Advantages and restrictions of holographic subsurface radars

Abstract

Holographic subsurface radars (HSR) are not in common usage now; possibly because of the historical view amongst radar practitioners that high attenuation of electromagnetic waves in most media of interest will not allow sufficient depth of penetration. It is true that the fundamental physics of HSR prevent the possibility to change receiver amplification with time (i.e. depth) to adapt to lossy media (as is possible with impulse subsurface radar or ISR). However, use of HSR for surveying of shallow subsurface objects, defects, orinhomogeneities is an increasingly proven area of application. In this case HSR can record images with higher resolution than is possible for ISR images. This paper presents experiments with HSR imaging in media with different degrees of attenuation, and illustrates the principle of HSR through an optical analogy.

Holographic subsurface radar for diagnostics of cryogenic fuel tank thermal insulation of space vehicles

“…In many cases the recorded holograms resemble the actual subsurface target due to the high attenuation of electromagnetic waves in typical media and consequent loss of the outer fringes or rings of the interference pattern [21]. But in media with low attenuation, it is possible to improve the resolution of the microwave images by using a hologram reconstruction algorithm [23,24].…”

“…The essential difference is the much lower spatial density of interference lines on microwave hologram interference patterns [21]. This is because at approximately the same characteristic dimensions of the systems, the radar wavelength is several orders of magnitude greater than wavelengths in the optical waveband.…”

Использование Методов Голографической Подповерхностной Радиолокации Для Неразрушающего Контроля Диэлектрических Конструкций

“…Так, при большом коэффициенте затухания подповерхностный объект будет наблюдаться только по оси главного лепестка диаграммы направлен-ности антенны (ДНА). При отклонении от оси главного лепестка для типов антенн, используемых в подповерх-ностной радиолокации, происходит достаточно резкое уменьшение коэффициента усиления антенны, и в сре-дах с высоким затуханием объект не наблюдается под косыми углами, т. е. интерференционная картина отсут-ствует, и голограмма не регистрируется [16]. Вместо радиоголограммы в этом случае, например на бетоне, регистрируется практически теневая картина, напомина-ющая рентгеновское изображение [7,14].…”

Design and Applications of Multi-Frequency Holographic Subsurface Radar: Review and Case Histories

“…Thus, it is possible to construct only a rough analogy between optical holography and HSR. Nevertheless, the analogy is critical for understanding of the physics of HSR, for interpretation of subsurface radar holograms, and for derivation of hologram reconstruction algorithms [8], [19], [20], [21], [22].…”