A New Data Set of Thermospheric Molecular Oxygen From the Global-scale Observations of the Limb and Disk (GOLD) Mission

摘要

The Global-scale Observations of the Limb and Disk (GOLD) instrument was launched on 25 January 2018 onboard the SES-14 commercial communications satellite and began nominal science operations in October 2018. Operating from geostationary orbit at 47.5°W longitude, GOLD images the Earth's thermosphere and ionosphere in the far-ultraviolet (132-162 nm), measuring critical geophysical parameters by continuously scanning the Earth's disk and limb 18 hours per day. GOLD also performs stellar occultation measurements using bright type O and B stars. Up to 10 occultations per day are obtained at latitudes ranging from 60°S to 45°N and two fixed longitudes, ~33°E and ~128°W. The occultation data provide a direct measurement of atmospheric absorption in the O_2 Schumann Runge continuum, which is used to retrieve the O_2 density profile from 130- to 200-km altitude. This paper describes the GOLD occultation measurement technique and the operational retrieval algorithm used to derive the Level 2 O_2DEN data product. The spatial, temporal, and local time sampling of the GOLD O_2 data product is summarized, and the data quality, retrieval errors, and validation plans are discussed. Occultations are observed under both daytime and nighttime conditions, providing the O_2 density over a complete range of local times. GOLD retrievals have an estimated precision of 10% and a vertical resolution of 5-10 km, depending on altitude. The data have sufficient accuracy and resolution to provide scientifically useful constraints on the O_2 abundance and variability. Initial comparisons show qualitative agreement, but also notable differences, between the GOLD O_2 data and the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar (NRLMSISE-00) empirical model predictions.