First Ocean Wave Retrieval from HISEA-1 SAR Imagery through an Improved Semi-Automatic Empirical Model
Round 1
Reviewer 1 Report
First Ocean Wave Retrieval from HISEA-1 SAR Imagery through An Improved Semi-Auto Empirical Model
The authors of the manuscript present an empirical method to retrieve SWH from HISEA-1 SAR images and applications to coastal typhoon waves. The novelty of this paper is a different, totally empirical regression method, is adopted. The authors also compare their retrieved SWH, with previous method, wave models such as WW3 and MFWAM, and with altimeter observation, showing significant improvement.
This paper is well written, and has a certain level of innovation overall. The retrieval procedure is relatively clear and thorough. However, There are still two main points in the paper that needs further optimization and modification. First, the proposed empirical method is linear, which cannot perform a maximum optimizing. For example, the azimuth angle, is also a nonlinearity indicator, affecting cutoff wavelength; the wind speed, will determine the peak wavelength, and so on. So the proposed method can only make the result “looks good”, but lack of the thorough investigation. Second, it shown that there are some buoy(Fig.1) and there may have tens of match-ups. But why there is no comparison result with buoy? If possible, please add this results.
Specific suggestion:
L93-94 “resolution with 100km swath. Detailed information…”
L118-119 Rewrite “Please refer to [33] for details…” without “please”.
L172-L181 why compare the ERA wind speed with buoy? wind speed is only one parameter of the method. Why don’t just compare SWH with buoy?
L223-225 Is there any threshold to define the extremely high value? And how to perform the replace of high intensity value?
L276-L277 not clear. Wave direction to azimuth is azimuth angle.
L287 nv in Eq12 is not defined
In Fig.11, what the color of the point indicate?
In Table3, the cutoff of subscene A3 is one third shorter than A1 and A2. It is very confusing because it almost the same area and same wave condition, so please check it carefully.
The Quality English Language is good overall.
Author Response
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Reviewer 2 Report
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Author Response
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Reviewer 3 Report
The authors studied retrieving ocean wave parameters from synthetic aperture radar (SAR) images acquired by China's HISEA-1 satellite. HISEA-1 is China's first miniaturized C-band SAR satellite, which provides high-resolution images for observing ocean waves. The authors proposed an improved semi-empirical model to estimate significant wave height from HISEA-1 SAR images. They first pre-processed the images to remove noise and artifacts. The model considers azimuth cut-off, wind speed, wave spectrum information and other factors to estimate significant wave height. Validations with multiple data sources showed the model could reasonably estimate significant wave height. The model was applied to monitor coastal and extreme ocean waves under typhoon conditions. The work shows the potential benefits of miniaturized SAR satellites for ocean wave monitoring.
The proposed methodology uses pre-processed images with removed noise and artifacts. The model also considers azimuth cut-off, wind speed and other factors to estimate significant wave height. Validations with multiple data sources showed some level of errors during the estimation of significant wave height. Notably, in extreme conditions, the proposed method requires the use of external model wind information. This is a weak point of the methodology, as most existing numerical models are known to poorly estimate extreme wind speeds.
The proposed method introduces another implementation and compilation of well-known SAR image processing techniques. The current work and method do not contain significant errors or misunderstandings in ocean SAR imaging principles. However, they do not achieve significant improvement in wave height retrieval quality compared to other similar works.
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Some sentences are long and complex, and could be split into shorter sentences for easier readability, e.g. "By summarizing the results of the semi-empirical algorithm defined earlier and the analyses by previous studies, an empirical algorithm for the SWH based on the C-band HISEA-1 is proposed" could be rephrased as two sentences.
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Abbreviations are not always spelled out on first use, e.g. "SM" is used before "stripmap mode" is defined. All abbreviations should be spelled out on first use.
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The conclusion could be expanded to better tie the key results and implications together for the reader.
Overall, the paper would benefit from close editing to address issues with English grammar, punctuation, and style. Tightening the language and improving clarity, sentence structure, transitions, and formatting would strengthen the readability, flow, and coherence of the paper for publication.
Author Response
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Round 2
Reviewer 3 Report
While the paper was improved concerning the previous version, the proposed algorithms suffer from systematic errors, especially for low wave height sea conditions. I hope these issues will be addressed in the next research.
