*2.1.4 Station 5*

 This station is in a bushy area where vegetation height ranges between 2 and 3 m. Many birds nest in the area, and the outcropping rocks have been exposed to their excrements during long periods. The surface of the sample chosen for the measurement was under such conditions. In **Figure 9**, a hand specimen from the same outcrop is shown; its exterior is chemically altered, while its interior shows the dark color of unaltered basalt. The radiometric response is shown in **Figure 10**. Reflectance is flat from 450 to 700 nm and quite similar to the response of the altered surface at Station 4-1, Record 1 (**Figure 11**) in the same interval.

#### **Figure 9.**

*Basalt hand specimen collected at Station 5. The white surface has been exposed and chemically altered, while the fresh portion appears black.* 

#### **Figure 10.**

*Radiometric response at Station 5. A combination of shade and chemically altered surface may correspond to the flat response between 400 and 700 nm. The reflectance increment between 700 and 950 nm is attributed to the effect of vegetation surrounding the station.* 

#### **Figure 11.**

*Spectral signature of chemically altered basalt in the shore of Lago Crater. It was obtained pointing to the darker portions of the rock. Reflectance increase in the lower part of the spectrum is attributed to dispersion effects.* 

Although no direct testing for the effects of bird's feces on basalt is available, bird droppings are known to chemically alter hard surfaces such as concrete [7]. These authors analyzed samples of concrete using scanning electron microscopy for morphological properties and X-ray spectrophotometry for surface elements, finding that the components of bird excrement penetrate microcracks causing it to become smoother. They also found that concrete materials exposed to bird feces lost weight more than the control samples.

#### *2.1.5 Station 8*

 This station is located on the rim of Lago Crater; the interest here was to obtain a clean vegetation record from the top of the rim. Three records are shown in **Figure 12**; they neatly show the radiometric signature of vegetation, with a reflectance peak centered at 550 nm and a large reflectance in the 700–950 nm NIR region, typical of healthy vegetation [8]. The records differ in percent reflectance but basically maintain the same

#### **Figure 12.**

*Station 8 is located on the top of the north rim of Lago Crater. The objective was to obtain the radiometric signature of vegetation around the crater.* 

*Radiometric Mapping of Hydrothermal Alterations in Isla Isabel, Mexico DOI: http://dx.doi.org/10.5772/intechopen.80530* 

spectral signature. The reflectance peaks centered at 550–980 nm are well defined and differ from the response of the geologic materials obtained in other stations.
