Sonobuoy data for the 2012 Blue Whale Voyages

Brief description

This dataset contains acoustic recordings from Directional Frequency Analysis and Recording (DIFAR) sonobuoys that were deployed throughout the 2012 Blue Whale Voyages conducted off Portland, Victoria, Australia from January – March (in the Bonney Upwelling). During the 20 days at sea 131 AN/SSQ-53D sonobuoys were deployed yielding more than 500 hours of acoustic recordings. In January a total team of three dedicated acousticians monitored round-the-clock for blue whales and in all weather conditions. In March the team size was increased so that five acousticians monitored and tracked blue whales round-the-clock.

The recording chain for all sonobuoy deployments through 25 March 2012 included a 3-dB communications antenna with a central frequency at 161 MHz and masthead amplifier connected to a passive four way splitter. The highest point of the antenna was approximately 14 m above sea level. The antenna, amplifier, and splitter were connected with low loss cable, and each output of the four way splitter connected to the DIFAR input of a WiNRaDiO 2902i sonobuoy VHF receiver. On 25 March the masthead amplifier failed and was removed from the recording chain. This failure prompted the use of recently acquired WiNRaDiO G39WSBe sonobuoy receivers. The A/D converter used throughout both voyages was a RME Fireface UFX.
The voltage outputs of all of the sonobuoy receivers were calibrated as a function of modulation frequency before the voyage, and DIFAR outputs from each of the 2902i and G39WSBe were connected to an instrument input of the UFX. The instrument inputs of the UFX (analog inputs 9-12) have a peak-peak voltage range of 80 V with digitally controlled gain that can be set between 10-65 dB, and this setting was noted in the Sonobuoy Deployment Log (see below) in order to measure received sound-pressure levels accurately. The digitised signals from the UFX were saved as 16-bit WAV files with 48 kHz sample rate using passive acoustic monitoring software Pamguard.

Directional calibration

The magnetic compass in each sonobuoy was calibrated/validated upon deployment as described by Miller et al. (2015, 2016). Calibration procedure involved measuring the mean bearing error and standard deviation of errors between the GPS-derived bearing from the sonobuoy to the ship and the magnetic bearing to the ship noise detected by the sonobuoy. 15-30 bearings were used for each calibration as the ship steamed directly away from the deployment location.

Intensity calibration

Obtaining calibrated intensity measurements from sonobuoys not only requires knowledge of the sensitivity of the hydrophone, but also the calibration parameters of the radio transmitter and radio receiver. Throughout the voyage, a hydrophone sensitivity of -122 dB re 1 V/µPa was applied to recordings via the Hydrophone Array Manager in PAMGuard. This value is defined in the DIFAR specification as the reference intensity at 100 Hz that will generate a frequency deviation of 25 kHz (Maranda 2001), thus the specification combines the hydrophone sensitivity and transmitter calibration. In line with manufacturers specifications, the WiNRADiO G39 WSB and 2902i both had a measured voltage response of approximately 1 V-peak–peak (approximately -3 dB) at 25 kHz frequency deviation (Miller et al. 2014), and this can be subtracted from the hydrophone sensitivity to yield an total combined factor of 125 dB re 1 V/µPa. These calibration settings, along with the shaped filter response provided by Greene et al. (2004) make it possible to obtain calibrated pressure amplitude from the recorded WAV audio files.

Sonobuoy deployment metadata (Sonobuoy deployment log)

This spreadsheet contains metadata on the deployment of sonobuoys deployed during the 2013 Antarctic Blue Whale Voyage. The first row contains column headers, while each subsequent row contains deployment information for a single sonobuoy.
Information contained in each column are:
buoyID: Buoy ID number is the sequential number of the buoy starting at 1 for the first buoy of the trip.
startDate: Date (UTC) at the start of the sonobuoy deployment (YYYY-MM-DD)
startTime: Time (UTC) at the start of the sonobuoy deployment (HH:MM:SS) 2 digit hour with 24 hour clock and leading zero.
stopDate: Date (UTC) at the end of the sonobuoy deployment (YYYY-MM-DD). While the recording is in progress this should be 1,2 4 or 8 hours after the startTime based on sonobuoy setting.
stopTime: Time (UTC) at the end of the sonobuoy deployment (HH:MM:SS). While the recording is in progress this should be 1,2 4 or 8 hours after the startTime based on the sonobuoy setting.
lat: Latitude of deployment in decimal degrees. Southern hemisphere latitudes should be negative.
long: Longitude of deployment in decimal degrees. Western hemisphere longitudes should be negative.
alt: Depth of the sonobuoy deployment in metres. For DIFAR sonobuoys either 30, 120 or 300.
recordingChannel: This is the channel number within the recorded wav-file that contains audio from this buoy as would be reported by Matlab. Channel numbers start at 1 (1-indexed) so usually this will be 1, 2 or 3.
magVariation: The magnetic variation in degrees. Positive declination is East, negative is West. At the start of a recording this will be entered from a chart. As the recording progresses, this should be updated by measuring the bearing to the vessel.
sonobuoyType: The an/ssq designation for the sonobuoy. Usually 53B, 53D, 53F, HIDAR, 57A/B, or 36Q.
receiver: The type and serial number of the calibrated radio receiver (WinRadio) used to receive the VHF signal. (wr15725, wr17274, wr15274, or wr15273)
preamp: The (unitless) gain in dB of any preamplifier (including the instrument preamp from the Fireface UFX). Usually 10 or 20 dB.
adc: The analog-to-digital converter (adc) used to digitize the audio. This is the sound card name and gain. All data were recorded on an RME Fireface UFX, so Ufx10 would be the RME Fireface UFX with a gain of 10 dB.
vhfFreq: The VHF channel number used to receive the sonobuoys. Sonobuoys have 99 pre-set VHF channels between

