the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jun 2022
Methods for Estimation of Ionospheric Layer Height Characteristics from Doppler Frequency and Time of Flight Measurements on HF Skywave Signals
Abstract. We demonstrate a methodology to estimate ionospheric virtual layer height characteristics using Doppler measurements from frequency locked time standard stations in conjunction with ionosonde measurements and ray-tracing models. We consider data from three events: the solar eclipse of 21 August 2017, a observations of the dawn terminator on 1 October 2019, and a time-of-flight study conducted 29 January 2020. Observations are consistent with a model in which mode splitting originates from different path length velocities associated with single and multiple hop modes as the virtual layer height changes. Support for this hypothesis comes from the complementary processes of 1) calculating Doppler shifts from virtual layer height changes and virtual layer height changes from Doppler shifts, and 2) the analysis of intermittent low-Doppler shift modes including correlation with ionosonde observations to help identify multihop propagation modes. We find that observations are in good agreement with measured data and simulations. We also find that the use of a precision frequency standard, such as a GPS-disciplined oscillator, at the receiving station is vital for ionospheric height measurements, since small errors in frequency estimation can lead to uncertainties on the order of tens of kilometers in resulting estimations of ionospheric height. The methods discussed herein provide a means to calculate path length estimates from distributed stations when integrated with other ionospheric measurements, helping to address the problem of under-sampling of the bottomside ionosphere.
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Status: closed
-
RC1: 'Comment on egusphere-2022-327', Anonymous Referee #1, 08 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-327/egusphere-2022-327-RC1-supplement.pdf
- AC2: 'Reply on RC1', Kristina Collins, 13 Oct 2022
-
RC2: 'Comment on egusphere-2022-327', Stephen Kaeppler, 24 Aug 2022
The paper presents three events and analysis to understand Doppler shifts observed using a few different methods, including by amateur radio operators. One event corresponded to the eclipse of 2017, and two other events corresponded to Doppler shifts associated with the terminator.
While the work that forms the investigation has merit and presents some novel observations, particularly with respect to the fact that the equipment used is amateur radio equipment, the new method being presented in the paper is unclear. I could not determine what was really the new science or the new technique/methodology presented in the paper. From the science perspective, there have been previous investigations of Doppler shifts during eclipses, at minimum, but those were not compared with the current results. There are two new aspects from this investigation which are important and should be emphasized. First, the observations were made with amateur radio equipment, so presumably some of these calibrations could be described and it is possible for others to replicate these results. Second, using ticks with WWV forms a new technique.
I recommend that this paper focuses a little bit more or adds some text to tie these events together into a more cohesive story.
I have the following major comments:
- The paper is disconnected in terms of connecting these three experiments together. Frankly, they seem like three discrete experiments that are loosely connected, although the second and third experiment seem different than the eclipse experiment. There needs to be more effort put toward having a cohesive line of logic for the reader. One suggestion might be to simply not talk about the eclipse results and focus instead on the second and third experiment since these seem like a more cohesive story.
- The paper seems to suggest estimating the virtual height using Doppler observations. From a pure radar signal processing perspective this doesn’t make sense since a narrow band CW signal has an infinite range resolution. If the intent is instead to correlate Doppler variations with virtual height variations, more modeling effort or theory is required to demonstrate that this can be done feasibly. In particular in Section 2, there should be some additional figures that demonstrate this methodology more clearly and what sort of results are being found. So for example, do you see systematic trends in the virtual height relative to Doppler? Those should be explained clearly and including figures. If this is the crux of the new technique, there should be more justification demonstrating that this technique works.
- You should quantify the errorbars on the virtual height estimation. This also may illustrate my point that if you use Doppler alone, you will end up with enormous errorbars. If that is the case, what conclusion can you draw about the virtual height? Regardless, the errorbars would help in terms of the quality of the investigation.
- The flow charge in Figure 3 and the enumerated list in Section 2 are confusing. I could not understand how this method/technique actually worked. This needs to be clarified and elaborated, perhaps with an example. What is the basis for equations 2 and equation 3? This was not explained.
- Near line 185, you have a sentence that states “Figures 8 and 9 show changes in the path velocity and length calculated…” this is a single sentence that describes two figures. What are the key take away points you want the reader to see in each of these figures? The single sentence is insufficient in the description. Also how were these quantities calculated in Figure 8? There are a lot of arrows and other things happening in the figure without a clear description in the text.
