the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jun 2025
Multipurpose incoherent scatter measurement and data analysis techniques for EISCAT3D
Abstract. EISCAT3D will be a high-power, high-duty-cycle, large-aperture multistatic radar system with digitally steerable aperture array antennas and solid-state transmitters. The advanced technology enables the system to form multiple simultaneous beams at each radar site and to use advanced transmission modulation techniques. Multipurpose transmission modulations that use the same radar pulses for probing all altitude regions of the ionosphere, and the lag profile inversion technique needed for deconvolving autocorrelation functions (ACFs) of the scattering process from the received signal at selected altitudes, have previously been developed for monostatic, single-beam radars. We generalize the concept of multipurpose modulations for multistatic, multibeam systems and introduce a lag profile inversion tool that can perform the ACF deconvolution with modest computing power. We also show that lag profile inversion is not needed for analysis of remote receiver data or D region pulse-to-pulse correlations. We deconvolve incoherent scatter ACFs from synthetic radar signals that correspond to a possible EISCAT3D multipurpose mode by means of lag profile inversion and fit plasma parameters to the deconvolved ACFs using an analysis tool that makes optimal use of data from all receive beams of the multistatic, multibeam system. The results demonstrate that the multibeam remote receivers provide significant benefits; the remote receiver data have less incoherent scatter self-noise than the core transceiver site data, they enable one to fill gaps critical for E region plasma parameter fits in monostatic ACF data, the data are accurate enough for E region ion-neutral collision frequency fits, and they enable D region measurements with arbitrary transmission modulations. We benchmark computational requirements of the lag profile inversion analysis and use both synthetic radar signal and real measurements with the KAIRA radio receiver and EISCAT VHF incoherent scatter radar to demonstrate D region measurements with a multibeam remote receiver.
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RC1: 'Comment on egusphere-2025-2462', Anonymous Referee #1, 18 Jul 2025
It’s a wonderful introduction about the experiment mode and data processing for the coming advanced tristatic radar system. Much information included. And I have some questions:
- As mentioned in paper, the antenna arrays are horizontal for the remoting receivers. So what is the lowest altitude of the common volume? And because the antenna gain would decrease when the elevation becomes small, what is the SNR level at the lowest altitude?
- What is the synchronous mode for the tristatic radar system? Does the remote site start to measure when the core site still transmits? What cause the blank in the Figure 3 (e)?
- Do you combine the ACFs from the core and remoting sites, when you invert the plasma parameters? How do you consider the effect of drift velocity from different sites in the spectrum if you put the ACFs together in the inversion?
- In the results of Figure 9, the decrease of Te appears with the increase of Ne. They are usually related in the inversion. Does the fluctuate at the altitude about 110-120km come from the coupling between the parameters or the true state of ionosphere?
By a way, there is an error for the expression at line 648.
Citation: https://doi.org/10.5194/egusphere-2025-2462-RC1 - AC1: 'Reply on RC2', Ilkka Virtanen, 16 Aug 2025
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RC2: 'Comment on egusphere-2025-2462', Anonymous Referee #2, 18 Jul 2025
This interesting manuscript explores transmission codes and analysis techniques for the nearly-completed EISCAT3D incoherent scatter radar. This new tri-static radar will have impressive flexibility and sensitivity and will require innovative modulation schemes to fully realize its potential. The manuscript describes such a scheme along with the processing required to implement it. It also includes the results of simulations of the mode as well as measurements from the KAIRA receive array used in conjunction with the EISCAT VHF transmitter to demonstrate some of the basic principles.
The modulation described in the manuscript is a multipurpose mode which combines various techniques to measure ACFs at a wide range of lags and range resolutions. This supports measurements from the D region through the E and F regions while maintaining a relatively high RF duty cycle.
I have the following questions for the authors which would help in the interpretation of the results.
- The manuscript describes the impact of self-clutter on the measurements and the reduction of this clutter in the data from the remote sites. One thing I did not see was whether the analyses and simulations covered the impact of range aliasing in the measurements from Skibotn. Looking at Figure 2, the pulse starting at 0 ms will also be seen in the returns after the pulse at 1.2 ms, but from ranges 180 km further away. This means that those samples will have contributions, for example, from both the D- and F-region altitudes. Has this been accounted for in the simulations? Is the added self-clutter included?
- Section 3.3 briefly mentions the problem of ground clutter in the Skibotn measurements. Given that the coded pulse itself is 600 microsec in duration, this means that any ground clutter will add to the 90 km of equivalent range that must be blanked from the first bauds of the pulse. Are there any estimates of the maximum range of the ground clutter returns around Skibotn? How severe are the impacts of the partial decoding of the pulse around this altitude? Might a shorter modulation be needed to make D-region measurements?
- Have the authors given any thought to the removal of returns from low earth orbit (LEO) satellites in the lag profile estimates? The region around 800 km altitude is becoming more and more problematic in this regard and it would be interesting to know how this modulation and processing might be impacted by such signals, at least in a general sense.
