Evaluating Radio Occultation (RO) Constellation Designs Using Observing
System Simulation Experiments (OSSEs) for Ionospheric Specification
Abstract
Low Earth orbit (LEO) radio occultation (RO) constellations can provide
global electron density profiles (EDPs) to better specify and forecast
the ionosphere-thermosphere (I-T) system. To inform future RO
constellation design, this study uses comprehensive Observing System
Simulation Experiments (OSSEs) to assess the ionospheric specification
impact of assimilating synthetic EDPs into a coupled I-T model. These
OSSEs use 10 different sets of RO constellation configurations
containing 6 or 12 LEO satellites with base orbit parameter combinations
of 520 km or 800 km altitude, and 24 degrees or 72 degrees inclination.
The OSSEs are performed using the Ensemble Adjustment Kalman Filter
implemented in the Data Assimilation Research Testbed and the
Thermosphere-Ionosphere-Electrodynamics General Circulation Model
(TIEGCM). A different I-T model is used for the nature run, the Whole
Atmosphere Model-Ionosphere Plasmasphere Electrodynamics (WAM-IPE), to
simulate the period of interest is the St. Patrick’s Day storm on March
13-18, 2015. Errors from models and EDP retrieval are realistically
accounted for in this study through distinct I-T models and by
retrieving synthetic EDPs through an extension Abel inversion algorithm.
OSSE assessment, using multiple metrics, finds that greater EDP spatial
coverage leading to improved specification at altitudes 300 km and
above, with the 520 km altitude constellations performing best due to
yielding the highest observation counts. A potential performance limit
is suggested with two 6-satellite constellations. Lastly, close
examination of Abel inversion error impacts highlights major EDP
limitations at altitudes below 200 km and dayside equatorial regions
with large horizontal gradients and low electron density magnitudes.