Graduation Year

2005

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

H. Leonard Vacher.

Keywords

GIS, Karst, Airborne, Laser, Mapping, ALSM, Light, Detection, Ranging, LIDAR

Abstract

A database of likely sinkholes in Pinellas County, Florida, created using airborne laser swath mapping (ALSM a.k.a LIDAR for light detection and ranging), correlates poorly with other databases of likely sinkholes created from modern and historic aerial photographs. Urbanization appears to be the cause of the poor correlation. Buildings obscure much of the ground surface in urban areas, and many man-made depressions can be confused with natural sinkholes. Additionally, the lack of air photos contemporaneous with the ALSM data hinders ALSM analysis in rapidly developing areas. Selecting a lightly-developed portion of the county for further study reduced the effects of urbanization. Air photos of this focus area, taken two years after the ALSM data were collected, image essentially the same surface as the ALSM data; therefore, ALSM and the air photos can be considered concurrent.

While correlations among the two databases in the focus area were better than in the county-wide comparisons, the incongruencies were still numerous and the validity of the databases was unsubstantiated. An additional database of likely sinkholes in the focus area, created using all available information, represents the most exhaustive search for sinkholes in Pinellas County to date. By assuming it is correct (i.e. it identifies true sinkholes), this composite analysis is used to assess the validity of the ALSM database and the air photo databases. Measuring the ALSM and air photo databases against the composite analysis reveals that, while ALSM outperforms the air photo methods, the ALSM and air photo analyses each fail to recognize true sinkholes more than 50% of the time. However, it also demonstrates that, while flawed, using the databases allows for a better-than-random chance of selecting a site free of sinkholes.

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