Landsat Imagery

Only a limited number of cloud-free Landsat 1-3 images were acquired of the glacierized areas of Colombia. The best are listed in table 6, and their area of coverage is shown in figure 16. The imagery has been used in this chapter to delineate the areal coverage of ice and snow on the Colombian nevados, but it is difficult to differentiate the snow cover from the glacier areas because of the small size of the Colombian glaciers and the limitation of resolution of the Landsat MSS sensor.

Figure 16.--Optimum Landsat 1, 2, and 3 images of the glaciers of Colombia.

Table 6.--Optimum Landsat 1, 2, and 3 images of the glaciers of Colombia

[See fig. 16 for explanation of symbols used in "Code" column]

The mapping and measurements of snow-and-ice areas from Landsat images tend to be less accurate than measurements of glacierized areas made by the use of vertical aerial photography. This is because of the limitations of the Landsat sensor, particularly the difficulty in differentiating snow from ice. However, the Colombian glaciers appear to be receding fairly rapidly, and until new aerial photography is acquired and analyzed of all the glacier areas, this study offers the best comprehensive baseline comparison of the glacierized areas of Colombia. Higher resolution Système Probatoire d'Observation de la Terre (SPOT) images were used by Vandemeulebrouck and others (1993) in their study of tephra and lahar deposits in the vicinity of the ice cap on Nevado del Ruiz (fig. 12). Both the Landsat 4 and 5 Thematic Mapper (TM) images (30-m pixels) and the SPOT images (20-m and 10-m pixels) provide higher resolution images than Landsat MSS images (79-m pixels). These and higher resolution, satellite-imaging systems in the future will slowly replace the aerial photogrammetric methods of mapping ice caps and outlet glaciers.