Polarized Light Pollution of Fixed-Tilt Photovoltaic Solar Panels Measured by Drone-Polarimetry and Its Visual-Ecological Importance

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Thanks for addressing the previous comments.

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Author Response

Point-by-Point Response to the Comments of Reviewer 1

Our manuscript was revised on the basis of the comments of three Reviewers. All changes suggested by Reviewer 1, Reviewer 2 and Reviewer 3 are marked with orange, green and blue, respectively. Below is our response to the comments of Reviewer 1.

Reviewer 1 wrote:     Thanks for addressing the previous comments.

                                    Minor editing of English language required

Answer: Thank you for your positive opinion about our 1st revised manuscript. During the 2nd revision, we tried again to improve the English of our 2nd revised manuscript.

Reviewer 2 Report (New Reviewer)

The authors present a drone-based polarimetry approach to detect the Polarized Light Pollution (PLP) of tilted photovoltaic panels. While this is an important endeavor, the paper appears to lack novelty for a scientific publication.

1. Employing a polarimeter on a drone to monitor photovoltaic panels may not constitute a novel approach.

2. The paper lacks clarity in expressing the calculation of 'd', and the definition of PLP provided in Line 145 is ambiguous. Referencing or providing explanations would help validate the concept.

3. The claim regarding insects' ability to locate the sea solely based on the polarization state of the surface raises questions. Additionally, presenting data on changes in insect populations would enhance the significance of the study.

4. It is unclear what suggestions the authors offer based on their observations.

Overall, the novelty of the method is not apparent. While the work appears necessary, it may not be suitable for publication as a scientific paper.

Author Response

Point-by-Point Response to the short Comment of Reviewer 2

Our manuscript was revised on the basis of the comments of three Reviewers. All changes suggested by Reviewer 1, Reviewer 2 and Reviewer 3 are marked with orange, green and blue, respectively. Below is our response to the comments of Reviewer 2.

Reviewer 2 wrote: The authors present a drone-based polarimetry approach to detect the Polarized Light Pollution (PLP) of tilted photovoltaic panels. While this is an important endeavor, the paper appears to lack novelty for a scientific publication.

            Overall, the novelty of the method is not apparent. While the work appears necessary, it may not be suitable for publication as a scientific paper.

1. Employing a polarimeter on a drone to monitor photovoltaic panels may not constitute a novel approach.

Answer: Reviewers 1 and 3 have a much positiver opinion. Our drone-polarimetric technique is a valuable novel tool and can be used for numerous different air-borne polarization measurements. Our present paper provides the second application of drone-based imaging polarimetry, namely the air-borne measurement of the reflection-polarization patterns of fixed-tilt solar panels in order to demonstrate and quantify the polarized light pollution of photovoltaic farms. The first application was our drone-based imaging polarimetry of dark lake patches (https://doi.org/10.3390/rs15112797). At the beginning of the Discussion we wrote the following:

This work has the following novelties: (1) Our drone-polarimetric method is new. Its first application was that Száz et al. [10] measured the reflection-polarization characteristics of dark lake patches and explained their ecological implication. The present paper deals with the results of the second application of drone-polarimetry. (ii) The reflection-polarization patterns of a fixed-tilt photovoltaic solar farm and the quantity of polarized light pollution of solar panels derived from these patterns are measured for the first time by us with drone-based imaging polarimetry. (iii) The measured reflection-polarization characteristics of the studied photovoltaic farm are discussed from the point of view of flying polarotactic aquatic insects being the most endangered victims of polarized light pollution.

Reviewer 2 wrote: 2. The paper lacks clarity in expressing the calculation of 'd', and the definition of PLP provided in Line 145 is ambiguous. Referencing or providing explanations would help validate the concept.

Answer: Ad 1) Since in the community of optical physicists and experts of polarimetric remote sensing the terms of the degree d and angle α of linear polarization are well known, in our present paper it would be redundant to define these variables and how they can be calculated from the well-known Stokes vector’s components. Nevertheless, to the revised Materials and Methods we added the following:

Furthermore, d is the degree (%) of linear polarization, and α is the angle of polarization measured clockwise from the vertical. The definition of both polarization variables is available in [19], for example.