Real-time monitoring and analysis (Acoustic event log)
During the 2012 Blue Whale Voyages Acousticians noted all whale calls and other acoustic events that were detected during real-time monitoring in a written Sonobuoy Event Log. Additionally, the acoustic tracking software, difarBSM, stored processed bearings from acoustic events and cross bearings in tab delimited text files. Each event was assigned a classification by the acoustician, and events for each classification were stored in separate text files. The first row in each file contains the column headers, and the content of each column is as follows:
buoyID: Buoy ID number is the number of the sonobuoy on which this event was detected. This can be used as a foreign key to link to the sonobuoy deployment log.
timeStamp_matlabDatenum: Date and time (UTC) at the start of the event represented as a Matlab datenum (i.e. number of days since Jan 0 0000).
Latitude: Latitude of the sonobuoy deployment in decimal degrees. Southern hemisphere latitudes should be negative.
Longitude: Longitude of sonobuoy deployment in decimal degrees. Western hemisphere longitudes should be negative.
Altitude: Depth of the sonobuoy deployment in metres. For DIFAR sonobuoys either 30, 120 or 300.
magneticVariation_degrees: The estimated magnetic variation of the sonobuoy in degrees at the time of the event. Positive declination is East, negative is West. At the start of a recording this will be entered from a chart. As the recording progresses, this should be updated by measuring the bearing to the vessel.
bearing_degreesMagnetic: Magnetic bearing in degrees from the sonobuoy to the acoustic event. Magnetic bearings were selected by the acoustician by choosing a single point on the bearing-frequency surface (AKA DIFARGram) produced by the analysis software difarBSM.
frequency_Hz: The frequency in Hz of the magnetic bearing that the acoustician selected from the bearing-frequency surface (DIFARGram).
logDifarPower: The base 10 logarithm of the height of the point on the DIFARGram
receiveLevel_dB: This column contains an estimate of the The RMS receive level (dB SPL re 1 micro Pa) of the event. Received levels were estimated by applying a correction for the shaped sonobuoy frequency response, the receiver’s frequency response, and were calculated over only the frequency band specified in each classification (see below).
soundType: soundType is the classification assigned to the event by the acoustician.

Aural and visual monitoring of audio and spectrograms from each sonobuoy was conducted for each sonobuoy deployment.
Detections from marine mammals, and other sources and were detected and classified manually, and their time and frequency bounds were marked on the PAMGuard spectrogram. Parameters for monitoring and recording, were stored within the PAMGuard database and as stand-alone Pamguard Settings Files (PSF).

During the voyage there were detections of pygmy blue whale song, and blue whale 'D-call' vocalisations. During the dedicated blue whale voyages the course of the ship was diverted to follow bearings to vocalising blue whales.

Whale tracking log (Written Whale Acoustic Tracking Log - Tangaroa 2015.pdf)

During the 2012 Blue Whale Voyages, noted all whale calls and other acoustic events that were detected during real-time monitoring in a Sonobuoy Event Log. A written summary of the event log was recorded during data collection at approximately 15 minute intervals, and this summary comprises the Whale Tracking Log.
- Tracking Log.
- Entries in the written Sonobuoy Tracking Log (on the bench in the acoustics workstation) also include total number of different whales heard in that 15 minute interval.
- If multiple whales/groups were detected, then the acoustician on-duty, in consultation with the lead acoustician and/or voyage management designateded one of the whales the 'target' whale, and attempted to encounter this target first.
- When targeting a whale/group, the acoustician on-duty continued to track all other whales/groups in the area as these tracked whales/groups may become the next target after obtaining concluding with the current target.
Date: (UTC) written only at top of datasheet

Time: (UTC) on the hour, 15 past, half past, and 15 to.

Track: Unique identifier for each whale/group tracked in the past 15 minutes.
Each track will have:
Position: Either an average bearing from a sonobuoy (eg 220 degrees from SB18) or a Lat/Lon from the most recent triangulation
Notes: What is the vessel action with respect to this tracked whale/group? (eg. Is this the current or previous 'target'? Are we presently photographing this whale? Did we finish photographing the whale?) Has the whale gone silent? Has this track crossed paths with another?

Lineage

Progress Code: completed

Statement: This dataset only contains acoustic events that were detected and analysed during the voyages. During periods when few sounds were present, all of the sounds were likely to be included in the acoustic event log. During periods when many sounds were detected, not all sounds could be included in the acoustic event log due to the limited amount of time and attention available for processing files.

While the intent was to record all acoustic data as WAV files during the voyage, there were a handful of occasions where acousticians accidentally failed to make recordings. During these occasions, whales were acoustically tracked, but no audio files were generated for archival. Failure to record occurred in January during Sonobuoy deployments numbered: 2, 32, 33, 35, 38, 42, 45.

Notes

Purpose
The primary research objective for these voyages was the development and assessment of acoustic methods for the detection, localisation and tracking of blue whales. These voyages were undertaken in order to address the practicalities of 24-hour/day real-time acoustic tracking. Achieving these goals requires characterising the capabilities of the acoustic tracking system, assessing the practicality and performance of different survey protocols, and integrating acoustic tracking with visual survey methods and mark-recapture methodologies. Specific Questions to Answer include: 1. Can the existing acoustic system locate blue whales? 2. What is the precision/accuracy of acoustic localisations? 3. What proportion of acoustic detections yield encounters? 4. What is necessary for 24 hour acoustic operations? 5. Assess practicality and performance of survey protocols including Acoustically assisted tracking and targeting of whales ("phase 1"), and line transect survey with acoustic monitoring ("phase 2") 6. Demonstrate integration of acoustics with Visual survey and Mark-recapture methods