Recent announcement from USGS:
OrbView-3 satellite images collected around the world between 2003 and 2007 by Orbital Imaging Corporation (now GeoEye) at up to one-meter resolution can now be downloaded at no cost through USGS EarthExplorer.
“This is a significant addition to the USGS archive and a valuable resource for the global science community,” said Matthew Larsen, Associate Director, Climate and Land Use Change. “Free access through the USGS archive amplifies the utility of the data, making it feasible for many researchers to study large areas at this level of accuracy.”
I took a quick peek at what is available for Cambodia (see graphic below). Would be nice to have more I suppose, but hey, better than nothing.
Orbview-3 Coverage Available for Cambodia
Here are the results of a short test of the satellite tracking by the Trimble R6 rover with GLONASS under forest canopy in Laos. At the time, we were tracking about 4-5 of the GPS satellites exmitting L2C signals, which better tracking performance than regular L2 under adverse conditions.
Forest Site with Undergrowth Cleared
Site 1 - Relatively Open - PDOP 1.6
Site 2 - Open Canopy - PDOP 1.6
Site 3 - Closed Canopy - PDOP 3.4 - Not bad !
Skyplot from Trimble Planning Utility for same time.
I initially got pretty excited by this discovery on http://earthexplorer.usgs.gov/ as some of the imagery is 2-4 ft in resolution and dates from the mid-60′s to mid-70′s. It was de-classified in two batches; 1996 and 2002. However, it seems that most of the imagery is quite cloudy (coincidence ?) and there is not much of the 2-4 ft stuff. Additional frustrations are that is costs money (alebeit a small amount – around $30) and cannot be downloaded. But anyone determined enough should be able to their hands on this.
I’m sure there a much larger collections that are not yet de-classified, covering the entire Khmer Rouge period in Cambodia. I wonder why.
Sceenshot of Black and white KH-7 High Resolution Surveillance Photo North of Phnom Penh. Image Date: 1967/05/24. Camera Resolution: 2 to 4 feet
Screen shot of image covering parts of Kampong Thom and Kampong Cham. Acquisition Date: 17-JAN-76. Camera Resolution: 20 to 30 feet.