Abstract The electron density distribution in the lunar ionosphere has been characterized by only a few tens of vertical profiles of detectable electron density. Reported density values are highly variable: observed vertical profiles of electron density have maximum values that differ by a factor of 100. Here we report ionospheric results from five two‐way S‐band radio occultation observations performed by the Danuri spacecraft. The observations were implemented successfully and suitable raw data were acquired, but the initial versions of the derived frequency residuals and corresponding electron density profiles contain undesirable systematic features. We hypothesize that these undesirable features may be associated with the coarse representation of the lunar gravity field (degree and order of 100 × 100) that was used to reconstruct the Danuri trajectory. Simulations using different representations of the lunar gravity field suggest that improving the resolution to 400 × 400 can change the reconstructed spacecraft trajectory enough to account for the undesirable systematic features in the frequency residuals and corresponding electron density profiles. It will be important to assess how results of single frequency radio occultation observations that were processed with a relatively coarse representation of the lunar gravity field are changed if they are reprocessed with an improved representation of the lunar gravity field. Such changes may be significant. If this issue is addressed, then it may improve understanding of the lunar ionosphere.
Withers et al. (Sun,) studied this question.