Precise Airborne LiDAR Surveying For Coastal Research And Ge(7)

International Archives of Photogrammetry and Remote Sensing, Volume XXXIV-3/W4 Annapolis, MD, 22-24 Oct. 2001

Figure 15. Flightlines over the 10 km x 10 km survey area forTegucigalpa, Honduras.

These flights produced a uniform and dense ALSM data pointcoverage over an approximately 10km × 10km area ofTegucigalpa. Figure 16 shows the point “cloud” distribution overthe city center at the confluence of the Rio Grande O Cholutecaand the Rio Guacerique. The only data gaps are on the riverswhere the water surface was often too specular to provide good

laser returns.

Figure 16. ALSM point cloud for central Tegucigalpa. Theindividual laser returns are colored to represent elevation.Channel cross-sections are shown in white.

We edited the ALSM data, compared them to ground surveys,and corrected for elevation biases. We generated a 1.5m × 1.5m“all points” DEM using all the ALSM last-return data. We thenapplied the TopScan vegetation-filtering algorithm to the last-return ALSM data. The filter parameters were chosen so thatreflections from trees were removed, but most reflections fromthe ground surface and buildings were retained. We constructed asecond, 1.5m × 1.5m “vegetation-removed” DEM from thefiltered ALSM data. We then used HEC-GeoRAS to define theriver channels and extract cross-sections from the “vegetation-removed” DEM’ (see figure 16).

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Heavy rains associated with Hurricane Mitch caused three majorlandslides in Tegucigalpa. The most devastating slide occurred onthe Cerro Berrinche in northwest Tegucigalpa. The El Berrinchelandslide destroyed an entire hillside community and dammed theRio Grande O Choluteca causing significant flooding in the citycenter. Figure 17 shows the topography of the El Berrinchelandslide after mitigation. The toe of the landslide has been cut

into a series of steps and stabilized with gabions.

Figure 17. Shaded relief image of the El Berrinche landslide inTegucigalpa.

5 DISCUSSION

Erosion along the Texas coast caused by the recent tropicalstorms in the Gulf of Mexico has intensified efforts to saveproperty and houses. ALSM can provide the topographic modelsneeded for geomorphic analysis and the delineation of areasparticularly susceptible to storm damage. Post-storm ALSMsurveys allow rapid and quantitative assessment of the amount oferosion and vulnerability of the coast to subsequent storms. In thepast, coastal geologists and engineers have either conductedregional studies with sparse data or local studies with detaileddata. With ALSM, however, it is possible to acquire detailed andaccurate topographic data over a broad coastal region allowinggeomorphic analysis across the continuum of spatial ndslide and flooding risks are strongly dependent ontopography. With ALSM it is possible to characterize topographyover large areas with sufficient resolution and accuracy to modelhydrologic and geomorphic processes with unprecedented detail.New, quantitative models for hydrologic and surficial processescan be developed and tested using high-resolution topographicdata.

6 REFERENCES

Blair, J.B., D. L. Rabine, and M. A. Hofton, 1999, The LaserVegetation Imaging Sensor: a medium-altitude, digitization-only,airborne laser altimeter for mapping vegetation and topography,ISPRS Journal of Photogrammetry and Remote Sensing, vol. 54,no.2-3, pp.115-122.

Burman, H., 2000, Adjustment of laser scanner data forcorrection of orientation errors, International Archives of