Another point to remember: The end points of an SRTM profile sometimes need to be adjusted downwards (or at the very least, verified) to account for the morphology above terrain that may have been included in the SRTM data.
-----Original Message----- From: Af [mailto:af-boun...@afmug.com] On Behalf Of Brian Webster Sent: Tuesday, July 21, 2015 11:22 PM To: af@afmug.com Subject: Re: [AFMUG] NED vs SRTM NED is the national elevation dataset and is based on actual ground elevation data and digitized topo maps. SRTM is a combination of RADAR and LIDAR data from the shuttle missions. They do not reflect actual ground elevation, they are a processed echo return of whatever radar and LIDAR returns that were received on the shuttle. The source of the data should also be known as to the resolution. SRTM data was published at 30 meter resolution meaning the hard data points are spaced at 30 meter intervals. NED data is available in various resolutions the most common nationwide being 1/3 arc second or 10 meter resolution or actual data points every 10 meters. This produces a much more accurate terrain model which in turn creates much more accurate RF propagation information. I have attached a real rough paper with images that illustrate the various differences in terrain data and resolution. Thank You, Brian Webster www.wirelessmapping.com www.Broadband-Mapping.com -----Original Message----- From: Af [mailto:af-boun...@afmug.com] On Behalf Of Adam Moffett Sent: Tuesday, July 21, 2015 6:19 PM To: af@afmug.com Subject: [AFMUG] NED vs SRTM If there's a 5 meter discrepancy between USGS National Elevation Data and the Shuttle Radar Topography Mission, who would you trust? Would you bet $500 on it? In this case, with NED I'll have LOS on a backhaul, and with SRTM I'm in the woods. I'm under the impression that SRTM sometimes gets you treetops rather than the ground. If I'm wrong I have alternate paths, but I'd have to pay for a new PCN....so it really is a $500 bet. :)
