README  % SWIFT drifter data, Jim Thomson jthomson@apl.uw.edu

Data products from the Surface Wave Instrument Float with Tracking (SWIFT) are ensembles from 512-second "bursts" of raw data.  These are in a single structure in Matlab.  The structure is a collection of individual structures, with data products for each burst.  Use square brackets to index all burst ensembles, i.e.: 
	>> plot([SWIFT.time],[SWIFT.sigwaveheight],'x')
and download the SWIFT code library at https://github.com/jthomson-apluw/SWIFT-codes for plotting tools, etc. 

SWIFT.time: UTC timestamp in MATLAB datenum format (serial days since 0 Jan 0000)

SWIFT.lat: latitude in decimal degrees

SWIFT.lon: longitude in decimal degrees

SWIFT.driftdirT: drift direction TOWARDS, in degrees True (equivalent to "course over ground")

SWIFT.dirftspd: drift speed in m/s (equivalent to "speed over ground")

SWIFT.sigwaveheight: significant wave height, in meters

SWIFT.peakwaveperiod: peak of period orbital velocity spectra (note convention is usually wave height spectrum)

SWIFT.peakwavedirT: wind direction, in degrees FROM North

SWIFT.wavespectra.energy: wave energy spectral density, in m^2/Hz, as a function of frequency.  Note that this is derived from orbital motions and is thus insensitive to low-energy swell conditions.  The technique is best suited to measuring short wind waves. 

SWIFT.wavespectra.freq: spectral frequencies, in Hz

SWIFT.wavespectra.a1: normalized spectral directional moment (positive east)

SWIFT.wavespectra.b1: normalized spectral directional moment (positive north)

SWIFT.wavespectra.a2: normalized spectral directional moment (east-west)

SWIFT.wavespectra.b2: normalized spectral directional moment (north-south)

SWIFT.wavespectra.check: spectral comparison of horizontal to vertical motion (only available with post-processing).  Should be equal to 1 for good data in deep water.

SWIFT.watertemp: water temperature, in deg C, at 0.5 m below the surface

SWIFT.salinity: water salinity, in PSU, at 0.5 m below the surface

SWIFT.windspd: wind speed, in m/s, at 1 m height above the wave-following surface

SWIFT.airtemp: air temperature, in deg C, at 1 m height above the wave-following surface