Q&A: Erratic Profiles
November 2019 Newsletter
The data above come from a profiling CTD, deployed in sea conditions that caused approximately 1-meter ship heave. Two things stick out – relatively unchanging salinity data during the downcast, and noisy data during the upcast (shown in light blue and pink).
Can you identify the cause of this problem?
The figure above shows a zoomed-in view of 200 – 240 meters depth. Ship heave is shown in the oscillations in descent rate. If you look closely, a “bump” in salinity and temperature corresponds almost perfectly with each motion of the ship. This is a clear indication that the pump isn’t working – when a CTD has a functional pump, the temperature and conductivity sensors have a consistent flow of water regardless of descent rate and sea conditions. The resulting pumped data are smooth, with minimal effect from ship heave.
Without a pump, the flow of water is dependent on the motion of the CTD package, where a faster descent rate will force more water through the plumbing. Data from the downcast are usually less affected, as the downward motion of the CTD package causes some flow through the plumbing. On the upcast however, water easily becomes entrained in the CTD’s plumbing, and may be unchanging, or will have a strong correlation with ship heave.
Read our Troubleshooting Guide for profiling CTDs to learn more troubleshooting techniques.
Related Posts
Featured Posts
Pride 2023
Celebrating and honoring our LGBTQIA+ communities At Sea-Bird Scientific, we are proud to stand with members of the LGBTQIA+ community during Pride Month 2023. As with last year, we changed our logo on social media to feature a rainbow throughout the month of June in...
What is the UN Ocean Decade?
Did you get a chance to read about the HyperNAV program that we support in partnership with NASA? Sea-Bird Scientific is proud to be part of the NASA PACE Mission, which contributes to the UN Ocean Decade's 7 Outcomes. On December 5, 2017, the United Nations declared...
World Oceans Week at Sea-Bird Scientific: The HyperNAV Program
A New Paradigm for Ocean Color Satellite Calibration The HyperNAV program is part of the NASA PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) Mission, set to launch in 2024. The NASA PACE Mission is an initiative aimed at helping scientists understand how carbon...