Ad 2) The following last paragraph of the Materials and Methods clearly explains the meaning and calculation of the variable plp:

In this work, plp = N_water/N_panel is the quantitative measure of the polarized light pollution of solar panels, where N_water is the number of panel pixel detected as water by a polarotactic insect and N_panel is the number of the whole panel area, which numbers were determined as follows: (1) We constructed a red mask (Fig. 1B) containing all solar panels visible on the picture taken by the polarization camera from the drone. (2) From this red mask, the over- or underexposed pixels were removed, and our software counted the number N_panel of remaining red pixels of the mask. (3) In the picture, we determined those pixels for which the conditions d > d* and |90^o - α| < α* are satisfied, which pixels would be sensed as water by a hypothetical polarotactic aquatic insect possessing polarization sensitiviy thresholds d* and α*. These pixels are marked by blue colour in the last row of Figs. 2, 3 (and Supplementary Figs. S1-S6). (4) The number N_water of blue pixels (without any over- or underexposed pixels) of the areas detected as water was also counted. (5) Finally, the quotient plp = N_water/N_panel was calculated.

Reviewer 2 wrote: 3. The claim regarding insects' ability to locate the sea solely based on the polarization state of the surface raises questions.

Answer: On the one hand, the word ‘sea’ does not occur in our paper.

On the other hand, polarotactic aquatic insects detect the water surface PREDOMINANTLY by means of the horizontal polarization of water-reflected light, and other cues (e.g. olfaction, colour, brightness) are only of secondary/terciary relevance. This evidence is experimentally proven for many insect species reviewed by Schwind (1989, 1991) and Horváth and Csabai (2014), for example.

Schwind R (1989) A variety of insects are attracted to water by reflected polarized light. Naturwissenschaften 76: 377-378

Schwind R (1991) Polarization vision in water insects and insects living on a moist substrate. Journal of Comparative Physiology A 169: 531-540

Horváth G, Csabai Z (2014) Chapter 5: Polarization vision of aquatic insects. pp. 113-145. In: Horváth G (editor) Polarized Light and Polarization Vision in Animal Sciences. Springer: Heidelberg, Berlin, New York

In our revised manuscript the word predominantly was added to the following sentences:

Because aquatic insects detect water bodies predominantly by perceiving the horizontally polarized light reflected from water surfaces [5], they are attracted to such light.

53^o was chosen, since water-seeking polarotactic aquatic insects detect water predominantly by means of the highly and horizontally plarized light coming mainly from this direction [6,31,32,33].

Furthermore, we chose only a single elevation angle of the camera’s optical axis, namely 53^o from the vertical, practically coinciding with , because polarotactic aquatic insects (main victims of specific PLP) detect water bodies predominantly with perception of the horizontally and maximally polarized light reflected from the water surface from .

Reviewer 2 wrote: Additionally, presenting data on changes in insect populations would enhance the significance of the study.

Answer: We do not know any thorough ecological monitoring of the changes in aquatic insect populations due to polarized light pollution. Note that such monitoring is time- and money-consuming.

Nevertheless, to the end of the revised Discussion we added the following:

The PLP of photovoltaic panels is indirectly demonstrated by the more and more frequent observations that the numbers of panel-collisions and the activity of insectivorous bats increase [13,17,18,37] at solar farms. The main reason of this can be the enhanced number of insects deceived and lured by the horizontally polarizated light reflected from solar panels.

37. 37. Barre K.; Baudouin A.; Froidevaux J. S. P.; Chartendrault V.; Kerbiriou Insectivorous bats alter their flight and feeding behaviour at ground-mounted solar farms. Journal of Applied Ecology 2024, 61, 328-339 (doi: 10.1111/1365-2664.14555)

Reviewer 2 wrote: 4. It is unclear what suggestions the authors offer based on their observations.

Answer: To the end of the Conclusions we added the following:

Inspired by the high polarized light pollution plp ≤ 58 % of the studied smooth (shiny)  photovoltaic solar panels, we suggest to reduce the degree of linear polarization d of panel-reflected light either by coverig the panel’s surface with a gridding composed of orthogonal thin (1-2 mm) white stripes, or by using an antireflecting, matte covering. Both methods can considerably reduce, or even eliminate the polarized light pollution of smooth black reflectors [4,8,9,11].

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

There is a sentence from the article template that was left by the authors in the references that needs to be removed, on line 427.

Author Response

Point-by-Point Response to the Comment of Reviewer 3

Our manuscript was revised on the basis of the comments of three Reviewers. All changes suggested by Reviewer 1, Reviewer 2 and Reviewer 3 are marked with orange, green and blue, respectively. Below is our response to the comments of Reviewer 3.

Reviewer 3 wrote:     Are all the cited references relevant to the research?

