# A Novel High-Precision Imaging Radar for Quality Inspection of Building Insulation Layers
## 4 Test and Imaging Results  
In order to verify the performance of the high-precision imaging radar, we constructed a typical insulation layer test site, which covers the insulation layer with different bonding mortar structures, such as spot bonding, spot and frame bonding, strip bonding, full bonding, and the actual bonding mortar structure, as shown in Figure 15.  
In this paper, three areas are selected for the test, shown in Figure 16. In combination with actual engineering needs, in order to improve collaborative efficiency, the survey line adopts a round-trip zigzag survey line. The high-precision imaging radar developed by us is used to lay out the survey line outside the insulation layer for measurement. The survey line spacing is 20 mm, and the signal triggering form adopts distance triggering. The measuring wheel rotates on the wall, and the radar collects a piece of data every 20 mm. Therefore, a 20 mm \(\times\) 20 mm grid is formed in space, and a piece of radar data of 512 sample points is obtained at each grid point.  
The data collected from the above three test areas are intercepted, flipped (the direction of the survey line is reversed), distance-normalized, and aligned to form a three-dimensional data volume arranged in accordance with the spatial position of the survey line, on the basis of which the temporal and spatial domain features are extracted and analyzed and from which the data are constructed for media layering. The established approximate spatial model is used to perform high-precision imaging and ultimately to form high-precision imaging of the insulation layer. Data processing explanation process is shown in Figure 17.  
As can be seen from Figure 18, the high-precision imaging radar can image bonding mortar structures of different structures. The energy of the cement disk and fully bonded region is balanced, the boundary structure is clear, and the frame structure can basically be presented. There are energy discontinuities, which may be caused by misalignment in the survey line layout or data splicing process.  
Figure 16: Survey lines, adopting a round-trip zigzag survey line.  
Figure 15: Design drawing of test site mortar distribution and the actual test scene.  
When applying the above imaging results, we found that due to the scattering effect at the edge of the cement disk, the diameter of the imaged region is slightly larger than the actual diameter of the cement disk. Under the current data processing method, the estimated diameter is approximately 0.008 m larger than the actual value. When the diameter of the cement disk is 0.05 m, the area is approximately 0.0027 m\({}^{2}\) larger. This means that when the bonding area of the cement disk is insufficient, missed detections are  
Figure 17: Data processing explanation process.  
Figure 18: The high-precision imaging results, which show the shape and size of the bonding mortar in different structures. (**a**) The designed drawing of the first survey area. (**b**) The designed drawing of the second survey area. (**c**) The designed drawing of the third survey area. (**d**) The radar detection results corresponding to (**a**). (**e**) The radar detection results corresponding to (**b**). (**f**) The radar detection results corresponding to (**c**).  
likely to occur. In the future, we will continue to research the data processing algorithm to suppress edge scattering waves and more accurately calculate the cement disk area.