ALMA Calibration

This document outlines the various quantities that will need to be measured or taken into account in order to collect and calibrate ALMA data. It is an update of Chapter 3 of the old Project Book, and supersedes it. Traditionally, “calibration” has often been thought of as strictly a postprocessing exercise in radio interferometry, essentially only involving things done to data after it has been collected. In this document we take a broader view, and include all quantities that must be measured before correlation of the antenna signals as well. These are still formally “calibrations”, since they are measurements of instrumental parameters – they are generally just measured less frequently. They are, however, no less important than the post-processing calibrations. In addition, we address some topics that are not even direct measurements, but are rather things that affect the measurement of our desired quantities. An example is the relativistic deflection of radio waves in the gravitational potential of the sun, which is not really a directly measured or calibrated quantity (except indirectly), but does certainly affect our ability to properly calculate delay, which in turn affects our ability to calibrate, for example, antenna station locations.