On-Orbit Radiometric Calibration of Hyperspectral Sensors on Board Micro-Nano Satellite Constellation Based on RadCalNet Data

Round 1

Reviewer 1 Report

General Remarks:

The authors present an on-orbit radiometric calibration model for Orbita Hyperspectral Sensor (OHS) on-board micro-nano satellite constellation based on based on the TOA reflectance product published by the Committee on Earth Observation Satellites (CEOS) radiometric calibration network (RadCalNet). They also performed an evaluation study of the temporal performance of OHS sensors claiming that the present results complement the promotion of low-cost commercial hyperspectral sensors for micro-nano satellite constellations. The authors have performed an appreciable study with appropriate calibration method followed by a performance evaluation procedure. I think conceptually the work is sound. The presentation of the work could have been improved to attract readers. Moreover, the quality of the figures should be improved. For instance, I listed a few corrections in the abstract and conclusion section which I feel the authors may rectify. Furthermore, the authors may have a thorough look into the text to find such cases in the presentation and revise the same prior to subsequent submission.

 

Specific comments:

Line 20 It should be “While observing the earth, eight integrations …”

Line 335-336 Extra dot (.) added in “It is noted that the surface reflectance retrieved from satellite data is visually consistent with the measured ground reflectance. spectrum curve of cotton”

Line 345-347 Rephrase the sentence “RadCalNet, which provides to public users with the top-of-atmosphere reflectance at 30-minute intervals at 10 nm intervals from 400 nm to 2500 nm, is very suitable for radiometric calibration of this hyperspectral satellite constellation.”

Line 365-368 The sentence is too wordy, and I do not have patience such a long sentence. Please rephrase it. “In this paper, aiming at the radiometric calibration of the "Zhuhai-1" satellite constellation designed with multi-integral stages, by constructing a normalized radiometric calibration model, the radiometric calibration of OHS-F satellite covering all CMOSs and integration stages was carried out using RadCalNet ground measured reflectance and atmosphere parameters.”

Lines 342-363 I would suggest the authors present a comparative treatment of the model with other existing models in the literature. This will connect the researchers to the earlier work.

Line 373-374 Rewrite as “…promotion of low-cost commercial hyperspectral sensor.

Line 383-384 The line seems incomplete “Except for the individual gas absorption bands and low signal-to-noise ratio bands, the fitting error of the comprehensive gain is below 10%;”

Line 386-387 I recommend writing as “Compared to the reflectance spectrum of cotton measured on the ground, the trend of surface reflectance curve retrieved by OHS-F satellite CMOS2 sensor is consistent.”

 

 

Author Response

Dear reviewer

Thank you very much for your valuable comments.

We have revised the modification suggestions put forward by you, and the detailed details have been answered in the attachment.

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This is a very interesting method and topic, as the radiometric calibration of a large number of SmallSat or CubeSat instruments while still being cost- effective and not resource-intensive is a known problem. However, there are important changes that need to be made before considering if this paper should be accepted:

- There is insufficient discussion about the final assesment of the calibrated radiometric quality (which I assume is in Figures 12b, 13b and 14b? Equations 9 and 10 seem to be in regard to the spectral radiances, the results are described in terms of the gain, which makes this very confusing).

- Why are there no plots of the resulting spectra in units of spectral radiance or brightness temperature for select scenes?

- There is insufficient citation of other calibrated sensors which use a similar calibration methodology or algorithm for comparison, or at least this is not made clear.

- Figure 5 is presented with no explanation.

- DN is never defined (Digital Number? not properly referenced)

- not defined what is meant by integrating sphere or integral series. Is this referring to a Ulbricht sphere? I assume that Integral series corresponds to the the four groups of integral configurations of the detector? If so, how is this related to the integral series?

       - because these things and their relationship with each other are not explained properly, the results of Figures 6 and 7 cannot be properly assess by the reader.

- Plots in Figure 11 have no axis labelling, and insufficient explanation of these plots are provided.

- The English in this paper needs serious revision, even the abstract contains multiple grammatical errors.

 

Smaller Issues:

- explain what is a gradient filter spectro[meter], and it's value compared to traditional spectrometer designs

- What is the radiometric noise performance?

- It is mentioned that the wavelength of 400nm - 1000 nm is divided into 32 spectral bands, but what is the spectral resolution in each band (i.e, how many spectral channels are in each band?

- citation for the 6S atmospheric radiative transfer model is needed

Author Response

Dear reviewer

Thank you very much for your valuable comments.

We have revised the modification suggestions put forward by you, and the detailed details have been answered in the attachment.

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Dear reviewer

Thank you very much for your valuable comments.

We have revised the modification suggestions put forward by you, and the detailed details have been answered in the attachment.

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

There is still a major issue with this manuscript that no explicit spectra in radiance or brightness temperature units plotted, nor are there any radiometric bias (with respect to the model) or standard deviation plots as a function of wavenumber provided. Without this, the reader has insufficient reference for the quality of the calibration, only that the gain fitting error and surface reflectance is provided. In addition, no solid justification for why this was no included was provided.

I highly recommend that this be added to the report, but I will leave this up to the Editor to decide.

In any case, because the authors clearly made considerable improvements to the paper, addressing the other concerns, this article is suitable for publication.

Reviewer 3 Report

I carefully read the revised manuscript of the article "On-orbit Radiometric Calibration of Hyperspectral Sensors on-board Micro-nano Satellite Constellation based on RadCalNet Data", authors: Qiang Zhang, YongGuang Zhao *, Lei Zhang, JiaQi Wu, Wan Li, Jun Yan, Xiaohua Jiang, Zhiyu Yan, Jing Zhao. I  conclude that the authors had sufficiently taken into account the comments made by me in the review. The quality of the presentation of the material has been significantly improved to understand the essence of the issues. I think that this version can be recommended for publication in the journal.