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We introduce CALAMITY, a precision bandpass calibration method for radiointerferometry. CALAMITY can solve for direction independent gains witharbitrary frequency structure to the high precision required for 21 cmcosmology with minimal knowledge of foregrounds or antenna beams and does notrequire any degree of redundancy (repeated identical measurements of the samebaseline).  We have achieved this through two key innovations. Firstly, we model theforegrounds on each baseline independently using a flexible and highlyefficient set of basis functions that have minimal overlap with 21 cm modes andenforce spectral smoothness in the calibrated foregrounds. Secondly, we use anoff-the-shelf GPU accelerated API (TENSORFLOW) to solve for per-baselineforegrounds simultaneously with per-frequency antenna gains in a singleoptimization loop. GPU acceleration is critical for our technique to be able tosolve for the large numbers of foreground and gain parameters simultaneouslyacross all frequencies for an interferometer with $\gtrsim 10$ antennas in areasonable amount of time. In this paper, we give an overview of our techniqueand using realistic simulations and demonstrate its performance in solving forand removing pathological gain structures to the level necessary to measurefluctuations in the 21 cm emission field from Hydrogen gas during the CosmicDawn and Reionization. If you want to start using CALAMITY now, you can find atutorial notebook athttps://github.com/aewallwi/calamity/blob/main/examples/Calamity_Tutorial.ipynb .

Precision Calibration of Radio Interferometers for 21 cm Cosmology with No Redundancy and Little Knowledge of Antenna Beams and the Radio Sky