When you walk outside at Summit Station without your sunglasses, all you see is blinding white in all directions. Snow reflects so much sunlight that sunglasses and copious amounts of sunscreen are necessities at all times. The scientific term for reflectivity is albedo, or the fraction of incoming light that a surface bounces back. The albedo around Summit Station is pretty close to one; almost 100% of the incoming light bounces back (towards our vulnerable eyes and skin!).
But ‘pretty close to one’ isn’t good enough for IGERT fellow Alden Adolph, who studies albedo in New Hampshire and, for the past month, at Summit Station. During the month of June, Alden made albedo measurements every day at one location, to see how albedo changed over the course of the month, and to relate albedo to other variables like grain size and snow density.
While the IGERTs were at Summit, Alden took advantage of the extra hands to address a question she’s been contemplating: how does albedo vary spatially? If she takes multiple measurements at just one location, is she capturing the whole picture? Or if she moves a few meters away, would the measurement be entirely different?
To answer this question, we set out with our handy field spectrometer, a long tape measure, and a few flags. We marked out a 50-meter by 50-meter grid on fresh, undisturbed snow.
Alden, our trusty instructor, showed us how to use the instrument.
Since albedo is the ratio of reflected to incoming light, each measurement has two parts: first we point the sensor toward the sun, then we point the sensor toward the ground. The sensor is attached to a long metal bar that needs to be level to the ground.
In the field, a measurement sounds something like this:
“Ding!” (The computer makes a very satisfying sound when it has completed a measurement.)
Repeat two more times, move 10 meters along the transect, and repeat. At the end of our grid, we had completed more than a hundred measurements that are currently waiting for Alden to process. Although the surface all looks bright to our eyes, the field spectrometer will do a much better job at distinguishing small variation in the albedo at Summit.