Calibration of the ngVLA

The Next Generation Very Large Array (ngVLA) will be a proposal-driven open-skies radio telescope that is being designed to address a broad range of high priority scientific questions in astrophysics. These motivations have been captured in the ngVLA Science Book, published in Dec 2018, including five identified Key Science areas spanning planet formation, astrochemistry, galaxy evolution, fundamental physics, and the dynamic multi-messenger sky. A detailed, low technical risk, costed concept of the facility to address these scientific forefronts has been completed and released publicly as the ngVLA Reference Design in Aug 2019. The Reference Design comprises 263 feed-low offset Gregorian antennas situated at fixed locations operating from 1.2 to 116 GHz with linearly-polarized feeds in phased or interferometric modes. The array will be centered at the existing VLA site with antennas spanning baselines from 11 m to 1000 km. The facility is designed to operate with high observing efficiency, and to support PIs and the broader community by delivering Science Ready Data Products. In light of this, most observations will be done in standard observing modes, with extensive automation (preparation of observations and data reduction pipelines). As part of data reduction, calibration of the data must be performed to remove corrupting effects arising from the electronics, antenna structure, and atmosphere. The calibration portion of the Reference Design includes water vapor radiometers to track (wet) tropospheric delays, capability for full polarization calibration, database storage/retrieval of calibration parameters (gain, bandpass, polarization leakage), and a switched-power absolute flux density scale tied regularly to celestial standards. For each standard observing mode, an associated calibration strategy is being developed, which will combine these calibrations in various ways, and will be a part of the data reduction pipelines. The ngVLA is a design and development project of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.