Define and Critique Data and Methods for Seascape Ecology:

Active and Passive Acoustics

Mike JechNOAA/NEFSC

Woods Hole, MA 02543Michael.Jech@noaa.gov

“Water column” data1) Active acoustic data are acquired, processed, and archived

within the same organization 2) Hence, there is no clearing house for these data – yet.3) Hurdles to creating this warehouse:

a. Meta-data. There is an international effort to create a standard for water column data. Should have a 1st generation standard within the next 1-2 years.

b. Data formats are manufacturer dependent. There has been an effort to standardize data format, but no consensus.

c. Data are processed for very specific purposes, e.g., single species stock assessments, academic projects.

4) NOAA National Geophysical Data Center has offered to archive and serve water column data – stay tuned.

Sound is used A LOT in water!!By both animals and humans

To find food

To communicate

For navigationTo find food

Listen to sounds

Sharing resources!

Sound is an effective and efficient way of sampling the underwater environment:1) Sound travels about 1500 m s-1 in water2) Sound can travel nearly around the planet

1 10 100 1,000 10,000

10,000

1,000

100

10

1

106

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10-2

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Echosounder Frequency [kHz]

Max

imum

Ran

ge [m

]

Typi

cal S

ampl

e Vo

lum

e [m

3 ]

Schools

Fish

Plankton

10-8

Range

Sample Volume

(Figure from MacLennan and Simmonds, Fisheries Acoustics, 1992)

Fig. 1. Spatio-temporal scope of a single observation by varioussampling devices and sensors. Resolution of the measurementis indicated by the lower-left side of the polygon and itsrange by the upper-right side. These represent the spatial extentof a single observation, not a time series. (Trenkel et al., MEPS, 2011)

Trenkel et al. (MEPS 442: 285-301, 2011)Proposals for Ecosystem Indicators Using Active Acoustics

Data• Start with voltage & time, everything else is derived• Remote sensing technology – information from a distance, i.e.,

beyond direct sensory detection of the target (sight and hearing)- Goal is to not affect targets

• Calibrated instrumentation – any changes in signal are not due to electronics

• Most common application is to learn about the “target” – source of sound or echo – which means you need to know about the propagating medium. - The less you know about the medium, the more uncertainty

you add to interpretation.• Issues with near-boundary regions (e.g., sea bed and surface)• Grand challenge is identification using acoustics alone- Verification is necessary

Acoustic Data Sources1) “Scientific” (calibrated, linear) systems

a. In the past, only expensive systems on government vessels had these. Now, many commercial systems conform to this.

b. In mid-Atlantic to Gulf of Maine, multi-frequency acoustic data are collected during fall and spring bottom trawl surveys, and dedicated herring surveys from 1998 to present.

2) “Commercial” systemsa. May or may not be useful.

i. Gain values must be recordedii. Data must be collected over areas larger than the

scale of an aggregation3) Processing effort goes up considerably for data collected

from systems that are not calibrated and have “dynamic” parameters (e.g., gains, depth, frequency)

Passive Acoustic Systems:Uses:1) Detect animals that vocalize

a. Whales, dolphins, fish2) Detect human-made objects

a. Vesselsb. Tags & telemetry (fish, mammal, turtle, …)c. Remote platforms (AUV, ROV, glider)

Systems (selected list):3) Marine Autonomous Recording Units (MARUs)

a. Used on Stellwagon Bankb. http://www.birds.cornell.edu/brp/hardware

4) DTAGa. Attach to whales; records orientation of animal and

soundshttp://www.whoi.edu/page.do?pid=39337

A. Active acoustic methods transmit sound (aka, ‘ping’) and listen for echoes1) Echoes contain information about the target(s):

a. DTime: distance to targetsb. Duration: 1 target = 1 echo length, so longer echoes =

more targetsc. Amplitude: Echo strength dependent on target

properties, such as size, type, numbersd. Frequency: possibly most important characteristic; all

echoes have very strong dependence on frequencye. Bandwidth: frequency content

i. narrow band systems are simple but limited interpretation potential

ii. wider bands (i.e., more frequencies) have more potential information, but at increased ‘cost’

Atlantic herring surveys in 2000

Herring Aggregations on the Northern Edge of Georges Bank (2001)

120 kHz

38 kHz

12 kHz

Atlantic herring