Monday, July 30, 2007
From Jon Ranson
It is a quiet day here on the Kochechum River. We broke camp this morning, packed all our gear into the boats and headed down river. Our mission of the day was to locate the areas where the Geosciences Altimeter Laser System (GLAS) aboard NASA's ICEsat satellite has made prior measurements. Tomorrow we'll begin taking ground-truth measurements to validate the satellite data.
The GLAS system measures tree height and produces what is called a wave form. That wave form can be used to measure canopy closure, which basically is the percentage of land covered by forest. We're fairly comfortable with the data collected by GLAS in many types of forest, but when we study the data of this region we suspect that the lidar may not be picking up forest height quite accurately here.
The best way to verify the satellite's measurements is to come here and make those same measurements by hand with old-fashioned forestry instruments. Of course, it is really hard and time-consuming to travel here, force our way through this tough terrain and swim through mosquitoes, but it's worth it.
We use these measurements to measure biomass of the forest. The biomass is the weight of the woody parts of the tree that exist above ground. Scientists can estimate biomass of a tree from measurements of its diameter or height. Normally the taller a tree is, the larger its diameter and the greater its biomass. Since biomass of trees generally is calculated to be about 50 percent carbon, the taller trees store more carbon. In short, the more accurate our tree height measurements are, the better we can understand Earth’s carbon cycle.
Also, the measurements we are recording now become a part of history. In the future, scientists will rely on them to understand how the forest has changed over time. So we make sure our measurements are accurate.
If GLAS is actually accurate here, then we'll verify that and be happy. But even if we find error, it's good. We'll bring home lots of ground-truth data and field observations that will help NASA scientists and engineers design a better instrument. So we can't lose. Still, it's hard work.
It was nice to be on the river today. We were able to observe the forest as we passed through it. Also, we got a break from mosquitoes. The river breeze makes it harder for mosquitoes to hunt. And we have motors so we were outrunning them. It made me smile to imagine them chasing us, hopeless and frustrated.
Of course, they were waiting for us on shore when we stopped to make camp. It's amazing how they congregate around our tents. It's as if they know that, at some point, some warm-blooded creature will come here and drop the bug gear briefly to make a mad dash into the tent. And then they rush in to feast.
It was also great to rest my feet after yesterday's extreme hike up the mountain. The rocks were slippery and the underbrush seemed to grab and tear at our clothes and gear. I don't usually complain much but all the way down the mountain my new boots hurt my feet incredibly badly. I slipped and fell on the rocks, cursing often. But the pain in my feet was more than offset by the incredible beauty of this place. I really love it here.