- It would be helpful to have a discussion about the different spatial resolutions of the measurements from Skibotn and those from the remote sites. The mono-static case at Skibotn is fairly straightforward as the 2.1-degree beam width implies a 3.7 km horizontal extent of the scattering volume at 100 km and 11 km horizontal extent at 300 km altitude. The basic range resolution of the measurements is 0.75 km from the phase coding, so each lag estimate comes from a roughly pancake-shaped region of space perpendicular to the beam steering direction. The remote site measurements are more complicated, however, because the impact of the phase coding does not reflect the altitude, even for a vertically oriented transmit beam. A signal scattered from one edge of the transmit beam at 100 km takes 25 microsec to reach the other edge of that beam (traveling perpendicularly to the transmit direction). It would be helpful if the authors could discuss how this might impact combining high range-resolution measurements from the three stations (Skibotn, Karesuvanto, and Kaiseniemi).
Citation: https://doi.org/10.5194/egusphere-2025-2462-RC2 - AC1: 'Reply on RC2', Ilkka Virtanen, 16 Aug 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-2462', Anonymous Referee #1, 18 Jul 2025
It’s a wonderful introduction about the experiment mode and data processing for the coming advanced tristatic radar system. Much information included. And I have some questions:
- As mentioned in paper, the antenna arrays are horizontal for the remoting receivers. So what is the lowest altitude of the common volume? And because the antenna gain would decrease when the elevation becomes small, what is the SNR level at the lowest altitude?
- What is the synchronous mode for the tristatic radar system? Does the remote site start to measure when the core site still transmits? What cause the blank in the Figure 3 (e)?
- Do you combine the ACFs from the core and remoting sites, when you invert the plasma parameters? How do you consider the effect of drift velocity from different sites in the spectrum if you put the ACFs together in the inversion?
- In the results of Figure 9, the decrease of Te appears with the increase of Ne. They are usually related in the inversion. Does the fluctuate at the altitude about 110-120km come from the coupling between the parameters or the true state of ionosphere?
By a way, there is an error for the expression at line 648.
Citation: https://doi.org/10.5194/egusphere-2025-2462-RC1 - AC1: 'Reply on RC2', Ilkka Virtanen, 16 Aug 2025
-
RC2: 'Comment on egusphere-2025-2462', Anonymous Referee #2, 18 Jul 2025
This interesting manuscript explores transmission codes and analysis techniques for the nearly-completed EISCAT3D incoherent scatter radar. This new tri-static radar will have impressive flexibility and sensitivity and will require innovative modulation schemes to fully realize its potential. The manuscript describes such a scheme along with the processing required to implement it. It also includes the results of simulations of the mode as well as measurements from the KAIRA receive array used in conjunction with the EISCAT VHF transmitter to demonstrate some of the basic principles.
The modulation described in the manuscript is a multipurpose mode which combines various techniques to measure ACFs at a wide range of lags and range resolutions. This supports measurements from the D region through the E and F regions while maintaining a relatively high RF duty cycle.
I have the following questions for the authors which would help in the interpretation of the results.
- The manuscript describes the impact of self-clutter on the measurements and the reduction of this clutter in the data from the remote sites. One thing I did not see was whether the analyses and simulations covered the impact of range aliasing in the measurements from Skibotn. Looking at Figure 2, the pulse starting at 0 ms will also be seen in the returns after the pulse at 1.2 ms, but from ranges 180 km further away. This means that those samples will have contributions, for example, from both the D- and F-region altitudes. Has this been accounted for in the simulations? Is the added self-clutter included?
- Section 3.3 briefly mentions the problem of ground clutter in the Skibotn measurements. Given that the coded pulse itself is 600 microsec in duration, this means that any ground clutter will add to the 90 km of equivalent range that must be blanked from the first bauds of the pulse. Are there any estimates of the maximum range of the ground clutter returns around Skibotn? How severe are the impacts of the partial decoding of the pulse around this altitude? Might a shorter modulation be needed to make D-region measurements?
- Have the authors given any thought to the removal of returns from low earth orbit (LEO) satellites in the lag profile estimates? The region around 800 km altitude is becoming more and more problematic in this regard and it would be interesting to know how this modulation and processing might be impacted by such signals, at least in a general sense.
- It would be helpful to have a discussion about the different spatial resolutions of the measurements from Skibotn and those from the remote sites. The mono-static case at Skibotn is fairly straightforward as the 2.1-degree beam width implies a 3.7 km horizontal extent of the scattering volume at 100 km and 11 km horizontal extent at 300 km altitude. The basic range resolution of the measurements is 0.75 km from the phase coding, so each lag estimate comes from a roughly pancake-shaped region of space perpendicular to the beam steering direction. The remote site measurements are more complicated, however, because the impact of the phase coding does not reflect the altitude, even for a vertically oriented transmit beam. A signal scattered from one edge of the transmit beam at 100 km takes 25 microsec to reach the other edge of that beam (traveling perpendicularly to the transmit direction). It would be helpful if the authors could discuss how this might impact combining high range-resolution measurements from the three stations (Skibotn, Karesuvanto, and Kaiseniemi).
Citation: https://doi.org/10.5194/egusphere-2025-2462-RC2 - AC1: 'Reply on RC2', Ilkka Virtanen, 16 Aug 2025
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