Understanding the limits of limb scans: Simulations of ICON's thermospheric wind observations

We present simulated observations from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI), the wind and temperature instrument on the Ionospheric Connection Explorer (ICON), and describe the algorithms used to estimate the thermospheric wind. MIGHTI measures interferometric limb images of the green and red atomic oxygen emissions at 557.7 nm and 630.0 nm, spanning 90-300 km. The Doppler shift of these emissions represents a remote measurement of the wind at the tangent point of the line of sight. However, this measurement is affected by the long path of the line of sight through the atmosphere: horizontal variations of wind and emission rate create errors in the retrievals that are generally a few m/s but can reach several tens of m/s near the terminators and equatorial anomalies. This represents a fundamental limitation on the accuracy of space-based limb measurements. We propose a technique to use the brightness measurements from both MIGHTI sensors to identify compromised wind measurements. We also characterize the expected precision using as-built instrument parameters.