Conclusions

Elevations measured using airborne lidar correlate well with NWI upland, palustrine, estuarine, and marine units. Lidar-derived elevation profiles provide greater detail than is present in small-scale NWI maps produced from aerial photographs and can be used to help map wetland habitats more accurately and in greater detail than is possible from aerial photographs alone. Mapping detail achievable with lidar approaches that of ground-based investigations. Where vegetation is dense, lidar-derived elevations may represent the top of massed vegetation rather than the ground surface, leading to potential habitat misclassification.

Measurements of shallow electrical conductivity using a ground-based EM instrument also correlate well with both NWI habitats and coastal environments determined during ground surveys. Measured conductivities range over more than three orders of magnitude. Highest conductivities are found at locations within marine and estuarine NWI units and in salt marsh, wind-tidal flat, and forebeach environments. Lowest conductivities are found at locations within upland and palustrine NWI habitats and in dune, VBF, and fresh marsh environments. Conductivity changes along island transects are consistent with, and more detailed than, mapped NWI units. Classification detail achievable with conductivity measurements exceeds that of small-scale NWI maps based on aerial photographs.

Lidar-derived elevation and EM-derived conductivities are strongly inversely correlated and each method has advantages and disadvantages. Both methods readily discern saline- and fresh-water environments and complement traditional, photograph-based wetland classification by helping classify distinct coastal environments that have similar signatures on aerial photographs. Overlap in elevation and conductivity among some habitats and environments suggests that a statistical approach to automated wetland classification based on lidar, EM, and aerial photographs could achieve greater detail and accuracy than current methods based on aerial photographic interpretation and limited field checking.

Further evaluation of the use of lidar and EM in coastal habitat classification should include (1) characterize and minimize land-surface elevation error where vegetation is dense; (2) determine the variation in measured conductivity in the coastal environment with seasonal changes in ambient temperature and precipitation patterns; (3) evaluate whether elevation and conductivity statistics derived from coastal environments in one area can be applied to classify similar environments in other, geographically distinct areas; and (4) migrate conductivity measurements to an airborne platform where large areas can be surveyed rapidly and multiple depths can be explored simultaneously.