Incoherent scatter radars (ISRs) are an important measurement tool for space weather research. However, ISR measurements require previous knowledge of the state of the ionosphere, especially the ratio of atomic oxygen ions (O⁺) to electrons. We present ISR measurements during the May 2024 "Mothers' Day Storm" and apply data assimilation-based O⁺ ratios, which should result in more accurate ISR measurements. The advantages and disadvantages of our method are compared to those of other approaches.