Velocity Profiler data flags

How ADCP structure function quality-control flags are applied

The Q (quality control) flags associated with shear-probe measurements are not compatible with the Ocean Sites Ocean Sites for quality control (QC) coding.

Every dissipation estimate from every probe must have Q flag. The numerical values of the Q flags are as follows:

Level 2:

Flag Mask	Bit	Flag attribute	Flag meaning	Threshold value	Ex: True =1 / False =0	Ex: Q value
1	Bit 0	Manually defined by user	Manually defined by user	Manually defined by user	0	0
2	Bit 1	segment_outlier	Flag data points <math> > 3 \sigma</math> away from segment mean for bin.	<math>3 \sigma</math>	1	2
4	Bit 2	profile_outlier	Flag data points <math> > 3 \sigma</math> away from beam-profile-mean.	<math>3 \sigma</math>	0	0
						Final Q = 2

Level 3:

Flag Mask	Bit	Flag attribute	Flag meaning	Threshold value	Ex: True =1 / False =0	Ex: Q value
1	Bit 0	Manually defined by user	Manually defined by user	Manually defined by user	0	0
2	Bit 1	insufficient_number_velocity_samples	Flag segments where the ratio of the number of viable values in the velocity difference to the total number of data points is less than the threshold	0.5	0	0
4	Bit 2	too_close_to_range_limits	Flag bins that are too close to the first or last range bin (I.e. not enough bins to do differencing)	3	1	4
						Final Q = 4

Level 4:

Flag Mask	Bit	Flag attribute	Flag meaning	Threshold value	Ex: True =1 / False =0	Ex: Q value
1	Bit 0	Manually defined by user	Manually defined by user	Manually defined by user	0	0
2	Bit 1	Rsquared_too_low	Flag values where <math> R^2 < </math> threshold	0.6	0	0
4	Bit 2	delta_epsi_too_large	Flag values where <math> \delta \epsilon / \epsilon > </math> threshold	0.6	1	4
8	Bit 3	A3_coeff_invalid	Flag values where <math> a_3 </math> < threshold	0	0	0
16	Bit 4	dll_intercept_too_low	Flag values where intercept (<math> a_0 </math>) < threshold	0	1	16
32	Bit 5	dll_intercept_too_high	Flag values where intercept > threshold (threshhold <math> = 2*yint\_{expected} = 2*(2*\sigma_v^2) </math>, where <math> \sigma_v </math> is expected accuracy in along-beam vel.	Instrument dependent	0	0
64	Bit 6	regression_poorly_conditioned	Flag values where there are fewer than a certain number of points for the regression	3	0	0
128	Bit 7	dll_slope_out_of_range	Flag values where slope <math> a_1 < 0 </math> as this would lead to negative epsilon.	0	0	0
						Final Q = 20

The Q flags are combined by their addition. For example a Q value of 20 means that the dissipation estimated failed both dissipation ratio limit test and the resolved variance test. A value of 255 means that all tests failed. The reasons for a failure can be decoded by breaking the value of Q down to its powers of 2. Note that importance (severity of the failure) is ranked by the numeric value of the flag mask.