The following excerpts are from Studies in Egyptian Culture No. 6: Non-Destructive Pyramid Investigation (1) By Electromagnetic Wave Method by Sakuji Yoshimura, Takeshi Nakagawa, Shioji Tonouchi, and Kazuaki Seki (Tokyo: Waseda University, 1987; grammatical errors remain uncorrected):
Seven measuring lines were installed east and west and four measuring lines north and south to scan the Sphinx over 70 meters from the east to the west and over 10 meters from the north to the south. The bedrock of the Sphinx contains more moistures than that of the pyramid. This would be because the Sphinx locates closer to an underground stream. A response was obtained which would indicate that there is a plash 2.5 to 3 meters below the ground surface near the south-eastern forefoot. On its body, a groove with a width of 2 meters, a depth of 3 meters, and a length of 2 meters was found which seems to extend underneath the body. At the center of the southern rock, vertical cracks were observed; however, the cracks never seem to affect the bedrock.
Four measuring lines were installed east and west and five measuring lines north and south to scan the Sphinx over 60 meters from the east to the west and over 7 meters from the north to the south. The northern bedrock seems to contain more moistures than the southern bedrock. The vertical cracks, run east and west across the Sphinx, would be produced naturally. On the body, there is a groove similar to that on the southern part, which seems to extend underneath the body. Under the Sphinx, therefore, there may be a tunnel. Further, near the front elbow, a geometrical cavity (1m x 1.5m x 7m) has been detected, possibly containing metal or granite.
The front of the Sphinx consists of pieces of limestone that have been arranged artificially and paved. With the passing of time, the arranged and paved pieces of limestone have been projected and recessed. At first, the team had been concerned about survey, as the turbulent reflection on the surface might disturb the sensor. Measuring lines (comprising reticulate 10 lines each) were set by meter east and west, and north and south. Inner part of both the forefeet, a geometrical cavity (1.5m x 3m) has been detected. The bottom has not been detected clearly, because the bottom may be uneven or there may be some articles. The cavity seems top extend from the east to the west, i.e., toward the chest; however, an offering table made of granite prevented survey.
At the western part beyond the offering table, two measuring lines were installed for survey east and west. The surface, which is not made of limestone and has a great number of cracks, was not measured correctly due to violent turbulent reflection on it. Rough survey has indicated the high possibility of the presence of a cavity 1 to 2 meters below the ground surface. The cavity may be connected to the above cavity located in front of the Sphinx, and may extend into the Sphinx. However, if these cavities are separated, it is very possible the former cavity located in front of the Sphinx is Sertab where the statue was installed. [pp. 7-8]
The Sertab mentioned above is more commonly called a serdab, a room in Old Kingdom tombs in which statues representing the ka of the deceased were placed. Eyeholes or slits were often provided so that the ka might gain access to its offerings. There is little reason, however, to think that the Sphinx served as a tomb.