LADC01

During the summer of 2001, the Minerals Management Service (MMS) and the National Marine Fisheries Service (NMFS), with other government scientists and those from several academic institutions, conducted a major marine mammal set of experiments, Sperm Whale Acoustic Monitoring Program (SWAMP) to study sperm whales in the northeastern Gulf of Mexico from 16 July through 21 August. Even though LADC was not affiliated with SWAMP, LADC scientists realized that it might be possible to have three bottom-moored hydrophones funded by ONR ready in time to make ambient noise measurements while the SWAMP exercise was being conducted. This was an excellent opportunity to have marine mammal "ground truth" while the bottom-moored hydrophones were recording, since SWAMP included surface visual observations, surface towed array acoustic measurements, digital acoustic and motion-sensing recording tags mounted on whales, and even a whale tag feeding locations to satellites.

All the acoustic measurements were accomplished with moorings which included Environmental Acoustic Recording System (EARS) buoys from NAVOCEANO. Three buoys were placed in a location of frequent sperm whale sightings.


The EARS buoys each had a single omni-directional hydrophone and an instrument package which autonomously recorded the acoustic signals up to 5859 Hz. The hydrophones for these buoys were tethered 50 m from the bottom. The remainder of the mooring, spanning almost all the rest of the water column, was devoted to environmental data sensors to collect temperature, conductivity, and pressure. The moorings were deployed at the 600, 800, and 1000 m contours on a downslope track. The acoustic recordings spanned 36 days.

During the experiment, Tropical Storm Barry passed within 100 mni of the EARS buoys.

Number of buoys:
3
Locations:

Area bounded by 28° N and 29°N Latitude and 88.5° W

EARS1: 28°24.0283'N and 88°59.7300W
EARS2: 28°30.5318'N and 89°02.7595W
EARS3: 28°33.1619'N and 89°04.1371W

Dates:
Leg 1: 16 to 19 July
Leg 2: 7 to 10 Aug
Leg 3: 29 Aug to 1 Sept
Days of recorded data:
EARS1: 35.45 days
EARS2: "
EARS3: "
Amount of data:

EARS1: 34 Gb
EARS2: "
EARS3: "

Depth:
EARS1: 993 m
EARS2: 791 m
EARS3: 632 m
Special Events:
Tropical Storm Barry


Environmental data:

In addition to the oceanographic measurements made continuously at each mooring described below, CTD and XBT measurements were made along the downslope and cross-slope tracks during the deployment cruise (Leg 1, 16 to 19 July), on thes mid-experiment cruise (Leg 2, 7 to 10 Aug), and on the retrieval cruise (Leg 3, 29 Aug to 1 Sept). During and just after Leg 1, the NAVOCEANO ship USNS BRUCE HEEZEN was in the area making oceanographic measurements. A total of 38 CTD and 77 XBT casts were made. Also on the mid-experiment cruise, a chirp sonar survey was conducted to determine bottom properties. These oceanographic and bottom measurements, together with those made at the moorings, increase significantly the quality of the acoustic propagation modeling which can be done.

Time series data were collected on the three vertical EARS moorings deployed during LADC01. Each vertical mooring was populated with a mix of self-recording temperature, conductivity-temperature, and conductivity-temperature-depth sensors. All sensors were programmed to collect data at two-minute intervals beginning at 1200Z on 18 July 2001. Temperature sensors had limited data storage capacity and recorded data until 16 August. Temperature-depth, conductivity-temperature-depth sensor had larger data storage capacity and continued to record information until recovery on 31 August.

On the 600 m mooring, temperature time series were collected at depths of 46, 52, 80, 105, 130, 180, 230, 280, 381, 481, and 582 m. Additional conductivity time series were collected at depths of 130, 230, and 582 m.

On the 1000-meter mooring, temperature time series were collected at depths of 8, 11, 41, 66, 91, 141, 191, 241, 341, 441, 541, 641, 741, 943 m. Additional conductivity time series were collected at depths of 91, 191, 541, and 943 m.

On the 800 m mooring, temperature time series were collected at depths of 5, 11, 39, 64, 89, and 741 m. Additional conductivity time series were collected at 741 m.