the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Aug 2023
A Survey on Applications of Small Uncrewed Aircraft Systems for Offshore Wind Farms
Abstract. Offshore wind farms are attractive energy sources due to the abundancy of wind resources close to population centers. Nevertheless, offshore locations present unique challenges for atmospheric observation and turbine inspection which are essential for wind farm design and maintenance. Small uncrewed aircraft systems (sUAS) are well suited for solving many difficulties inherent to offshore sites. In the past decade, sUAS have risen as a versatile and cost-effective platform for a large variety of scientific and commercial operations relating to atmospheric observation and infrastructure inspection. Most sUAS fall into one of two classes: fixed-wing or rotorcraft. Fixed-wing aircraft offer high endurance and range at the cost of constrained maneuverability. Rotorcraft are agile and user-friendly platforms, but offer limited endurance. We present a survey on the challenges and opportunities of utilizing fixed-wing and rotorcraft sUAS for wind resource assessment, operational observation, and inspection of offshore wind farms.
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Interactive discussion
Status: closed
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RC1: 'Comment on wes-2023-87', Anonymous Referee #1, 17 Sep 2023
Sasse et al. make an attempt for a survey on applications of small UAS for offshore wind energy applications. It is certainly interesting to elude on that topic and there is a big potential in using the systems for that purpose. However, the survey seems to be premature, especially because use-cases for UAS for offshore applications have not really been established and are only just developing. The scope of the survey here is not very clearly defined and the shown cases probably do not show a complete picture of the market. Especially the market for inspection is much larger than the few cases that are shown here from within the research community.
It seems that the authors have a stronger expertise in atmospheric science. For that reason, I would recommend to focus on that aspect in the manuscript and go into some more detail and analysis of the potential, the challenges and the prospects of the technology.Â
The sections about inspection are not reflecting the state of the art and the full market of solutions. A simple google search of "wind turbine inspection drone" provides a long list of companies providing services in the field: "flyability.com", "aerialtronics.com", "skyspecs.com", "equinoxsdrones.com", "iberdrola.com". These are only the five first ones.
For this reason I cannot recommend the manuscript for publication in WES at this point, because it might give a wrong impression of the state of the art.
General comments:
- Why does the study emphasize offshore applications? Many of the showed studies are actually onshore and UAS may have significant advantages there as well. Wind ressource assessment is significantly more challenging in complex terrain.
- Two main applications are regarded in the survey: inspection and wind ressource assessment. Other applications such as the delivery of small replacement parts are not regarded, but are commercially of interest and discussed in research and industry.
- The introduction is mostly about atmospheric measurements. Hardly any comprehensive review of inspection is provided.
- For a survey of the potential of UAS for offshore wind, I miss some analysis on cost and benefit. This will eventually define if a technology can be commercially successful.Specific comments:
- p.2, l.60: Even though UAS were envisioned for AWAKEN, i am not aware that any were deployed so far. Actually, manned research aircraft are planned instead.
- p.3
- p.8, l.152: lidar, not radar
- p.9, Table 4: Europe: It is not true that a PDRA is neccessary. If none exists for that use-case, a specific operations risk assessment (SORA) can be made according to the defined process. The PDRA is only meant to speed up the process for common applications.
- p.10, l.207: what does it mean "it is believed that...". Were these observations made or not?
- p.15, l.264: I think the first applications for copters for inspection go much further back than the given references.
- p.15, ll.269: it remains very unclear what kind of inspection was made with footage of the campus from overflights.
- p.16, l.287: were only iced regions photographed? How was it decided? Manually?
- p.17, l.317: this is a key problem of the manuscript: "we believe..". In a research article, some qualified statement should be possible.Â
Citation: https://doi.org/10.5194/wes-2023-87-RC1 -
RC2: 'Comment on wes-2023-87', Anonymous Referee #2, 25 Sep 2023
Reiew of the manuscript „A Survey on Applications of Small Uncrewed Aircraft Systems for Offshore Wind Farms“
By Robert Sasse, C. Alexander Hirst, Eric Frew and Brian Argrow
Â
The title of the manuscript caught my attention and made me accept to act as reviewer immediately, as I share the opinion that UAS have a high potential for contributing to advances in the field of offshore wind energy. However, the manuscript remains very general and superficial both in content and in presentation, and I therefore vote for rejection. I would encourage the authors to submit a completely new version of this important topic in the future.
