Just wondering how other users are dealing with potential instrument drift of backscatter, CDOM, and chlorophyll data from Pioneer Array gliders’ FLUORT instruments. I am trying to compare these data across multiple glider missions on different gliders, so solving the drift and offset issues is critical. As far as I’ve been able to determine, these instruments are factory calibrated (L1a level) before deployment and no further calibrations are performed either pre-deployment or upon recovery.
So, the question is, what type of calibrations or other manipulations have others performed on FLUORT data that have proven successful to allow you to compare data across multiple glider missions?
Robert,
Several folks reset the dark counts used to calculate the different parameters using data collected during deep dives (>500 m). The dark counts are subject to a certain degree of variability due to electronic noise, and every glider will have a different noise “signature”. By resetting the factory dark counts to the glider dark counts, you can remove the differences between gliders due to the “signature”. Because the instruments use LED lamps, drift is not as much of a concern as resetting the dark counts.
Another step to consider is cross-comparing the data to the moorings and discrete samples collected during the deployment and recovery cruises (see links below). You can use the latitude and longitude data from the glider (dead reckoning underwater, so some degree of error) to find periods when they are close to one of the OOI moorings. The moorings have FLORTs on the near-surface instrument frames (7 m depth). You could combine times when the glider is close to a mooring (with “close” being somewhat relative) with the discrete sample data to help characterize the sensors (chlorophyll only) and cross-compare them.
Best regards,
Chris
https://dataexplorer.oceanobservatories.org/#ooi/all/cruise/GI.CRUISE.4af7b7d6-5d77-57d2-8752-3c57b393e5f8.0/data