README.txt

These data are hourly maps of ocean surface currents, estimated on a fixed grid approximately 6km x 6km, from Seasonde HF measurements of radial currents collected during the RISE (River Influences on Shelf Ecosystems) project.   The data period is June 2004 through December 2006.  There are 22,656 hourly maps, with a total of more than 13x10^6 current vectors.
 
The instruments used were Seasonde HF current mappers in the Long-Range configuration.  Radial current measurements were obtained from three sites:
LOO1	Loomis Lake WA   46d 25.995m N, 124d 03.531m W  
MAN1  Manhattan OR     45d 38.419m N, 123d 56.508m W
YHL1  Yaquina Head OR  44d 40.570m N, 124d 04.630m W

Each site consists of a transmitter with whip antenna, and a receiver with compact receive antenna consisting of one monopole and two crossed-loop elements.   Returning energy is processed onsite into cross-spectra vs. range, and then into radial currents vs. range and azimuth using direction-finding (Barrick et al., 1994; Lipa and Barrick, 1983;  see Paduan and Graber (1997) for an introduction).  The data and parameters reflecting on quality are recorded on site, and also transferred via phone or Internet to a central processing system at OSU for further processing to Òtotal vectorsÓ, which combine the radials from individual sites into 2-dimensional current vectors in regions of overlap.  The primary tool for the radials-to-totals mapping is the HF Radar Mapping Toolbox version 4.1, for Matlab, written by Mike Cook and Jeff Paduan of Naval Postgraduate School (Cook and Paduan, 2003).

Operating frequencies were:
LOO1:  4.419MHz (2004-2005), 4.412MHz (2006)
MAN1: 4.787MHz (2004/06), 4.800MHz (after 2004/06)
YHL1:  4.427 MHz (2004/06), 4.400MHz (after 2005/06/10), 4.412 (after 2006/04/19).

Measured antenna patterns were used at all three sites.

All times are UTC, and correspond to the center of the hourly data collection period.

Measured radial data were collected from hourly output of 3-hour averages centered on the indicated time, in radial rings of 6km width, which were further divided into azimuthal bins of 5 degrees. 

Total currents are estimated using hourly radial data by combining, in a least-squares sense, the radial data from at least two sites which fall within a fixed radius of the estimation grid point.  For these data, a combining radius of 14km was used.  Radial vectors falling over land were excluded from estimation of total currents.  Maxima for radial and for total currents were set to 1.2 m/s and 1.8 m/s respectively, based on examination of input data.  While stronger currents are known in a narrow zone off the mouth of the Columbia River, the scales tend to be shorter than resolved in this measurement.

Measured Parameters:

Gmt:   Year, Month, Day, Hour, Minute, Second of each map (start time), 1 line per hourly sample
Xgrid:  longitude (negative is West) of each mapping grid point (degrees).
Ygrid:  latitude (positive is North) of each mapping grid point (degrees)
U, V:  eastward and northward current in cm/s.   One line per hour, each line contains a value for each xgrid/ygrid location.
Cuu, Cuv, Cvv:  the geometric dilution of precision (GDOP) for each hourly current estimate, arising from the geometry of the radial vectors that contribute to each total.  Larger values indicate less reliable currents.  Depends only on geometry of contributing radials; no reduction for numbers greater than 1.  Same format as U,V.
fitDif:  measure of RMS difference of radial currents from the radials based on total current estimate from least-squares model (HFRadarmap).  Same format as U, V.
NumRadials: array of number of radials used in each current estimate.  Same format as U,V

References
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.
 B. J. Lipa and D. E. Barrick (1983), Least-squares methods for the extraction of surface currents from Codar crossed-loop data: Application at ARSLOE, IEEE Journal Oceanographic Engineering, vol. OE-8, pp. 226-253.
Cook, M.S., and J.D. Paduan, 2003: Processing HF radar data using the HFRadarmap software
system. Radiowave Oceanography the First International Workshop, University of
Miami, Rosentiel School of Marine and Atmospheric Science, 11-16.
J.D. Paduan and H.C. Graber (1997), ÒIntroduction to High-Frequency Radar: reality and mythÓ.  Oceanography, 10(2), 36-39.