Ship Detector
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The Ship Detector Remora is a repository with user-friendly interfaces to detect ship passages and weather events from Long-Term Spectral Averages (LTSAs). This package was initially developed for this Ph.D. thesis and since then has been expanded for the Sound Monitoring Project to support Marine Protected Area management, as well as additional monitoring projects.
Events are identified from Long-Term Spectral Averages (LTSA). LTSAs are averaged spectra of a specified time bin and frequency range and aligned over time, resulting in a long-term spectrogram which preserves the temporal-spectral resolution of the acoustic data. The LTSA is analyzed in blocks of data (windows), where the power spectral density estimates (PSD) are averaged in three frequency bands. The three frequency bands are referred to as low-, medium-, and high-frequency bands (see Figure 1). Start and end times of the ship passages and weather events are detected and stored if the three averaged PSD meet multiple conditions:
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Condition 1: Amplitude is above a time-dependent amplitude threshold (
). The threshold is computed using a histogram method of the averaged PSD, where the histogram is divided into two equal regions, and the mode of each region is taken as the lower and upper levels. The time-dependent threshold is calculated as the mean of the lower- and upper-levels. -
Condition 2: The event duration above the threshold in the three bands must be longer than a specified time, referred to as Close Passage Duration Threshold. Additionally, the duration in the higher band must be shorter than the medium band, which allows discarding dolphin detections. Or, the event duration above the threshold in the lower and medium band must be longer than a specified time, referred to as Distant Passage Duration Threshold. Additionally, the duration in the medium band must be shorter than the lower band, which allows discarding sperm whale detections.
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Condition 3: Ship passages are distinguished from weather events when averaged received levels of the event in the lower band is above a specified percentage of the background noise in the window.
To ensure that events on the edges of the analysis window are detected, an overlapping sliding window is applied. Sliding time and length of the window can be defined by the user to improve the performance of the detector on different acoustic data sets.
Learn how to download or clone the Triton repository with the Ship Detector Remora repository in the quick setup section and how to add the Remora to Triton.
In the Control Window, use Tools pull-down menu, and select Make LTSA from Directory of Files.
First, it will prompt you to select file type: use 1 for WAV files or 2 for XWAV files and specify folder containing audio files. After, it will prompt you to set the LTSA parameters:
- Time Average: length of time for each spectral average
- Frequency Bin Size for LTSA (Hz)
Since these parameters are data sample rate dependent, setup with caution. The default parameters for broad-band HARP data sampled at 200 kHz are usually 5s averages and 200 Hz frequency bins. For lower sample rate such as Soundtrap data (i.e., 48 kHz or 96 kHz), the default parameters are usually 5s averages and 48 Hz frequency bins.
After, select the folder to save the LTSA. It is recommended to choose the same folder as the audio files so that the LTSA can provide a link and index to these fine-scale data files.
❗ The amount of time required to create the LTSA is over several hours, so it is recommended to run overnight, or take time to enjoy a ☕.
The goal behind the Interactive Detector is to test different settings used by the Batch Detector to improve the performance of the detector.
First, load the LTSA file (.ltsa) from the Control Window, use File pull-down menu, and select Open LTSA File.
Adjust the brightness and contrast of the LTSA plot from the Control Window which are usually set to 40 dB brightness and 100% dB contrast.
After the LTSA file (.ltsa) is loaded in the Triton Plot Window, launch the Interactive Detector from the Control Window by using Remoras pull-down menu and selecting Interactive detector (LTSA).
It will display the Ship Detector Motion Control Window where settings can be loaded from existing files, modified and/or saved.
The Ship Detector Motion Control Window contains all the adjustable parameters of the detector. You can load one of the existing settings file from Load/Save Settings pull-down menu, and select Load Detector Settings File. After, select the Refresh button to plot the results of the detector from the current LTSA window.
Based on the detector thresholds being triggered (see Detectors' Conditions), the results are displayed in different colors and symbols:
- Ship passages are shown in green.
- Weather events or others are shown blue as ambient.
- Events that triggered the Close Passage Duration Threshold are shown as a circle.
- Events that triggered the Distant Passage Duration Threshold are shown as a cross.
Once you have found the best parameters for your data, save the settings to a file in the Ship Detector Motion Control Window, use the Load/Save Settings pull-down menu, and select Save Detector Settings File.
