Cross correlation analysis improves time domain measurements

The authors introduce several approaches to analyzing time-domain measurement data which the cross correlation to reveal data obscured by the measurement noise. They introduce cross-correlation-based variances (#σ²) to estimate the Allan variance, the modified Allan variance, and the time variance in the presence of the measurement system noise. These variances substantially lower the short-term measurement noise floor; however, they require significantly more data. measurement system noise. #σ² bears a precise relation to the three-cornered-hat σ. The short-term noise floor for σ_y(1 s) was reduced by a factor of 100 relative to the initial hardware and software configuration. The improvement described enable low noise measurements that were not possible earlier at 5 MHz