1. Spectral Profiler Probe for In Situ Snow Grain Size and Composition Stratigraphy (NPO 47992) Daniel Berisford 1, Noah Molotch 1,2, Thomas H. Painter 1, 1.NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 2.INSTAAR, University of Colorado, Boulder, CO Copyright 2011

2. Traditional Grain Size Measurement Hand lens grain size estimation has been the standard for many years. This method is subject to human interpretation and can be quite inaccurate, especially when considering the existence of many different grain shapes (shown on next slide). This makes it virtually impossible to manually estimate the relative grain dimension that is applicable to longer wavelengths used by remote sensing instruments, such as spectrometers, RADAR, and passive microwave radiometers.

3. Traditional Grain Size Measurement http://www.comet.ucar.edu/class/hydromet/09_Oct13_1999/docs/cline/comet_snowhydro/sld038.htm

4. NIR Spectroscopy Fig. from Painter et al., Journal of Glaciology 2007 NIR spectroscopy can be used to infer the “optically equivalent grain size” by comparing the shape of the reflectance spectrum to an ideal spectrum of homogeneous spherical grains generated by a radiative transfer model. (Nolin and Dozier, Remote Sens. Environment, 2000; Painter et al., J. Glagiology, 2007; Stamnes et al., Applied Optics, 1988.)

5. NIR Contact Spectroscopy Originally developed for snow pits Advantages – Less subjective – Repeatable – Faster – Data applicable to remote sensing Painter et al., Journal of Glaciology 2007

6. Contact Spectroscopy Gives optical equivalent grain size. If the snow were comprised of homogeneous spherical ice grains, this is the size of grains that would give the observed spectrum. This value is most applicable to remote sensing applications, including spectroscopy, passive microwave, and active RADAR missions. obtained by integrating absorption feature at 1030nm and comparing to radiative transfer model Painter et al., 2007; Nolin and Dozier, 2000.

7. Spectral Profiler Probe Performs contact spectroscopy in-situ Sends optics down a bore hole in the snow Shines light laterally into the snow and collects reflectance spectra Fiber optic sends signal to spectrometer on surface No snowpit! Much faster and less disturbing than pit methods probe carrier body drive tube optical camera spectral reflectance probe nylon brush aluminum sleeve fiber optic to spectrometer

8. optical inspection camera spectral reflectance probe nylon brush In-bore light source Spectral Profiler Probe Hardware

9. fiber optic to spectrometer base plate aluminum sleeve drive tube reflectance probe clamp

10. 2 configurations with bifurcated fiber fiber light – uses external light source to minimize heating of the snow from the light source. In-bore light: uses light source on probe tip for brighter illumination in snow with large crystals or contamination

11. Field Testing Storm Peak Lab, Steamboat Springs, CO probe stowed for transport Niwot Ridge, CO Black tarp to block sunlight Black tarp not shown for clarity

12. Storm Peak Lab Feb 2010 results Initial results show sensitivity to grain size and ability to capture trends missed by pit-based spectroscopy. Results show slight over-prediction of grain size using in-bore light, and under- prediction using fiber light, as compared to pit contact spectroscopy. Thorough discussion and additional results will be presented in manuscript submitted Nov. 2011 for publication in Cold Regions Science and Technology.

13. Acknowledgements Prof. Michael Durand (grain size algorithm development and calculations) Jennifer Petrzelka Ty Atkins Alex Arnsten Ian McCubbin (Storm Peak Lab) Gannet Hallar (Storm Peak Lab) Part of this work was performed at the Jet Propulsion Laboratory/California Institute of Technology under contract from NASA.