# The Effect of Space Objects on Ionospheric Observations: Perspective of SYISR
## 5 Conclusions  
In this study, we drew attention to the effect of greatly increased existing and potential (planned-to-be-launched) LEO constellation satellites on ground-based radar ionospheric observations, where we took the newly built SYISR as an example. We first showed the effect of space objects in the RTI, ACF/power spectra profiles, and ionospheric parameters. Subsequently, we attempted to eliminate space object pollution using the SO-CFAR algorithm. However, pollution from smaller space objects remained, whose reflected echo is comparable to or lower than the background ionosphere, which results in inaccurate findings for the retrieved ionospheric electron density. We quantitatively assessed the space object effect based on the current space object orbit database using a simulation. There remain ~9000 (~37% of the total number of space objects) space objects, whose effect is difficult to eliminate. This pollution should linearly increase when the space object number increases in the future. This study clarifies the effect of space objects on ionosphere observations by the SYISR and is beneficial both to our signal process and to ionospheric parameter inversion, given the frequent occurrence of space objects around the SYISR.  
Conceptualization, [PERSON] and X.Y.; Data curation, [PERSON]; Formal analysis, [PERSON]; Funding acquisition, [PERSON]; Methodology, [PERSON]; Project administration, X.Y.; Supervision, X.Y. and F.D.; Visualization, [PERSON] and X.Y.; Writing--original draft, [PERSON]; Writing--review & editing, X.Y., F.D., B.N., L.J., C.K., N.Z., J.L., Y.W., H.Y., M.L. and Y.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Project of Stable Support for Youth Team in Basic Research Field, CAS, grant number \"YSBR-018\", the B-type Strategic Priority Program of CAS, grant number \"XDB41000000\", the National Natural Science Foundation of China, grant number \"41427901\" and Meridian Project.  
Figure 7: Simulated radar cross section (RCS, color map) and the equivalent spherical diameter (ESD, dotted line) of the space objects that retain the risk of polluting the ionosphere observations by SYISR versus integration pulse number and altitude based on the radar equation. (**a**) The range is 150–600 km with a high ionospheric background (SNR = 6 dB), and the detection threshold of the pollution elimination algorithm is four times that of the background ionosphere. (**b**) The range is 600–1200 km with a low ionospheric background (SNR = 0 dB), and the detection threshold of the pollution elimination algorithm is two times that of the background ionosphere. We used the pulse width of 480 μs in the simulations.  
Data Availability Statement: The experiment results in the figures are available at [[https://osf.io/2m3](https://osf.io/2m3) tf]([https://osf.io/2m3](https://osf.io/2m3) tf). The Two-Line Element (TLE) database and RCS information of space objects in this paper is published at the CeleStack website ([[https://celestrak.com](https://celestrak.com)]([https://celestrak.com](https://celestrak.com))).  
The authors declare no conflict of interest.