A New Astronomical Parameter from Remote Sensing Data: Astronomical Clearness Index (ACI)

Abstract

Eastern Anatolia Observatory (DAG) project was initiated in Erzurum/Turkey in 2011. DAG will have Turkey’s largest (4 m) and first infrared telescope. The installation process is planned to be by taking its first light in the end of 2021. This study was focused on a new analysis method about the atmospheric properties of DAG site in terms of the cloudiness as known the most vital atmospheric parameter for ground-based astronomical observatories. In this regard, the cloudiness for DAG site is comprehensively examined using the “Cloud Mask” (CMa) and “Cloud Type” (CT) products from Satellite Application Facility on Support to Nowcasting and Very Short-Range Forecasting (NWC SAF). Firstly, the cloudiness and the cloud types over DAG site were determined. Secondly, NWC SAF CMa and CT data have been redefined for astronomical purposes, and the pixel values/meanings in CMa and CT images have been reduced from 6 to 4 and from 21 to 4 pixels, respectively. Thirdly, these new data were used to define a new index named as “Astronomical Clearness Index” (ACI), and finally, the observable days for DAG site were determined using this newly defined index.