                                    Must be improved

Answer: In the 2nd revised manuscript, the number of self-citations was drastically decreased. The following 15 self-references were deleted:

7. Horváth, G.; Kriska, G.; Malik, P.; Hegedüs, R.; Neumann, L.; Åkesson, S.; Robertson, R. Asphalt Surfaces as Ecological Traps for Water-Seeking Polarotactic Insects: How can the Polarized Light Pollution of Asphalt Surfaces be Reduced?; Nova Science Publishers, Inc.: Hauppauge, New York, USA, 2010
8. Blahó, M.; Herczeg, T.; Kriska, G.; Egri, Á.; Száz, D.; Farkas, A.; Tarjányi, N.; Czinke, L.; Barta, A.; Horváth, G. Unexpected attraction of polarotactic water-leaving insects to matt black car surfaces: mattness of paintwork cannot eliminate the polarized light pollution of black cars. Public Library of Science One 2014, 9, e103339 (doi: 10.1371/journal.pone.0103339)
9. Wildermuth, H.; Horváth, G. Visual deception of a male Libellula depressa by the shiny surface of a parked car (Odonata: Libellulidae). International Journal of Odonatology 2005, 8, 97-105 (doi: 10.1080/13887890.2005.9748246)
10. Kriska, G.; Malik, P.; Szivák, I.; Horváth, G. Glass buildings on river banks as “polarized light traps” for mass-swarming polarotactic caddis flies. Naturwissenschaften 2008, 95, 461-467 (doi: 10.1007/s00114-008-0345-4)
11. Malik, P.; Hegedüs, R.; Kriska, G.; Horváth, G. Imaging polarimetry of glass buildings: Why do vertical glass surfaces attract polarotactic insects? Applied Optics 2008, 47, 4361-4374 (doi: 10.1364/AO.47.004361)
12. Robertson, B.; Kriska, G.; Horváth, V.; Horváth, G. Glass buildings as bird feeders: Urban birds exploit insects trapped by polarized light pollution. Acta Zoologica Academiae Scientiarum Hungaricae 2010, 56, 283-293
13. Bernáth, B.; Horváth, G. Visual deception of a Great White Egret by shiny plastic sheets. Ornis Hungarica 1999, 8-9, 57-61
14. Bernáth, B.; Szedenics, G.; Molnár, G.; Kriska, G.; Horváth, G. Visual ecological impact of a peculiar waste oil lake on the avifauna: dual-choice field experiments with water-seeking birds using huge shiny black and white plastic sheets. Archives of Nature Conservation and Landscape Research 2001, 40, 1-28
15. Bernáth, B.; Szedenics, G.; Molnár, G.; Kriska, G.; Horváth, G. Visual ecological impact of "shiny black anthropogenic products" on aquatic insects: oil reservoirs and plastic sheets as polarized traps for insects associated with water. Archives of Nature Conservation and Landscape Research 2001, 40, 89-109
16. Horváth, G.; Bernáth, B.; Molnár, G. Dragonflies find crude oil visually more attractive than water: Multiple-choice experiments on dragonfly polarotaxis. Naturwissenschaften 1998, 85, 292-297 (doi: 10.1007/s001140050503)
17. Horváth, G.; Blahó, M.; Egri, Á.; Kriska, G.; Seres, I.; Robertson, B. Reducing the maladaptive attractiveness of solar panels to polarotactic insects. Conservation Biology 2010, 24, 1644-1653 (doi: 10.1111/j.1523-1739.2010.01518.x)
18. Blahó, M.; Egri, Á.; Barta, A.; Antoni, G.; Kriska, G.; Horváth, G. How can horseflies be captured by solar panels? A new concept of tabanid traps using light polarization and electricity produced by photovoltaics. Veterinary Parasitology 2012, 189, 353-365 (doi: 10.1016/j.vetpar.2012.04.016)
19. Horváth, G.; Varjú, D. Polarization pattern of freshwater habitats recorded by video polarimetry in red, green and blue spectral ranges and its relevance for water detection by aquatic insects. Journal of Experimental Biology 1997, 200, 1155-1163 (doi: 10.1242/jeb.200.7.1155)
20. Bernáth, B.; Gál, J.; Horváth, G. Why is it worth flying at dusk for aquatic insects? Polarotactic water detection is easiest at low solar elevations. Journal of Experimental Biology 2004, 207, 755-765 (doi: 10.1242/jeb.00810)
21. Csabai, Z.; Boda, P.; Bernáth, B.; Kriska, G.; Horváth, G. A “polarisation sun-dial” dictates the optimal time of day for dispersal by flying aquatic insects. Freshwater Biology 2006, 51, 1341-1350 (doi: 10.1111/j.1365-2427.2006.01576.x)

