Measurement and Analysis of Loran-C Sky Waves throughout the Day

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper discusses the LORAN-C longwave radio signals' composition during the day and day-to-night transitions, discussing the appearence and interferences between the ground and ionospheric (here named: sky) waves. Numerous results from the measurements are shown, which gives a good insight into the actual behaviour of LORAN-C over large distances - this, as the authors suggest, can (or must) be used as a basic input for the future systems that would distinguish between the ground wave (more accurate) and the ionospheric wave. The current state-of-the-art of propagation description models is included, which is very useful, as LORAN-C is located within the so-called Hollingworth frequency range - far away from the modal propagation, typical for VLF (for 100 kHz the number of modes is huge), and relatively close to the range where the ray-path-tracing is accurate. The assumptions made by the Authors are essentially related to ray-path-tracing, which can be assumed as accurate for the described signals and the descrobed propagation paths. Overall, the article is clear and a good base for further research on LORAN-C.

A few minor comments:

Line 87 - What are the 'uniform standards'? Is it the e.g. normalized amplitude?

Lines 93-94 - Figure description melted with the main text;

Figure 1 - what are the features shown in magnification in part b) of the Figure?

Figure 2 - the caption is not very clear. What is the exact meaning of the 'accumulation'/'cumulative times' (line 121)? The plots are the results of what action done with the signal? Are the functions' descriptions (the four digit numbers) the names of the LORAN-C chains? (It is not very clear in Table 1, the rows could be more separated from each other).

Figure 5 should be divided into separate figures. Also, the order of locations shown in this figure is not reflected in the main text, this is slightly confusing.

Comments on the Quality of English Language

The language is very fine.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript, focusing on the analysis of Loran-C Sky Waves, presents interesting findings within the realm of Electronics. However, some corrections and clarifications are necessary for final acceptance:

1. - The format appears problematic on the last line of page 2, where it seems the text continuation is mixed with Figure 1 legend. This issue requires attention for improved readability and coherence.

2. - Could the authors elucidate the methodology behind data normalization? A clear explanation of this process would enhance understanding for readers.

3. - The authors should provide a more comprehensive explanation of Figure 1 to ensure clarity. Readers may struggle to identify different signal stations depicted in the figure without clearer guidance.

4. - The meaning of the legend "6000, 6780, 7430, ..." in Figure 2 is ambiguous and requires further elaboration. Clarifying this aspect would aid in the interpretation of the figure.

5. - The caption of Figure 2 appears on a different page, which disrupts the flow of the document. Perhaps revising the captions with more comprehensive explanations would improve coherence.

6. - While FFT/IFFT is referenced in another paper, a brief explanation within this manuscript would facilitate readers' understanding, thereby enhancing the overall readability.

7. - The contribution of the paper could be highlighted more effectively. Emphasizing the unique insights or novel findings would underscore its significance within the field.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study analyzed Loran-C signals' characteristics at various distances. Due to small amplitude and interference, a linear average method was used. Close to the receiver, ground wave aided observations. Further distance amplified sky-wave, affecting accuracy in navigation. Far distances received stable sky-wave signals.

In the paper, the authors describe the method they apply and detail how they have carried out the process of acquiring signal data from various stations distributed in China, indicating the distance between them and the transmitting point, along with other relevant data, followed by the analysis of this data. Three stations (Rongcheng, Xuancheng and Helong) in North sea chain were selected to analyze the received signals at different propagation distances.

Follows some recommendations to enhance the paper:

·       Considering the methodology employed, let's delve into the specific steps involved in analyzing Loran-C reception signals, offering more comprehensive insights into data collection and analysis techniques. It is important to note that a uniform ratio is not applied to signal measurements. Incorporating data from multiple days can enhance the analysis, providing more conclusive results. Additionally, it is crucial to address limitations of the linear average method, such as potential information loss and interference from nearby stations. Suggestions for alternative approaches or mitigation strategies should be provided.

·       Exploring potential real-world applications of accurately identified skywave signals is paramount, highlighting their utility in lower ionosphere parameter inversion and practical signal analysis. These applications underscore the significance of accurately identifying and interpreting Loran-C signals in various contexts.

·       In terms of future research, there is a pressing need to expand on the necessity for further advancements in Loran-C technology. 

·       A more comprehensive discussion of the implications of the findings is imperative, particularly regarding their significance for navigation accuracy and the broader field of radio wave propagation studies. Understanding the broader implications of the research enhances its relevance and applicability.

Finally, authors should refine the conclusion to succinctly summarize key insights and recommendations for future research. Emphasizing the importance of ongoing exploration and innovation in Loran-C technology is crucial. Additionally, welcoming new measures and studies would enrich the research landscape and contribute to advancements in the field.

Comments on the Quality of English Language

The English is adequate, with a few minor adjustments needed.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have considerated my suggestions, therefore it is fine.