Targets’ Radial and Tangential Velocities Estimation Based on Vortex Electromagnetic Waves
Round 1
Reviewer 1 Report
a) The submitted manuscript is lack of novelty and contribution, since the Doppler effect has been studied in some literatures. Compared to the existed methods, what's the main novelty of this manscript?
b) Generally, the tangential velocity is much small, how the measure this in reality? Only simulation results are not sufficient to validate the approach effectiveness.
c) What's the expression of s(t) in Line 83?
d) How to understand the statement 'the same weights are applied to target echo' in Line 85?
e) How to obtain Eq. (4) should be derived more clearly.
f) The simulation scenario is set too simple. For example, how about the noise influence on the estimation results? Furthermore, why the tangential velocity error is much higher than the radical radial velocity error in TABLE 3? This conclusion might be not correct.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
I have no comments.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
Li et al. have proposed a 2D target velocity detection method for VEW radar. The method utilized the target Doppler information of VEW. In order to achieve the 2D target velocity, a dual OAM modes pulse is designed and in order to consider the range immigration caused by the long observation time, a modified RFT is applied to get the compound Doppler frequency. Then the authors performed simulation experiments to verify the method. Two cases with different number of motion targets are simulated and discussed. This could be useful information for Radar detection. Overall, this paper is well organized, with claims well supported. I would thus recommend the acceptance of this paper with the following modification suggestions.
1. In the second paragraph of the introduction, the authors mentioned several existing approaches to detect the 2D or 3D target information. Can the authors command what’s the advantages of their method compared with the existing ones? With the facts that longer observation time and complicated post-processing (modified filter function, radical speed ambiguity et al.) needed, what’s the highlights of this method?
2. In the simulation part, the authors need provide more information on the details. For example: how is the VEW generated in this simulation? Is it the same as the general method mentioned in figure 1? If so, what’s the parameters used? Is the parameter chosen affecting the results?
3. In this method, 2 OAM modes are used. Can the author comment on the importance of mode number? Suppose 3 modes are designed, will the redundant information benefit the method?
4. In the simulation study of 2 targets, the tangential velocity error of the 2 targets are quite different. Is there any cause of this difference?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
* Correct English language errors; specifically change "radical" to "radial" , "rational" to "rotational" and "immigration" to "migration" in all instances. Line 26, change "Differ" to "Different". Line 46, change ""by" to "of". Line 93, change "1 order" to "order l". Line 97, change "match" to "matched". Line 103, change "which" to "and". For equation (14), define fa and for equation (16), define B.
There appears to be some sloppy notation which can lead to confusion at the outset. Specifically, in line 83, the LHS of the equation should be multiplied by "l", the OAM mode number, so the exponents in which it appears in equation (2) would make sense, and the mode number would not be invoked twice (as l2 ) if the expression at line 83 is invoked in (2); same goes for equations (10) and (11).
Furthermore in equation (2), the exponents in the last terms in the first 2 lines should be divided by "c" in order for their units to make sense (i.e. be unitless). Finally, in the last line of equation (2), there ought to be a factor representing the radar scattering cross-section or reflection coefficient. The coefficient "alpha" is not defined until after equation (6) so it should not appear in (2).
In equation (6), it seems that the velocity factor in the exponent of the second exponential term should be "vr" and not "vt".
In line 102, emphasize that you are now invoking a more general Doppler shift which captures the total Doppler frequency shift experienced by the echo, by inserting "total" in front of "Doppler".
* Add references to:
Klemes, M. Reception of OAM Radio Waves Using Pseudo-Doppler Interpolation Techniques: A Frequency-Domain Approach. Appl. Sci. 2019, 9, 1082. https://doi.org/10.3390/app9061082
(For completeness, the above reference also makes use of the Doppler effect on OAM radio waves, although it is pseudo-Doppler, and is used for multiplexing in wireless communications. It explains and derives the Doppler effect on OAM waves in the transverse direction, but distinct from the "conventional" or radial Doppler effect. You may consider it as a guide to explaining how the tangential Doppler effect on OAM radar waves originates, with the aid of additional illustrations, to enhance the explanatory power of your paper.)
Klinaku, S and Valbone, B. The Doppler effect and similar triangles, Results in Physics 2019, 12, pp 846-852.
( This second reference contains a simple and exact geometric derivation of the transverse Doppler effect, which is part of a more general Doppler formula, but is generally negligible compared to the radial Doppler effect. Nevertheless, the OAM Doppler effect must be distinguished from this transverse component of the radial doppler effect, as for example the OAM Doppler effect does not depend upon frequency (or wavelength) of the RF signal, or it is shown to be negligible. )
* Reference #27 is the same as reference #6, so delete the redundant #27 and change citations of it to cite #6.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