On the other hand, the following 14 self-references were kept, because they are relevant for this paper:

4. Horváth, G.; Kriska, G.; Malik, P.; Robertson, B. Polarized light pollution: a new kind of ecological photopollution. Frontiers in Ecology and the Environment 2009, 7, 317-325 (doi: 10.1890/080129)
5. 7. Kriska, G.; Horváth, G.; Andrikovics, S. Why do mayflies lay their eggs en masse on dry asphalt roads? Water-imitating polarized light reflected from asphalt attracts Ephemeroptera. Journal of Experimental Biology 1998, 201, 2273-2286 (doi: 1242/jeb.201.15.2273)
6. 8. Horváth, G.; Kriska, G.; Robertson, B. Chapter 20. Anthropogenic polarization and polarized light pollution inducing polarized ecological traps. In Polarized Light and Polarization Vision in Animal Sciences; Horváth, G., Ed.; Springer: Heidelberg, Germany, 2014; pp. 443-513.
7. 9. Száz, D.; Mihályi, D.; Farkas, A.; Egri, Á.; Barta, A.; Kriska, G.; Robertson, B.; Horváth, G. Polarized light pollution of matte solar panels: Anti-reflective photovoltaics reduce polarized light pollution but benefit only some aquatic insects. Journal of Insect Conservation 2016, 20, 663-675 (doi: 10.1007/s10841-016-9897-3)
8. 10. Száz, D.; Takács, P.; Bernáth, B.; Kriska, G.; Barta, A.; Pomozi, I.; Horváth, G. Drone-based imaging polarimetry of dark lake patches from the viewpoint of flying polarotactic insects with ecological implication. Remote Sensing 2023, 15, 2797 (doi: 3390/rs15112797)
9. 11. Fritz, B.; Horváth, G.; Hünig, R.; Pereszlényi, Á.; Egri, Á.; Guttmann, M.; Schneider, M.; Lemmer, U.; Kriska, G.; Gomard, G. Bioreplicated coatings for photovoltaic solar panels nearly eliminate light pollution that harms polarotactic insects. Public Library of Science One 2020, 15, e0243296 (doi: 10.1371/journal.pone.0243296)
10. 12. Kriska, G.; Csabai, Z.; Boda, P.; Malik, P.; Horváth, G. Why do red and dark-coloured cars lure aquatic insects? The attraction of water insects to car paintwork explained by reflection-polarization signals. Proceedings of the Royal Society B 2006, 273, 1667-1671 (doi: 10.1098/rspb.2006.3500)
11. 13. Pereszlényi, Á.; Horváth, G.; Kriska, G. Atypical feeding of woodpeckers, crows and redstarts on mass-swarming Hydropsyche pellucidula caddisflies attracted to glass panes. Urban Ecosystems 2017, 20, 1203-1207 (doi: 10.1007/s11252-017-0672-3)
12. 14. Bernáth, B.; Kriska, G.; Suhai, B.; Horváth, G. Wagtails (Aves: Motacillidae) as insect indicators on plastic sheets attracting polarotactic aquatic insects. Acta Zoologica Academiae Scientiarum Hungaricae 2008, 54, 145-155
13. 15. Horváth, G.; Zeil, J. Kuwait oil lakes as insect traps. Nature 1996, 379, 303-304 (doi: 1038/379303a0)
14. 16. Horváth, G.; Malik, P.; Kriska, G.; Wildermuth, H. Ecological traps for dragonflies in a cemetery: the attraction of Sympetrum species (Odonata: Libellulidae) by horizontally polarizing black gravestones. Freshwater Biology 2007, 52, 1700-1709 (doi: 10.1111/j.1365-2427.2007.01798.x)
15. 22. Gál, J.; Horváth, G.; Meyer-Rochow, V.B. Measurement of the reflection-polarization pattern of the flat water surface under a clear sky at sunset. Remote Sensing of Environment 2001, 76, 103-111 (doi: 10.1016/S0034-4257(00)00196-6)
16. 26. Horváth, G.; Bernáth, B.; Suhai, B.; Barta, A.; Wehner, R. First observation of the fourth neutral polarization point in the atmosphere. Journal of the Optical Society of America A 2002, 19, 2085-2099 (doi: 10.1364/JOSAA.19.002085)
17. 33. Horváth, G.; Csabai, Z. Chapter 5. Polarization vision of aquatic insects. In Polarized Light and Polarization Vision in Animal Sciences; Horváth, G., Ed.; Springer: Heidelberg, Germany, 2014; pp. 113-145.

