**3.2 Spectral indexes**

The indices obtained with RGB images were interpreted visually, grouping them into three classes (high, medium and low) according to their potential to discriminate different plant cover on the soil. **Figure 3** shows an example of each class.

**Table 4** illustrates the classification of the different indexes into three categories according to their potential to discriminate covers, with different levels of soil protection before erosive processes.


#### **Figure 3.**

*Vegetation indexes with RGB data, classified according to their potential to discriminate different types of land cover.*


#### **Table 4.**

*Classification of spectral indexes according to their potential to identify different levels of soil protection.*

The Vegetation Index Green (VIgreen), was ranked first regarding its potential to discriminate different ground covers. The Modified Green Red Vegetation Index and the Excess Green Minus Excess Red Index were placed in this same category. These indexes presented very similar results and could show differences, even in an apparently homogeneous area such as bare Soil coverage. Additionally, these indices showed very good ability to differentiate unprotected soil in interplant areas in a plantain crop. In the Image, the red colors represent bare soil with little to no plant protection and therefore a high risk of erosion.

With a medium capacity to differentiate some levels of soil protection, by vegetation cover, the Soil Adjusted Vegetation Index, Index Excess Green, Color Index of Vegetation, Green Leaf Index and Index Excess Green resulted. These indexes in general tend to slightly underestimate the areas with high erosion risks, in comparison with the previous indexes, especially in covers where the density of the vegetation is lower, as is the case of annual crops and shrubs.

On the other hand, the indexes with potential slime to zoning erosive risk in soil covers were the VARI and the vNDVI, which do not manage to differentiate exactly the part of the soil discovered between the crops and practically group the different types of soils in a heterogeneous class without plant protection.
