The UTM projected GeoTIFF was imported into ArcGIS v9.3 and reprojected using the data management tool Project Raster (ArcToolbox, Data Management Tools, Projections and Transformations) from UTM Zone 18N, NAD 83 to Geographic, WGS84. The options specified in the Project Raster tool were:
1. Input coordinate system: NAD_1983_UTM_Zone_18N
2. Output coordinate system: GCS_WGS_1984
3. Geographic transformation method: NAD_1983_WGS_1984_5
4. Resampling technique: BILINEAR
5. Output cell size: 0.000022 (decimal degrees, default as calculated by ArcMap for a 2 meter cell size)
The geographic transformation selected is the most accurate one provided by ESRI as it ties in WGS84 with ITRF96, thus reflecting the earth centered offset (x-y-z) between WGS84 and NAD83 (from the ESRI Knowledge Base Document Number 24159).