Compensating for window effects in the calculation of spectrographic instantaneous bandwidth.

Exact results derived by Cohen and Lee are used to study the distortion induced by the window in the computation of instantaneous bandwidth via the spectrogram. These concepts have been recently used in an interesting study regarding lesion-induced blood flow disturbances, where an approximation was made to compensate for the window effects. We show that this compensation is accurate for stationary signals, but becomes increasingly poorer as the signal becomes less stationary (e.g., large frequency modulations). We propose an alternative technique to reduce the window distortions, and point out the use of other time-frequency distributions that do not suffer such distortions.

Verification of the bulk method for calculating overwater optical turbulence.

A two-week overwater experiment has been performed to verify the bulk aerodynamic method for calculating the index of refraction structure function parameter, C(2)(N). Meteorological data were obtained on shipboard adjacent to a 13-km optical path over Monterey Bay. Model C(2)(N) and measured C(2)(N) values agree to within 33% on the average when there is spatial homogeneity. During periods of strong sea-surface temperature gradients, disagreements by a factor of 10 are common.

Calculation of optical extinction from aerosol spectral data.

A major overwater experiment, MAGAT-80, has been undertaken to verify the use of aerosol spectrometers to calculate optical extinction in the marine boundary layer. Techniques for data averaging and for extrapolation to large particle sizes are described. Coincident optical, aerosol, and meteorological measurements by ship, aircraft, and an overwater optical range show that aerosol spectra can be used to predict extinction to within 40%.