## 4 Results
### Luoyang Site Case Study
#### 4.1.3 Reconnaissance of Archaeological Marks in Luoyang  
The reconnaissance of archaeological marks was performed by the inspection of both single date and the stacking-averaged data. This was made up of 40 scenes (see Figure 6). The two approaches provide similar results for the detection of shadow marks. Ground truth clarified that the shadow marks were related to rammed earth structures (to an approximate height from 20 cm to 3 m) belonging to the Northeast Inner City Wall, marked by the red arrows in Figure 6.  
Figure 5: Layout of Easten Han to Northern-Wei Dynasty Luoyang Capital City located (from [38]). In Figure 4 green box denotes its location. (**a**) detail of the imperial palace area highlighted by the pink rectangle from panchromatic satellite Pleiades image (**b**) photo of the excavation in Taiji Hall. As regards the crop marks multi-temporal analysis did not provide relevant results. The best results have been from the analysis of single date, among which the scene acquired on 19 March 2013, as illustrated in Figure 7. In order to enhance the crop anomalies, the subset image covering the ancient capital city was firstly performed by Gaussian filter, as illustrated in Figure 7. Two regular features linked to subsurface archaeological remains can be clearly identified, marked by \"a\" and \"b\". According to the archaeologists, feature \"a\" with positive crop marks, probably corresponds to a man-made pit with rich nutrients, and feature \"b\", linked to negative crop marks, due to vegetation stress, is interpreted as buried foundations of buildings. Then the ratio change detection method was applied by comparing the SAR amplitude images of 19 March 2013 (the numerator) and 11 June 2013 (the denominator), as illustrated in Figure 8. Previous investigations indicated that the winter wheat on the archaeological site revived and was in the elongation phase on 19 March 2013 and was harvested on 11 June 2013. Consequently, the crop marks of SAR images can be maximized through the ratio between those two acquisitions. However, in this case, the ratio performance is worse than the Gaussian filtering (see Figure 8), possibly due to noise occurrences on the two acquisitions. In short, the preliminary results demonstrated that the optimal selection of one SAR image is effective, as currently used for optical images, for detecting buried archaeological remains. Figure 6: Shadow marks of the Northeast Inner City Wall on the Eastern-Han to Northern-Wei Dynasty Luoyang city site (highlighted by the green polygon in Figure 4) using a stacking-averaged SAR image. The ancient wall is highlighted by the purple polygon with its details illustrated in the upper subset. Shadow marks are shown by red arrows. Lower image shows a detail of the City wall. Figure 8: Crop marks relating to the Eastern-Han to Northern-Wei Dynasty Luoyang city site (highlighted by the green polygon in Figure 4). The scene shows the ratio calculated using the amplitude of SAR images of 19 March 2013 and 11 June 2013. Positive and negative crop marks were detected, marked by (**a**) and (**b**). Figure 7: Crop marks relating to the Eastern-Han to Northern-Wei Dynasty Luoyang city site (highlighted by the green polygon in Figure 4) on the SAR image of 19 March 2013 performed by the Gaussian filter. Positive and negative crop marks have been detected, marked by (**a**) and (**b**). On 22-24 July 2013, Luoyang was hit by a flood caused by heavy rain, _i.e._, the accumulated precipitation record in this period was 102 mm in the downtown region. The disaster brought damage and economic loss to the city; at the same time, it provided an opportunity for soil and damp mark enhancement linked to buried-archaeological structures. We applied the multi-temporal SAR images of 25 July and 29 July 2013 for analysis. After visual inspection, we found that the soil marks related to buried structures on the Gaussian filtered image of 25 July 2013 (one day after the heavy rain) were clearly noticeable.