GHOTI: Using the GOES-R EXIS/SPS detectors to create a low-latency, high-cadence, TSI proxy and spectral models

The GOES-R series of geostationary satellites include a redesigned instrument for solar spectral irradiance: the Extreme ultra-violet and X-ray Irradiance Sensor (EXIS). Our team will be using the Sun Position Sensor (a set of high-cadence broadband visible light diodes) on GOES-16 and GOES-18 EXIS instruments to construct a high-cadence proxy for Total Solar Irradiance (TSI). This has two advantages over the existing TSI measurements: 1) the measurements are taken at 4 Hz, so the cadence of our TSI proxy is much faster than existing measurements, such as the 6 to 24-hour measurements produced by SORCE or TSIS-1, and 2) from a geostationary position, the time series of measurements is virtually uninterrupted. Our calibration of the GOES-R EXIS diode measurements includes thermal and sun-satellite distance corrections, while the irradiance calibration relies on TSIS-1 TIM TSI composites. Another measurement from GOES-EXIS that will be used is the Magnesium II core-to-wing ratio. The MgII index is a proxy for chromospheric activity and is measured by EXIS every 3 seconds. The combination of the two proxies is used to generate a model of the full solar spectrum similar to the NRLSSI2 empirical model. We are in the final year of a four-year grant to develop the TSI proxy and the SSI model.