Cooperative Ecosystem Studies Unit, South Florida-Caribbean CESU – Elevation Data Research Grant

Recently, the Gawlik Lab at FAU found that the computed hydroperiods from EDEN data are more variable and patchy in WCA1 (A.R.M. Loxahatchee National Wildlife Refuge) than other sub-regions (Figure 1), seemingly reflecting fine scale topographic variation from the many small tree islands in WCA1. To assess whether the hydroperiod and water depth differences are the result of elevation changes in the digital elevation model (DEM), the EDEN DEM and DOQQs (1-m, 2004) were overlaid and examined. It was noticed that some cells in WCA1 did have DEM values as much as 30 cm greater than the surrounding cells, while no obvious
difference in landscape patterns were shown (Figure 2). It was suspected that elevations for such
cells might be measured on small tree islands or other higher ground, and the interpolation
process (to create the DEM) did not smooth out these measurements as it did in other sub-regions
with larger tree islands prevalent (Figure 3). Further investigation confirmed that different rules
were applied when interpolating the DEM in WCA1 (Telis and Higer, USGS, personal
communication). The high variability in fine scale topography in WCA1 poses special problems
for the interpolation of the DEM, because it is not clear how much of that variability should be
smoothed to match the DEM in other areas and how much should be preserved, and thus reflect
the unique character of WCA1. To provide a solid foundation for subsequent analyses of EDEN
data, it will be necessary to quantify the patterns of variability and error in the DEM within
WCA1. The success of the proposed research will help refine the EDEN dataset and greatly
benefit the research and management activities in WCA1.

The research included in this agreement is designed to answer questions critical to restoration success. There are three related research Objectives that are contained within the current cooperative program:

Objective 1 – This Objective will develop a reference base of ground elevation data and other information, primarily for WCA1.

Objective 2 – This Objective will develop a statistical comparison of modeled EDEN DEM to measured ground elevations.

Objective 3 – This Objective will document a SAS program for batch processing of EDEN surfaces.