# Lithological Discrimination of Khyber Range Using Remote Sensing and Machine Learning Algorithms
## 5 Discussion
### Color Composites  
Numerous researchers have used various color composite techniques to identify different lithologies [95; 96; 97; 98; 99; 100; 101; 102]. A review of the literature has shown that there is no strict rule dictating the use of any particular color composite combination for lithological mapping. The color composite combinations that effectively discriminated the lithologies in the study area included RGB:632, RGB:468 and RGB:754, RGB:147 of ASTER and OLI, respectively, as shown in Figures 8a,b and 9a,b. The Murree formation (M), Shagai formation shale (SS), Ghundai Sar formation (GS), and Lowara Mena complex (LMC) have been very well mapped by these combinations. The contact between Ghundai Sar formation (GS), Lowara Mena complex (LMC), Landi Kotal slates (LK), Khyber limestone (K), and Murree formation (M) is clearly marked. Fieldwork was carried out to collect samples for laboratory studies and to cross-check the relationship between remote sensing results and field observations, as shown in Figure 14. Overall good results were obtained using FCC in this study, highlighting the areas of changing lithological character that could be matched with field results (Figure 14). Using an RGB band combination makes it simple to identify lithological contacts and can greatly aid with the laborious lithological contact mapping in the field. To use this strategy, one must be aware of the targeted pixels' highly reflecting peaks, which will make them stand out as bright pixels. For instance, the ASTER RGB:468 composite suggests that all of the constituent materials--clays, iron oxides, and calcites--are mapped onto the red band because of their strong reflecting feature in band 4. Additionally, calcite exhibits a reflecting feature in band 6, indicating that the combination of red and green in the band combination RGB:468 causes calcite to exist in yellow-hued tints. Because calcite lacks iron, it has no absorption at band 6 and has absorption at band 8, which is caused by CO3. The electromagnetic spectrum's SWIR area contains all of the chosen bands. Clays, carbonates, and sulfate minerals exhibit characteristic absorption characteristics in this wavelength range, resulting in unique colors on the image representing the dominant lithological character. These bands were chosen mainly because it is important to draw attention to the spectral diagnostic characteristics of carbonate band 4, sercite/illite band 6, and ferruginous alteration (iron oxides) band 8. Because all hydroxyl-containing minerals have a high reflectance in band 4, this band was chosen to emphasize the majority of clay minerals as brilliant red. The clay absorption feature is in the center of band 6, and the carbonate feature is at the center of band 8. Band 8 highlights the following elements: tourmaline, carbonates, biotite, and epidote. Figure 8b displays the findings for the normalized RGB:468 band combination of ASTER. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Eigenvectors** & **Band 1** & **Band 2** & **Band 3** & **Band 4** & **Band 5** & **Band 6** & **Band 7** & **Eigenvalues** \\ \hline PC1 & \(-\)0.3733 & \(-\)0.3856 & \(-\)0.3966 & \(-\)0.396 & \(-\)0.336 & \(-\)0.3722 & \(-\)0.3826 & 0.9429 \\ \hline PC2 & \(-\)0.432 & \(-\)0.3733 & \(-\)0.2315 & \(-\)0.1587 & 0.5635 & 0.4568 & 0.2627 & 0.6768 \\ \hline PC3 & 0.2586 & 0.1392 & 0.0233 & \(-\)0.2248 & 0.7028 & \(-\)0.2594 & \(-\)0.549 & 0.205 \\ \hline PC4 & 0.5289 & 0.1785 & \(-\)0.4088 & \(-\)0.6192 & \(-\)0.1317 & 0.2448 & 0.2462 & 0.0605 \\ \hline PC5 & \(-\)0.0177 & \(-\)0.0194 & \(-\)0.0204 & \(-\)0.0826 & 0.2248 & \(-\)0.7219 & 0.6484 & 0.0079 \\ \hline PC6 & 0.2269 & \(-\)0.044 & \(-\)0.7473 & 0.6118 & 0.0856 & \(-\)0.0672 & \(-\)0.0452 & 0.005 \\ \hline PC7 & \(-\)0.525 & 0.8114 & \(-\)0.2501 & \(-\)0.0552 & 0.018 & 0.003 & \(-\)0.0079 & 0.002 \\ \hline \end{tabular}
\end{table} 
Table 7: Statistical details of eigenvectors of each OLI band against the individual principal components.