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This paperexplores the application of the RASCAN holographic radar for non-destructive subsurface imaging of works of art and architecture. This radar provides high-resolution plan-view images of the shallow subsurface in dielectric materials.The radar is particularly sensitive to small metallic targets, but also to variations in moisture content. Originally developed for detection of hidden bugging devices, sounding of building construction details, and detection of landmines, here the utility of the RASCAN radar for art and architectural preservation studies is demonstrated by several bench-top experiments on stone andwooditemswith different subsurface defects and features, aswellas actual field tests on a decorative marble medallion in the floor of theTemple of San Biagio in Montepulciano, Italy, and Frescoes in the Church of San Rocco in Cornaredo, Italy. Historical research indicates that the medallion in San Biagio was laid circa1590 during the funeral ceremony of a Prelatio of the family Casata Cervini.The actualburialplace ofthe Prelatioisnot recorded, but a radar scan ofthe medallion, and follow-up scansofa bench-top modelsuggest the possibilityofa cavity that could containremains orrelics.In San Rocco, smalldelaminationswere detected behind the frescos

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.

This paper describes a new application of holographic radar for non‐destructive testing applied to cultural heritage items. A holographic radar, called RASCAN, operates in continuous wave multi‐frequency mode at 4 GHz range and produces images with high in‐plane resolution (about 2 cm). Marble items and other stones have been investigated to validate the method to search for subtle cracks, moisture or to unveil details of structures at shallow depth (up to 2 wavelengths). Other important materials are aged wood items that are investigated for tunnels made by insects. Then the holographic radar imaging has been experimentally compared with infrared thermography to understand the advantages and disadvantages of these methods and to derive indications for solving the problem common in all geophysics of inherent non‐uniqueness.