HISEA-1: The First C-Band SAR Miniaturized Satellite for Ocean and Coastal Observation
, Lingsheng Meng 1,3,4, Ting Xie 1,2,3, Lei Huang 4,5 and Xiao-Hai Yan 4,5,*
Round 1
Reviewer 1 Report
My overall impression of this manuscript is that it's a nice short communication highlighting the potential of the HISEA-1 SAR satellite. Since this is a short communication I assume the main goal was to introduce readers to the instrument and provide some representative examples. I was quite impressed with the initial imagery, and it certainly peaked my interest!
I would be fine seeing this published with minor revisions. My main request is that the authors describe a bit more some of the sensor/data specfics. My understanding is that this is a commercial satellite, so questions arise about data access, data format, whether it can be processed using (for example) the existing SAR toolboxes, etc. It would also be useful to know what the revisit time is. If these points were addressed then I would recommend publication.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
This short communication provides the readers the first view of C-band SAR Hisea-1 and its ocean applications for the first time. My remarks include:
(1) Since this is the first paper regarding Hisea-1, specification of Hisea-1 are needed. For instance, how many modes of HISEA-1 and the corresponding resolution, swath coverage? And the availability of the data of HISEA-1?
(2) Lines 33-34 mentioned the C-band SAR Gaofen-3. But no ref is about Gaofen-3. See below some important references of Gaofen-3 (ocean wind & wave), which should be cited here. Again, I would like to see some comparison between the two Chinese C-band SAR Gaofen-3 and Hisea-1.
(3) Lines 91-92.
"Based on the SAR image spectra, the length and direction of the ocean wave could be estimated."
-- In fact, the wavelength and direction you estimated from the SAR image spectra is NOT the geophysical ocean wavelength and direction, due to the fact that nonlinear SAR-wave relation makes the SAR image spectra distorted compared to ocean spectra. Thus, you have to estimate the ocean spectra. Many algorithms exist, and one of them is Wang, H., Wang, J., Zhang, B., Zhu, J., 2019. regarding Gaofen-3.
"The wave height could be calculated after calibration."
Yes, calibration is important, but not enough. You should also establish algorithm, theoretically or empirically, to retrieve. One example (empirical) for Gaofen-3 is Wang et al. 2018. And another theoretical one (called MPI method) for Gaofen-3 could be found in Li et al., 2018 (see section 4.2 in their paper).
(4) And what about the radiometric calibration of Hisea-1? What is the NRCS radiometric accuracy and Noise Equal Sigma Zero? Is there any plan for the external calibration experiment? This is the critical issue for wind speed retrieval for the experence of Gaofen-3, see Wang, H., Li, H., Lin, M., Zhu, J., Wang, J., Li, W., Cui, L., 2019.
References:
Yang, J., Wang, J., Ren, L., 2017. The first quantitative remote sensing of ocean internal waves by Chinese GF-3 SAR satellite. Acta Oceanologica Sinica, 36, 118.
Wang, H., Yang, J., Mouche, A., Shao, W., Zhu, J., Ren, L., Xie, C., 2017. GF-3 SAR Ocean Wind Retrieval: The First View and Preliminary Assessment. Remote Sensing, Remote Sensing 9, 694.
Wang, H., Wang, J., Yang, J., Ren, L., Zhu, J., Yuan, X., Xie, C., 2018. Empirical Algorithm for Significant Wave Height Retrieval from Wave Mode Data Provided by the Chinese Satellite Gaofen-3. Remote Sensing, 10, 363.
Li, X.-M., Zhang, T., Huang, B., Jia, T., 2018. Capabilities of Chinese Gaofen-3 Synthetic Aperture Radar in Selected Topics for Coastal and Ocean Observations. Remote Sensing, 10, 1929.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Please put scales in all imagery to show and distinguish spatial resolutions between modes. Figure 1 is duplicated (but it may be an artefact of the manuscript)
In the introduction, it could be interesting to add the mass and size of HISEA-1 (both satellite and payload) to complement the information on the SAR instrument.
For the sun-synchronous orbit, define which is the Mean Local Solar Time and specific altitude (not range).
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors addressed all my concerns in the revision, improving the manuscript significantly. I think the paper in this form is suitable for publication in Remote Sensing.
