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Abstract:
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SAV Linear Features Mapping
During ground-truthing of polygon beds north of Albany, observations were made of frequent occurrences of very narrow linear beds of Vallisneria located adjacent to the shoreline. These features generally appeared to be in the two-to-three meter width size, and because they did not provide a signature were not visible on the color aerial photographs. In some instances, the plants were over-shadowed by tree cover along the shoreline. These features were subsequently mapped from the ground.
Submerged aquatic vegetation (SAV) is an important habitat and site of primary production in many aquatic ecosystems but there was no baseline information on SAV extent or distribution in the tidal freshwater Hudson River. In 1994, a collaboration was initiated between the Institute of Ecosystem Studies (IES), the Hudson River National Estuarine Research Reserve/NYSDEC, the Cornell Laboratory for Environmental Applications of Remote Sensing (CLEARS), now the Cornell Institute for Resource Information Systems (IRIS) <http://www.css.cornell.edu/iris/index.htm>. In addtion, the New York Sea Grant, the Hudson River Estuary Program, and the National Oceanic and Atmospheric Administration (NOAA) are identified as partners. These groups provided diverse expertise to enable the first broad delimitation of SAV in the Hudson.
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Purpose:
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The project was undertaken in two separate time periods with different sources of funding. In 1995, Phase I (Hyde Park to Castleton) was initiated with National Oceanic and Atmospheric Association and Hudson River Foundation funds. Subsequently in 1997, the remaining portions (Hastings to Hyde Park and Castleton to Troy) were undertaken in Phase II with New York. State Environmental Protection Funds through the Hudson River Estuary Program.
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Supplemental_Information:
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GRAB SAMPLE DATA
For the mapping of linear features, grab samples were taken in the field at 141 locations in this stretch. Each location was recorded on an enlarged aerial photograph using visible shoreline landmarks for reference. Each record was given an identification number. Observations about plants were recorded on field data sheets with the grab sample identification number and notes. No plant data are available for three of the 141 grab sample locations. All linear features were dominated by Vallisneria as determined from the grab sampling.
Grab sample locations recorded on aerial photographs were transferred to drafting film overlays registered to 1:14,400 scale base maps. A point symbol for each grab sample was drawn on the scaled maps. Placement of the points was determined using the features on the U.S. Geological Survey 7.5 minute topographic map that correspond to visible features on the photos.
QUALITY ASSURANCE USING GPS
Global Positioning System (GPS) data was collected at 45 of the 141 grab sample locations. To verify and support the placement of grab sample locations on the map, the GPS points were plotted to scale and corresponded to the mapped data.
DIGITIZATION
Linear SAV were digitized as line features obtained from the Mylar overlays that were prepared from field observations and spot sampling using a CalComp Drawing Board II digitizing board and mouse with ArcInfo software. Linear features were present on three topographic quadrangles (Albany, Delmar, Troy South). Tolerances (Weed, Arc, Snap) were all set to zero. Four Tic marks were used for Albany (Fuzzy tolerance = 0.08) and eight each for Delmar and Troy South (Fuzzy tolerance = 0.23 and 1.20 respectively). Tics for each map were entered in the NAD27 latitude/longitude coordinates and registered on the map using the digitizing mouse. All linear features on the overlays were large enough for digitization. All other digitization procedures are consistent with digitization of SAV polygons.
Visual comparisons were periodically made between Mylar overlays and digitized features. Proof plots of linear features were created at the scale of 1:14,400 for comparison with original map overlays to ensure accurate representation. The digitized linear feature data was edited for cartographic consistency. The lines representing submerged aquatic vegetation were adjusted to reflect the appropriate generalized position of the linear features. Maps were transferred to ArcView for presentation and statistical calculations.
Data have been converted from NAD27 to NAD83.
Mapping of linear features, grab samples and GPS quality control functions resulted from a collaboration between Cornell IRIS and the Institute of Ecosystems Studies (IES). IES performed digitization; data merging and conversion performed by IRIS.