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, 1975
data_date	1975
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 1975. DEM is raster format at 1m horizontal resolution. This photography covers the study area when the trees were between 13 and 16 years old.
raster_vector	RASTER
filename	cwm_berwyn_dem_75.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 North False Easting: 400000m False Northing: 100000m Altitude reference - OSGB Vertical Datum mean sea level (Newlyn).
data_quality	YES
resolution	Horizontal : 1m Vertical: 0.1m Source scale of aerial photography - 1:25 000, near vertical, focal length 6". A 2m version of this dataset is also available.
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 on 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 Planimetric accuracy of DEM: RMS 1.5m Height accuracy of DEM: RMS 1.7m 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. At the date of photography the trees were between 13 and 16 years old. Only two photogrammetric models were required to cover the entire area. The flight lines ran approximately north - south. The overlap between the models was a lateral overlap.
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