Waldemar H. Lehn

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The temperature inversions that produce superior mirages are capable of supporting gravity (buoyancy) waves of very low frequency and long wavelength. This paper describes the optics of single mode gravity waves that propagate in a four-layer atmosphere. Images calculated by ray tracing show that (1) relatively short waves add a fine structure to the basic(More)
A mirage is seen when atmospheric refraction distorts or displaces an image. We describe a mirage simulator that uses digital imaging equipment to generate mirage images from normal photographs. The simulation program relocates horizonal image lines into positions that they appear to occupy, according to rays traced from observer to object. Image-brightness(More)
We trace the history of atmospheric refraction from the ancient Greeks up to the time of Kepler. The concept that the atmosphere could refract light entered Western science in the second century B.C. Ptolemy, 300 years later, produced the first clearly defined atmospheric model, containing air of uniform density up to a sharp upper transition to the ether,(More)
A survey of reported sightings of lake monster phenomena suggests that many of them may be attributable to atmospheric image distortion. The existence of the necessary conditions (surface temperature inversion and hence strong atmospheric refraction) can be inferred from most of the reports. Under such conditions familiar objects can easily take on(More)
Interactive computer graphics is applied to the transmission of visual images through the lower atmosphere. The required input data to the computer consist of an atmospheric temperature profile and light-pen sketches of three objects at various distances from the observer. A transfer characteristic, computed from a bundle of rays leaving the observer, maps(More)
The first recordings of the Novaya Zemlya (NZ) effect were made during Willem Barents' third Arctic expedition. Ray-tracing analyses of the three key observations, on 24-27 January 1597, show that all the reported details can be explained by adopting one common and realistic type of temperature inversion. In particular, the Moon-Jupiter conjunction could(More)
Systematics of the Novaya Zemlya (NZ) effect are discussed in the context of sunsets. We distinguish full mirages, exhibiting oscillatory light paths and their onsets, the subcritical mirages. Ray-tracing examples and sequences of solar images are shown. We discuss two historical observations by Fridtjof Nansen and by Vivian Fuchs, and we report a recent(More)
Superior mirages of simple appearance are occasionally observed over distances exceeding 70 km. These mirages cannot be explained in terms of standard textbook models; rather, they are shown to arise from fairly complex atmospheres. Two observations of different types, observed at Resolute Bay, Canada, are presented. The first is the basic three-image(More)
The Novaya Zemlya effect, historically identified with the premature rebirth of the sun during the polar night, is a long range optical ducting phenomenon in the lower atmosphere. An occurrence of the effect was observed at Tuktoyaktuk, Canada (69 degrees 26'N, 133 degrees 02'W) on 16 May 1979, when the minimum solar altitude was - 1 degrees 34'. The sun's(More)