Spectral Profiler Probe for In Situ Snow Grain Size and Composition Stratigraphy

(NPO 47992)

Daniel Berisford1, Noah Molotch1,2,

Thomas H. Painter1,

1. NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

2. INSTAAR, University of Colorado, Boulder, CO

Copyright 2011

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.

Traditional Grain Size Measurement

http://www.comet.ucar.edu/class/hydromet/09_Oct13_1999/docs/cline/comet_snowhydro/sld038.htm

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.)

NIR Contact Spectroscopy

• Originally developed for snow pits

• Advantages– Less subjective– Repeatable– Faster– Data applicable to remote

sensingPainter et al., Journal of Glaciology 2007

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.

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

optical inspection camera

spectral reflectance probe

nylon brush

In-bore light source

Spectral Profiler Probe Hardware

Spectral Profiler Probe Hardware

fiber optic to spectrometer

base plate aluminum sleeve

drive tube

reflectance probe

clamp

2 configurations with bifurcated fiberfiber 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

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

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.

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.