Status: this preprint is currently under review for the journal ESSD.
Spectral correction factors for the removal of glint perturbations in above-water radiometry
Barbara Bulgarelli,Davide D'Alimonte,Giuseppe Zibordi,and Tamito Kajiyama
Abstract. Spectral correction factors for the removal of glint perturbations in above-water radiometric measurements are theoretically computed for representative inland, coastal and open-ocean waters, accounting for spectral and atmospheric dependences. The simulation framework relies on the measurement protocol adopted by AERONET-OC and endorsed by the ocean color community to support the validation of satellite aquatic radiometric products. The theoretical computation of the correction factors, here termed glint correction factors or-factors, is performed in the 340–1020 nm spectral range by coupling i. a highly accurate plane-parallel scalar code to simulate the angular distribution of the spectral sky-radiance impinging at the water surface, with ii. a three-dimensional Monte Carlo code to model radiance reflections at a wind-roughened water surface. The impact of glint due to sky-radiance originating from the sun region (conventionally termed sun-glint) is separately discussed. Computed glint correction factors—for both the total sky radiance and its sole diffuse component—are available at Zenodo (https://doi.org/10.5281/zenodo.20609990).
Received: 16 Jun 2026 – Discussion started: 13 Jul 2026
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Spectral correction factors for the removal of glint perturbations in above-water radiometry
Review for ESSD
This paper presents updated estimates of the ρ look-up-table (LUT) for the glint removal from above-water measurements using Mobley’s approach, yet for an azimuth Δϕ=90°, which is not what recommended by Mobley, but the operational choice in the AERONET-OC network.
There are a number of facts from this paper that I find positive, and a number that I find negative. The editor may decide whether these latter ones compromise publication or not.
On the positive side I acknowledge the quality of the work. This is definitely the state of the art of radiative transfer, and both the finite element code and Monte Carlo simulator are unique tools that can provide the deepest insight on optics, maintaining the highest accuracy. The care on the atmospheric modelling is excellent, and hence, this whole scientific approach has high potential.
The motivation for a new ρ LUT beyond those that already exist is not clearly stated. I understand that the authors improved their modelling of the physical setup, but they also must explain what are the current physical or numerical inconsistencies that motivate the creation of yet another LUT. But even if the authors explained it, such a need is not very clear to me. There appears to be a proliferation of ρ’s in the recent years that is only adding entropy. I anticipate that, at the end, all but the small group of expert users will get confused and simply apply Mobley’s coefficients.
I downloaded the data. I cannot understand why the authors are releasing ρ values for Δϕ=90° only. I understand this is the azimuth of AERONET-OC and that the authors may not care much about other setups, but unfortunately that azimuth is only a value across a continuum of possible values. The authors are shooting themselves on the foot if they self-impose that limitation, given that the calculations were made for all, as it can be seen in the plots. Most users, especially those operating on smaller platforms, will choose Δϕ=135°, whereas automated sensors on ships face a different range of constraints, and have variable Δϕ. This definitely diminishes the impact of the paper.
The other big issue has to do with a basic requirement in science, which is reproducibility. The calculations come from proprietary software that cannot even be purchased. Hence, a reviewer or an independent scientist cannot reproduce the results. Yes, textual explanations on the simulation setup are provided, but that is largely insufficient. To me that would be a sufficient case for rejection, but it is the editor who has to make the decision after revising the journal policies.
On a smaller level of importance is coining the name “glint correction factor” for ρ. Now we don’t only have yet another set of ρ’s. We even have a new name. As a whole community, are we not even able to agree on a common nomenclature after 30 years that we are using these terms?
The comments on other authors’ results and on their own results are scientifically sound but excessively focused on the numerical point of view. I would prefer a more didactic tone, with more insight into physics, so that young researchers could use this document to learn about above-water radiometry. As an example, in lines 95-98, it is said that ρ tends to increase spectrally with increasing wind speed, driven by the spectral distribution of skylight. But why is that? Because the model is trying to explain reflected light with a significant contribution of sunlight using a reference measurement that is largely devoid of sunlight.
