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CSES (China Seismo-Electromagnetic Satellite) is a newly launched electric-magnetic satellite in China. A GNSS occultation receiver (GOR) is installed on the satellite to retrieve electron density related parameters. In order to validate the radio occultation (RO) data from the GOR on board CSES, a comparison between CSES RO and the co-located COSMIC RO data is conducted to check the consistency and reliability of the CSES RO data using measurements from 12 February 2018 to 31 March 2019. CSES RO peak values (Nm F2), peak heights (hm F2), and electron density profiles (EPDs) are compared with corresponding COSMIC measurements in this study. The results show that (1) Nm F2 between CSES and COSMIC is in extremely good agreement, with a correlation coefficient of 0.9898. The near-zero bias between the two sets is 0.005363×105 cm -3 with a RMSE of 0.3638×105 cm -3 , and the relative bias is 1.97 % with a relative RMSE of 16.17 %, which are in accordance with previous studies according to error propagation rules. (2) hm F2 between the two missions is also in very good agreement with a correlation coefficient of 0.9385; the mean difference between the two sets is 0.59 km with a RMSE of 12.28 km, which is within the error limits of previous studies. (3) Co-located EDPs between the two sets are generally in good agreement, but with a better agreement for data above 200 km than those below this altitude. Data at the peak height ranges show the best agreement, and then data above the peak regions; data below the peak regions, especially at the altitude of about the E layer, show relatively large fluctuations. It is concluded that CSES RO data are in good agreement with COSMIC measurements, and the CSES RO data are applicable for most ionosphere-related studies considering the wide acceptance and application of COSMIC RO measurements. However, particular attention should be paid to EDP data below peak regions in application as data at the bottom side of the profiles are less reliable than that at the peak and topside regions. [ABSTRACT FROM AUTHOR]

• High correlation between data of CSES and Swarm on global scale. • High correlation on intersecting ground track probe data. • High correlation on relative relationship between nighttime and daytime data. • In situ electron density is underestimated by CSES LAP. • LAP data are available for application on relative variation studies. A preliminary validation of the in situ electron density data obtained by CSES, a newly launched electromagnetic satellite in China on Feb. 2, 2018, using the Swarm satellites LP measurements, is carried out in this study to assess the consistency and reliability of the LAP observations onboard CSES. Three ways are implemented to achieve the goal: (1) comparison of the global distribution patterns for both the daytime and nighttime data, (2) comparison of the data between CSES and Swarm at intersecting ground tracks with similar local time, and (3) comparison of the relative relationship between nighttime and daytime data using the nighttime enhancement space climatology phenomenon. The results show that the in situ electron densities estimated by LAP onboard CSES are in good agreement with data from the Swarm satellites in terms of global distributions, local details and relationship between nighttime and daytime data. A systematic bias between them is also found: LAP density estimates are much lower than that of Swarm satellites. However, the highly consistent relative variations between the two datasets proves the electron density dataset of LAP onboard CSES for now is applicable for the relative data variation applications on ionosphere-related studies. Further calibration of the LAP dataset is recommended using electron density data obtained by different measurements. [ABSTRACT FROM AUTHOR]