Meet Chuck – Our Field Spectroradiometer
Sonoma State University
Reflectance. To most of us, it is just light bouncing back from a surface. Most of us refer to it when talking about a mirror or road signs. To a JIRPer, it is the reason behind our most frequent and prominent sunburns. As a glaciologist, reflectance is the key to understanding the relationship between incoming solar radiation, glaciers, and melt. When dust or ash or algae is deposited on a glacier’s surface, it gets darker and melts more. It is important for us glaciologists to measure and understand these processes. But how?
To measure the glacier surface reflectance, JIRP faculty member Allen Pope introduced us to the field spectroradiometer. We named it Chuck. Why you may ask? Because it stuck. That’s pretty much the only requirement to name things here at JIRP.
Chuck the field spectroradiometer is a lightweight box you can easily carry into the field. So what does a spectroradiometer do? It measures the amount of visible and near-infrared light being reflected off a surface. Along with the spectroradiometer comes a Spectralon panel. Spectralon is a ceramic white palette which is very bright in almost all wavelengths, making it close to 100% reflective. This Spectralon is used as a reference for how much light is present where you are currently taking surface reflectance measurements.
To use Chuck the spectroradiometer, you hold it as far away from you as possible and point it at your intended surface. First, you take a snap of your Spectralon to get a reference reflectance. This device is highly sensitive meaning that the color clothing you are wearing or your shadow can significantly influence its results. Next, you take a measurement of your surface and then you can see a graph on the computer screen showing your results. This graph shows highs and lows throughout visible and near-infrared light indicating which colors are being reflected and which are being absorbed.
Excited at how easy it was to use Chuck, we ran around camp and found various surfaces to measure and then compare. We pointed Chuck at brightly colored clothing, green moss, white snow, dark pools of water, and more! In measuring the reflectance of a reddish-tan granite, the graph peaked near the red point of visible light. This is the result we would have expected considering the tint of the rock. White snow matched up with our expectation of a bright and even reflectance spectrum throughout the visible light (because white is made up of all colors of light) but darker in the near infra-red (which is typical), and so our results made logical sense, which is always encouraging.
This exercise allowed us first hand experience with one of the research tools used by scientists. Allen’s research then uses this type of field data to help better interpret satellite imagery, for example. We were able to explore potential for what we could learn being able to get this data from specific locations in the field. Automatically retrieving the data also allowed us to consider and discuss the data while we were still collecting it in the field. (On another day, we used the data to calculate how much darker algae on the snow made the surface.) Aside from data collecting this was a fun activity that allowed me to understand reflectance in a clearer way then I had previously.