System Testing Deployments

Prior to system deployment a number of tests were conducted to assess a prototype mooring for flotation, power autonomy, two way communication and data acquisition. In a final test, a fully functional mooring was deployed for several days north of Dia island in Heraklion bay and its overall performance was assessed.

At the same time, more tests were conducted on land to evaluate the time synchronization accuracy among the moorings. High accuracy -which is crucial for localization algorithms to function- is achieved through GPS/ PPS pulses

2020 Deployment - Sougia

The deployment of the SAveWhales observatory for the first year mission was done SE of Sougia in Southern Crete. The system was operational from 1 July, when the three acoustic stations were deployed (see positions below) , to 2 October 2020 when SWAN1 was recovered. During this period there were several whale detections, whereas a variety of other sounds (dolphins, ships, explosions, etc.) were recorded. In the period from 20 July to 11 August 2020 a verification campaign was conducted in the broader Sougia area aiming at the comparison of localization results from the SAvEWhales system with actual visual observations, nevertheless there were no whale encounters in the particular time window.

Deployment: The deployment of the acoustic stations SE of Sougia at water depths of about 500 m was carried out from the fishing vessel FV ELENA and took place between 30 June and 1 July. The deployment task was quite demanding due to the large water depths and bottom slopes (slope angles reaching or exceeding 20°). In this connection, it was decided to carry out the deployment of each acoustic station in two steps:

• First deploy a simple float at the target location of the buoy. For each float two anchor lines in a Λ shape were used such as to minimize the risk of entanglement of the suspended 100-m hydrophone cable with the anchor lines. The two anchors were deployed perpendicular to the isobaths such as to allow for motion of the buoy in the direction of the isobaths (primary direction of the currents). This step was implemented on June 30, 2020

• Then, after confirming the proper function of the moorings, replace the simple floats with the SWAN acoustic stations. This step was implemented on July 01,2020

The deployment locations of the acoustics stations were as follows

SWAN1 Lat: 35°13'20.7" N Lon: 23°50'2.8" E

SWAN2 Lat: 35°13'44.6" N Lon: 23°50'39.9" E

SWAN3 Lat: 35°13'27.6" N Lon: 23°51'13.9" E

These locations are marked on the map below. The water depth at the buoy locations varies between 470 and 550 m. The buoy separations between SWAN1 and SWAN2 were ~1200 m, between SWAN1 and SWAN3 ~1000 m and between SWAN2 and SWAN3 ~1800 m. The resulting obtuse opening angle is ~110°. The buoy locations do not remain fixed but change with time due to the presence of currents.

During operation period of the SWAN acoustic stations there were minor problems with some of the system components that were fixed with in situ visits. The largest problem was the loss of SWAN2 and SWAN3 stations in the aftermath of IANOS hurricane. Luckily the storage unit of SWAN3 had been restored in mid September, so the raw data till that time are saved. Furthermore the processed data (arrival times, position data, etc.) from SWAN2 and SWAN3 were transmitted in real time to FORTH, so they are available too.

Sperm whales – detection and localizations: Sperm whales were detected five times: Once on 14 July and then four times between 6 and 26 September. Each detection lasted for hours and 3D localizations were carried out when resolvable surface-reflected were available, when the animals were closer than 5-6 km. Unfortunately, no sperm whales were detected or spotted during the verification campaign which took place between 20 July and 11 August in the broader Sougia area.

Other sounds – Noise: During the system operation, a large variety of other sounds were also registered:

• Ambient noise due to wind, waves and distant noise sources

• Snapping shrimp: Pulsed sounds recorded mainly at SWAN3 less at SWAN1 and least at SWAN2 which is at a larger distance from the coast

• Dolphin sounds: Clicks and buzzes mainly during nighttime, more frequently at SWAN1 and SWAN3 than at SWAN2

• Ship sounds: Continuous and pulsed sounds from vessels passing by at distances up to 20-30 km, most of them identified using the MarineTraffic ship tracking service.

• Repeated explosions used for underwater surveillance (SOSUS charges)

• Explosions used for fishing (!!!)

The fact that the three hydrophones operate in different noise backgrounds, not only quantitatively (same sources received at different levels) but also qualitatively (different noise sources), complicates the identification and association of the target click signals. In this connection special methods had to be developed to filter, detect and associate sperm whale signals of interest.

2021 Deployment - Sougia

Based on past year's experience, a different deployment area was opted this time, so that moorings are better protected from strong underwater currents. The new area laid a few miles to the west of the previous one, in a similar sea depth of about 450 m. The two moorings that were lost in the previous deployment (SWAN2 and SWAN3) were replaced, and all three moorings were fortified with extra floating devices for increased buoyancy. Major upgrades were also performed to both the internal software of the moorings and the main system software on the land.

The system was deployed on May 26 2021 and a number of preliminary tests and adjustments were performed in the next few days to ensure its functionality and stability. Since then, and for about 100 days until its retrieval on Sept 3 2021 the system was operating on a 24/7 basis, detecting and/or localizing sperm whales and other cetaceans in the area. On each event, the system conveyed the appropriate information to MarineTraffic which broadcasted it to all registered vessels in the greater area.

During its operation, the system routinely detected/localized sperm whales and other similar click sources in the area. Preliminary calculations, estimate its duty cycle to about 25%