Ionospheric Simulation System for Satellite Observations and Global Assimilative Model Experiments — ISOGAME
- Tuesday, 01 January 2013
Modeling helps develop improved systems to study the ionosphere.
Modeling and imaging the Earth’s ionosphere as well as understanding its structures, inhomogeneities, and disturbances is a key part of NASA’s Heliophysics Directorate science roadmap. This invention provides a design tool for scientific missions focused on the ionosphere. It is a scientifically important and technologically challenging task to assess the impact of a new observation system quantitatively on our capability of imaging and modeling the ionosphere. This question is often raised whenever a new satellite system is proposed, a new type of data is emerging, or a new modeling technique is developed. An example is the proposed COSMIC-Follow-On mission (COSMIC stands for Constellation Observing System for Meteorology, Ionosphere, and Climate). The proposed constellation would be part of a new observation system with more low-Earth orbiters tracking more radio occultation signals broadcast by Global Navigation Satellite System (GNSS) than those offered by the current GPS and COSMIC observation system.A simulation system was developed to fulfill this task. The system is composed of a suite of software that combines the Global Assimilative Ionospheric Model (GAIM) including first-principles and empirical ionospheric models, a multiple- dipole geomagnetic field model, data assimilation modules, observation simulator, visualization software, and orbit design, simulation, and optimization software.
The software system can assess the improvements to GAIM that assimilate data collected using a concerned observing system. The GNSS observation system, for instance, consists of the GNSS constellations that transmit L-band radio signals, low-Earth orbiting GNSS receiver constellations, and groundbased GNSS receiver networks. The satellites and ground networks can be designed with an existing, or any, distribution to meet user requirements, such as achieving global coverage with uniformly distributed observations. Under this system, an empirical ionospheric model or the GAIM physics model simulates a nominal or disturbed ionosphere for a specific experiment. The observation simulator uses the designed observing scenario (LEO constellations and ground-based receiver networks) to simulate total electron content (TEC) observations along receiver-transmitter radio links. An Observation System Simulation Experiment (OSSE) can then be conducted by assimilating the synthetic observations into GAIM to quantitatively assess the degree of improvement of modeled ionospheric specifications under the observing scenario. The model that is used for data assimilation assessment can differ substantially from the model that is used to simulate the observations. Visualization software is used to examine and analyze the assimilating model’s performance.