In the following, the reasons for the decline are discussed, with the aim to encourage a deeper investigation of different aspects in ordert o submit a publication that advances the understanding of UAS as tool for filling research gaps.
Major comments:
- The authors compare different types of UAS, but only fixed-wing and multicopters. However, VTOL systems gain more and more importance in atmospheric research, as take-off and landing require less infrastructure, and the training state for handling these systems is much easier to obtain compared to large-size fixed-wing UAS. If this article intends to provide an overview, these sstems should definitely be discussed in detail, as they may be a good solution for some offshore applications.
- The manuscript does not determine any requirements for the data that should be obtianed by the UAS. However, this would be very important to know in order to judge if the endurance is enough, and what kind of flight permissions you need. Please be more specific - at what altitudes do you want to sample, how frequently, what vertical resolution is needed, what horizontal resolution, if you sample at different sites, what flight patterns, do you want to study the development of the boundary layer from the coast to the wind farm, or investigate the difference upstream and downstream? Here you could show how some specific flight pattern could help for wind energy.
- A very big topic for offshore wind energy is long-reaching wakes for stable conditions, which is not mentioned at all in the manuscript. I see large potential of UAS here, as it seems that models are currently not able to capture stable conditions, e.g. https://www.schweizerbart.de/papers/metz/detail/prepub/89817/Evaluation_of_a_Wind_Farm_Parametrization_for_Meso?l=DE
https://www.nature.com/articles/s41598-018-20389-y
https://wes.copernicus.org/articles/5/29/2020/
This topic should at least be addressed in the introduction, but in my opinion this is one of the largest motivations for UAS measurements, and should be emphasized in the flight planning as well.
- I think there are too many too general statements, e.g. l. 58 „could provide atmospheric stability information“, „sUAS offer new capabilities for observation around installed wind turbines“. This is too simplistic. Please take into account legislative restrictions, e.g. up to which altitudes are you allowed to fly with what kind of permit? Is this sufficient? What effort is it to get permits to fly BVLOS, in your country, or maybe even in different countries, as you start comparing UAS flights in different countries? Another example is the study of ice buildup (l. 62). Do you really ant to fly under icing conditions? What is required to make sure you won’t loose your UAS during such operations?
- Section 2: Again a very general introduction. Up to which altitudes do you want to fly? What are the limitations? If you compare to Europe, it is quite easy to operate drones up to 120 m within line of sight and away from infrastructure and persons – is this really helpful for offshore applications? E.g. https://www.mdpi.com/2504-446X/5/3/63
- 76: explain why rotorcraft are „user-friendly“. They have several disadvantages that are not mentioned. For example they create a downwash and vibrations which may influence measurements. Instead you mention that they „can be flown with precision in compact indoor environments“ – this has nothing to do with offshore applications. Instead, it would b e good to know about limitations of different systems concerning wind speed, wind shear, turbulence…
- Very general statement in l. 84: „Fixed-wing aircraft are a popular alternative to rotorcraft“. I doubt this. Maybe this is true for very small fixed-wing aircraft which cannot do any damage. But then please be more specific and describe theses systems and their limitations.
- The choice of aircraft which are described e.g. in Fig.1-3 seems random. It is only about systems that have been flown offshore? Or systems used to perform atmospheric measurements? Why not include other systems for comparison, e.g. the SUMO (https://link.springer.com/article/10.2478/s11600-012-0042-8) or ALADINA (https://amt.copernicus.org/articles/8/1627/2015/), or the MMAV which as been used to study turbulence and low-level jets (https://link.springer.com/article/10.1007/s10546-011-9662-9, https://acp.copernicus.org/articles/16/8009/2016/) . Please justify your choice.
- l. 103: „Wind vectors are a standard sUAS measurement“. This is not really the case. Determining the 3D wind vector from UAS is quite challenging and requires certain accuracy of different sensors. Multi-hole probes do not work at all during hover, but this is not stated in your text.