The authors claim on lines 84-85 that Mobley generated his ρ LUT using the Cox and Munk model without the 0.003 background term. I have checked the Hydrolight documentation, in particular the “Technical note 1” of Hydrolight 5, and the 0.003 term indeed appears. Authors shall clarify this.
The labels of Figures 5, 6, 7, 8 are hard to read due to the font size, and Figures 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18 are totally unreadable. In addition, there appear to be rendering issues, so the resolution is poor.
In some cases, where multiple panels are displayed on the same figure, the axis scale is kept fixed, at the cost of being unable to grasp the numbers that are actually displayed. Example: Figure 9.
The abstract must synthetise the paper as a whole. So far it lacks a summary on the numerical results and a comparison with former ρ estimates.
I am missing information on the simulation of the optical proper of the water column. I understand that this aspect is of minor importance, given that the subject under examination is the reflection of the surface, but one still needs to make a simulation using specific water conditions. The authors are encouraged to disclose this.
The introduction states that the water leaving radiance is the primary product of aquatic remote sensing. This statement is not correct. The primary product is reflectance, as it is the quantity provided by satellite products, and the source of information that is extracted by remote sensing algorithms.
I cannot understand the distinction between L_i and L_sky in equations 1 and 2. I believe they are the same. In fact, if one inspects analog equations by other authors such as Mobley and Harmel, one finds that they use the same variable for both. Hence, authors must unify the nomenclature. Indeed, equation 3 confirms that L_i is nothing more than L_sky for a fixed geometry. That does not justify a new variable name.
Related to the previous comment, a table of mathematical symbols would highly help the reading.
Authors may revise the prose with the aid of a native speaker or a LLM. For instance, I find here several examples of what I call “JRC English”, namely expressions such as “It is highlighted that…”, “Still recognizing that…”, “Acknowledging that…”. Also, the division of the text in blocks might be improved. In particular, I find the Summary and Conclusions section rather disorganized.
Barbara Bulgarelli,Davide D'Alimonte,Giuseppe Zibordi,and Tamito Kajiyama
Data sets
Spectral correction factors for the removal of glint perturbations in above-water radiometryB. Bulgarelli, D. D'Alimonte, G. Zibordi, and T. Kajyiama https://doi.org/10.5281/zenodo.20609990
Barbara Bulgarelli,Davide D'Alimonte,Giuseppe Zibordi,and Tamito Kajiyama
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Spectrally resolved glint correction factors for above-water radiometric measurements were computed for a wide range of atmospheric, wind and illumination conditions typical of inland, coastal and open-ocean regions. Computations, relying on the FEM and MOX radiative transfer codes, adopt the AERONET-OC observation geometry and account for both the total sky radiance and for its sole diffuse component. Computed glint correction factors are available at https://doi.org/10.5281/zenodo.20609990.
Spectrally resolved glint correction factors for above-water radiometric measurements were...
Spectral correction factors for the removal of glint perturbations in above-water radiometry
Review for ESSD
This paper presents updated estimates of the ρ look-up-table (LUT) for the glint removal from above-water measurements using Mobley’s approach, yet for an azimuth Δϕ=90°, which is not what recommended by Mobley, but the operational choice in the AERONET-OC network.
There are a number of facts from this paper that I find positive, and a number that I find negative. The editor may decide whether these latter ones compromise publication or not.
On the positive side I acknowledge the quality of the work. This is definitely the state of the art of radiative transfer, and both the finite element code and Monte Carlo simulator are unique tools that can provide the deepest insight on optics, maintaining the highest accuracy. The care on the atmospheric modelling is excellent, and hence, this whole scientific approach has high potential.
