The objectives and rational of the study are clearly stated in the introduction. Statistical analysis performed for various objectives are explained clearly and sufficient comparisons and methods were presented. All the figures and tables provide detailed information. Based on the objectives and present status of the mission, remote sensing data collected by HYPSO-1 could be very valuable for the ocean color community. However, thorough validation studies across various aquatic environments is required to unlock the full potential of the mission. More missions like HYPSO-1 will advance ocean color hyperspectral remote sensing to untangle the complexity of aquatic environments.

Decision Summary

Decision

Accept manuscript after minor grammatical corrections and clarifications.

Grammatical Corrections

Line 157: Hindered ‘by’ clouds.

Line 163: Was this supposed to be altitude? Will the altitude of the satellite be changed for every target?

Lines 484-487: These lines can be rewritten.

Line 487: Is to of atmosphere radiance? Please clarify.

RadCalNet: Provide more information on hyperspectral camera specifications and resolutions (spectral, number of wavelengths, range etc) of data produced by RadCalNet.

Lines 503-505: Redundant lines, can be rewritten.

Fig.11 or Figure 11 (lines 500 and 520): maintain consistent reference.

Line 529: As the focus of study is not machine learning, the starting line of the paragraph can be moved towards the end.

Figure 14: can the authors provide images acquired by the sensors over the same area?

Line 578: Can authors provide information on how homogeneous are the selected areas, either through ranges of ToA or other values?

Accept manuscript after minor grammatical corrections and clarifications.

Author Response

Thank you for your thorough and detailed review. Your feedback is greatly appreciated and will be taken into consideration as we made revisions to the manuscript. With time the data is intended to become useful to the wider community.

Here are our responses.

Line 157: Hindered ‘by’ clouds.

The preposition is added to the sentence to make it complete.

Line 163: Was this supposed to be altitude? Will the altitude of the satellite be changed for every target?:

The attitude describes the orientation of the satellite and is not related to its position. This is subject to change between captures to point towards the specific target of interest. The altitude or height of the satellite cannot be controlled by satellite bus and will remain the same between the different captures.

Lines 484-487: These lines can be rewritten.

An attempt at rewriting these lines to make it clearer is given below. This is included in the revised manuscript as well.

The top of \gls*{toa} reflectance is a measure of the amount of light that is reflected off the Earth and its atmosphere when illuminated by the sun. It is calculated using the following formulas~\cite{landsat_7_handbook}

\begin{equation}\label{eq:rad_to_ref}

\rho_{\mathrm{p}}=\frac{\pi \cdot \mathbf{L}_\lambda \cdot \mathbf{d}^2}{\operatorname{ESUN}_\lambda \cdot \cos \theta_\mathbf{S}}

\end{equation}

\noindent Where $\rho_{\mathrm{p}}$ is the \gls*{toa} reflectance, $\mathbf{L}\lambda$ is the radiance, $\mathbf{d}$ is the distance between the Earth and the sun, $\operatorname{ESUN}\lambda$ is the mean solar exo-atmospheric irradiance, and $\theta_{\mathbf{S}}$ is the Solar zenith angle. This formula is used to compare the \gls*{toa} reflectance of data from the HYPSO-1 instrument with data from selected RadCalNet sites. These sites provide inferred \gls*{toa} reflectance. As a result it is possible to compare the measurements from HYPSO-1 using the calibration coefficients acquired on ground with the data provided by RadCalNet without fur there processing.

Line 487: Is to of atmosphere radiance? Please clarify.RadCalNet: Provide more information on hyperspectralcamera specifications and resolutions (spectral, number ofwavelengths, range etc) of data produced by RadCalNet.

The following sentence has been added to the manuscript with the appropriate refrence:

Radcalnet provides top-of-atmosphere reflectance data with uncertainties at a 10 nm resolution in the range of 400-1000 nm at intervals of 30 minutes. The data is intended to be representative for a nadir-viewing perspective.

Lines 503-505: Redundant lines, can be rewritten.
Rewritten as follows.

