the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Detection and Localization of F-layer Ionospheric Irregularities with Back Propagation Method Along Radio Occultation Ray Path
- 1Blekinge Institute of Technology, Karlskrona, Sweden
- 2Molflow, Gothenburg, Sweden
- 3RUAG Space AB, Gothenburg, Sweden
- 1Blekinge Institute of Technology, Karlskrona, Sweden
- 2Molflow, Gothenburg, Sweden
- 3RUAG Space AB, Gothenburg, Sweden
Abstract. The back propagation (BP) method consists of diffractive integrals computed over a trajectory path, projecting a signal to different planes. It unwinds the diffraction and multipath, resulting in minimum disturbance on the BP amplitude when the auxiliary plane coincides with the region causing the diffraction. The method has been previously applied in GNSS Radio Occultation (RO) measurements showing promising results in the location estimate of ionospheric irregularities but without complementary data to validate the estimation. In this study, we investigate with wave optics propagator (WOP) simulations of an equatorial C/NOFS occultation with scintillation signatures caused by an equatorial plasma bubble (EPB), which was parametrized with aid of collocated data. In addition, a few more test cases were designed to assess the BP method regarding size, intensity and placement of single and multiple irregularity regions. The results show a location estimate accuracy of 10 km (single bubble, reference case), where in multiple bubble scenarios only the strongest disturbance would be resolved properly. The minimum detectable disturbance level and the estimation accuracy depend on the receiver noise level, and in the case of several bubbles on the distance between them. The remarks of the evaluation supported the interpretation of results for two COSMIC occultations.
Vinícius Ludwig-Barbosa et al.
Status: open (until 29 Jul 2022)
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RC1: 'Comment on amt-2022-57', Anonymous Referee #1, 23 Apr 2022
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1st Review of “Detection and localization of F-layer ionospheric irregularities with back propagation method along radio occultation ray path” by Ludwig-Barbosa et al.
I am afraid that I don’t think this is an interesting paper and it is not appropriate to be published because:
- The authors seem to have contradictory understanding about the use of back propagation methods to localize the ionospheric irregularities. On one hand, the authors, as titled, studied the back propagation method to localize F-layer ionospheric irregularities in this manuscript. On the other hand, the authors seem to have deep suspicion about this method. For example, in L137-140, the authors mentioned that “BP method has been used to detect irregularities in F-region in studies using both simulations and real occultation measurements. However, there is a lack of RO events combined with collocated data provided by different systems where the true location of the irregularity region is precisely known”. So can the back propagation method localize the irregularities or not? Clearly there are only rare chances we can find RO events collocated with other observations. Also if other observations can provide true location of irregularity, why do we need RO data for this purpose then?
The study took an RO case used in Carrano et al. (2011) as a starting point to perform their simulations. The authors thought the location of the plasma bubble in this case can be well estimated because it collocates with observations from a radar and a ground-based VHF receiver. I agree that from different observation platforms you can derive more physical parameters related to the irregularity. But one reason why Carrano et al. (2011) didn’t use the back propagation method to infer the location of irregularity was the phase data (which is required to back propagate the signal) was not available for this case.
In my opinion, the back propagation method is not something new. It has been used to localize the ionospheric irregularities in simulation study and real RO measurements.
- The simulation of the single bubble case in this study was similar/same to the modeling described in Carrano et al. (2011). What is new in the study is that more cases with different sizes, fluctuation intensities and placements were designed to test the impact on the estimation accuracy. But I am not sure how applicable of those designed simple cases is to represent the real ionospheric irregularities, and not very convinced by the conclusions made through such simple analysis. The authors claimed that the location estimation accuracy of the back propagation method was ~10 km based on idealized single plasma bubble setting. In this study, the space between each BP phase screen is 50 km. If shorten the distance between phase screens, would the estimation accuracy be enhanced? Also the authors mentioned that “in multiple bubble scenarios only the strongest disturbance would be resolved properly”. How good would it be considered as “resolved properly”? If there’re several local minima in the standard deviation curve, wouldn’t different local minima correspond to locations of multiple irregularity regions?
- The writing is poor, unclear and redundant. For instance,
L47-48: “the location of irregularities patches is not self-reliant”: what does “self-reliant” mean herein?
L111-113: “the excess path due to ionospheric … which … which … due to slightly different propagation paths”: please rephrase this sentence.
L118-120: “Such regions …, which specifically corresponds to sizes up to the Fresnel scale”: I can’t tell what you are trying to express here, especially the clause.
L131-132: “The high-order bias … by Kappa or Bi-local correction”: This sentence is not needed.
I would stop addressing the remaining ones here, and suggest the authors read the whole manuscript carefully and try to make each statement clearer and more concise.
Specific comments:
L14: “Fresnel-Huygens’” → Huygens-Fresnel
L39: “RF” → first time to mention. No abbreviations
L52: “parametrization” → parameterization
L128-129: the authors introduced the “inbound” and “outbound” herein, but also used other terms such as “first” and “second”, “left” and “right” to describe the same meaning. It would be better to just use one set of such terms.
L149: “in the propagation and vertical direction”: vertical direction is not clear to me, vertical to what? Do you mean “along- and across- propagation directions”?
L149: “outer scale”: what does this “outer scale” indicate?
L154: “a envelope” → “an envelope”
L166-167: Could the authors please give a simple explanation of your WOP or tell me where in the text you introduced your “WOP”?
L192: “SLTA” → No abbreviation here since it is mentioned for the first time.
L208: “left side”?
L219-220: Please explain where the threshold value comes from. There’s no Figure A.
L294-295: “In reality, …by BP method estimation”: what do you mean by “slightly farther away from the LEO”? Why not “closer to the LEO”?
A18: fs,WOP → fs,wop
L378: 80 km?
L381: horizontal direction?
L382: 2x1018 → 218
Vinícius Ludwig-Barbosa et al.
Vinícius Ludwig-Barbosa et al.
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