Global-scale Observations of the Limb and Disk (GOLD): Far-UV Imaging Spectrograph Background at Geostationary Orbit

Abstract

The GOLD mission is a NASA mission of opportunity aboard the communications satellite SES-14. It provides an unprecedented new data set for expanding our understanding of the Thermosphere-Ionosphere system, as it is positioned in a geostationary orbit above the mouth of the Amazon river (47.5 degrees West). The GOLD instrument is an imaging spectrograph that measures the Earths emissions from 132 to 162 nm in the Far-UV on the limb and disk. These measurements are used to image thermospheric temperature and composition near 160 km on the dayside disk at half-hour time scales. These images are indicative of the changes in, and evolution of, the lower thermosphere. This is the region where some of the atmospheric thermal tides and waves from lower altitudes dissipate their energy and where the solar and geomagnetic changes can cause dramatic changes in the space environment. Daily observations began in October 2018, following instrument commissioning. This paper examines the types of background signals of the GOLD instrument. GOLD sees two types of background, one that depends on wavelength (spectral background) and one which does not (detector background). The spectral background is caused by both spectral features at shorter wavelengths than observed and imperfections in the optical surfaces of the instrument. Detector background is mostly gamma ray impacts on the “open faced” microchannel plate detector due to the radiation environment at geostationary orbit. This detector background can be examined through “non-illuminated” pixels on the detector. The detector background can vary on a scale of minutes and the variability may be attributed to rapid changes in the solar wind, solar flares, and activity in the magnetosphere. GOLD data is publicly available at http://gold.cs.ucf.edu.