Regression methods for evaluation of the underwater noise levels in the Slovenian Sea

Significant independent variables with p-values less than 0_05, meaning that there was a more than 95 % probability that these variables were related to the dependent variable Leq,125Hz_ The grey fields indicate insignificant independent variables with p-values greater than 0_05_ The abbreviation n_a_ means not applicable_

p-values	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
p (vv)	0.000	0.000	0.000	0.000	0.000
p (hp)	0.019	0.509	0.111	0.867	0.599
p (ρL,2NM)	0.097	0.022	0.000	0.033	0.000
p (ρL,5NM)	0.000	0.000	0.000	0.215	0.002
p (ρL,Tireste)	0.001	0.000	0.000	0.033	0.000
p (ρL,Venice)	0.256	0.110	0.036	0.000	0.000
p (dredg. act.)	n.a.	0.000	n.a.	n.a.	n.a.
p (clean. act.)	n.a.	n.a.	0.021	n.a.	n.a.

Examples of underwater noise levels related mainly to the ship traffic in the global seas and oceans_

Location, depth of the hydrophone and depth of the sea water	Year of study	Underwater noise levels at different frequencies	Location, depth of the hydrophone and depth of the sea water	Year of study	Underwater noise levels at different frequencies
Scotian Shelf, Canada, hydrophone depth of 31 m and water depth of 79 m [3]	1972–1985	Winter average noise levels at zero wind speed [3]:30 Hz: 90.8 dB re μPa2/Hz45 Hz: 90.5 dB re μPa2/Hz80 Hz: 87.9 dB re μPa2/Hz150 Hz: 81.9 dB re μPa2/Hz300 Hz: 74.1 dB re μPa2/Hz600 Hz: 64.4 dB re μPa2/Hz900 Hz: 64.3 dB re μPa2/Hz	Ramsey Sound, Pembrokeshire, West Wales, UK, hydrophone depth of 20 m and a water depth of 460 m [7]	2009	Sound pressure levels [7]:Between 5 Hz and 10 Hz: - 92.6 dB re 1 μPa ± 3.9 dB re 1 μPa during spring - 104.7 dB re 1 μPa ± 2.2 dB re 1 μPa during summer Around 100 Hz: - 85.9 dB re 1 μPa ± 2.4 dB re 1 μPa during spring - 104.6 dB re 1 μPa ± 2.4 dB re 1 μPa during summer
India, shallow water, hydrophone depth of 5 m and water depth of 25 m [4]	2006	Average noise levels [4]:98 Hz: 130.3 dB re μPa/√Hz195 Hz: 128.6 dB re μPa/√Hz293 Hz: 127.3 dB re μPa/√Hz586 Hz: 127.6 dB re μPa/√Hz977 Hz: 127.4 dB re μPa/√Hz3027 Hz: 127.1 dB re μPa/√Hz4023 Hz: 127.1 dB re μPa/√Hz	Guanabara Bay, SE Brazil, hydrophone depth of 2 m and a water depth of 4 m [8]	2011–2012	The highest mean sound pressure level [8]):At 187 Hz:111.6 ± 9.0 dB re 1 μPaAt 15.89 kHz:76.2 ± 8.3 dB re 1 μPa
Indian Ocean, the lagoon of a coral atoll, hydrophone depth of 2–15 m and water depth of 50 m [5]	2005	Spectral maxima observed at 1 kHz and 7.5 kHz [5]:1,000 Hz: 72 dB re μPa/√Hz2,000 Hz: 65 dB re μPa/√Hz7,500 Hz: 80 dB re μPa/√Hz	Port of South Louisiana (H-3), Port of Houston (H-1), NE Gulf of Mexico, hydrophone depth from 250–1,370 m [9]	2010–2012	The highest values L01 (T = 1 h) at two sites (H-3 and H-1) nearest to high-shipping lanes [9] in LF band (10–500 Hz) were:130 dB re 1 μPa and 128 dB re 1 μPa, respectively(L01 = sound levels that were exceeded 1% of the time)
Northeast Pacific Ocean, SW of the San Nicolas Island, California, USA, hydrophone depth of 1,090–1,106 m [6]	1966 – 2006	Mean ambient noise levels:−30–50 Hz in 1964–1966: 73–75 dB re 1 Pa2/Hz−30–50 Hz in 2003–2004: 85 dB re 1 Pa2/Hz [6]	Celtic Sea, northern and southern North Sea in UK, hydrophone depth of 100 m and a water depth of 200 m [10]	2013–2014	Median noise levels for 1/3 octave bands from 63 Hz to 500 Hz [10]:81.5–95.5 dB re 1μPa

Regression equations in which the dependent variable Leq,125Hz was predicted by the significant independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice, dreadg_ act_, clean_ act_, vv and hp)_

Measuring periods	Regression equations
13.02.2015–05.05.2015	Leq,125Hz = 0.752*vv − 2.659*hp + 0.263*ρL,5NM – 0.153*ρL,Trieste + 77.786
26.09.2015–31.12.2015	Leq,125Hz = 0.248*vv + 0.192*ρL,2NM + 0.167*ρL,5NM – 0.117*ρL,Trieste + 1.181*dred. + 77.375
18.08.2016–01.11.2016	Leq,125Hz = 1.869*vv + 0.265*ρL,2NM – 0.551*ρL,5NM + 0.368*ρL,Trieste – 0.009*ρL,Venice – 1.87* clean.a. + 84.6
06.07.2017–07.08.2017	Leq,125Hz = 1.063*vv − 0.122*ρL,2NM + 0.151*ρL,Triestre – 0.017*ρL,Venice + 71.912
18.08.2018–31.12.2018	Leq,125Hz = 0.562*vv + 0.364*ρL,2NM − 0.126*ρL,5NM + 0.121*ρL,Trieste – 0.017*ρL,Venice + 91.705

