Metadata

DOLfYN generally uses the *MKS* system. Common variables and units are listed in Table 1:

Table 1 : The units of common variables found in DOLfYN data objects.

Name	Units	Description/Notes
time	sec since 1970/01/01 00:00:00	Time data (unaware of timezone)
vel	m/s	Velocity vector data
range	m	Distance from the instrument’s transducer head(s)
depth	m	Instrument depth
c_sound	m/s	Speed of sound used in velocity calculations
press / pressure	dbar	Pressure measured by the instrument
temp	deg C	Temperature measured by the instrument
accel	m/s2	Vector acceleraton of the instrument
angrt	rad/s	Angular rotation rate of the instrument
mag	mG or nT	Magnetometer data
velraw	m/s	Velocity without motion-correction
velrot	m/s	Rotational motion velocity (computed from angrt)
velacc	m/s	Translational motion velocity (computed from accel)
acclow	m/s2	Low-pass filtered acceleration signal
heading	deg	Instrument heading* (clockwise from North)
pitch	deg	Instrument pitch*
roll	deg	Instrument roll*
orientmat	—	earth to instrument orientation matrix
amp	dB or counts	Measured sound level amplitude
corr	% or counts	Correlation between the sent and received pings.
ambig_vel	m/s	Ambiguity velocity
ensemble	—	Ensemble counter
error	—	Instrument error code
status	—	Instrument status code
tke_vec	m2/s2	Variance of velocity components (0: u’u’, 1: v’v’, 2: w’w’)
stress_vec	m2/s2	Reynolds stress array (0: u’v’, 1: u’w’, 2: v’w’)
U_mag	m/s	Horizontal velocity magnitude
U_std	m/s	Standard deviation of horizontal velocity magnitude
epsilon	m2/s3	Turbulence dissipation rate
psd	<var units>2/<freq units>	Spectra, calculated as power spectral densities
f	Hz	Spectral frequency
omega	rad/s	Spectral radial frequency

DOLfYN Attributes

The attrs data-group of xarray Datasets is a place for user-specified meta-data and DOLfYN-specific implementation data. The most common variables found here are described in Table 2.

Table 2 The entries in dat.attrs that are used in DOLfYN.

Name	Description/Notes
fs*	This is the sample rate of the instrument [Hz]
coord_sys*	The coordinate system of the data object. When a data object is rotated to a new coordinate system using the dat.velds.rotate2() method, the value of dat.attrs['coord_sys'] is updated to reflect the final coordinate system. Valid values are: beam, inst, earth, and principal. For further details on these coordinate systems see the Rotations & Coordinate Systems section.
rotate_vars*	The variables in the data object that should be rotated when rotating the data object.
declination**	The magnetic declination where the measurements were made (in degrees that magnetic North is right of True North). Set this value using dat.velds.set_declination(<value>).
declination_in_orientmat*	A boolean specifying whether the dat.orientmat includes the declination. If this is True, then the earth coordinate system is True (i.e., v is velocity toward True North).
principal_heading	The heading of the +u direction for the ‘principal’ coordinate system [degrees clockwise from north].
has_imu*	A boolean indicating whether the instrument has an IMU (inertial measurement unit) or AHRS (attitude heading reference system).
inst_make*	The manufacturer name.
inst_model*	The instrument model.
DutyCycle_NBurst*	The number of pings in a burst.
DutyCycle_NCycle*	The time – in number of pings – before the next burst starts. (this may be incorrect for some instrument types, please report issues)
inst2head_vec	The vector from the center of the ADV inst reference frame to the center of the head’s reference frame, in coordinates of the inst reference frame. It must be specified in order to perform motion correction. For ADPs this is always zero because the two coordinate systems are centered at the same place.
inst2head_rotmat**	The rotation matrix that rotates vectors from the instrument reference-frame to the head reference-frame. For ADCPs this is always the identity matrix. Valid values are: 3-by-3 valid rotation matrices, or: 'eye', 'identity', or 1 all of which specify that it is the identity matrix. This is typically used for cable-head ADVs where the ADV head is not oriented the same as the ADV pressure case. It must be specified in order to perform motion correction.
motion accel_filtfreq Hz	The filter-frequency for the computing translational motion from the acceleration signal of an IMU. This is only used for motion correction. This high-pass filter is applied prior to integrating acceleration. This value is only used if when accel_filtfreq is not explicitly specified when motion-correcting
motion vel_filtfreq Hz	The filter-frequency for the computing translational motion from the acceleration signal of an IMU. This is only used for motion correction. This high-pass filter is applied after integrating acceleration. This value is only used if when vel_filtfreq is not explicitly specified when motion-correcting.
latlon†	The location of the measurements in decimal degrees. Latitude is positive North of the equator, longitude is positive west of the prime-meridian.

*: These entries are set and controlled by DOLfYN, and are not meant to be modified directly by the user.

**: These entries are set and controlled via dat.set_<property name> methods.

†: These entries are not used or set by DOLfYN, but they are useful measurement meta-data and are listed here to assist in standardizing the location and format of this information.