Building our Acoustic Payload

Searching for humpback whale vocalizations in the middle of the Pacific Ocean is sort of like searching for a needle in a haystack. So, how do you search for a needle in a haystack? You build a sophisticated audio payload and keep your fingers crossed. Luckily our needle is a loud one!

The construction of our acoustic payload required a lot of software and hardware engineering because we wanted our hydrophone to detect whales from miles away, and keep data from being lost in case of a mishap. Therefore, we acquired a “smart” digital hydrophone (HP) called the Ocean Sonics icListen 200 kHz, which can record a wide range of frequencies and target most cetaceans (Image 1).

Image 1. Ocean Sonics Hydrophone

Image 1. Ocean Sonics Hydrophone

All sorts of things could happen to a dangling HP in the middle of the ocean, so we attached the HP to Europa’s sub to ensure we wouldn’t lose it to entanglement or predation (Image 2). However, the self-noise of the sub is relatively loud, and we found that it interfered with the acoustic sampling. Therefore, we embarked on a design to decouple as much of the sub noise as possible and enlisted the help of an acoustician, Mike Holt, who has built similar devices his entire career. He helped us make a mount that would be durable but not too heavy, biofoul resistant for the several month mission and allows sound transference to occur. Thus, we used a thick-walled 3” type K copper pipe, which is an excellent biofoul deterrent and provides mounting strength. We mounted it to the center of the sub so that it did not add drag or change the pitch of the sub (Image 3).

Image 2. Pelagic white tip shark chasing an entangled Wave Glider

Image 2. Pelagic white tip shark chasing an entangled Wave Glider

Image 3. Hydrophone mounted to center of sub

Image 3. Hydrophone mounted to center of sub

To mask the mechanical noise, Mike first designed an inner casing tube out of low-density polyethylene into which the HP would slide. To keep it from hitting the bottom or the sides we manually cut 15 donuts of 10 pores per inch by 0.75” thick polyurethane open cell foam to encase the HP. We then sealed the tube and filled it with medical grade castor oil, which is well matched to the impedance of seawater. After testing it for leaks, we slid the inner casing into the outer copper pipe modified with 250 drilled holes. The holes enabled the interference to be no greater than 12th lambda of the highest frequency of interest (Image 4).

Image 4. Murray and Beth building hydrophone casing

Image 4. Murray and Beth building hydrophone casing

Overall, the entire process was painstaking but worth the effort to boost our chances of finding our needle in a haystack.

For question, please email HUMPACS@jupiterfoundation.org


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Europa’s Super Blue Blood Moon Photos

The Super Blue Blood Moon was a sight to see! Don’t you think so? Many awoke in the early morning hours to watch the moon turn red, and those who missed it were able to view stunning photographs of it on the internet. Amazing photographers from all over the world captured shots of this ‘once in a blue moon’ event.

On January 30th, from 6:15 p.m. to 7:15 p.m. HST with location coordinates of 18.99°N, 149.50°W, Europa was able to capture a photo series of the moon rising! She wasn’t able to catch the moon when it turned red because it was too high in the sky. We only had a short window (an hour) of when the moon was in the camera view. Even so, the pictures are remarkable, as they are likely the only pictures in the world captured that night by an autonomous ocean vehicle (see image series below). In the first photo of the series, it was still light because the sun had just set. As the moon rose, the images became darker but then lightened again as the moon rose further into the sky because of its brightness.

To obtain this image series, we calculated the trajectory, angle, and rising time of the moon relative to Europa's location. We then steered Europa to face the right direction where the camera could capture the moon rising in front of her. During that hour (starting at 6:15) we set the camera payload to take a photo every 15 minutes, totaling five pictures.

Who knows what will be taking pictures of the next Super Blue Blood Moon on January 31, 2037!

For questions, please email HUMPACS@jupiterfoundation.org

Mahalo!


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 Deploying Europa 

On January 15, 2018, we successfully deployed our Wave Glider (WG), Europa, to embark on our most ambitious mission to date, HUMPACS (Humpback Pacific Survey). It was a beautiful day when we launched Europa; the wind was relatively light, and the sea state was calm. Conditions such as these enable a smooth process of loading and unloading WGs from our 32 ft boat, the May Maru.  

Our team worked for a year to prepare Europa's payloads and ensure her success during the three-month mission at sea. Thus, we celebrated the triumph by pouring a bottle of champagne over Europa before letting her swim away (see video below). Please note that we drank what was left of the bottle after working hours! Once deployed, a school of dolphins joined Europa; bow riding and spinning while escorting her out to sea (see video below). We perceived this as a good omen to our cetacean mission!!! 

We deployed Europa off Puako, the northwest coast of Hawai'i Island. As she made her way around South Point, the southernmost tip of the Island (and the USA), strong currents from a big winter swell kept pushing her off course. This was a little discouraging because Europa was only a few days into her mission and we didn't want her to go astray. Nevertheless, Europa pulled through and she’s making impressive progress, averaging ~1.5 knots. Europa is scheduled to reach her first seamount anywhere between February 18th-21st. Track Europa's journey here.

Europa is transmitting multiple data types to us via satellites, in real-time. Some of the data are available to view in our Data Portal. We just assembled a graph of daily sea surface temperature (SST) means that will be updated periodically to display recent data. An additional SST logger called a HOBO, which is more precise, is attached to Europa but its data can't be accessed until the mission is complete. Stay tuned for more updates!

For questions, please email HUMPACS@jupiterfoundation.org

Mahalo!
 


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