time. Sea breeze is driven by a land-sea temperature difference, and so would likely manifest most strongly after the hottest part of the day, starting at noon. Surface currents lag wind forcing by approximately three hours, so 19:00 GMT should represent the most likely time to find sea breeze. The currents observed are not necessarily sea breeze, which should produce currents of greater magnitude than 8.23 cm/s.