As a reminder, this station's recent history includes its annual equipment swapout (December 7th - 8th, 2015), at which time the EXO Sonde was reinstalled after been absent for warranty repairs since July 21st, 2015. These repairs included an upgrade to a titanium bulkhead and the replacement of the CT module (conductivity/temperature sensor, which reports salinity as well) with an improved CT2 module. It was hoped that the reengineered CT2 module would eliminate the many problems with failures of the temperature and salinity parameters experienced over this station's lifetime since late 2013. After the 12/8/2015 swapout was completed, no further updates were received apart from an announcement on February 5th, 2016, that Jahson Alemu would no longer be our primary local contact for the Tobago buoys.
As of May 16th, 2016, the following observations can be made about this buoy's data stream:
- The EXO Sonde was indeed reconnected during the annual swapout and started producing data on December 8th, 2015, after its 4.5 month absence.
- The EXO Sonde went offline from March 18th to 23rd, 2016. My guess would be that the instrument was removed for five days during some kind of maintenance operation but it is possible that it simply failed.
- Since last December, apart from the 5-day interruption in March, the EXO seems have produced consistent and reliable sea temperature data.
- However the EXO's salinity data appears to be somewhat questionable. At first it reported in the neighborhood of 36 PSU, which then rapidly and steadily fell by more than 2 PSU over only 7 days from January 26th to February 2nd, 2016. After the 5-day outage in March its reports remained low, maxing out at about 33 PSU but falling in recent days below 31 PSU. As of this writing I am not confident that the conductivity (salinity) part of this sensor is functioning properly. This may indicate that the CT2 module has not corrected all of the problems of the CT module, or it may suggest that the required monthly on-site recalibrations are not proceeding correctly (or with the required frequency).
- The EXO's turbidity sensor ceased to report after the 5-day outage in March, and may in fact have been removed. The other sensors (blue-green algae, chlorophyll, fDOM) continue to fluctuate above and below zero and it is uncertain whether these data provide any value.
- The analog AirT/RH sensor remains offline, as it has been since mid-2014. Based on my experience with a similar failure and repair at the Calabash Caye buoy I tend to believe that this is a problem with buoy wiring and not a failure of the RM Young sensor itself.
- We do, however, have both air temperature and humidity reports from the integrated WXT unit. Although these reports cannot be validated by redundant readings from the analog AirT/RH sensor, they do appear to be believable.
- Wind speeds and directions, as well as barometric pressures, continue to be reported redundantly by multiple sensors, and all appear to be consistent and correct.
- The diagnostic RH (humidity) sensors within the buoy's two sealed junction boxes (JBs) show some cause for concern. The "Met" JB humidity levels remain acceptably low, although they have been climbing throughout the buoy's lifetime, and desiccant replacement might be helpful. Prior to the 12/8/2016 swapout the "Main" JB's humidity levels ranged between 60% and 90%, which is more or less the same as outside RHs and is unacceptably moist. After the swapout these RHs dropped to the 40% - 55% range, which is an improvement but still alarmingly high, and they have been increasing ever since. Main JB RHs presently range from about 55% to 70%. The Main JB should be examined to ensure that it is free of cracks, that its o-ring is intact and properly seated, and that its desiccant is fresh.
I will post any further updates that are received at AOML. The next annual maintenance operation should be carried out this coming December, or earlier.
Mike J+