- Figure 5 shows some eclipse data for a control day and the day of the eclipse. During 1400-1600 UT, the Doppler measurements appear to have similar magnitudes on the control day versus the day of the eclipse? Why is that the case? I think this would benefit from using some temporal smoothing – like a running mean or median. The trends should be clearer.
- In Figure 9 and 10, I am confused when the Ionosonde data is used relative to your estimates of the virtual height? It does seem cyclic to me to use ionosonde data for a virtual height and then is your algorithm modifying the virtual height to match the doppler observations? Please clarify this in the text.
- Figure 12 should have error estimates associated with the data points.
Citation: https://doi.org/10.5194/egusphere-2022-327-RC2 - AC1: 'Reply on RC2', Kristina Collins, 13 Oct 2022
Status: closed
-
RC1: 'Comment on egusphere-2022-327', Anonymous Referee #1, 08 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-327/egusphere-2022-327-RC1-supplement.pdf
- AC2: 'Reply on RC1', Kristina Collins, 13 Oct 2022
-
RC2: 'Comment on egusphere-2022-327', Stephen Kaeppler, 24 Aug 2022
The paper presents three events and analysis to understand Doppler shifts observed using a few different methods, including by amateur radio operators. One event corresponded to the eclipse of 2017, and two other events corresponded to Doppler shifts associated with the terminator.
While the work that forms the investigation has merit and presents some novel observations, particularly with respect to the fact that the equipment used is amateur radio equipment, the new method being presented in the paper is unclear. I could not determine what was really the new science or the new technique/methodology presented in the paper. From the science perspective, there have been previous investigations of Doppler shifts during eclipses, at minimum, but those were not compared with the current results. There are two new aspects from this investigation which are important and should be emphasized. First, the observations were made with amateur radio equipment, so presumably some of these calibrations could be described and it is possible for others to replicate these results. Second, using ticks with WWV forms a new technique.
I recommend that this paper focuses a little bit more or adds some text to tie these events together into a more cohesive story.
I have the following major comments:
- The paper is disconnected in terms of connecting these three experiments together. Frankly, they seem like three discrete experiments that are loosely connected, although the second and third experiment seem different than the eclipse experiment. There needs to be more effort put toward having a cohesive line of logic for the reader. One suggestion might be to simply not talk about the eclipse results and focus instead on the second and third experiment since these seem like a more cohesive story.
- The paper seems to suggest estimating the virtual height using Doppler observations. From a pure radar signal processing perspective this doesn’t make sense since a narrow band CW signal has an infinite range resolution. If the intent is instead to correlate Doppler variations with virtual height variations, more modeling effort or theory is required to demonstrate that this can be done feasibly. In particular in Section 2, there should be some additional figures that demonstrate this methodology more clearly and what sort of results are being found. So for example, do you see systematic trends in the virtual height relative to Doppler? Those should be explained clearly and including figures. If this is the crux of the new technique, there should be more justification demonstrating that this technique works.
- You should quantify the errorbars on the virtual height estimation. This also may illustrate my point that if you use Doppler alone, you will end up with enormous errorbars. If that is the case, what conclusion can you draw about the virtual height? Regardless, the errorbars would help in terms of the quality of the investigation.
- The flow charge in Figure 3 and the enumerated list in Section 2 are confusing. I could not understand how this method/technique actually worked. This needs to be clarified and elaborated, perhaps with an example. What is the basis for equations 2 and equation 3? This was not explained.
- Near line 185, you have a sentence that states “Figures 8 and 9 show changes in the path velocity and length calculated…” this is a single sentence that describes two figures. What are the key take away points you want the reader to see in each of these figures? The single sentence is insufficient in the description. Also how were these quantities calculated in Figure 8? There are a lot of arrows and other things happening in the figure without a clear description in the text.
- Figure 5 shows some eclipse data for a control day and the day of the eclipse. During 1400-1600 UT, the Doppler measurements appear to have similar magnitudes on the control day versus the day of the eclipse? Why is that the case? I think this would benefit from using some temporal smoothing – like a running mean or median. The trends should be clearer.
- In Figure 9 and 10, I am confused when the Ionosonde data is used relative to your estimates of the virtual height? It does seem cyclic to me to use ionosonde data for a virtual height and then is your algorithm modifying the virtual height to match the doppler observations? Please clarify this in the text.
- Figure 12 should have error estimates associated with the data points.
Citation: https://doi.org/10.5194/egusphere-2022-327-RC2 - AC1: 'Reply on RC2', Kristina Collins, 13 Oct 2022
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