BASE http://www.rdinstruments.com/ NOTES
SPECIFIC TO 38 kHZ and 75 kHZ Teledyne RDI System
Pass Suspect Fail
Level 1 - Red  (required)
Bit status (Built In Test) - diagnostics[1] BIT result is zero BIT result is non-zero BIT result is NA
Echo amplitude/intensity[2] If no rise (difference between previous and current bin) is greater than 30 counts If a rise on one beam is greater than 30 counts If a rise on two or more beams is greater than 30 counts
Pitch/Roll     >30deg pitch
Heading     >359.9deg or negative
UV - Horizontal velocity[3] The velocity magnitude is less than or equal to 125 cm/s The velocity magnitude is greater than 125 cm/s and less than or equal to 200 cm/s The velocity magnitude is greater than 200 cm/s
Vertical Velocity[4] The difference is less than or equal to 30 cm/s The difference is greater than 30 cm/s and less than 50 cm/s The difference is greater than or equal to 50 cm/s
Correlation magnitude - echo return correlation, single beam[5] Workhorse Long Range 75 kHz:  At least 3 of the 4 correlation magnitude values for each bin are greater than 64.                 Ocean Observer 38 kHz: At least 3 of the 4 correlation magnitude values for the bin are greater than or equal to 110. Workhorse Long Range 75 kHz:  Only 2 of the 4 correlation magnitude values for each bin are greater than 64.                 Ocean Observer 38 kHz: Only 2 of the 4 correlation magnitude values for the bin are greater than or equal to 110. Workhorse Long Range 75 kHz:  If 1 or none of the 4 correlation magnitude values for each bin are greater than 64.                 Ocean Observer 38 kHz: If one or none of the 4 correlation magnitude values for the bin are greater than or equal to 110.
     
Level 2 – Yellow (recommended)      
Battery voltage (V1 & V2) two batteries      
Water temperature     >50degC or <-5degC
Pressure     negative or >range of sensor
Timestamp     stuck time or future time
Std deviation of speeds      
Transmit current - amount of current transmitted per ping, related to battery voltage      
Correlation coefficient - derived parameter from correlation magnitude, across beams      
Speed of sound (derived)     >1600m/s or <1400m/s
Signal to noise level >70% >30% or <70% <30%
Surface (or bottom) reflection/ detection      
Percent solutions - number of beams used[6] The above values for each bin are flagged as good The above values for each bin flagged as suspect or failed for less fewer than 50% of the bins The above values for each bin are flagged as suspect or failed for greater than or equal to 50% of the bins
Percent good pings (PGP)[7] Workhorse Long Range 75 kHz:  Total percent good pings is greater than 10%.                 Ocean Observer 38 kHz: Total percent good pings is greater than 25% Workhorse Long Range 75 kHz:  Total percent good pings is greater than or equal to 5% and less than 10%.                 Ocean Observer 38 kHz: Total percent good pings is greater than or equal to 22% and less than 25%. Workhorse Long Range 75 kHz:  Total percent good pings is less than 5%.                 Ocean Observer 38 kHz: Total percent good pings is less than 22%
Error velocity - four beam disagreement indicator[8] Error velocity in each bin is less than or equal to 15 cm/s Error velocity in each bin is greater than 15 cms/s and less than or equal to 30 cm/s or equals -32678 Error velocity for each bin exceeds 30 cm/s
[1]
 :
A Built-In-Test (BIT) performed internally will ensure the general health of the instrument.  The BIT is performed with each ping to check for such issues as demodulator and timing card errors.  Workhorse ADCPs (75 kHz) report BIT for each ensemble, while the 38 kHz Ocean Observer ADCPs must be commanded.
[2]
 :
The echo intensity for an ADCP is a measure of the signal strength intensity returned to the transducer.  Because the ADCP technology uses the scattering from small particles in the water column to measure currents, reflections from larger objects associated with a drilling rig may overwhelm the scattering from the smaller particles.  Objects that may reflect the transmission include the drilling riser, tensioning cables, rig support structure and other sensors suspended in the water column.  If the echo intensity is high it may indicate a boundary, school of fish, or an obstruction in the water column.  Low echo intensities represent insufficient scatterers in the water column or that the range limits of the sensor have been exceeded.

An echo intensity test is applied by comparing the echo intensity at a particular bin to the echo intensity of the previous bin.  For this definition, the test is only applied beginning with bin 15.
[3]
 :
The horizontal velocity test represents a gross error check.  Current velocities are not expected to exceed a certain value.  This test compares the horizontal velocity within each bin.  The maximum horizontal velocity magnitude is calculated from the east and west components of the horizontal velocity, compared to a threshold value, and flagged accordingly.
[4]
 :
Using the four acoustic beams, two vertical components of the flow are calculated, in addition to the two horizontal components.  The vertical velocity recorded is the average of the two vertical velocities sensed.  High vertical velocities indicate turbulence in the water column and non-homogeneous horizontal currents.  The vertical velocity test is applied next by comparing the vertical velocity in each bin to a threshold value and flagged accordingly.
[5]
 :
Correlation magnitude is a measure of the pulse-to pulse correlation in a ping for each cell depth.  The correlation magnitude should have a constant, though slightly variable value throughout the profile.  The correlation magnitude test ensures that the highest quality velocity data are kept.
[6]
 :
Properly check the entire ensemble of data - excluding bins flagged as failed or suspect in the echo intensity test since that test is a surface detection test designed to eliminate sections of the profile that are obstructed.
[7]
 :
Percent good is the ratio of good pings per total pings for each ensemble.  Causes of low percent good values include low coorelation, large error velocity and fish detection.  The percent good test ensures that the minimum number of samples and minimum theoretical standard deviation in the data are met.  Gulf Oil companies use two RDI ADCP models and the test differs for each.
[8]
 :
Error velocity is a measure of the disagreement of measurement estimates of opposite beams.  It is derived from each pair of opposing beams and therefore represents two independent measures of vertical velocity, possibly indicating inhomogeneous flow.