The calculation of \gls*{toa} reflectance in \Cref{fig:toa_ref} and \Cref{fig:toa_ref_rrv} was performed using two different solar spectra. The first solar spectrum is the ChKur solar spectrum~\cite{chkur_solar_spectrum}, which is also used for the Landsat missions~\cite{landsat_7_handbook}. The second solar spectrum used is the Thuillier solar spectrum~\cite{thuillier_solar_spectrum, rs13122420}. Both solar spectra were used to calculate the TOA reflectance in figures \Cref{fig:toa_ref} and \Cref{fig:toa_ref_rrv}, and the latter has a higher spectral resolution.

Fig.11 or Figure 11 (lines 500 and 520): maintainconsistent reference.
Unsure what happened in the submitted manuscript. Latex is supposed to fix that. The error(s?) seem to be removed on newer compilations of the rendered text..

Line 529: As the focus of study is not machine learning, the starting line of the paragraph can be moved towards the end.

Changed the staring sentence to the following
"Stripes in hyperspectral datasets commonly limit their use~\cite{Ortiz2019}.”

Figure 14: can the authors provide images acquired by the sensors over the same area?

A campaign to collect the data needed to further investigate the signal strength of the HYPSO-1 sensor is desirable. Acquiring simultaneous close to nadir over-passes with other sensors can be challenging and would extend this review process potentially by several weeks if not months. We kindly ask the reviewer to accept the limitations of this particular section of the manuscript. Hopefully a more extensive study on the signal strength will follow.

Line 578: Can authors provide information on how homogeneous are the selected areas, either throughranges of ToA or other values?

The areas were selected by hand, but a plot has been added to show the different spectra that reside within the marked areas in terms of mean signal, standard deviation and normalised characteristics in hopes to make the section more transparent.

Reviewer 2 Report

HYPSO-1 satellite (a 6U CubeSat carrying a hyperspectral imager) and its performances for imaging ocean color was fully introduced in the paper. This is very helpful for readers being interesting in using the satellite images and some other satellite designers.

Author Response

Thank you for highlighting the usefulness of the information provided in the paper regarding the HYPSO-1 satellite and its capabilities for imaging ocean color. Your feedback is greatly appreciated. Hopefully, if fully accepted by all reviewers the manuscript will prove beneficial for readers and satellite designers.

Reviewer 3 Report

This manuscript comprehensively described the development and operation of the newly launched a hyperspectral imager onboard HYPSO-1 satellite. The in-orbit performance of the imager including the spectral resolution, spatial resolvability and signal to noise ratio (SNR) are also characterized. The manuscript was written and organized well and I would like to recommend for publication as the following concerns are addressed.

1. The legend of Fig.11 is confusing. I would suggest that each panel has its own legend.

2. In section 3.3, the authors compared the TOA reflectance measured by HYPSO-1 and computed by the bottom-of-atmosphere (BOA) reflectance measured at RadCalNet site. But how to compute TOA from BOA reflectance need to be introduced.

3. The subtitle of section 3.3 is ‘Radiometric Validation and Calibration’, but no calibration procedure is found in this section.

4. There are some typos or grammar error. For example, two “and” in line 171; one more “and”in line 317; The first letter of ‘fig.11’should be capitalized.

5 ‘Goal’appeared in the manuscript is ‘Goal’or ‘goal’(line 665-688). Please to be consistent.

Author Response

We extend our sincere thanks to the reviewers for their meticulous review and constructive criticism, which has been instrumental in enhancing the manuscript.

The legend of Fig.11 is confusing. I would suggest that each panel has its own legend.

Agreed. This has been separated into two different figures with their own respective legends.

In section 3.3, the authors compared the TOA reflectance measured by HYPSO-1 and computed by the bottom-of-atmosphere (BOA) reflectance measured at RadCalNet site. But how to compute TOA from BOA reflectance need to be introduced.

The RadCalNet sites provide TOA reflectance based on the measurements that they conduct. This hs been clarified in the text with references.

The subtitle of section 3.3 is ‘Radiometric Validation and Calibration’, but no calibration procedure is found in this section.

