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The transformations of kinematical quantities under a change of observer are derived. In particular, the laws of velocity composition and of acceleration composition are presented. Classical relativistic effects related to a change of observer are discussed, along with their experimental verifications: length contraction, Doppler effect and aberration. The final part is devoted to the images of moving objects, discussing their apparent shape, as well as apparent superluminal motions.

There is no intent to minimize the importance of the radio methods described in this chapter compared to the techniques described in the previous chapters. Several of the methods described in Chapter 9 are simply variants of basic radio systems previously covered, while others are not quite as widely used techniques as ionosondes, ISR’s, riometers, etc.

This chapter deals with questions concerning the preparation of the record sections presented in the appendix. All sections are plotted in a reduced time scale using the reduction velocity 6 km/s.

Many analogies have been found between results of wide-angle observations in western Germany and similar investigations in the USSR. The pattern of travel-time curves and the wave form of characteristic arrivals show a strong similarity between both parts of Eurasia. There is in general a small positive velocity gradient in the upper 10 km of the crust and a strong gradient at the base of the crust which may consist of a lamellation of layers with different velocities. Characteristic differences have been found mostly for structures of the lower crust.

Observations by means of Very Long Baseline Interferometry (VLBI) have revealed an increase in the extent and a change in the orientation of the parsec-scale radio structure of the quasar 2134+004. The changes occurred without any large radio outburst and are very different from those generally seen in superluminal radio sources.

Whereas the classical “depth-cues” for statical perspective are inherently ambiguous (they can be used in painting “depth” on a plane surface!), cues from dynamical perspective offer real exterospecific information. These cues can be self-induced (through ego-motion) and thus enable the observer to experiment with the visual world, and thus to objectivate the observations. Gibson (1950) exploited these facts in his well-known treatment of the perception of spatial lay-out through motion parallax. Gibson’s analysis has justly drawn a lot of attention, but less well known is the fact that several of the Gibsonean entities, e.g. the famous “focus of expansion”, are rather problematic concepts. The more well-known Gibsonean concepts apply to the movement of an observer with respect to a plane surface, and we concentrate on this simple case here.

During exploration surveys performed by SEISMOS-GmbH, seismograms were obtained along two profiles 180 km long, one extending from Braunschweig to the Rothaargebirge, the other from Nienburg to Hoher Meisner, intersecting in the Soiling area. The travel times are clearly influenced by different thicknesses of sediments and variations of the velocity distributions in the crust. Therefore interpretation was done by a ray-tracing method, which takes into account lateral velocity variations.

In 1970 refraction seismic measurements were carried out along the International profile VII. Shotpoints were situated in Czechoslovakia, but shots were also observed between the Bohemian Massif and the northern Limestone Alps. Two slightly different models for the crustal structure along this profile are presented. They were obtained by model calculations using ray-tracing techniques. Additional data from boreholes and deep reflections faciliated interpretation and helped in reducing the ambiguity of models.

From the seismic crustal studies carried out in the past 25 years it can be stated that the classic two-layer model is too simple and must be regarded as a rough approximation Seismic refraction and reflection measurements show that the earth’s crust is composed of layers including numerous low-velocity layers. In horizontal direction, there are rapid changes of the elastic parameters. Thus, the picture of lamellae or sandwichlike structure has been proposed.

Starting from two quarries at the Hoher Meissner and west of Gottingen an overlapping seismic-refraction profile runs northwards and ends in the North German Plain between Hannover and Bremen. The data along this profile are presented as record sections of normal and squared traces. The attempt was made to increase the signal-to-noise ratio by velocity stacking and by application of the modified method of correlation after SHIMSHONI and SMITH (1964). A simple crustal model, including time corrections for sediments, is derived. According to this the crustal thickness decreases from 28 to 26 km between the Soiling and the Deister mountains.

Continuous infrasonic recordings made at Windless Bight, 26 km from the summit crater of Erebus, between March and December 1984, show an abrupt change both in the average interval between explosions and in the maximum infrasonic amplitudes on 13 September. Before the change the average interval was 2.8 days, and the maximum infrasonic amplitude was 6.3 microbar peak, and afterwards the average interval was about 1.5 h, and the maximum amplitude on 17 September was 32 microbar peak. From 13 September to 8 December, when activity ceased for 13 days, about 1000 explosions occurred.