EXO Sonde performance at Speyside / Angel's Reef, 2013-present

This post is part of a planned series of posts to share the results of my recent evaluation of data produced by all of the CREWS/CCCCC buoys over their lifetimes, from 2013 to the present.  This post will discuss the performance of the EXO Sondes, which were deployed to collect sea temperature and salinity data but are also capable of monitoring other 'water quality' parameters such as turbidity, algae, fDOM, pH and DO.

At the Speyside / Angel's Reef buoy (ARTO1), performance by the EXO Sonde has been generally poor.  The Speyside EXO was first deployed on November 25, 2013 and this analysis is based on data collected through June 4, 2015.  Although this period spans a total of 556 days, ARTO1 experienced a few short maintenance operations that brought the buoy temporarily to land, so that the actual length of deployment over this period was only 552 days, or about 18 months' worth.

Here is a graph of sea temperature (°C, in blue) and salinity (PSU, in red) from ARTO1, plotted against decimal year:

Please click on this image to see it in larger form.

Over the course of the last year and a half, the EXO Sonde at Speyside has had four periods of time during which the EXO could be said to have produced reasonable sea temperature and salinity data:

• Nov 25, 2014 to Jan 22, 2014 (58 days, after which Sal goes bad)
• Mar 20, 2014 to Jun 6, 2014 (78** days, after which Sal goes bad)
• Sep 11, 2014 to Sep 22, 2014 (11 days, after which Sal goes bad)
• Mar 26, 2015 to May 8, 2015 (43 days, after which Sal goes bad)

**The 78-day period from March 20th to June 6th, 2015 includes a moment on May 20th when salinities abruptly drop by about 1 PSU and then continue to fall slowly for 17 days before becoming very obviously corrupted.  The May 20th drop occurs at the time when the EXO appears to have been physically disconnected from the buoy for two hours, judging from the absence of voltage data.  An actual salinity drop coincident with this (presumed) maintenance operation is not likely, though it is not clear whether this salinity drop should call into question the integrity of the salinity data record prior to this time or subsequent to it.  This analysis avoids the question by giving the EXO the benefit of the doubt and assuming that both pre- and post-drop data are reasonable, up until the probe very obviously fails on June 6th.  However a more conservative analysis would score this performance as 61 days (pre-drop) or 17 days (post-drop) of reasonable data, rather than the 78 days listed here.

As of this writing the conductivity probe at ARTO1 is nonfunctional, and has reported corrupted salinity data since May 8th and corrupted sea temperatures since June 3rd.

Based on these statistics the EXO's conductivity probe, which reports both sea temperatures and conductivities (from which salinities are calculated), has performed reasonably well for 190 days out of the buoy's 552 operational days, or about 34% of the time.

A similar analysis performed on this buoy's sister station at Buccoo Reef, Tobago (BUTO1) found that that EXO performed reasonably well for 263 days out of that buoy's 464 operational days, or about 57% of the time.  The complete analysis for that EXO may be found at this link.

(signed)
Mike Jankulak