Instrument comparison: corrected stellar scintillometer versus isoplanometer.

The scintillation pattern from a single star can be utilized to provide information on the refractive turbulence along the line of sight. Instruments that provide refractive turbulence parameters are the isoplanometer and the stellar scintillometer. Attention is drawn to the fact that the National Oceanic and Atmospheric Administration theoretical treatment and implementation of the stellar scintillometer is incomplete. The theory is corrected for spectral effects and finite aperture. A comparison is made of simultaneously obtained isoplanometer values and stellar scintillometer-derived values for isoplanatic angle. The measurements are obtained from an electro-optical/meteorological experiment conducted at Pennsylvania State University in April and May 1986. An atmospheric drop-off model is used to extrapolate the scintillometer measurements beyond the heights probed. Agreement between the two instruments is significantly improved after the appropriate corrections are applied to the scintillometer data. These data were obtained during widely varying meteorological conditions that provided the opportunity for comparisons over a wide range of isoplanatic angles (3 to 14 µrad). Over the 5 days that data were obtained, relative percent departures of mean isoplanatic angles derived from the corrected stellar scintillometer are within 10% of the mean isoplanometer isoplanatic angle values. The uncorrected departures range from 16% to 24%.