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In this Issue:

Chasing the Shadow of Harvey
Sea-Bird Scientific at Oceanology International in London
Improving Glider CTD Data with Flow and Optimized Sample Rate
Sea-Bird Scientific Sensor Performance Feedback
Tech Tip: Optimizing CTD Data on Moving Platforms
Meet Our People
Facebook Spotlight
Upcoming Events

 

Chasing the Shadow of Harvey

Photo Credit: TAMU Geosciences Communications and Media Relations

Shortly after the wake of Hurricane Harvey, a little robot could be found skipping along a dark underwater cloud in the Gulf of Mexico. The Gulf Explorer, a Liquid Robotics Wave Glider owned by Texas A&M’s Geochemical and Environmental Research Group (GERG), was deployed on September 8th, 2017 equipped with sensors to measure several variables such as salinity and water temperature and the ability to transmit data back to shore every 30 minutes. Its mission: to better understand and monitor freshwater flowing into the Gulf of Mexico from Hurricane Harvey’s passage. Radiating from river deltas on the coast, this plume of freshwater potentially threatened the Flower Garden Banks National Marine Sanctuary, a protected coral reef ecosystem hosting breathtaking biodiversity. At the time of the deployment, it was unclear whether this freshwater plume would reach the sanctuary and its impact if it did. Read more about the initial deployment here.

The Gulf Explorer is currently out of the water, prepping for another voyage as scientists review the data from the first deployment. The journey of the Gulf Explorer is a prime example of how unmanned and autonomous vehicles are opening new doors for more efficient and cost-effective surveys.

 

Sea-Bird Scientific at Oceanology International in London

Sea-Bird Scientific is looking forward to exhibiting this week at London's Oi 2018. Sea-Bird Scientific will have several folks on hand to meet with you and discuss your programs, applications and plans all week at Stand K100. Our UK partner Planet Ocean will also be exhibiting and available to discuss your needs, at Stand K100.

 

Improving Glider CTD Data with Flow and Optimized Sample Rate

Underwater gliders have been undergoing a form of divergent evolution; the streamlined torpedo is giving way to designs that range from a winged squid to a miniature stealth bomber. Regardless of form, the glider’s mission remains the same: soar through ocean and collect data along the way.
Unlike standard profiling applications or shipboard surface sensors, these gliders combine a unique blend of vertical profiling and horizontal surveys. This creates a unique sampling challenge, as the glider CTD must capture data on a temporal and spatial scale in dynamically changing environments. In a 2011 Case Study, Sea-Bird Scientific explored the requirements behind obtaining quality CTD data from a glider CTD. We found the following to be important, incorporating these traits into the GPCTD:

  • Pumped flow fixes the response time of the temperature and conductivity sensors. While unpumped CTDs are susceptible to variable flow from inconsistent glider speeds, pumped CTDs have a known response time. The operator can correct for dynamic sampling errors that occur at temperature and salinity gradients, providing better computation of variables such as salinity and density.
  • Ducted T-C sensors ensure that the temperature and conductivity sensors are measuring the same parcel of water.
  • Proper sampling rate ensures that the glider CTD is capturing temporal misalignments in temperature and conductivity sensors, and data is precise enough to capture small changes.

Read more here.

Figure 1: A profile between 200 – 250 db with 3 CTDs: a reference 9plus CTD sampling 24 samples/second (black), a continuously pumped Glider CTD sampling 1 sample/2 seconds (red), and a discontinuously pumped Glider CTD samples 1 sample/8 seconds (blue).

Figure 2: The same profile as Figure 1, with Glider CTD data corrected for T-C temporal alignment and conductivity cell thermal mass. Note the similarity between the 24 Hz reference CTD (black) and the fast-sampling Glider CTD (red) after corrections. The slow sampling, discontinuously pumping CTD (blue) retains large discrepancies from the reference CTD.

 

Sea-Bird Scientific Sensor Performance Feedback

Sea-Bird Product Management team would like to invite you to participate in a brief survey about your experience with our fluorometer instruments. Your response will help us immensely in improving your experience with our ECO sensors. Your opinion is very important to us. Please feel free to pass the survey on to someone else if they are better equipped to respond.  This survey is very brief and will take no more than 8 minutes to complete.

Feedback on Sensor Performance - Fluorometers (ECO)

Tech Tip: Optimizing CTD Data on Moving Platforms

The term “moving platform” encompasses a diverse array of systems and vehicles. Any standard vertically-profiling CTD package is a moving platform, as is an AUV or ROV, or even a shipboard Thermosalinograph.  As these platforms move through the water, they expose the CTD to dynamically changing conditions that affect the CTD’s ability to accurately measure data and resolve important changes. Yet, despite large differences in moving platform application and speed, two primary rules allow for significant improvements in data quality.

  1. Use a pump. Conductivity sensor response time is flow-dependent, and the flow rate of an unpumped CTD on a moving platform will depend on the vehicle’s speed, which is usually inconsistent. Pumped flow ensures a constant flow rate across the sensors, allowing the user to align the temperature and conductivity sensors, ensuring both sensors measure the same water parcel at the same time.
  2. Adjust the CTD’s sampling speed to the vehicle’s movement speed. If an instrument is sampling too slowly, the response time of the sensors is too slow, or the vehicle is moving too quickly, the CTD will miss important details in the data (such as large temperature and salinity gradients). The table below shows sensor response times and sampling frequencies required to resolve changes in data over a given distance.

For more information, see Application Note 98: Considerations for CTD Spatial and Temporal Resolution on Moving Platforms. Also see Improving Glider CTD Data with Flow and Optimized Sample Rate (above) for a miniature case study demonstrating these effects with a Sea-Bird Scientific Glider CTD.

Limiting Sensor Response Time * Instrument Sample Frequency (delta t) Measurement
Spatial Resolution
Realized Spatial Resolution
(2X Measurement Resolution)
0.060 s 8 Hz
0.125 s
0.45 m 0.90 m
0.060 s 24 Hz
0.042 s
0.15 m 0.30 m
0.1 s 1 Hz
1 s
3.6 m 7.2 m
0.1 s 4 Hz
0.25 s
0.9 m 1.8 m
0.1 s 8 Hz
0.125 s
0.45 m 0.9 m
0.5 s 4 Hz
0.25 s
1.8 m 3.6 m
1 s 1 Hz
1 s
3.6 m 7.2 m
5 s 8 Hz
0.125 s
18.0 m 36 m
30 s 1 Hz
1 s
108.0 m 216 m
60 s (1 min) 8 Hz
0.125 s
216.0 m 432 m
180 s (3 min) 1 Hz
1 s
648.0 m 1296 m

 


Meet Our People:
Juliana Chen Engineering Technician, NAVIS Support

Juliana received her B.S. in Oceanography from the University of Washington, where she focused on Ocean Technology. Before joining Sea-Bird, Juliana worked as a research assistant in ARGO Lab during her undergraduate days at the University of Washington. She spent the majority of her spare time in college on the Under-Water Remotely Operated Vehicle (UWROV) team, designing and building ROVs for both the International MATE Competition and research.

Juliana joined Sea-Bird last year as an Engineering Technician, NAVIS Support. She is responsible for providing customer support for NAVIS floats, NAVIS fleet health, and customer data analysis. In her spare time, Juliana enjoys Hapkido (Korean martial art), cake decorating, and cooking.

We’re Hiring! Want to join the Sea-Bird team? Have a look at our open positions and let us know if anything interests you.

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Oi London 2018: London, UK. March 13 - 15, 2018

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