- l. 132: The manuscript states that most wind parks are within 30 km from the coast, which is „easily covered“ by fixed-wing UAS. Of course there is no doubt that fixed-wing systems can fly that far. However, what should they do there? How much battery capacity is needed for the flight pattern they are supposed to perform there? And even more challenging: How can the system get the permission to fly such far distances? On the other hand, why not think of a copter based on a converter platform, taking measurements every hour and landing automatically in the docking station?  Of course htis depends on what you want to measure. For transects through wakes  this may not be suitable.
- 2.4 operations: please be much more specific. What is „adverse weather“? what is required – do you need to fly in clouds? In icing? What is the problem with stron g turbulence? What is too much turbulence? Above the ocean it should be less than above land anyway due to less thermal heating of the surface and lower surface roughness. How does turbulence „reduce aerodynamic performance“? Please explain.
- l. 161: „Offshore sUAS operations reduce the severity of aircraft failure, due to the lack
- of other low-altitude aircraft, people and structures“ please be more specific and take into consideration the regulations! At least for the North Sea this is definitely not true. There are helicopters flying low-level to the wind turbines, there is regular air traffic and gneral aviation, plus military areas. How close are you allowed to fly to wind turbines?
- l. 164: „Other hazards that can affect sUAS operation include GPS failure, communication dropouts, airspace deconfliction, and hardware failures“ This is a very important point! What level of redundancy is required to perform such operations? What are the regulations on robustness? Is it technically and economically feasible to deploy this in UAS of what size?
- l. 188 Inspection flights: please explain how they are done with conventional methods, and what flight pattern and flight time is needed to address this with UAS
- Please explain the choice of case studies. Case study 1 has nothing to do with wind energy and only operates within 2 km off the coast. So what is the relevance for offshore wind enegy applications? The statement „This study demonstrates the RAAVEN’s ability to be flow over the ocean for extended periods of time.“ is quite strange – of course it is technically feasible that UAS fly above water. The question is how can you obtain a permission to actually fly BVLOS Case study 2 refers to flights up to an altitude of 2.5 km. Again, what is the relation to wind energy? There is a good idea to do take-off from a vessel. Expand this idea, would be very interesting for offshore wind energy, where many vessels are available for construction and maintenance.
- 6-12 are not helpful for the manuscript.
- The example of a campus inspection has nothing to do with wind energy. There are several impressing applications of mapping with UAS
- The price of commercial systems is not of scientific interest (l. 281)
- I think in the conclusion there is the most important statement „studies deploying sUAS in and around offshore wind farms are lacking“. The question is why. In my opinion the answer is not the technical feasibility, but operational and legislational constraints. These should be discussed in the manuscript to make it really relevant for wind energy science.
Â
Minor and more detailed comments:
Abstract:
- I think it is too simplified to say that fixed-wing systems have high and rotorcraft limited endurance. This may be true for certain conditions, e.g. same weight, but should be stated explicitly.
- l. 25 and many other: please be more specific with the term „winds“. What are you talking about – the three-dimensional wind vector? Wind direction? Wind speed
- l. 26: Please explain „anemometer (… prop…)“
- l. 28 ff: The paragraph about in-situ measurements is quite simplified. E.g. for measuring turbulence, a much higher temporal resolution of at least 10 Hz is required
- l. 32: satellites provide a higher spatial resolution? Maybe you are referring to spatial coverage? If you are really referring to spatial resolution, please be more specific, give examples of the accuracy and spatial resolution of the measurements.
- l. 41 : I think you should also mention limitations of wind lidar (which could be overcome by additional UAS measurements), lime limited vertical resolution, no signal in clouds (could be improved by BVLOS measurements – under hich conditions is it posisble to do this?). Further, there are different lidar systems, like scanning lidars, where the temporal resolution depends on the scanning mode
- l. 90: takeoff/landing „footprint“ – what do you mean? Infrastructure? Runway? Catapult?
- l. 117: hast he lidar been used on UAS? A wind lidar? What weight?
- l. 118: how is the wind vector calculated from cameras? Please explain shortly.
- l. 123: explain more in detail the measurement of turbulence dissipation rate and structure function parameter
- l. 142: is the 3D Mesonet based on copters? Up to which altitudes do they fly? What is „high frequency atmospheric state data“? Hourly profiles? 24/7?
- l. 191: Please explain „sUAS have potential to mitigate natural challenges related to accessing and inspecting offshore wind turbines“
- l. 305 what are „fielded sUAS“?