Run the detector on the entire LTSA file by selecting the Batch run detector from the Ship-Detector in the Remoras pull-down menu.
It will display the Ship Detector Batch Window where you can load the settings file, verify all the parameters, and modify them if needed before running the detector. A common parameter to modify in this window is the transfer function, which may vary from one recording to another.
Then, click the Run Detector button to start the detector. The processing time will vary based on the LTSA parameters, from a couple of minutes to a maximum of 20 minutes.
The detector stores the start and end times of the detections, the corresponding labels, and settings in a .mat file in the specified output folder. It also creates a .tlab file, which contains the same information but in the format that Triton reads detection labels file.
Visualize the detections in the Triton Plot Window by loading the .tlab file from the Control Window, use Remoras pull-down menu, and select Visualize detections & Open LTSA File.
It will display the Visualize labels Window, where you can load a maximum of two .tlab files if you want to compare results. From the Visualize labels Window, you can control the movement of the LTSA plot forwards or backward, and the display of the detections. Labels from the first file are displayed in white and the second file in red.
If you have other detection files, such as manual detection files that you want to compare with the ship detector results. You can create a .tlab file by selecting Visualize detections & Create labels from text file.
.txt files format accepted:
- Text file from Raven software.
- Text file with three columns: real start time (serial date number), real end time (serial date number), labels.
Raven selection table is expected to have 13 columns. The first 7 columns are Raven’s default measurements, the next 4 columns are additional Raven measurements, and the last 2 columns are Annotation columns. Columns can be labeled anything, for this build, the column header names are:
Selection View Channel BeginTimes EndTimes LowFreqHz HighFreqHz BeginDate BeginClockTime EndClockTime DeltaTimes Behavior Notes
However, only column 8-10 and 12 are read to create the .tlab, which corresponds to the column header names: BeginDate, BeginClockTime, EndClockTime, and Behavior.
Begin Date must be of the format mm/dd/yyyy. Raven’s default is yyyy/mm/dd so make sure you convert to the mm/dd/yyyy format. The clock times can be in the format hh:mm:ss.ssss or h:mm:ss.ssss. An example of this is shown below:
Begin Date Begin Clock Time End Clock Time
10/04/2019 9:30:00.5123 10:00:30.1234
mm/dd/yyyy format and that your times have the decimal seconds (tends to be dropped in Excel). Your selection table must encompass the same time period as your .ltsa file. If you have multiple selection tables within the LTSA timespan, you will need to concatenate your Raven selection tables (making sure to only have the header on the first line).
If you do not have a Raven selection table as input, or would like to bypass the formatting issues, you can simply use a three column text file as input (without headers), with start time (in serial date number), end time (in serial date number), and notes.
Click here to see example text in '.txt' file
737301.257199074 737301.262376993 ship
737301.285584111 737301.286192383 ambient
737301.309148587 737301.312769330 ship
737301.330624409 737301.332742718 ship
The goal behind the use of the Evaluation Interface is to evaluate and/or modify the output from the Batch Detector. The user can evaluate random subsamples of detections, or correct false detections of ship passages using this interface, where snippets of LTSAs for each detection are displayed consecutively for easier evaluation.
Launch the Evaluation Interface from the Control Window by using the Remoras pull-down menu, Ship-detector, and selecting Evaluate detections.
The following interface will be displayed:
Load the detection .mat file by selecting the detection folder in the interface, 
, followed by the corresponding .ltsa file by selecting the ltsa folder.
Press the green Plot button to start to visualize the detections:
Detections labeled as ship passages are displayed with a green line on top of the plot, and red if labeled as ambient.
The size of the window, frequency ranges and brightness can be adjusted. Also, you can use Start Detection to jump to the desired detection.
Any modification done with the Evaluation Interface will update the corresponding .mat file and .tlab file. If the user had specified in the settings file to store detections to a '.csv' file, this file will be updated as well.
The modification process can be done by annotating the entire window once or by selecting detections using the buttons in the Modify Label Detections section in the interface, as follows:
Evaluate a subsample of detections by selecting the Evaluate Random Subsamples button in the interface, and specify the number of subsamples you want to evaluate, as follows:
In this example, the user evaluates 20 subsamples from a total of 121 detections. Use the Modify Label Detections section in the interface to modify the false detection to the correct label. All modifications are evaluated and stored in a '.csv' file to compute the performance metrics of the detector. The performance metrics are true positives, false positives, true negatives, false negatives, precision, and recall.
