Calibrator cycle time calculator
Explanation of input parametersThe calculation of the recommended calibrator cycle time depends on a number of parameters:
- Observing frequency and maximum baseline length are set by the observer's science.
- Seeing monitor phase stability: this gives the phase stability parameter (in µm) measured by the ATCA seeing monitor. It is typically 50-2000 µm. 50 µm is typical of good winter nights, whereas 1500 µm is more typical of poorer summer days. In thunderstorms, it can reach 6000 µm.
- Phase screen speed: This gives the pattern speed of the phase screen, and determines how rapidly the phase changes. Typical values for the phase screen speed are 1 to 10 m/s. The phase screen speed is traditionally thought to be the wind speed of the turbulent layer (the turbulent layer is that part of the atmospheric where fluctuations dominant the phase stability). As a generalisation, the turbulent layer will be at greater heights, with corresponding higher wind speeds (relative to the ground) in better observing conditions.
- Kolmogorov exponent β/2: The phase structure function is generally modelled as φ2 ~ bβ. For so-called three dimensional turbulence (which is of interest for the ATCA in all but 6km arrays) β/2 ~ 0.83. For the ATCA in a 6km array, two dimensional turbulence theory is thought to be valid, and β/2 ~ 0.33.
Original: Bob Sault (22-Nov-2004)
Modified: Bob Sault (26-Nov-2004), Phil Edwards (18-may-2011)