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Citation: https://doi.org/10.5194/wes-2023-87-RC2 -
AC1: 'Comment on wes-2023-87', Robert Sasse, 02 Nov 2023
Thank you to both reviewers for taking the time to provide feedback.
Both reviewers make excellent points regarding issues with scope and point to areas that require more thorough investigation. At this time, we think it is therefore wisest to withdraw the manuscript to conduct significant revisions. Thank you again to the reviewers for providing helpful suggestions.
Citation: https://doi.org/10.5194/wes-2023-87-AC1
Interactive discussion
Status: closed
-
RC1: 'Comment on wes-2023-87', Anonymous Referee #1, 17 Sep 2023
Sasse et al. make an attempt for a survey on applications of small UAS for offshore wind energy applications. It is certainly interesting to elude on that topic and there is a big potential in using the systems for that purpose. However, the survey seems to be premature, especially because use-cases for UAS for offshore applications have not really been established and are only just developing. The scope of the survey here is not very clearly defined and the shown cases probably do not show a complete picture of the market. Especially the market for inspection is much larger than the few cases that are shown here from within the research community.
It seems that the authors have a stronger expertise in atmospheric science. For that reason, I would recommend to focus on that aspect in the manuscript and go into some more detail and analysis of the potential, the challenges and the prospects of the technology.Â
The sections about inspection are not reflecting the state of the art and the full market of solutions. A simple google search of "wind turbine inspection drone" provides a long list of companies providing services in the field: "flyability.com", "aerialtronics.com", "skyspecs.com", "equinoxsdrones.com", "iberdrola.com". These are only the five first ones.
For this reason I cannot recommend the manuscript for publication in WES at this point, because it might give a wrong impression of the state of the art.
General comments:
- Why does the study emphasize offshore applications? Many of the showed studies are actually onshore and UAS may have significant advantages there as well. Wind ressource assessment is significantly more challenging in complex terrain.
- Two main applications are regarded in the survey: inspection and wind ressource assessment. Other applications such as the delivery of small replacement parts are not regarded, but are commercially of interest and discussed in research and industry.
- The introduction is mostly about atmospheric measurements. Hardly any comprehensive review of inspection is provided.
- For a survey of the potential of UAS for offshore wind, I miss some analysis on cost and benefit. This will eventually define if a technology can be commercially successful.Specific comments:
- p.2, l.60: Even though UAS were envisioned for AWAKEN, i am not aware that any were deployed so far. Actually, manned research aircraft are planned instead.
- p.3
- p.8, l.152: lidar, not radar
- p.9, Table 4: Europe: It is not true that a PDRA is neccessary. If none exists for that use-case, a specific operations risk assessment (SORA) can be made according to the defined process. The PDRA is only meant to speed up the process for common applications.
- p.10, l.207: what does it mean "it is believed that...". Were these observations made or not?
- p.15, l.264: I think the first applications for copters for inspection go much further back than the given references.
- p.15, ll.269: it remains very unclear what kind of inspection was made with footage of the campus from overflights.
- p.16, l.287: were only iced regions photographed? How was it decided? Manually?
- p.17, l.317: this is a key problem of the manuscript: "we believe..". In a research article, some qualified statement should be possible.Â
Citation: https://doi.org/10.5194/wes-2023-87-RC1 -
RC2: 'Comment on wes-2023-87', Anonymous Referee #2, 25 Sep 2023
Reiew of the manuscript „A Survey on Applications of Small Uncrewed Aircraft Systems for Offshore Wind Farms“
By Robert Sasse, C. Alexander Hirst, Eric Frew and Brian Argrow
Â
The title of the manuscript caught my attention and made me accept to act as reviewer immediately, as I share the opinion that UAS have a high potential for contributing to advances in the field of offshore wind energy. However, the manuscript remains very general and superficial both in content and in presentation, and I therefore vote for rejection. I would encourage the authors to submit a completely new version of this important topic in the future.
In the following, the reasons for the decline are discussed, with the aim to encourage a deeper investigation of different aspects in ordert o submit a publication that advances the understanding of UAS as tool for filling research gaps.
Major comments:
- The authors compare different types of UAS, but only fixed-wing and multicopters. However, VTOL systems gain more and more importance in atmospheric research, as take-off and landing require less infrastructure, and the training state for handling these systems is much easier to obtain compared to large-size fixed-wing UAS. If this article intends to provide an overview, these sstems should definitely be discussed in detail, as they may be a good solution for some offshore applications.
