Overwater measurements of mean and fluctuating meteorological parameters have been made coincident with optical scintillation measurements. These data have been used to verify the NPS bulk aerodynamics model for calculating the index of retraction structure function, (C sub N)-squared. The average disagreement between calculated and measured values was 33% verifying the validity of the model. IR measured sea surface temperatures cannot be used in the model and this is discussed. (Author).

The lack of correlation between the Airborne Forward Looking Infrared Detector predicted performance by the program UFLR and the actual performance due to meteorological fluctuations was examined. Calculated performances for the detection, classification and identification of four surface targets using actual radiosonde profiles were compared to the performances using radiosonde data affected by random atmospheric variations of pressure, temperature and relative humidity. A total of 192 performances were created using this method. A visual display and a statistical analysis of the actual and simulated performances was performed. Error margins were determined in the predicted detection ranges for height levels of 1,500 ft., 5,000 ft. and 10,000 ft. It was also determined that the FLIR performance may be degraded up to 10 nautical miles for a height level of 5,000 ft., and up to 12 nautical miles for a height level of 10,000 ft. due to the random atmospheric variations. Theses.

The effects of turbulence on the performance of imagers or on beam forming optical systems are well expressed by the optical transfer function or its essential equivalents, the modulation transfer function or the mutual coherence function for the atmosphere. These quantities can be adequately expressed in terms of the Fried model by means of a single number, the turbulence structure constant for optical index, (C sub n) squared, provided that a properly path-weighted value is obtained. The behavior as a function of wavelength and range is also well understood. The quantity (C sub n) squared, which varies with the micrometeorology, can be determined in its properly path-weighted form with a slit-scanning telescope system developed at NPS. A portable system is available which includes an on-line data processing system that gives immediate numerical and graphical results for the properties of the atmosphere, together with performance prediction for a given optical system. The direct optical measurement of weighted (C sub n) squared for the path avoids the necessity of making a large number of measurements of (C sub t) squared at points along the path. Measurement of (C sub n) squared by the slit-scanner method also obtains a direct result independent of assumptions as to the statistical form of the turbulence.

Overwater measurements have been made of the turbulence structure constant for index of refraction, C sub n squared, by means of scintillation for comparison with predictions of C sub n squared based on meteorological measurements carried out at the same time, during the 'Monterey Aerosol Generation and Transport' (MAGAT-1980) experiment. Scintillation was chosen as the optical measurement because it gives heaviest weight to points on the optical path near the center of the path, minimizing the shoreline effects. The overwater path length was 13.3 km. The light source was a 10.6 micrometer CO2 laser. This combination of range and wavelength was adequate to avoid saturation effects.

A system for laser spot profile analysis has been developed and tested, and field test experiments proposed for the evaluation of laser designator performance. Silicon television tube cameras are used to determine the OTF of the atmosphere and to view the laser designator spot. Fourier transform computer techniques are then used to separate the effects of the atmosphere from the effects of laser instability and platform motion. (Author).

Low altitude (81 m.) narrow-beam laser reflectance measurements were made from the nearly ocean-like water surface under the Golden Gate Bridge. For short wavelength waterways superimposed on swell, the signal amplitude probability distribution showed periods of zero return signal, even for vertical incidence, apparently due to tipping of the average water surface. The nonzero signals show an antilog-normal probability distribution, skewed toward higher signal than that provide by a normal (Gaussian) distribution. With incidence angle displaced from the vertical, the distribution shape is retained but with more frequent zero reflections. The decrease with angle of the average signal, including the zeros, is well fitted with a Gram-Charlier distribution, as seen by earlier observers using photographic techniques which masked these details of the structure. For the simpler wave pattern due to a long sustained wind direction, the signal amplitude probability distribution is log-normal with no zero signal periods, for this case, the distribution shifts toward exponential at large angles from the vertical. For surface states intermediate between the above two extremes the distribution is often normal. The larger return signal resulting form the skew toward larger amplitudes from lognormal are more favorable for disposable laser altimeters than previously believed. Also for an altimeter which may be swinging from a parachute or balloon, the return at angles from the vertical remains high. The presence of occasional zero return signal does degrade the accuracy of altitude somewhat for a descending altimeter, but the signal available assures performance at larger altitudes than previously expected.