<title>Overall atmospheric MTF and aerosol MTF cutoff</title>

Abstract

The limits of image quality through the atmosphere depend on the overall atmospheric modulation transfer function (MTF) cutoffs. The first spatial frequency cutoff, or 'knee,' of the overall atmospheric MTF curve depends on aerosol MTF. The second spatial frequency cutoff, limited by threshold contrast required in the output image, also depends on turbulence. Measurements of atmospheric MTF over a 5.5 km horizontal path near the ground were made for a large range of spatial frequencies at several wavelengths in the visible and near-IR spectrum along with measurements of turbulence by a passive edge wander technique. On-line measurements of particulate size distribution were made using a Particle Measurement System, Inc. (PMS) probe, and on-line meteorological data (air temperature, relative humidity, wind speed, wind direction, and solar flux) were obtained from a weather station a few meters away from the imager. The experimentally-derived MTF curve is compared to well-known models for turbulence MTF and aerosol MTF. The determination of aerosol MTF from macroscale parameters is crucial to prediction of image quality through the atmosphere and can be implemented in image restoration.