# The Comparison of Electron Density between CSES In Situ and Ground-Based Observations in China
## 1 Introduction  
The China Seismo-Electromagnetic Satellite (CSES), also called ZhangHeng-1 (ZH-1), was successfully launched on 2 February 2018. There are eight scientific payloads on the CSES, including a high-precision magnetometer (HPM), an electric field detector (EFD), a search coil magnetometer (SCM), a plasma analyzer package (PAP), a Langmuir probe (LAP), a high energetic particle package (HEPP) and high energetic particle detector (HEPD), a GNSS occultation receiver (GOR) and a tri-band beacon (TBB), which can provide ionospheric observations of electromagnetic fields, plasma and energetic particles [1]. As the accuracy of physical parameters in the ionosphere cannot be directly checked, the comparison with other observations or models is the main way to evaluate the quality of the satellite data. For the CSES data, [PERSON] et al. [2] found that the three HPM sensors have good consistency after in-orbit linear correction. The comparison of HPM data between CSES and Swarm shows that both the vector and the scalar differences are quite consistent, and the responses to a geomagnetic storm were similar for the two satellites. [PERSON] et al. [3] reported that the observation of EFD highlights a very good agreement with the theoretical value, and can respond to both natural and artificial sources. The results of [PERSON] et al. [4] show that the electromagnetic field recorded by CSES EFD and SCM has a good correlation with the simulated result. The correlation coefficients of electron density (Ne) observed by the LAP payload between CSES and the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite, Swarm constellation and the International Reference Ionosphere (IRI) model are all high, and the variation patterns also have similar trends between conjugate data [5; 6; 7]. By analyzing thedata in the commissioning phase, [PERSON] et al. [8] attested that the particle rates of the HEPD proton and electron are consistent with radiation models, as well as their distribution along the orbit. [PERSON] et al. [9] found that not only the satellite housekeeping data, but also the scientific data of HEPD show very good stability. [PERSON] et al. [10] found that the measurements of CSES GOR are consistent with those of ionosonde and incoherent scatter radar (ISR) in Millstone Hill, including F2 layer peak electron density (NmF2), its height (hmF2) and electron density profile. The study of data validation for other satellite missions have also been carried out by scientists, which gives confidence for scientific research using these data. The electron density and temperature of the Swarm constellation were compared with ISR, ionosonde and COSMIC data, and the sufficiently high correlation coefficients were reported by [PERSON] et al. [11]. The study of [PERSON] et al. [12] shows that the data from Global-Scale Observations of the Limb and Disk (GOLD) match well with the GPS TEC in the morphology of equatorial ionization anomaly (EIA) and its seasonal variability. By comparing the thermospheric neutral wind observed by the Ionospheric Connection Explorer (ICON) spacecraft, and four ground-based specular meteor radars, [PERSON] et al. [13] found the agreement between space-based and ground-based winds. [PERSON] et al. [14] reported that the morphology of the total electron content (TEC) from FORMOSAT-7/COSMIC-2 and GPS TEC is similar, and the absolute TEC of MOSAT-7/COSMIC-2 shows an overall consistency with Swarm-B observations. The data quality is worth being researched for a long time. Eight years after Swarm launched in 2013, scientists are still comparing the Swarm data with other observations for future improvement [15; 16]. Although the comparisons between LAP Ne and other observations/models have been carried out in previous studies [5; 6; 7], the data analysis is still needed from different aspects to meticulously and extensively evaluate the observations. CSES payloads operate in two different modes, called survey and burst modes.