Significant independent variables with p-values lower than 0_05, meaning that there was a more than 95 % probability that these variables were related to the dependent variable Leq,63Hz_ The grey fields indicate insignificant independent variables, with p-values greater than 0_05_ The abbreviation n_a_ means not applicable_

p-values	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
p (vv)	0.000	0.000	0.000	0.000	0.000
p (hp)	0.001	0.061	0.240	0.923	0.010
p (ρL,2NM)	0.005	0.691	0.048	0.003	0.036
p (ρL,5NM)	0.007	0.015	0.000	0.556	0.000
p (ρL,Trieste)	0.327	0.794	0.000	0.119	0.000
p (ρL,Venice)	0.037	0.087	0.023	0.342	0.000
p (dredg. act.)	n.a.	0.000	n.a.	n.a.	n.a.
p (clean. act.)	n.a.	n.a.	0.002	n.a.	n.a.

The Pearson correlation coefficients between the dependent variable (Leq,63Hz) and the independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice_, dreadg_ act_, clean_ act_, vv and hp) in all measuring periods_

Pearson's correlation coefficient	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
r (vv)	0.58	0.51	0.54	0.39	0.35
r (hp)	−0.02	0.06	0.08	0.08	0.07
r (ρL,2NM)	0.13	−0.06	0.05	−0.04	0.05
r (ρL,5NM)	0.06	−0.06	0.02	0.09	0.08
r (ρL,Trieste)	−0.02	−0.03	0.08	0.12	0.12
r (ρL,Venice)	−0.10	−0.05	−0.05	0.01	−0.11
r (dredg. act.)	n.a.	0.31	n.a.	n.a.	n.a.
r (clean. act.)	n.a.	n.a.	−0.10	n.a.	n.a.

Multiple correlation coefficients (r) between dependent variables (Leq,63Hz and Leq,125Hz) and independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice, dreadg_ act_, clean_ act_, vv and hp) in all measuring periods_

Multiple correlation coefficients	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
r (Leq,63Hz)	0.59	0.55	0.57	0.40	0.40
r (Leq,125Hz)	0.41	0.21	0.59	0.29	0.23

The Pearson correlation coefficients between the dependent variable (Leq,125Hz) and the independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice, dreadg_ act_, clean_ act_, vv and hp) in all measuring periods_

Pearsons correlation coefficients	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
r (vv)	0.39	0.18	0.55	0.24	0.15
r (hp)	−0.02	0.01	0.09	0.04	0.02
r (ρL,2NM)	0.11	0.06	0.07	0.02	0.12
r (ρL,5NM)	0.05	0.05	−0.04	0.17	0.02
r (ρL,Trieste)	−0.02	0.02	0.01	0.18	0.04
r (ρL,Venice)	−0.08	−0.01	−0.09	−0.01	−0.10
r (dredg. act.)	n.a.	0.10	n.a.	n.a.	n.a.
r (clean. act.)	n.a.	n.a.	−0.10	n.a.	n.a.

Coefficients of determination (R2) between the dependent variables (Leq,63Hz and Leq,125Hz) and the independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice, dreadg_ act_, clean_ act_, vv and hp) in all measuring periods_

Coefficients of determination	From 13.02.2015 to 05.05.2015	From 26.09.2015 to 31.12.2015	From 18.08.2016 to 01.11.2016	From 06.07.2017 to 07.08.2017	From 18.08.2018 to 31.12.2018
R2 (Leq,63Hz)	0.35	0.30	0.33	0.16	0.16
R2 (Leq,125Hz)	0.17	0.05	0.34	0.09	0.05

Regression equations in which the dependent variable Leq,63Hz was predicted by the significant independent variables (ρL,2NM, ρL,5NM, ρL,Trieste, ρL,Venice, dreadg_ act_, clean_ act_, vv and hp)_

Measuring periods	Regression equations
13.02.2015–05.05.2015	Leq,63Hz = 1.378*vv − 3.898*hp + 0.357*ρL,2NM + 0.103*ρL,5NM – 0.014*ρL,Venice + 63.450
26.09.2015–31.12.2015	Leq,63Hz = 1.117*vv − 0.093*ρL,5NM + 4.304*dred.act. + 67.800
18.08.2016–01.11.2016	Leq,63Hz = 2.227*vv + 0.165*ρL,2NM – 0.627*ρL,5NM + 0.528*ρL,Trieste – 0.012*ρL,Venice – 3.1*clean.a. + 81.77
06.07.2017–07.08.2017	Leq,63Hz = 2.762*vv − 0.196*ρL,2NM + 70.065
18.08.2018–31.12.2018	Leq,63Hz = 1.555*vv + 1.116*hp + 0.112*ρL,2NM − 0.216*ρL,5NM + 0.268*ρL,Trieste – 0.022*ρL,Venice + 73.576