The '.csv' file is stored in the same folder as the loaded '.mat' detection file and it is named according to the number of subsamples selected. In this case, the '.csv' file is named 'Eval_20_Ship_detections_GofMX_GC05_disk09_5s_100Hz.csv'.
Click here to see example text in '.csv' file
ISOStartTime ISOEndTime StartTime EndTime DetectorLabels Detector UserEval TP FP FN TN Precision Recall Comments
2012-07-22T07:33:40.000Z 2012-07-22T08:19:05.000Z 41112.31505 41112.34659 ambient 0 0 0 0 0 1 0.857142857 1 Caveat! False Negative does not include the missed detections by the thresholds of the detector. Mannually review the missed detections using the Visualize Detections interface and add them to the total number of False Negative
2012-07-23T08:58:05.000Z 2012-07-23T09:22:25.000Z 41113.37367 41113.39057 ship 1 1 1 0 0 0 NaN NaN
2012-07-24T00:43:05.000Z 2012-07-24T01:22:45.000Z 41114.02992 41114.05747 ship 1 1 1 0 0 0 NaN NaN
2012-07-24T08:24:25.000Z 2012-07-24T09:46:10.000Z 41114.35029 41114.40706 ambient 0 0 0 0 0 1 NaN NaN
2012-07-27T09:24:15.000Z 2012-07-27T10:05:15.000Z 41117.39184 41117.42031 ship 1 1 1 0 0 0 NaN NaN
2012-07-27T18:33:50.000Z 2012-07-27T19:01:30.000Z 41117.7735 41117.79271 ambient 0 0 0 0 0 1 NaN NaN
2012-07-28T12:47:00.000Z 2012-07-28T13:19:35.000Z 41118.53264 41118.55527 ship 1 1 1 0 0 0 NaN NaN
2012-07-28T18:47:20.000Z 2012-07-28T19:10:15.000Z 41118.78287 41118.79878 ship 1 1 1 0 0 0 NaN NaN
2012-07-30T13:06:10.000Z 2012-07-30T13:39:50.000Z 41120.54595 41120.56933 ship 1 0 0 1 0 0 NaN NaN
2012-08-01T22:02:20.000Z 2012-08-01T22:35:50.000Z 41122.91829 41122.94155 ship 1 1 1 0 0 0 NaN NaN
2012-08-02T12:58:25.000Z 2012-08-02T13:27:00.000Z 41123.54057 41123.56042 ship 1 1 1 0 0 0 NaN NaN
2012-08-02T19:43:10.000Z 2012-08-02T20:25:30.000Z 41123.82164 41123.85104 ship 1 1 1 0 0 0 NaN NaN
2012-08-02T23:31:10.000Z 2012-08-03T00:44:10.000Z 41123.97998 41124.03067 ship 1 1 1 0 0 0 NaN NaN
2012-08-03T05:57:15.000Z 2012-08-03T06:37:25.000Z 41124.24809 41124.27598 ambient 0 0 0 0 0 1 NaN NaN
2012-08-03T20:58:35.000Z 2012-08-03T22:45:15.000Z 41124.87402 41124.94809 ship 1 1 1 0 0 0 NaN NaN
2012-08-05T13:54:15.000Z 2012-08-05T14:17:15.000Z 41126.57934 41126.59531 ship 1 1 1 0 0 0 NaN NaN
2012-08-05T16:44:20.000Z 2012-08-05T18:19:05.000Z 41126.69745 41126.76325 ambient 0 0 0 0 0 1 NaN NaN
2012-08-07T04:50:35.000Z 2012-08-07T05:21:30.000Z 41128.20179 41128.22326 ship 1 1 1 0 0 0 NaN NaN
2012-08-08T02:16:20.000Z 2012-08-08T02:50:15.000Z 41129.09468 41129.11823 ship 1 0 0 1 0 0 NaN NaN
2012-08-08T13:27:30.000Z 2012-08-08T14:34:40.000Z 41129.56076 41129.60741 ambient 0 0 0 0 0 1 NaN NaN