U-Space Utilisation of Airspace under Various Layer Function Assignments and Allocations

Round 1

Reviewer 1 Report

This paper addresses the problem of flight control in urban areas where many drones should share the urban space (U-space) for their missions. The authors analyze how traffic density, airspace structure, and vertical distribution airspace rules affect the safety, capacity, and efficiency of fights. They set two experiments and define 6 hypotheses, 2 regarding experiment 1, and 4 regarding experiment 2. They define 3 independent variables and 10 dependent variables. They state that they compare 2 concepts in experiment 1, having 90 conditions, and 4 concepts in experiment 2, having 180 conditions. They have several findings. I’ll mention two. They find that safety increases with the number of cruising layers when traffic density is high, and detect that there is a trade-off between allowing aircraft to redistribute between layers on the go and distributing aircraft by pre-allocating layers.

The problem addressed in this paper is recognized by the scientific community and municipalities will realistically face it very soon. Therefore, the topic addressed in this paper is of high importance to readers of the journal Drones. The authors’ attempt to address the problem is non-trivial. Although they neither state explicitly nor implicitly, their approach is multi-objective (MO) with at least 3 design/decision variables and up to 10 objectives. However, it seems that, somehow, the authors lose their research clearance in the complexity of their approach. They mix up design variables and decision variables. They mix up dependent and independent variable - traffic density, which, actually is neither of two but a given parameter, which the traffic system should adapt to.  They violate the scientific procedure. They first set experiments and after that they define hypotheses. Moreover, they do not provide sufficient information to enable experiment repeatability. Their writing style is rather, let's say, art-oriented than science-oriented, especially in the rich use of synonyms, and imprecise terminology, which affect the reader to understand the presentation hard. They mix up system- and user-oriented approaches. They investigate the U-space traffic management system but they use a user-oriented metric – availability, instead of, let’s say, throughput.

The authors should strictly follow the scientific procedure starting from idea/belief/intuition over a definition of hypotheses, creation and execution of proper experiments for hypotheses verification to a discussion of obtained results and the conclusions. The authors should use consistent and precise terminology, as well as SI units. For example, check which is the common definition of “efficiency” at https://en.wikipedia.org/wiki/Efficiency, or the difference between “drone” and “aircraft” at https://transport.ec.europa.eu/transport-modes/air/aviation-safety-policy-europe/unmanned-aircraft-drones_en.  A percentage is a dimensionless number (pure number); it has no unit of measurement (see e.g. https://en.wikipedia.org/wiki/Percentage); and it can not be given in terms of time. Define all variables and provide their possible values. Be clear about the difference between conflict and intrusion. From 3.7 seems that conflict is a special intrusion but from Figure 10 it can be seen that there are much more conflicts than intrusions. Figure 15a is not mentioned in the text. 

They can use MO concept to rearrange the concept of their research.

This research has the potential for publication but the presentation must be rearranged substantially.

 

 

Additional to the comment in the previous section:

extensive use of the pronoun "this" without a clear relation to the replaced word.

"This" instead of "these" in line 65,

not introduced units "kts", and "ac",

many terms not related to the rest of the paper in lines 395-398,

The semantics of the sentence in lines 400-402 are not clear,

"if" instead of "whether" in the first footnote under Table 5,

the result of hypothesis verification is true or false, but not accepted, check the use of accepted throughout the discussion section. 

etc.

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Although I suggested substantial revision, the authors made minor revision. They did not even make sufficient effort to correctly revise the manuscript. Eg. the authors say that Table 3. shows the dependent variables of the two sub-experiments in the revised manuscript, while there is no variable in the table in the revised manuscript. They replace the Variable type/Dependent Variable in the previous manuscript with Metric category/Metric in the revised manuscript.

This paper should be revised substantially. 

Terminology should be consistent and precise. 

Author Response

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Author Response File: Author Response.pdf