The Images

Figure: Physics Building Atrium shows an optical image of the atrium of the OSU physics department. This is a considerably larger and more detailed scene than is typically used for demonstrations of millimeter-wave active images. The scale of the atrium is a length of about 50 m, a height of about 20 m and a varying width of 7-15 m. The wall on the left is curved. At the far end are open staircases and platforms with glass partitions and railings.

The upper panel of

shows the same image, but with modulated mode mixing. For this work the illuminator was located on the floor near the right of the atrium, with the direct path of illumination from the transmitter to receiver blocked. For all of the ceiling beams, it can be seen that the bottoms of the beams are more strongly illuminated than their sides. Since many materials have similar diffuse scattering this shadowing is important for image contrast. Similar effects are observed in the optical, for example along the terminator line of the moon illuminated by the sun.

A number of prominent features are associated with the open staircase in the far end of the atrium. From front to back are a glass front piece (topped by a metal railing), the up stairs going from right to left, a glass divider between the stairs, the up stairs going from left to right and the drywall of the atrium. While some of these features are observable in the upper panel, many more and additional detail are observable in lower panel of Figure: Physics Building Atrium GHz Image . For example, the supports of the front stairs are clearly visible (as are the turning platforms). The handrails are also observable, but not as clearly. Additionally, lighting for the atrium is provided by the reflection of light from diffuser disks suspended by wires in the volume of the atrium. These wires are more easily visible in the millimeter image than in the optical image, appearing diagonally from the lower left to the middle right portion of the image.