Changed the title to “Top-of-Atmosphere Radiometric Validation”

There are some typos or grammar error. For example, two “and” in line 171; one more “and”in line 317; The first letter of ‘fig.11’should be capitalized.

The typos have been corrected and another proof-reading has been conducted. Unsure how the fig got a small letter, but this problem no longer resided in the latest version of the manuscript.

5 ‘Goal’appeared in the manuscript is ‘Goal’or ‘goal’(line 665-688). Please to be consistent

Changed all to be with capitalized G.

Reviewer 4 Report

1. Abstract - helpful to mention number of channels, and swath width in pixels and km in the abstract - so readers can judge if this is an instrument they're interested in. These basic parameters are not even completely present in Table 1.

Line 24 - perhaps mention sediment-laden or CDOM-rich riverine plumes; optical water quality monitoring is a significant application.

Line 50 - tradeoff with what - SNR?

Line 63 - somewhere, possibly here, it would be helpful to compare and contrast this mission with some of the big ones; eg Hyperion on EO-1 and the forthcoming PACE. What is different about this mission relative to the massive style satellite campaign?

Line 127 - do you mean "at latitudes higher than the polar circles"?

Line 157 - hindered BY clouds

Line 157 - maybe mention that rapid revisit can mitigate the impact of broken clouds (can accumulate more complete obs)

Line 191 - say why the capture time is 1 minute; is it power, storage, overheating.....?

Line 209 - does this mean it is not possible to simultaneously acquire and downlink? Design feature?

Line 214 - what characteristics would additional ground stations require - frequency/size?

L316 - do you mean spatially distinct?

L424 - did you want to mention what spectral smile is?

Table 6: Are the times UTC? (just suffix with 'z' to make it clear) Presumably that is lat and lon for the two sites?

L523 - period (not periodd)

Sec 3.4: Perhaps this section should be named "Spatial Striping" - so it is clear that it is not spectral. Why would you use an ocean scene, which is generally darker, to measure the striping rather than a uniform area of cloud, which will be much brighter, yielding a higher signal to noise ratio measurement? There is probably a good reason I'm not seeing - but it is an obvious question.

Figure 13: label the vertical axis on the figure 'across-track pixel' rather than spatial position. The three images on the RHS need something to orient and scale them; just two arrows at a right angle in one figure indicating North and East and a scale would be sufficient (eg each arrow=0.1 degrees or 5km or whatever). There is not enough explanation of the origin of the figure on the LHS; particularly the circular feature centred on pixel 250, band 30. Is the issue that the dust moved, or that it moved from being irrelevant to in the field? You are assuming too much engineering knowledge of the reader in this caption.

L560:to make it clearer, say "The change in radiometric sensitivity between laboratory calibration and the observing of the test image is likely due to the relocation of dust and small particles within the imaging system arising from vibration during the spacecraft launch."

L568 " ... all four sensors have spectral...."

Table 8: Inconsistent labelling of the areas; use "Dunedin, New Zealand", and "Santa Catalina Is., USA". An arrow indicating north on each image would be helpful. What is the relevance of including the mass in this table?

L618 - ...the mean acquisition elevation....

L626: ...cost of a reduced SNR for a given aperture.

L678 - you should mention that a small cubesat is relatively cheap so a realistic option to improve revisit times is to launch several of them.

L720 - "stable" in what sense - radiometrically? Vibrations during flight, or during launch?

L727 change "sounder" to "deeper" or "more comprehensive" insight

Author Response

We would like to express our gratitude for taking the time and effort to thoroughly review our paper. Your valuable feedback and constructive criticisms have helped us to improve the quality of the manuscript. Your insights and suggestions have been helpful in addressing the weaknesses and inaccuracies of the manuscript. We have taken into consideration all of your comments and have hopefully made the necessary revisions to the manuscript. See below for details.

Abstract - helpful to mention number of channels, and swath width in pixels and km in the abstract - so readers can judge if this is an instrument they're interested in. These basic parameters are not even completely present in Table 1.

