Direct measurements of the ionospheric electron density profiles with advanced Topside Ionospheric Sounders (TIS) on nanosatellites at ~800 km altitude are proposed. The TIS instrument design will be based on the Double-Probe &Topside-Ionosphere-Sounder (DPTIS) instrument design, previously developed by LDI for deployment on small satellites under Phases 1 and 2 AFRL-SBIR contracts (2016). The DPTIS design will be miniaturized adapting it to a CubeSat environment. Automatic processing of the measured vertical-incident topside ionograms, and calculation of the electron density profiles (EDP) from the height of the spacecraft to the F2 layer peak is proposed, including the height hmF2 and electron density NmF2 of the F2 layer peak. The inversion of the topside ionograms does not use any model assumptions. Automatic assimilation of the topside EDPs in existing ionospheric models, both physics-based and empirical, will facilitate the generation of realistic ionospheric weather models in near-real-time. The proposed assimilation technique adopts the method currently applied to the assimilation of ground-based NmF2/hmF2 measurements by the Global Ionospheric Radio Observatory (GIRO) into the ISO-standard for the ionosphere, the International Reference Ionosphere (IRI) model. Assimilating measured NmF2/hmF2 data from the proposed CubeTIS will significantly increase the coverage over land and, most importantly, will extend this coverage over the oceans, by generate reliable nowcast of the realistic ionospheric plasma distribution over land and oceans, and short term forecasting. Global difference maps depicting the differences between quiet-time average NmF2/hmF2 model and realistic assimilative model predictions will provide the basis for the development of an Ionospheric Disturbance Index (IDI) as function of location and time. Potential NASA Applications (Limit 1500 characters, approximately 150 words) NASAs satellite navigation applications need be corrected for retarding/refracting effects in the ionosphere. Even with using double-frequency methods (TOPEX/Jason, GNSS) to eliminate first order effects, higher order effects need be considered. CubeTIS data assimilated in IRI generate such a model. The recent GOLD and ICON satellites rely on the IRI to generate some of their Level 2 data products. The near-real time assimilative IRI using CubeTIS data has the potential to significantly enhance the accuracy of data products from these missions Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words) Nowcasting of Ionospheric Disturbance Indices, derived from a fleet of CubeTIS measurements, will provide a warning system for most regions on the globe in support of ionospheric or transionospheric radio frequency systems, like GPS, HFGeo, and OTHR systems.The CubeTIS radio sounder system can be the starting design point for a rescue ground-penetrating radar to survey post-catastrophe areas.
