Evaluation of airborne image data and LIDAR main stem data for monitoring physical resources within the Colorado River ecosystem

Abstract

This study evaluated near-infrared LIDAR data acquired over the main-stem channel at four long-term monitoring sites within the Colorado River ecosystem (CRE) to determine the ability of these data to provide reliable indications in changes in water elevation over time. Our results indicate that there is a good correlation between the LIDAR water-surface elevations and ground measurements of water-edge elevation, but there are also inherent errors in the LIDAR data. The elevation errors amount to about 50 cm and therefore temporal changes in water-surface elevation that exceed this value by the majority of data at a particular location can be deemed significant or real.

This study also evaluated airborne image data for producing photogrammetric elevation data and for automated mapping of sand bars and debris flows within the CRE. The photogrammetric analyses show that spatial resolutions of ≤ 10 cm are required to produce vertical accuracies < 20 cm and that digitally acquired data cannot yet support this monitoring requirement. The mapping analyses indicate that CIR image data are far superior to true-color and panchromatic image data in mapping sand bars and debris flows. The analyses also show that the CIR color information provide almost as much mapping capability as do the combination of CIR color and CIR image texture. Therefore, CIR image data should always be given preference in image data collections, not only for the physical resource program, but also for the biologic resource program.

First posted December 13, 2002