Ask an Explorer

The following questions were received and answered by the mission.

Questions from: Alfred

What is the purpose of the Bonaire expedition?

Answers from: Nicole Morris, Web Coordinator, NOAA Office of Ocean Exploration and Research

The goal of the Bonaire expedition is to survey this unique environment over a greater depth range than can be reached with compressed air scuba, using three autonomous underwater vehicles (AUVs), technical diving, and (in a future year) a manned submersible.

Questions from: Alfred

Can you tell me all the technologies that you use?

What kind of habitat are you exploring?

Answers from: Art Trembanis, Project Co-principal Investigator, University of Delaware

There are many difficult challenges for those looking to explore the ocean realms, from the intense pressure associated with the weight of the overlying water column to the corrosive power of seawater; the sea does not easily reveal her secrets. Explorers, therefore, have to rely on a diverse toolkit of advanced technology in order to facilitate scientific discovery.

On this expedition, we have gathered a wide array of advanced technologies.

First off, we have a team of technical divers breathing exotic gas mixes that enable the divers to dive to extreme depths in excess of 91 meters (300 feet) while working and collecting scientific data. Next we have a set of two long vertical thermistor chains, called BOAs, that precisely and rapidly measure small temperature fluctuations over the reef and fore slope. These arrays stay out for weeks at a time carefully recording data to onboard computers helping scientists detect possible internal waves. Last but not least — and a first ever for a project of this type — we have brought a set of three autonomous underwater robots called autonomous underwater vehicles (AUVS).

The AUVs are unmanned mini-submarines that are the real workhorses of this expedition, putting in long hours covering distances and depths that would be time consuming or nearly impossible for traditional surface diving. AUVs have never previously been to Bonaire in any number and having three here at once allows us to multiply the amount of coverage and types of measurements that we are collecting. One robot can be mapping the shallow reef while another is exploring the deep twilight zone and a third vehicle can be conducting long-range measurements of the water quality — all from one central location.

All of these technologies exist to enable the scientific objectives of exploring the extent and health of the coral reef here in Bonaire. Technology has always been a critical component in ocean exploration, providing the thrust to advance the scientific narrative without which we would be ill prepared to skim below the surface.

Questions from: Randy

How many AUV dives have been completed, and to what depths and durations for the Fetch and each of the Gavias?

Answers from: Art Trembanis, Co-principal Investigator, University of Delaware; Mark Patterson, Principal Investigator

Great question Randy!

The AUVs have been running almost continually since January 11, with as many as 3 robots in the water at the same time. During the peak of operations, each robot would log between 2 to 6 hours in the water each day. While we have been too busy running the vehicles collecting data to actually stop and do a full detailed accounting of the time and duration, a conservative estimate is that each of the Gavia vehicles logged about 120 dive missions, ranging in temporal length from 10 minutes to 2 hours and depths from 2 meters (7 feet) to a maximum recorded depth of 220 m (722 ft).  The vehicles are capable of more than that but wanted to stay safely within our operating limits. Just the other day, on our last day of operations with the UBC Gavia, we managed to complete 14 missions before lunch time — each running a kilometer long survey out over the reef and back.  

During our survey operations with the Hafmynd Gavia, we completed mapping survey dives of 1.5 to 2 hours routinely.  The vehicle remained submerged the entire time, navigating with the aid of an advanced inertial navigation system (similar to those used on commercial aircraft) and would then surface within meters of the intended pickup location.  These surveys ran from the shallow back-reef (depths of 2 to 3 m/7 to 10 ft) offshore to depths of between 100 to 220 m (328 to 722 ft), depending on the shape and slope of the fore-reef. A single such dive allowed us to completely map a 400- by 400-m (1,312- by 1,312-ft) square area of the seabed at one go.  

While diving, the AUVs complete a number of simultaneous measurements both mapping the reef structure with sound and light and also recording information about the water quality conditions (e.g. temperature, salinity, turbidity, etc.). The advantage of having multiple AUVs in the water at the same time is that we can send each robot out to survey a different patch of the reef simultaneously thus doubling or tripling our work output. Trying to do the same amount of work using traditional surface vessel towed systems or diver based operations would be an exceedingly more lengthy process.  

With the Fetch1, we've done about 100 dives thus far, running side scan sonar, O2 and pH, video, and CTD. Our greatest depth has been 75 m (246 ft), but most of the operations have been shallower as we are trying to get strip transects of the corals on the video. It has been a challenging environment, as terrain following is very hard around the drop-offs at the edge of the reef. We've probably covered 23 kilometers (14 miles) of the bottom so far.

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