Reviewer 3 wrote: There is a sentence from the article template that was left by the authors in the references that needs to be removed, on line 427.

Answer: The criticitized sentence was removed.

Round 2

Reviewer 2 Report (New Reviewer)

Firstly, in my review, I do not take into account the opinions of other reviewers. While the tool presented may have some value, the methodology lacks novelty.

 1. It's important to note that not all readers are experts in polarimetric imaging. The paper assumes familiarity with terms like 'd' and 'α', which may not be well-known to all readers.

2. Ecological monitoring of changes in aquatic insect populations is essential for understanding the significance of monitoring efforts. Without this context, the meaning of the monitoring is unclear.

Overall, the authors have not adequately addressed the concerns raised in the review process. Therefore, I maintain my opinion that this manuscript is not suitable for publication.

Author Response

Our response () is uploaded.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

As part of a larger series of papers with similar scientific goals and methodologies, the authors explore the typical polarized light pollution due to solar farms, consisting of large amounts of inclined dark yet partially reflective solar panels. The main goal of the study is to establish whether such solar farms attract water-seeking insects with polarization vision. To this reviewer, it is convincingly demonstrated that most likely they do. However, the paper could be significantly strengthened with enhanced argumentation and more experimental details.

- This research is presented exclusively from the literal and metaphorical point of view of the insects. It would valuable to also discuss the value to, e.g., the solar farm owner, as dead insects may also reduce the efficiency of the panels. Moreover, drones are frequently used to monitor the cleanliness of the panels, and it may be beneficial to use polarimetric data to assess the amount of dust deposited on the panels. Finally, high reflectivity by definition implies that the solar panels could be made more efficient.

- The argumentation would be solidified if indeed a more-then-average amount of insects (dead or alive) would be observed at this (or another) solar farm. Is this indeed the case?

- As the authors discuss, also the grass field in between the solar panels is identified as “water”. How is this possible? Was the grass wet? Would regular grass fields then also attract insects? It would be useful to explain why the solar panels really change the situation with respect to a regular grass field.

- While the angle of linear polarization is only determined by geometry and there are no surprises there, the degree of linear polarization would be determined by material properties. It would therefore be very useful to provide a more detailed description of the panels. Do you see a blueish hue from the silicon? Is there a cover glass? Does it have AR coating? And do you observe any wavelength-dependence within the error bars for the RGB channels?

- Please add experimental details for the polarization camera. Particularly the small volume and weight will be of great interest to the drone community. Moreover, please specify the lens and its field-of-view. Also, the bandpasses of the RGB filters are not exactly ± 50 nm, see your own paper https://www.mdpi.com/2072-4292/15/11/2797 . That paper is referred to for the error analysis, which is only very sparsely described there. While this reviewer thinks that an absolute error of ~3% is realistic, it would be useful to discuss and separate the sources of error: photon/detection noise, induced polarization/cross-talk from the lens, differential pixel gains, aliasing, etc. Please discuss how you established the ~3% by calibration.

- Please note that there techniques are described in the literature to deal with the aliasing due to the 4x4 superpixels. See https://opg.optica.org/ol/abstract.cfm?uri=ol-34-20-3187 https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11132/111320K/Spatio-temporal-hybrid-color-polarization-channeled-sensors/10.1117/12.2529562.short for Fourier-based techniques . Also, you could defocus the lens to ensure the MTF to be compatible with the sensor.

- The sentence trying to explain Umov’s Law is incorrectly phrased.

- Fig 5AB does not add much…

- Could you also look backwards to gain access to the Brewster angle?

The title sentence has a weird construction.

Author Response

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Reviewer 2 Report

This paper measured the reflection-polarization patterns of fixed-tilt photovoltaic panels from the viewpoint of flying polarotactic aquatic insects, using drone-based imaging polarimetry. In this paper, authors present the reflection-polarization patterns and the temporal change of polarized light pollution of solar panels measured from two orthogonal viewing directions between sunrise and sunset on a sunny and an overcast day, and discuss their visual-ecological importance.

Although the authors emphasize their drone-polarimetric technique fill in the gap between near-and remote-pol-sensing, and is a valuable new tool that can be used for many different air-borne measurements. But this technology have been described in detail in the author's previous paper called “Drone-Based Imaging Polarimetry of Dark Lake Patches from the Viewpoint of Flying Polarotactic Insects with Ecological Implication” (https://doi.org/10.3390/rs15112797). In general, the originality and innovation of this paper is not enough. Therefore, I cannot recommend this paper for publication in Remote Sensing.

Overall, the manuscript is well written and clearly organized.

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