Have you tried google earth's area feature? I haven't done any ground truthing, but when you draw lines to measure area they follow the contour of the land so it may be correcting for contour. Some search results on this below. I fyou find a good answer you might let the list know since I'm sure you're not the only one looking for an accurate solution for this.
Tim Some links from a google search (didn't explore the results extensively but I bet you can find you answer on google) http://earth.google.com/support/bin/static.py?page=guide.cs&guide=22365&topic=23730 http://www.google.com/support/forum/p/earth/thread?tid=7524013d2d00c19e&hl=en Starting search: http://www.google.com/search?q=earth+accurate+area+measurments#sclient=psy&hl=en&source=hp&q=google+earth+accurate+area+measurments&pbx=1&oq=google+earth+accurate+area+measurments&aq=f&aqi=&aql=&gs_sm=e&gs_upl=3887l4510l0l4748l7l4l0l0l0l0l0l0ll0&bav=on.2,or.r_gc.r_pw.&fp=d9c7c918cd9c9933&biw=1599&bih=804 --- Tim Brown http://Time-science.com <http://time-science.com/> - Innovative Image Technologies http://www.gigavision.org - Gigapixel timelapse systems [email protected] Office: (801) 893-1314 | (866) 411-3836 Cell: (801) 554-9296 On Thu, Jul 14, 2011 at 11:43 PM, Carol Boggs <[email protected]> wrote: > In the pre-gps era, I calculated the area of one of my study sites using a > high resolution USGS map. Recently we checked that value using a GPS. For > the part of the study site that is fairly flat, the numbers match up very > well. However, for the part that has a significant downhill slope, they do > not. The difference is striking - the gps-derived value is nearly 40% > smaller than the USGS map-derived value. The gps values were differentially > corrected and done with a Trimble that should be accurate enough that I > would not expect a difference of over a hectare between the map and gps area > values. > > Does anyone have any experience or advice for dealing with area > calculations in areas of ~3-5 ha, involving significantly uneven ground? > > thanks, > Carol > > Carol Boggs > Dept. of Biology > Stanford University > summer: > Rocky Mtn. Bio. Lab > Crested Butte, CO >