The motivation for a new ρ LUT beyond those that already exist is not clearly stated. I understand that the authors improved their modelling of the physical setup, but they also must explain what are the current physical or numerical inconsistencies that motivate the creation of yet another LUT. But even if the authors explained it, such a need is not very clear to me. There appears to be a proliferation of ρ’s in the recent years that is only adding entropy. I anticipate that, at the end, all but the small group of expert users will get confused and simply apply Mobley’s coefficients.
I downloaded the data. I cannot understand why the authors are releasing ρ values for Δϕ=90° only. I understand this is the azimuth of AERONET-OC and that the authors may not care much about other setups, but unfortunately that azimuth is only a value across a continuum of possible values. The authors are shooting themselves on the foot if they self-impose that limitation, given that the calculations were made for all, as it can be seen in the plots. Most users, especially those operating on smaller platforms, will choose Δϕ=135°, whereas automated sensors on ships face a different range of constraints, and have variable Δϕ. This definitely diminishes the impact of the paper.
The other big issue has to do with a basic requirement in science, which is reproducibility. The calculations come from proprietary software that cannot even be purchased. Hence, a reviewer or an independent scientist cannot reproduce the results. Yes, textual explanations on the simulation setup are provided, but that is largely insufficient. To me that would be a sufficient case for rejection, but it is the editor who has to make the decision after revising the journal policies.
On a smaller level of importance is coining the name “glint correction factor” for ρ. Now we don’t only have yet another set of ρ’s. We even have a new name. As a whole community, are we not even able to agree on a common nomenclature after 30 years that we are using these terms?
The comments on other authors’ results and on their own results are scientifically sound but excessively focused on the numerical point of view. I would prefer a more didactic tone, with more insight into physics, so that young researchers could use this document to learn about above-water radiometry. As an example, in lines 95-98, it is said that ρ tends to increase spectrally with increasing wind speed, driven by the spectral distribution of skylight. But why is that? Because the model is trying to explain reflected light with a significant contribution of sunlight using a reference measurement that is largely devoid of sunlight.
The authors claim on lines 84-85 that Mobley generated his ρ LUT using the Cox and Munk model without the 0.003 background term. I have checked the Hydrolight documentation, in particular the “Technical note 1” of Hydrolight 5, and the 0.003 term indeed appears. Authors shall clarify this.
The labels of Figures 5, 6, 7, 8 are hard to read due to the font size, and Figures 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18 are totally unreadable. In addition, there appear to be rendering issues, so the resolution is poor.
In some cases, where multiple panels are displayed on the same figure, the axis scale is kept fixed, at the cost of being unable to grasp the numbers that are actually displayed. Example: Figure 9.
The abstract must synthetise the paper as a whole. So far it lacks a summary on the numerical results and a comparison with former ρ estimates.
I am missing information on the simulation of the optical proper of the water column. I understand that this aspect is of minor importance, given that the subject under examination is the reflection of the surface, but one still needs to make a simulation using specific water conditions. The authors are encouraged to disclose this.
The introduction states that the water leaving radiance is the primary product of aquatic remote sensing. This statement is not correct. The primary product is reflectance, as it is the quantity provided by satellite products, and the source of information that is extracted by remote sensing algorithms.
I cannot understand the distinction between L_i and L_sky in equations 1 and 2. I believe they are the same. In fact, if one inspects analog equations by other authors such as Mobley and Harmel, one finds that they use the same variable for both. Hence, authors must unify the nomenclature. Indeed, equation 3 confirms that L_i is nothing more than L_sky for a fixed geometry. That does not justify a new variable name.
Related to the previous comment, a table of mathematical symbols would highly help the reading.
Authors may revise the prose with the aid of a native speaker or a LLM. For instance, I find here several examples of what I call “JRC English”, namely expressions such as “It is highlighted that…”, “Still recognizing that…”, “Acknowledging that…”. Also, the division of the text in blocks might be improved. In particular, I find the Summary and Conclusions section rather disorganized.
I hope this set of comments is of help.