Watershed Concepts 2003 This is a Digital Elevation Model (DEM) over the NE quadrant of the Steep Gully quadrangle, Louisiana. The data were derived from LIDAR measurements performed in 2002, and are presented at a elevation posting interval of five meters. The model is in USGS (non-SDTS) DEM format. These data were produced for the Louisiana Federal Emergency Management Agency (FEMA) Project - Phase 2 of Louisiana LIDAR Data Development: Rapides Parish, Louisiana under the Watershed Concepts contract number EMT-2002-CO-0048, Task Order 013. DEM data are useful for terrain analysis and modeling including slope and aspect calculations. They may be used to produce shaded relief maps and contour maps. The metadata for this image are encapsulated into several documents. The metadata are not complete if you did not receive the following files along with the data set: >dem_3009202ne.mtd - this metadata in mp (metadata parser) compatible ASCII text form >dem_3009202ne.html - this metadata in HTML form >dem_3009202ne_faq.html - this metadata presented as Questions and Answers >dem_3009202ne.sgml - this metadata in SGML form >dem_3009202ne.xml - this metadata in XML form The information depicted on this map are the results of the survey on the dates indicated and can only be considered as indicating the general conditions existing at the time. 200202 Approximate date of LIDAR survey used to build the source data for this data set complete none planned -90.5625 -90.5000 +30.9375 +30.8750 none framework DEM digital elevation model elevation None Louisiana Rapides Parish none These unaltered data may not be redistributed without all of the elements of the metadata listed in the Supplemental_Information section of this metadata document. Watershed Concepts David Key, P.E Mailing and physical address

3333 Regency Parkway, Suite 120

Cary North Carolina 27511 (919)868-5155 The DEM was produced with an origin at an even increment of the DEM point spacing to allow adjacent tiles to be appended without resampling. One of the primary goals of this project was to produce higher accuracy elevation data than was available for the Amite River Basin. Because of the wide array of uses for the data products, many standards had to be taken into consideration for data production. Among these were the FEMA standard for LIDAR capture and data processing, and the USGS standard for Digital Elevation Models. With regard to the USGS standard for Digital Elevation Models, the resolution of the data produced in this project is higher than that for which the standard guidelines were developed. Although this was the overriding goal of the project, it also requires the data follow the standard more loosely than if the data were spaced at the same intervals and resolution as regulated by the standard. The USGS standard provides guidelines for 5 primary types of DEMs. The main difference between the types is the geographic coverage of the data and the resolution of GRID values within the DEM. The smallest geographic extent and grid spacing (and thus the most accurate DEM) documented in the standard is the 7.5 minute DEM (which is a typical USGS Quadrangle). The standard states that the resolution of the 7.5 minute DEM “will have a 10 or 30 meter grid spacing”. The DEMs produced in this project are tiled to USGS Quarter Quadrangles (or ¼ of the typical 7.5 minute quad). The GRID spacing is 5-meters, as opposed to the 10 or 30 meter requirement of the standard. It should also be noted that when these DEMs are viewed with the USGS DLG Viewer software, there are inconsistencies in the elevation data reported by the viewer. These inconsistencies have not been observed in other viewers, including ArcInfo, ArcView, ERDAS and Terramodel. The reason for the inconsistencies is that the DEM generated by ArcInfo utilizes data elements of the USGS standard that DLG Viewer does not take into account when computing elevations. Based on the USGS "Standards for Digital Elevation Models", a DEM file is organized into a series of three records, A, B, and C. The A record contains information defining the general characteristics of the DEM, including its name, boundaries, units of measurement, minimum and maximum elevations, number of B records, and projection parameters. Each B record consists of an elevation profile with associated header information, and the C record contains accuracy data. Each file contains a single A and C record, while there is a separate B record for each elevation profile. Two data elements in particular appear to cause the rendering inconsistencies with the DLG Viewer software. The data elements are the z resolution (data element 15, record b) and the local datum for the profiles (data element 4, record b). The DLG viewer appears to ignore one of the math expressions or uses a default value to compute the elevations. The other viewers listed above can do the math and show the z-values properly. In these viewers, elevations are computed by multiplying the z-values by the z resolution and then adding the local datum value. By either using a default value for the z resolution or datum, or not taking one of these elements into consideration when computing the elevation, the DGL Viewer is not displaying the correct elevation. According to the USGS "Standards for Digital Elevation Models" the z resolution does not have to be a multiple of 10 (e.g 1, .1, .01, etc.). This is the case for the DEMs created by ArcInfo for this project (e.g. .286508). As far as the local datum for the profiles, ArcInfo uses the lowest elevation in the file. According to the USGS Standard, the local datum does not have to be set to zero. The DEM has been clipped to the area of the 3.75 minute cell comprising the SE of the Steep Gully . All lattice points outside this area that comprise the balance of the minimum bounding rectangular area in UTM coordinates have the 'no data' elevation value of -32767. Wayershed Concepts 2003 computer file 200202 Approximate date of LIDAR survey data used to build lattice LAT_3009202ne Regular lattice of elevation values LAT_3009202ne was processed with ArcInfo LATTICEDEM to produce a USGS format DEM. 2003 3001, Inc. LIDAR Manager mailing and physical address

5525 Mounes, Suite 102

New Orleans LA 70123 (504) 733-3001 Metadata imported. L:\Task13\metadata\Template\CCCP\dem_template.xml 16433400 Raster Point Universal Transverse Mercator 15 0.9996 -93.000000 +00.000000 500000 0 coordinate pair 5 5 Meters North American Datum of 1983 Geodetic Reference System 80 6378137 298.257 North American Vertical Datum of 1988 0.01 Survey Feet Explicit elevation coordinate included with horizontal coordinates 20030620 3001, Inc. mailing and physical address

5525 Mounes Street, Suite 102

New Orleans LA 70123 (504) 733-3001 (504) 734-8938 FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998