Title: The GLO (GFCR Limb Occultation) Sensor: A Sensor Concept for Upper Troposphere and Lower Stratosphere (UTLS) Composition and Transport Studies, as well as Middle Atmospheric Monitoring
Presenting Author: Scott Bailey
Organization: Virginia Tech
Co-Author(s): R. Bevilacqua, D. Korwan, F. Santiago, J. Bobak, S. Restaino (Naval Research Laboratory), C. Randall (University of Colorado and Laboratory for Atmospheric and Space Physics), L. Gordley, B. Marshall, M. Hervig (GATS, INC)

The GLO (GFCR Limb Occultation) instrument is a VNIR/SWIR space-based solar occultation sensor concept to measure O3, H2O, CH4, CO, HF, HCN, HCl, HDO, N2O, CO2 (for temperature), and aerosol profiles at less than 1 km vertical resolution. These species are measured through a combination of Gas Filter Correlation Radiometry GFCR channel pairs and single wavelength channels. The instrument has been designed to particularly target transport and composition in the Upper Troposphere Lower Stratosphere (UTLS), but is suited to observations throughout the middle atmosphere. GLO can be thought of as a miniaturized, updated version of HALOE (2D focal plane arrays instead of single detectors per channel as used by HALOE), with improved vertical resolution and the addition of three spectrally pure, broadband channels (0.45. 1.020, and 1.556 microns) for stratospheric aerosol extinction. In addition, the VNIR channels will be used in combination with selected GFCR SWIR channels to provide information about aerosol composition, and integrated properties of the aerosol size distribution (effective radius, and volume and area density). With its small form factor and modest spacecraft accommodation requirements, GLO is well-suited for constellation applications. We will describe one such implementation, on a mission concept called SOCRATES - Solar Occultation Constellation for Retrieving Aerosols and Trace Elements Species. SOCRATES will quantify the role of the UTLS in climate change and in particular characterize the transport of UTLS constituents from the Asian Monsoon and episodic sources at tropical and mid latitudes. Under ESTO sponsorship, we are currently building a balloon-borne version of GLO. The schedule calls for instrument initial completion in the fall of 2019, ground based testing in the first half of 2020, a first balloon opportunity in September 2020, and a potential second opportunity in September 2021. The instrument concept, measurement approach, retrieval uncertainties, and potential applications will be discussed.