organisation	MLURI
user_name	David Miller
user_organisation	Macaulay Land Use Research Institute Craigiebuckler Aberdeen United Kingdom AB15 8QH
date	4/7/97
data_set_name	Cwm Berwyn, Digital Elevation Model, 1992
data_date	June 1992
description	Digital elevation model of the forest canopy and surrounding land for the Cwm Berwyn study site in Wales. Data derived by digital photogrammetry from aerial photography flown in June 1992. DEM is raster format at 1m.
raster_vector	RASTER
filename	cwm_berwyn_dem_95.img
software	Erdas Imagine, V.8.2, OrthoMAX module (Autometric Inc.)
formats	Erdas Imagine (*.img), Erdas 7.5 (.gis, *.lan), ESRI GRID
operating_system	Solaris 2.4 and Solaris 2.5
format	Erdas Imagine *.img
projection	United Kingdom Ordnance Survey National Grid Modified Transverse Mercator Airy spheroid (1830) Scale factor at central meridian: 0.9996 Central meridian: 2 degrees West Origin: 49 degrees North False Easting: 400000 False Northing: 100000 Altitude reference - OSGB Vertical Datum mean sea level (Newlyn).
data_quality	YES
resolution	Horizontal : 1m Vertical: 0.1m Source scale of aerial photography - 1:10 000, near vertical, focal length 6".
attributes	DEM values represent altitude, in metres, above OSGB vertical datum.
methods	Digital photogrammetric techniques were used to derive the DEM. The input data was colour aerial photography, 1:10 000, scanned at 800dpi oin an AGfa flatbed scanner. Ground control was provided by a MidasII GPS.
other	The DEM is a mosiac of three photogrammetric moels. The area of overlap between each DEM was minimized and the average value taken for each cell within the overlap. in SE of ground control data: 0.4m (additional horizontal check points were selected from the orthophotograph - cwm_berwyn_ortho_95 - to ensure consistency between the multidate imagery. Planimetric accuracy of DEM: RMS 0.7m Height accuracy of DEM: RMS 1.8m The height accuracy quoted is that for check points, at ground level. The accuracy will vary across the forest canopy due to variability in the canopy surface and other shadowing effects, particularly in the proximity of rides, roads and breaks in the canopy. The quality of the DEM is noticably poorer in the top half of the dataset and in the area to the north east of the Cwm. The effects (an apparent " smearing" of the canopy surface) would appear to be caused by insufficient contrast within the original photographs.
copyright	Copyright lies with: Macaulay Land Use Research Institute, Aberdeen and Forestry Commission, Edinburgh.
contact	Dr David Miller Macaulay Land Use Research Institute Craigiebuckler Aberdeen AB15 8QH Tel: +44 1224 318611 x 2240 Fax: +44 1224 311556 Email: d.miller@macaulay.ac.uk