Another one bites the dust!

A mere 26 days after re deploying Metis with a new cable and hydrophone, and hearing fantastic whale song, the hydrophone once again was preyed upon! Is is really hard to tell if it is a shark or a barracuda, non-the-less, we are not sure why this is happening. The sea surface temperature has been about the same (78.8°F). We have had a Wave Glider equipped the same way, in these same waters every winter season for years, and never experienced this. This time we have a little audio to go with it. While there is no Jaws music in the background, it does sound like a freight train hit the hydrophone.

P.S. Europa is still happily cruising along and about 400 NM away from Isla Clarión, Mexico. More on this in our next blog.

Hydrophone cable with several rake marks.

Take a look and listen at the audio and spectrogram below of the exact time when the hydrophone got bitten off!

Clear Humpback Whale Song followed by either a shark or a barracuda biting off the hydrophone

The Sound of Silence

Each year, we have made significant improvements to the audio quality of our HUMPACS payload.

From the first year HUMPACS EAST in 2018 to HUMPACS WEST in 2019, we dropped the hydrophone mount ~4” to help isolate it from the sub. This dramatically improved the amount of noise we were getting from the rudder and the wing stops and even allowed us to not have to filter out so much of the rudder noise (see our Can You Hear Me Now blog).

For HUMPACS PMNM 2020, we again made more improvements, this time to the sub itself, by adding washers and high-density rubber pads to strategic locations (see our Europa Arrives in the PMNM blog).

For HUMPACS MEXICO 2021, we again mitigated more of the self-noise sub sounds which has significantly improved our audio quality.

Here is an example spectrogram of what the whales sounded like from the improved system as Europa left Puako for HUMPACS MEXICO. We are thrilled with the quality!

Feelin' Groovy

Europa has completed about one-third of her voyage north as she continues to cruise across deep ocean basins between the shallow banks, islands and atolls of PMNM. We monitor her health and download audio files and pictures of the sub daily. So far, we have posted some pretty interesting audio files. Below are some pictures of Europa’s sub showing the umbilical with tension and some slack. We painted one side of the umbilical so that we can tell if it gets any twist. Looking pretty straight now!!

Europa sub (PMNM)

Europa sub (PMNM)

Meanwhile, back in Puako, we were able to capture some pretty cool pictures off our Wave Glider, Metis, which is towing a hydrophone and streaming live whale song off Puako. These are of a bottlenose dolphin swimming around the sub, perhaps just curious or trying to catch one of the many fish that hang out around the vehicle. Something very similar has likely happened to Europa while transecting the environmentally rich waters of PMNM. Our hope is to get lucky enough to capture some images like these off Europa during her voyage.

Metis sub (Puako)

Metis sub (Puako)

Metis sub (Puako)

Metis sub (Puako)

Take a look and listen to the audio we captured at the moment when the bottlenose dolphin is hanging out with Metis.

Spectrogram of audio clip below

Bottlenose dolphin with humpback whales chorusing in the background

End of year...

Our HUMPACS project has made for an exciting and busy year. To wrap it up, Beth had the opportunity to present the results of our HUMPACS East mission at the World Marine Mammal Conference in Barcelona, Spain Dec 6-12, 2019. She presented in the session on “Assessing Marine Mammals in the High Seas” as well as in the workshop “Using smart acoustic technology to detect, classify, localize and track marine species”.

Beth presenting at the WMMC

Beth Goodwin, Rose Fisher, Jillian Duggan, Ashley Noseworthy (left to right)

We have another HUMPACS mission planned for 2020! Check back in with us in January, in the mean time wishing you all a Joyful Holiday and a Happy New Year!!

Can You Hear Me Now?

When we were preparing for the first leg of HUMPACS, referred to as HUMPACS East, we found ourselves faced with a tough decision when it came to how the hydrophone should be mounted.

“Do we hang the hydrophone, or try to hard mount it as close to the sub as possible?”

When doing hydrophone operations just outside of Puako, Hawaii, we have found that you get the best audio if you hang the hydrophone at least 30 feet below the sub. This, obviously, is due to the fact that we’re basically decoupling the hydrophone from the sub. We also are able to pick up more sounds when we’re deeper.

Hearing that, you might wonder why we decided to hard mount the hydrophone during HUMPACS East.

Well, what we have also learned through years of experience monitoring the gliders off the coast of the Big Island is that when we have a hydrophone hanging, ocean currents become a much larger problem.

There are different currents at different depths, and so even though the glider (float, sub and hydrophone) are all relatively in vertical alignment, each part of them is getting pushed and pulled by a different current.

In Hawaii, it’s not that big of a deal for us because we keep the gliders in a relatively small area the majority of the time, and we can go rescue the glider if we really need to.

When sending it across the Pacific Ocean, it’s a different story. There are no rescue missions. It just has to work!

For that reason, we decided to keep the hydrophone hard mounted directly to the sub, with no separation or “acoustic isolation”. We knew that the background noise (flow noise, wing springs and rudder) would be very loud. However, we confirmed that even with all this loud background noise we would be able to detect humpback whales, as we did a proof of concept with humpbacks singing off Puako before sending it east. All this was worth it to know that the hydrophone would be very safe. After all, we’d never made this trek before, (no one had for that matter), so we didn’t know what kind of abuse it might encounter. Sharks, rubbish, wear and tear, getting tangled up by the umbilical. These were all big concerns, and, at the time, we needed to play it as safe as possible.

HUMPACS East

Copper Hydrophone Mount

All these concerns continued to stand true with HUMPACS West. We still agreed that the unknowns about drifting were too much of a risk, so we mounted it close, but not hard mounted.

Since we did not encounter any drift that could have entangled the hydrophone, nor any shark bites, for HUMPACS West, we decided to see what the minimum distance was that we could drop the hydrophone and achieve higher quality audio. We still needed to keep the hydrophone safe, but we wanted more vibration isolation between the sub and the hydrophone itself.

After testing many different materials and changing up the distance of which we dropped the hydrophone below the sub we came to the conclusion that a three inch drop using EPDM Fiberglass Reinforced rubber sheets to mount was the way to go. It improved our audio and also kept the hydrophone safe at the same time. As an additional safety measure, we added a deflector bar to the bottom of the sub to help prevent shark bites and entanglement on the hydrophone.

HUMPACS West

EPDM Fiberglass Reinforced Hydrophone Mount

Take a look at the two spectrograms below and see the difference in noise levels. HUMPACS West is exponentially more quiet than HUMPACS East. There is also almost a complete elimination of the 650Hz and 975Hz harmonics from the rudder module. This, alone, is a very improved piece of the puzzle, as the primary range that we listen and view the humpbacks’ song is in that <1KHz range.

HUMPACS West Spectrogram

HUMPACS East Spectrogram

As you can see, HUMPACS West is much more quiet as far as background noise goes. What’s that do for us? Well, if the background noise is less, then it becomes substantially easier to detect humpback whales (and other species). This improvement should greatly improve our post processing efforts, and is more efficient at detecting as many humpbacks as possible.

Currently, Europa is a little over 700nm (nautical miles) west of the Big Island of Hawaii. Follow its journey on the HUMPACS page!

Aloha!