- The manuscript does not determine any requirements for the data that should be obtianed by the UAS. However, this would be very important to know in order to judge if the endurance is enough, and what kind of flight permissions you need. Please be more specific - at what altitudes do you want to sample, how frequently, what vertical resolution is needed, what horizontal resolution, if you sample at different sites, what flight patterns, do you want to study the development of the boundary layer from the coast to the wind farm, or investigate the difference upstream and downstream? Here you could show how some specific flight pattern could help for wind energy.
- A very big topic for offshore wind energy is long-reaching wakes for stable conditions, which is not mentioned at all in the manuscript. I see large potential of UAS here, as it seems that models are currently not able to capture stable conditions, e.g. https://www.schweizerbart.de/papers/metz/detail/prepub/89817/Evaluation_of_a_Wind_Farm_Parametrization_for_Meso?l=DE
https://www.nature.com/articles/s41598-018-20389-y
https://wes.copernicus.org/articles/5/29/2020/
This topic should at least be addressed in the introduction, but in my opinion this is one of the largest motivations for UAS measurements, and should be emphasized in the flight planning as well.
- I think there are too many too general statements, e.g. l. 58 „could provide atmospheric stability information“, „sUAS offer new capabilities for observation around installed wind turbines“. This is too simplistic. Please take into account legislative restrictions, e.g. up to which altitudes are you allowed to fly with what kind of permit? Is this sufficient? What effort is it to get permits to fly BVLOS, in your country, or maybe even in different countries, as you start comparing UAS flights in different countries? Another example is the study of ice buildup (l. 62). Do you really ant to fly under icing conditions? What is required to make sure you won’t loose your UAS during such operations?
- Section 2: Again a very general introduction. Up to which altitudes do you want to fly? What are the limitations? If you compare to Europe, it is quite easy to operate drones up to 120 m within line of sight and away from infrastructure and persons – is this really helpful for offshore applications? E.g. https://www.mdpi.com/2504-446X/5/3/63
- 76: explain why rotorcraft are „user-friendly“. They have several disadvantages that are not mentioned. For example they create a downwash and vibrations which may influence measurements. Instead you mention that they „can be flown with precision in compact indoor environments“ – this has nothing to do with offshore applications. Instead, it would b e good to know about limitations of different systems concerning wind speed, wind shear, turbulence…
- Very general statement in l. 84: „Fixed-wing aircraft are a popular alternative to rotorcraft“. I doubt this. Maybe this is true for very small fixed-wing aircraft which cannot do any damage. But then please be more specific and describe theses systems and their limitations.
- The choice of aircraft which are described e.g. in Fig.1-3 seems random. It is only about systems that have been flown offshore? Or systems used to perform atmospheric measurements? Why not include other systems for comparison, e.g. the SUMO (https://link.springer.com/article/10.2478/s11600-012-0042-8) or ALADINA (https://amt.copernicus.org/articles/8/1627/2015/), or the MMAV which as been used to study turbulence and low-level jets (https://link.springer.com/article/10.1007/s10546-011-9662-9, https://acp.copernicus.org/articles/16/8009/2016/) . Please justify your choice.
- l. 103: „Wind vectors are a standard sUAS measurement“. This is not really the case. Determining the 3D wind vector from UAS is quite challenging and requires certain accuracy of different sensors. Multi-hole probes do not work at all during hover, but this is not stated in your text.
- l. 132: The manuscript states that most wind parks are within 30 km from the coast, which is „easily covered“ by fixed-wing UAS. Of course there is no doubt that fixed-wing systems can fly that far. However, what should they do there? How much battery capacity is needed for the flight pattern they are supposed to perform there? And even more challenging: How can the system get the permission to fly such far distances? On the other hand, why not think of a copter based on a converter platform, taking measurements every hour and landing automatically in the docking station?  Of course htis depends on what you want to measure. For transects through wakes  this may not be suitable.
- 2.4 operations: please be much more specific. What is „adverse weather“? what is required – do you need to fly in clouds? In icing? What is the problem with stron g turbulence? What is too much turbulence? Above the ocean it should be less than above land anyway due to less thermal heating of the surface and lower surface roughness. How does turbulence „reduce aerodynamic performance“? Please explain.
