## 5 Conclusions  
Scalar irradiance at the ocean surface can be derived from satellite estimates of planar irradiance using the scaling factor from Hydrolight computations. For a clear sky, the scaling factor is a function of wavelength, SZA and ozone amount. The scalar erythermal dose rates calculated at the ocean surface are noticeably higher than the planar erythermal dose rates; their ratio varies from 1.5 to about 3.0. In-water attenuation of \(E_{d}\) and \(E_{o}\) with depth is quite similar. Differences in the corresponding K-functions are very small for the wide range of input parameters, which include depth, wavelength, SZA, chlorophyll concentration and ozone amount.  
A dominant factor defining the UV penetration depths is chlorophyll concentration. Other input parameters play a less significant role in the spatial distribution of the penetration depths. The penetration depths vary from a few meters in areas of productive waters to about 30-35 m in the clearest waters. The machine learning algorithm shows a very good performance with the selected NN architecture in predicting the penetration depths. The NN reproduces the planar penetration depth with errors \(<\)\(\pm\)2%.  
Conceptualization, A.V. and N.K.; methodology, A.V. and N.K.; software, D.H.; validation, A.V., D.H. and Z.F.; formal analysis, A.V.; investigation, A.V.; resources, Z.F.; data curation, Z.F.; writing--original draft preparation, A.V. and N.K.; writing--review and editing, J.J., D.H. and Z.F.; visualization, A.V. and D.H.; supervision, N.K. and J.J.; project administration, N.K.; funding acquisition, N.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by NASA through the PACE science team program.  
OMI Level 1b UV radiance data are available through NASA's Goddard Earth Sciences Data and Information Services Center (GES DISC) at [[https://disc.gsfc.nasa.gov/datasets/OML1](https://disc.gsfc.nasa.gov/datasets/OML1) BRUG_004/summary]([https://disc.gsfc.nasa.gov/datasets/OML1](https://disc.gsfc.nasa.gov/datasets/OML1) BRUG_004/summary). The TSIS-1 HSRS 0.1 nm spectral resolution (\"p1 nm\") dataset was obtained from the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder, [[https://lasp.colorado.edu/lisird/data/tsis1_hrss](https://lasp.colorado.edu/lisird/data/tsis1_hrss)]([https://lasp.colorado.edu/lisird/data/tsis1_hrss](https://lasp.colorado.edu/lisird/data/tsis1_hrss)). OMI Level 2 total ozone data are available at [[https://disc.gsfc.nasa.gov/datasetsOMTO3_003/summary](https://disc.gsfc.nasa.gov/datasetsOMTO3_003/summary)]([https://disc.gsfc.nasa.gov/datasetsOMTO3_003/summary](https://disc.gsfc.nasa.gov/datasetsOMTO3_003/summary)). MODIS Level 3 4 km chlorophyll data are available at [[https://oceancolor.gsfc.nasa.gov/](https://oceancolor.gsfc.nasa.gov/)]([https://oceancolor.gsfc.nasa.gov/](https://oceancolor.gsfc.nasa.gov/)). All accessed on 30 March 2022.  
We are grateful to the OMI processing team for providing OMI data.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} AU & Astronomical Unit \\ BWF & Biological Weighting Function \\ CDOM & Colored Dissolved Organic Matter \\ DNA & Deoxyribonucleic Acid \\ DU & Dobson Unit \\ FOV & Field of View \\ IOP & Inherent Optical Property \\ MOBY & Marine Optical Buoy \\ MODIS & Moderate Resolution Imaging Spectroradiometer \\ OCI & Ocean Color Instrument \\ OMI & Ozone Monitoring Instrument \\ RMS & Root Mean Square \\ RT & Radiative Transfer \\ SZA & Solar Zenith Angle \\ TOA & Top of the Atmosphere \\ TSIS-1 HSRS & Total and Spectral Solar Irradiance Sensor Hybrid Solar Reference Spectrum \\ UV & Ultraviolet \\ \end{tabular}