WHAT SATELLITE PICTURES CAN’T TELL YOU…

William Ruzek
USA - 24 August 2011

Studying satellite images for off-road challengesThe use of satellite imagery for geo-location has grown enormously over the past decades, from a few low resolution paper images in the 1980s to millions of extremely high resolution digital images at our finger tips in the 21st century, many of which are freely available on Google Earth. These data from NASA Landsat and other high resolution sensors greatly improve our understanding of the world and its surface. Like the other river sources explored, discovered, and confirmed by CERS, the Salween River source location and confirmation was based upon NASA Landsat, Shuttle Radar Topography Mission (SRTM) data, and Google Earth imagery with the aid of GPS.

An examination of the imagery of the Salween River and a measurement of its various tributaries placed its source at a glacier on the Qinghai/Tibet border only 30km (as the crane flies) from the G109 highway to Lhasa. Professor Liu of the Chinese Academy of Science confirmed this glacial source last fall, and his findings await publication. The Salween source was the destination of the Summer 2011 CERS expedition, a perfect complement to the other major Asian river sources confirmed by CERS. With only 30km of off-road travel needed, the expedition seemed to be an easy in-and-out trip, with time left for sight seeing. Little did we know we were very wrong.

Careful analysis of the high resolution Google imagery revealed a track coming off of highway G109 and heading eastward toward the source. The already short trip seemed to be even easier – someone else had been there. With guidance from the GPS and various satellite and paper maps, the track was found and we began our anticipated short trip toward the source. 

Sinking too deep, waiting for help to arrive

While satellite images at various resolutions, multi-spectral imagery, and topographic maps can clearly depict the Earth’s surface in great detail, no historic imagery can show you or prepare you for the consistency of the soil on the dirt tracks. For that detail, you need boots on the ground and direct experience with the area. Within a short time we were stuck in thick permafrost mud, only to become stuck again as we pulled ourselves out. The track we had been following must have been made in a drier season. After an entire day of getting stuck we had traveled only 21km, and set up base camp still 23km from the source.

By analysis of the imagery and maps again, it seemed we could drive farther the next day and get within a few km of the source. The Landsat imagery and topographic maps showed no barriers to driving closer to the source. But even high resolution satellite data can be deceiving. The area between us and the source seemed to be a rolling meadow of steppe grass, with hills easily climbable by the Land Rovers. An exploratory team of two Land Rovers was sent out to find a route to the source. Once out of base camp, we found the optical illusion the imagery was playing.Caught in snowstorm When we got closer we found the fields to be riddled with permafrost pot holes, roughly a meter in diameter and nearly as deep—a perfect match for a Land Rover tire! With these depressions scattered about randomly, we had no room to maneuver the Land Rovers any closer to the source. The only options left were horseback or attempting a tricky navigation up the river bed. We opted for the horses, which turned out to be an unforgettable near-death adventure by itself, but the source was ultimately reached and the coordinates confirmed. 

Satellite imagery and GPS can track location to within a few meters, lead you back to base camp in a blizzard, and can be used to measure the length of the entire Salween river to  and confirm the source of its headwaters. But in the end, this technology cannot prepare you for field conditions, and can sometimes paint a deceivingly smooth picture of impassable terrain. The trip always looks easier on the map, but maps don’t always tell the whole truth. In the end we found the muddy truth to be the difference between an armchair traveler and a China explorer in the field.