Hello, I am wondering if the velocity field is considered invalid when the pitch and roll limits extend the values(30 degree) ? The data provided by GA01SUMO-ADCP have the pitch/roll values ranging from -150 to 150 degree (after converting from deci-degree). Is it something wrong with this instrument or just all the velocity data are invalid?
Regards,
Chain
Chain,
I’ve dug into this and we (OOI) have the wrong units set for the heading, pitch and roll. Instead of decidegrees, the units should be centidegrees. So, instead of dividing by 10 to get the pitch and roll into degrees, you need to divide by 100. Once you do that, the pitch and roll data should fall within acceptable ranges. I’ve added a ticket to our internal bug tracking system to get this error corrected.
Thanks,
Chris
Dear Chris,
Thanks for your reply. I also wonder if there is some documents to specify the QC/QA of ADCP for the pitch and roll. If the pitch/ roll exceeds the value(e.g. 30) can we consider the velocity field should not be used?
I have checked the ADCP data from GA03FLMA, GA03FLMB,GA01SUMO and found they contained large amounts of these ‘unqualified’ data. If so, is there anything we can do to adjust them?
Thanks,
Chain
Chain,
According to the vendor (Teledyne RDI) documentation, for the pitch and roll values, “anything beyond 15 degrees will cause bias to the data that cannot be removed.” The QARTOD manual for the QA/QC of in-situ current observations would flag any value that exceeds that tilt max of 15 degrees (1500 centidegrees) as failed.
Looking at the data from the three platforms you mentioned, I only see a few instances where the tilts exceed that limit. Again, the unit string assigned to the heading, pitch and roll variables is incorrect. The correct units for the heading, pitch and roll is centidegrees. If you did not convert the units, you could use a test limit of ±1500 centidegrees. Any pitch or roll exceeding that value should be excluded from you analysis.
Cheers,
Chris