Hubbard Brook LTER Site Digital Data


DATA LAYER SUMMARY

Grid:  hb_dem
Data Layer:  Digital elevation model (DEM)

DATA SOURCE
Map scale:  1:24000
Media:  digital

Description:  The USGS 7.5-minute digital elevation models (DEM's) contain regular arrays of surface elevations at a spacing of 30 meters in both the x and y directions.  DEM data can be used to generate a number of products, including contour maps, slope and aspect maps and terrain models.  This grid coverage was generated from USGS 7.5' Topographic Quadrangles; Mount Kineo, NH - 1973, Woodstock, NH - 1980. 


DATA FORMAT

Software:  ARC Version 7.0.4 (ESRI, Inc.)
Projection:  UTM Zone 19


ACCURACY

The accuracy of a DEM is dependent upon its source and the spatial resolution, that is grid spacing, of the data profiles. One factor influencing DEM accuracy is source data scale and resolution. A dependency exists between the scale of the source materials and the level of grid refinement possible. The source resolution is also a factor in determining the level of content that may be extracted during digitization. For example, 1:250,000-scale topographic maps are the primary source of 1-degree DEMs. 

Another factor is the horizontal and vertical dimension of the DEM. Horizontal accuracy of DEM data is dependent upon the horizontal spacing of the elevation matrix. Within a standard DEM, most terrain features are generalized by being reduced to grid nodes spaced at regular intersections in the horizontal plane. This generalization reduces the ability to recover positions of specific features less than the internal spacing during testing and results in a de facto filtering or smoothing of the surface during gridding. 

Vertical accuracy of DEM data is dependent upon the spatial resolution (horizontal grid spacing), quality of the source data, collection and processing procedures, and digitizing systems. As with horizontal accuracy, the entire process, beginning with project authorization, compilation of the source data sets, and the final gridding process, must satisfy accuracy criteria customarily applied to each system. Each source data set must qualify to be used in the next step of the process. Errors have the effect of compounding for each step of the process. Production personnel are directed to account for each production step leading to the final DEM.   


DATA DEVELOPMENT

Date Created:  Unknown
Original Projection: UTM
Last updated:  Unknown
  
NOTES
This grid was generated from USGS ASCII file.


DETAILED DESCRIPTION

Cell Size =              30.000         Data Type:            Floating Point
Number of Rows    =         173
Number of Columns =         316

           BOUNDARY                                STATISTICS

Xmin =               274935.000         Minimum Value =              182.000
Xmax =               284415.000         Maximum Value =             1000.991
Ymin =              4866015.000         Mean          =              591.758
Ymax =              4871205.000         Standard Deviation =         173.763

                          COORDINATE SYSTEM DESCRIPTION

Projection                  UTM
Zone                         19
Datum                     NAD27
Units                    METERS             Spheroid             CLARKE1866
Parameters:


ITEMS HB_DEM.STA

COLUMN   ITEM NAME        WIDTH OUTPUT  TYPE N.DEC  ALTERNATE NAME     INDEXED?

    1  MIN                    8    15     F      3                        -
    9  MAX                    8    15     F      3                        -
   17  MEAN                   8    15     F      3                        -
   25  STDV                   8    15     F      3                        -

Record              MIN             MAX            MEAN            STDV

     1          182.000        1000.991         591.758         173.763