GEODATABASE
Remotely Sensed Data

            Evaluation of the current and past environmental conditions that exist in these cenotes relies substantially on information interpreted from remotely sensed data.  Identification of the full extent of features has been accomplished by interpreting both satellite and aerial images.  This data is also utilized to determine which of the 18 cenotes are still water-filled, or which ones have subsequently filled with deposits of travertine.  Low altitude aerial photographs also confirm the presence or absence of water and/or vegetation.  Fracture and joint trends in the pattern of cenote occurrence are identified from remotely sensed data, and are critical in the structural analysis of the area.  Through the interpretation of this information coordinated with field-collected data, a better understanding of the speleogenesis can made.

Panchromatic Aerial Photography

            Aerial photographs provide the best scale and resolution for primary identification of the cenotes in the study area.  Three separate 9 inch by 9 inch panchromatic, 1:40,000 scale photos have been acquired from the Mexican mapping agency INEGI (Instituto Nacional de Estadística, Geografía e Informática), Ciudad Victoria office.  They were ordered by phone using the geographical coordinates of one of the cenotes as a reference point.  The small mosaic of pictures is from one north-south flight line, and each photo has a large degree of frontlap (80 %) with its neighbors.  They are identified in flight line L-346 and are numbered 288, 290 and 292.  The northernmost picture (# 292) encompasses almost all of the cenotes, but they lie in the far western edge of the image.  This creates some level of distortion that warps their spatial distribution in the image.  The photo used in the study area map has been digitally scanned at a very high resolution (500 dpi) and recorded as a *.tif file.  This image was then geo-referenced using the tools in ARC GIS that accomplish this task.

Multispectral Data
            The relevance of multispectral analysis during environmental evaluation is a technique that is well recognized.  In the particular instance of this study area, both properties related to vegetation and to water are important when interpreting images.  The data source is a set of Landsat pathfinder images that has been made available through the North American Landscape Characterization (NALC) project.  This is a joint project between the EPA, USGS, and NASA to provide a consistent data set for a wide range of research applications.  The specific data for this study area was acquired from the Texas Natural Resources Information System (TNRIS) Borderland Information Center (BIC).

            Four different image acquisition times are included in the data set and have been classified as: 1970-1, 1970-2, 1980, and 1990.   The first two images, 1970-1 and 1970-2 where made from the Landsat 1 platform that was launched in July 1972, using the Landsat Multispectral Scanner (MSS).  The 1980 and 1990 images were shot from either the Landsat 4 or 5 platforms, launched in 1982 and 1984 respectively.  Reflectance values from MSS bands 1-4 (originally identified as MSS bands 4-7 on earlier datasets) were measured, collecting data for the following wavelengths of electromagnetic energy:

                        Band 1 ® 0.5-0.6 mm ® green

                        Band 2 ® 0.6-0.7 mm ® red

                        Band 3 ® 0.7-0.8 mm ® near infrared

                        Band 4 ® 0.8-1.1 mm ® broad spectral near infrared