**3.1 Vegetation indices**

**Figures 2-4** show the results for the vegetation indices shown in **Table 1** with reference to the phenological stages. The vegetation indices were applied to the barley crop over area (a) (red line) and area (b) (blue line). The response of VIs with respect to barley growth was evaluated by contrasting the minimum to the abovementioned areas. The results show that VIs display a distinct variation corresponding to the barley development and they could be used as cultivar-independent phenological indicators. It can be observed that there is a high correlation between the results of VIs. Indeed, VIs could be used in field spectroscopy for the detection of buried structures. The use of more than one VI for the detection of crop marks is suggested in order to enhance the final results. Furthermore, it is clear from these graphs that VI values vary from one phenological stage to another. Although the same dataset was used for all these vegetation indices, each of the VIs demonstrates

#### **Figure 2.**

*Vegetation values for area (a) for (buried structure, red dots) and area (b) for (vegetated area, blue line) during phenological cycle for NDVI.*

**Figure 3.**

*Vegetation values for area (a) for (buried structure, red dots) and area (b) for (vegetated area, blue line) during phenological cycle for EVI.*

#### **Figure 4.**

*Vegetation values for area (a) for (buried structure, red dots) and area (b) for (vegetated area, blue line) during phenological cycle for SR.*

a different response at different phenological stages. It may be seen clearly in the Flowering stage that there is a distinction between area (a) and area (b). **Figure 2** presents a typical example of the spectral profile of area (a) and area (b) using the NDVI. There is an upward trend of area (b) (blue line) compared with area (a) (red line) in which there is a downward trend, throughout the phenological

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**Figure 5.**

*Detecting Underground Military Structures Using Field Spectroscopy*

cycle. Evidently, this happens using the SR vegetation index. Moreover, it is remarkable to note that for the SR vegetation index (**Figure 3**), in test area (b) (blue line), the reflectance response is higher than test area (a) (red line), throughout the phenological cycle. Obviously, the reflectance response in test area (b) (blue line) follows a steeper upward path in the Tilling and Flag Leaf Emerging stages. In the Boot stage, the reflectance of area (b) (blue line) increases dramatically. In the Head Emerging and Flowering stages, the reflectance decreases, but there is a differentiation between the two test areas. This differentiation is not arbitrary but reinforces the diagnosis of existence/nonexistence of military underground structures. In addition, for the EVI (**Figure 4**), the reflectance response changes over time. Specifically, there is an upward trend in area (a) (red line) in the Tilling and Flag Leaf Emerging stages. In contrast, there is an upward trend in area (b) (blue line) in

Ground spectroradiometric measurements can provide the spectral response of the vegetation in detail [29]. The analysis of the spectral data shows the maps of vegetation indices (NDVI, EVI, and SR) for area (a) (**Figure 5**) and area (b) (**Figure 6**), during Flag Leaf Emerging stage. Comparing area (a) with area (b) using NDVI (**Figure 5**), it appears that area (b) obtains lower values due to the nonexistence of underground structures, while area (a) has similar vegetation but higher NDVI values due to the existence of underground structures. In addition, using the EVI (**Figure 6**), area (a) has higher values due to the existence of underground structures, while area (b) has lower values due to nonexistence of structures. Similarly, using the SR vegetation index (**Figure 6**), area (b) has clearly lower values due to the existence of underground structures, while area (a) (**Figure 5**) has higher values due to nonexistence of structures. The green color illustrates high value of indices that distinguish the existence of structures. The existence of underground structure can be clearly seen by comparing area (a) with area (b), during the Head Emerging stage. The analysis of the spectral data shows the maps of vegetation indices (NDVI, EVI, and SR) for area (a) (**Figure 7**) and area (b)

*Image maps showing NDVI, EVI, and SR field data for area (a) during Flag Leaf Emerging stage.*

*DOI: http://dx.doi.org/10.5772/intechopen.86690*

the Head Emerging and Flowering stages.

**3.2 Image maps**

### *Detecting Underground Military Structures Using Field Spectroscopy DOI: http://dx.doi.org/10.5772/intechopen.86690*

cycle. Evidently, this happens using the SR vegetation index. Moreover, it is remarkable to note that for the SR vegetation index (**Figure 3**), in test area (b) (blue line), the reflectance response is higher than test area (a) (red line), throughout the phenological cycle. Obviously, the reflectance response in test area (b) (blue line) follows a steeper upward path in the Tilling and Flag Leaf Emerging stages. In the Boot stage, the reflectance of area (b) (blue line) increases dramatically. In the Head Emerging and Flowering stages, the reflectance decreases, but there is a differentiation between the two test areas. This differentiation is not arbitrary but reinforces the diagnosis of existence/nonexistence of military underground structures. In addition, for the EVI (**Figure 4**), the reflectance response changes over time. Specifically, there is an upward trend in area (a) (red line) in the Tilling and Flag Leaf Emerging stages. In contrast, there is an upward trend in area (b) (blue line) in the Head Emerging and Flowering stages.