Agreed. The text has been added to the abstract, and the table has been updated to also include this information. The swath width is dependent on the view geometry, but values for nadir pointing geometry has been added.

Line 24 - perhaps mention sediment-laden or CDOM-rich riverine plumes; optical water quality monitoring is a significant application.

Good idea! The application focused on optical water quality is also mentioned now.

Line 50 - tradeoff with what - SNR?

Yes, among other things. The sentence has been extended to exemplify some of the potential tradeoffs.

Agreed! A sentence was added prior to line 63 in the original manuscript to distinguish these globally covering missions from the HYPSO-1 CubeSat mission.

Line 127 - do you mean "at latitudes higher than the polar circles"?

Agreed. The sentence makes more sense with the suggested edit and thus it is added to the revised manuscript

Line 157 - hindered BY clouds

Fixed

Line 157 - maybe mention that rapid revisit can mitigate the impact of broken clouds (can accumulate more complete obs)

Added a sentence to emphasis this point.

Line 191 - say why the capture time is 1 minute; is it power, storage, overheating.....?

It is mainly due to radio communication. This is now mentioned in the subsequent sentence.

Line 209 - does this mean it is not possible to simultaneously acquire and downlink? Design feature?

As there are no moving parts on the CubeSat the orientation of the satellite will need to be changed to be able to communicate properly with the ground station. Unless the objective is to acquire an image over the ground station this will conflict with the orientation needed to capture a specific target. This is now better described in the text as well.

Line 214 - what characteristics would additional ground stations require - frequency/size?

Their most important feature would be to be geographically well spread out. The frequency needed would be S-band. This should now be better clarified in the text.

Line 316 - do you mean spatially distinct?

Agreed.

Line 424 - did you want to mention what spectral smile is?

Here, smile effects are optical aberrations where the center wavelength of a spectral band appears at a different positions in the focal plane array compared to the edges of the same spectral band. This sentence has been added to the subsequent line in the manuscript

Table 6: Are the times UTC? (just suffix with 'z' to make it clear) Presumably that is lat and lon for the two sites?

Yes! Good addtion. The table is now updated to follow the ISO standard for timestamps. And the terms “lat” and “lon” has been added to the site name locations in the same table.

Line 523 - period (not periodd)

Fixed.

The section name is edited to clarify its content. Clouds should yield better results, but as the response of the focal plane array is linear the images easily get oversaturated over such bright targets. While the spatial destriping using a uniform ocean scene seem to work well for the blue and green region of the spectrum the striping effects are still prominent in the red and NIR region. With time the calibration coefficients associated with each capture should improve. Hopefully a more dedicated campaign to ensure a properly flat radiometric response will be conducted during the next few months. These perspectives have also been added to the manuscript.

Agreed. The axis titles have been changed on the LHS figure and orientation and spatial dimensions are now indicated on the RHS figure. The text has been updated to discuss the dust particle in greater detail as well. The dust particle moved during launch, and new calibration coefficients were needed to compensate for this. This is now added to the text.

Line 560:to make it clearer, say "The change in radiometric sensitivity between laboratory calibration and the observing of the test image is likely due to the relocation of dust and small particles within the imaging system arising from vibration during the spacecraft launch."

Thanks! Edited the line to use the suggested formulation.

Line 568 " ... all four sensors have spectral...."

The sentence is edited to « All four sensors used for comparison produce images that have a spectral resolution similar to HYPSO-1»

Updated the table. The reason for including mass is to show that some of the sensors that are used for comparison are significantly larger and thus more expensive to launch. This is also discussed in the text now.

Line 618 - ...the mean acquisition elevation....

Fixed.

Line 626: ...cost of a reduced SNR for a given aperture.

Fixed.

Line 678 - you should mention that a small cubesat is relatively cheap so a realistic option to improve revisit times is to launch several of them.

Added a sentence pointing this out.

Line 720 - "stable" in what sense - radiometrically? Vibrations during flight, or during

Added “against vibrations during launch and pointing maneuvers” to clarify

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