Atmospheric turbulence modulation transfer function for infrared target acquisition modeling

Abstract

A new direction for the US Army Night Vision and Electronic Sensors Directorate is the development of ultra-narrow field of view (UNFOV) infrared target acquisition (TA) systems. Frequently, the performance of these systems is limited by atmospheric turbulence in the imaging path. It is desirable to include the effects of atmospheric turbulence blur in infrared TA models. The current TA models are currently linear shift invariant (LSI) systems with component modulation transfer functions (MTFs). The use of additional MTFs, to account for atmospheric turbulence, requires that the turbulence blur have LSI properties. The primary unresolved issue with the treatment of turbulence blur as an MTF is the LSI characteristics of the blur. Significant variation in spatial blur and temporal blur prohibit the use of a single MTF in an LSI target acquisition model. Researchers at Ben-Gurion University (BGU) use a TA model that includes an LSI blur, which is a temporal average of the turbulence blur. The research described here evaluates the BGU-type treatment of atmospheric MTF and determines it reasonable for inclusion in the US Army's TA model. In addition to the spatial characteristics, the temporal variation of the turbulence blur is also described.

Optimization Design Method of Optical Remote Sensor Based on Imaging Chain Simulation

“…The main consideration is turbulence MTF and aerosol MTF. For space optical remote sensing applications, the turbulent MTF in the far field and short exposure condition can refer to literature [9,10]. Aerosol impact on image comes mainly from low altitude atmosphere part.…”

Wave structure function and long-exposure MTF for laser beam propagation through non-Kolmogorov turbulence

“…A laser beam propagating through unstable random atmosphere experiences phase and amplitude variations due to turbulence disturbances leading to such effects as beam wander, beam spreading, and intensity fluctuations better known as scintillations [6,8,10]. This turbulence is caused by refractive index inhomogeneities along the propagation path and it has significant degrading impact on the performance of free-space optical (FSO) communication systems as well as on the quality of imaging systems described by the modulation transfer function (MTF) [11][12][13]. In addition factors like aerosol scattering, molecular absorption caused by snow, fog, and rain can also severely degrade the quality of imaging systems [9].…”

Short-exposure turbulence effects on the modulation transfer function of annular aperture optical systems

“…The standard theory for modeling atmospheric turbulence impacts in systems performance models [1][2][3] has been Fried's 4 short-exposure atmospheric modulation transfer function (MTF). Reanalysis of Fried's approach has shown that when diffraction influences on the phase structure function are included, 5 the tilt-phase (TP) correlation term is numerically evaluated, 6 and path-dependent turbulence strength variations are considered.…”