**2. Methodology**

**Figure 1.** Location of Cozumel Island in Mexico.

uvalas, and poljes-locally called "cenotes" and "rejolladas"), altitude mapping and digital models of elevation, shading, and slope generated with LiDAR (light detection and ranging)

The word LiDAR is an acronym for the term *LIght Detection And Ranging*, that is to say, detection and measurement of light. This technique is currently becoming a basic tool in studies based on topographical analysis and precision of the information base [3–5]. The use of LiDAR products has greatly improved and has a significant influence in the earth science disciplines [6, 7]. Its usefulness is emergent in shallow reliefs and those with little

data were used for identification and cartography.

34 Trends in Geomatics - An Earth Science Perspective

altitudinal difference.

To achieve the objectives, the following were necessary (**Figure 2**):

Phase 1. Revision of the inventory of exokarstic forms (caverns, dolines, uvalas, and poljes – "cenotes" and "rejolladas") reported in Cozumel Island [1, 2, 13–17], as well as the reports from the association of speleologists MAYAB AC [18] were consulted, 37 of the reported karst units were recognized in these studies, and a georeferenced database was also generated for the purpose of making the information available for reference.

Phase 2. Construction of a unified LiDAR mosaic of the terrain of Cozumel Island. To do so, the data from point clouds in 32 TIFF information files generated by the ALS 40 system and an information area of 62,556.27 km2 [19] were revised and corrected; the data resolution is 5 m for the X and Y axes and 15–20 cm for the Z axis. The resolution scale is 1:10,000 for each cartographic model.

Phase 3. The application of filters for the elaboration of morphometric digital models of elevation, slope, and shadows. The digital model of elevation was derived from the simple method

**Figure 2.** Flow diagram of the methodology.

of nearest neighbor interpolation, rated at 0.05 cm elevation, recognizing up to 16 m of altitude in the area of study [20]. For the terrain shading method, an azimuth of 272° and an elevation of 30° was used, and for the slope map, eight categories of classification were set manually, where the highest category is >40° [21].

was taken into account; groups that presented values in ascending order from the center to the shores were sought out, since this characteristic indicates that there are depressions. Furthermore, a visual interpretation was done in which the identification criteria was the geometric form of said groups. In this case, the semicircular form is associated with the dolines and the irregular forms with processes of the formation of uvalas. The dimensions are congru-

**Figure 3.** Elevation map with a vertical difference of 0.50 cm and terrain shading model (azimuth 227° and elevation 30°)

Identification of Karst Forms Using LiDAR Technology: Cozumel Island, Mexico

http://dx.doi.org/10.5772/intechopen.79196

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with details about the known karst formations. Prepared by author based on LiDAR data [8].

Finally, with the contrast of the slope (see **Figure 4**), where the association of the semicircular forms and forms with a gradient greater than 25° – corresponding, in the majority of cases, to the borders of the uvalas or collapse cenotes – the altimetric difference was up to 8 m of depth. The units with lower gradients (<25°) and altitude contrast (up to 1 m in height) are related

In the records of dolines and uvalas in the region of study, the existence of 37 karstic forms are reported, all of which have been reported as points (with latitude and longitude coordinates), the majority of which measure less than 10 m in diameter [1, 17]; with the interpretation of the models derived from the LiDAR data, 109 forms were able to be identified, with their

Furthermore, the density of dolines and uvalas in square kilometers is shown in **Figure 6**. The concentration can be explained by the fact that the area of the highest relief (>10 masl), which corresponds to a marine terrace in which the karstification processes are more evident than in the periphery as well as other morphological genesis (dunes, coastal mountain ranges, lagoons, and shoals), located along the coast and the north of the island, and whose forma-

diameter and depth. The cartography of all of the sites is shown in **Figure 5**.

tions can be buried or subterranean (such as caverns and grottoes).

ent with that which was identified in the shading model.

to dissolution dolines.

Phase 4. Analysis of the distribution of units in the inventory and their contrast with the new models of identified forms. In each one of the models, 109 dolines and uvalas were visually identified, using the high resolution models and the contrast of the altimetric data, slope, and shading. Likewise, the information was contrasted with the 37 units reported in the previous studies. Furthermore, field trips were carried out during the months of June and July 2014 to confirm the occurrence of the dolines and uvalas, where the cartographic prospection at 1:10,000 scale was verified.
