AN EXAMPLE OF HOLOGRAPHIC RADAR USING AT RESTORATION WORKS OF HISTORICAL BUILDING

Abstract

The former Senate building, Saint-Petersburg, Russia is being refltted for using it by the Constitutional court of Russian Federation. The team of Remote Sensing Laboratory was invited to participate in this work. The case is that the under∞oor water heating system had been installed in the Senate building. The arrangement of pipes hasn't been precisely documented. Besides, there are power and communications cables as well as metal mesh under the concrete ∞oor of the building. Workers were afraid of damaging pipes and cables during laying the parquet ∞oor. Main purpose was to investigate the building ∞oor and to deflne exact position of pipes and cables with the help of subsurface holographic radars developed by Remote Sensing Laboratory. 1. INTRODUCTION The paper covers a possible use of holographic subsurface radars difierent from traditional impulse radars (1). They are distinguished by the type of frequency spectrum. The impulse radar has continuous frequency spectrum while the holographic radar has discrete one. Impulse radars have larger penetration depths because they have variable ampliflcation in the stroboscopic receiver. The signal re∞ected from deeper objects is amplifled more than the signal from shallow objects. This is the main advantage of impulse radars. The holographic radar has the same ampliflcation for all objects. In this case, the penetration depth depends on medium attenuation and its homogeneity at shallow depths. Shallow heterogeneities would shade deeper objects in recorded images. At shallow depths, the holographic radar has a distinct advantage in resolution over the impulse radar because the radar frequency range can be easily adapted to the demands of a particular task. Another extremely important advantage of this holographic radar technology is the possibility to image, without reverberation, dielectric materials that lie above a metal surface (2). Such materials cannot be efiectively inspected with traditional time-domain impulse radar technology. Reverberation of pulses between the radar antenna and shallow metal objects obscures the actual location and shape of these objects which are seen as multiple re∞ections (often called ghosts or phantoms) of the transmitted impulse signal on a relatively uniform background (3). Holographic radars could be easily adapted to the US Federal Communications Commission regulations and demands as the radar can use free frequency bands that don't interfere with other devices. Also, they are cheaper than impulse radars. 2. EXPERIMENTS