- l. 161: „Offshore sUAS operations reduce the severity of aircraft failure, due to the lack
- of other low-altitude aircraft, people and structures“ please be more specific and take into consideration the regulations! At least for the North Sea this is definitely not true. There are helicopters flying low-level to the wind turbines, there is regular air traffic and gneral aviation, plus military areas. How close are you allowed to fly to wind turbines?
- l. 164: „Other hazards that can affect sUAS operation include GPS failure, communication dropouts, airspace deconfliction, and hardware failures“ This is a very important point! What level of redundancy is required to perform such operations? What are the regulations on robustness? Is it technically and economically feasible to deploy this in UAS of what size?
- l. 188 Inspection flights: please explain how they are done with conventional methods, and what flight pattern and flight time is needed to address this with UAS
- Please explain the choice of case studies. Case study 1 has nothing to do with wind energy and only operates within 2 km off the coast. So what is the relevance for offshore wind enegy applications? The statement „This study demonstrates the RAAVEN’s ability to be flow over the ocean for extended periods of time.“ is quite strange – of course it is technically feasible that UAS fly above water. The question is how can you obtain a permission to actually fly BVLOS Case study 2 refers to flights up to an altitude of 2.5 km. Again, what is the relation to wind energy? There is a good idea to do take-off from a vessel. Expand this idea, would be very interesting for offshore wind energy, where many vessels are available for construction and maintenance.
- 6-12 are not helpful for the manuscript.
- The example of a campus inspection has nothing to do with wind energy. There are several impressing applications of mapping with UAS
- The price of commercial systems is not of scientific interest (l. 281)
- I think in the conclusion there is the most important statement „studies deploying sUAS in and around offshore wind farms are lacking“. The question is why. In my opinion the answer is not the technical feasibility, but operational and legislational constraints. These should be discussed in the manuscript to make it really relevant for wind energy science.
Â
Minor and more detailed comments:
Abstract:
- I think it is too simplified to say that fixed-wing systems have high and rotorcraft limited endurance. This may be true for certain conditions, e.g. same weight, but should be stated explicitly.
- l. 25 and many other: please be more specific with the term „winds“. What are you talking about – the three-dimensional wind vector? Wind direction? Wind speed
- l. 26: Please explain „anemometer (… prop…)“
- l. 28 ff: The paragraph about in-situ measurements is quite simplified. E.g. for measuring turbulence, a much higher temporal resolution of at least 10 Hz is required
- l. 32: satellites provide a higher spatial resolution? Maybe you are referring to spatial coverage? If you are really referring to spatial resolution, please be more specific, give examples of the accuracy and spatial resolution of the measurements.
- l. 41 : I think you should also mention limitations of wind lidar (which could be overcome by additional UAS measurements), lime limited vertical resolution, no signal in clouds (could be improved by BVLOS measurements – under hich conditions is it posisble to do this?). Further, there are different lidar systems, like scanning lidars, where the temporal resolution depends on the scanning mode
- l. 90: takeoff/landing „footprint“ – what do you mean? Infrastructure? Runway? Catapult?
- l. 117: hast he lidar been used on UAS? A wind lidar? What weight?
- l. 118: how is the wind vector calculated from cameras? Please explain shortly.
- l. 123: explain more in detail the measurement of turbulence dissipation rate and structure function parameter
- l. 142: is the 3D Mesonet based on copters? Up to which altitudes do they fly? What is „high frequency atmospheric state data“? Hourly profiles? 24/7?
- l. 191: Please explain „sUAS have potential to mitigate natural challenges related to accessing and inspecting offshore wind turbines“
- l. 305 what are „fielded sUAS“?
Â
Â
Citation: https://doi.org/10.5194/wes-2023-87-RC2 -
AC1: 'Comment on wes-2023-87', Robert Sasse, 02 Nov 2023
Thank you to both reviewers for taking the time to provide feedback.
Both reviewers make excellent points regarding issues with scope and point to areas that require more thorough investigation. At this time, we think it is therefore wisest to withdraw the manuscript to conduct significant revisions. Thank you again to the reviewers for providing helpful suggestions.
Citation: https://doi.org/10.5194/wes-2023-87-AC1
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