THE ADVANCED DIGITAL SNOW SONDE

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1 THE ADVANCED DGTAL SNOW SONDE Osamu ABE*, Hiroo SATO**, Mitsuharu CHBA** and Shizuo TANASAWA** * Shinjo Branch of Snow and ce Studies, NED, Shinjo, Japan ** ADTEX Co. Ltd., Takasaki, Japan ABSTRACT: The advanced digital snow sonde (DSS) having four sensors was designed and tested in this study. Using the DSS three kinds of snow profiles could be obtained in a few minutes. The DSS measures snow depth from the surface, reflectivity of red light at the end of a cone, the force of the cone to penetrate the snowpack, and the alternating current electrical conductivity of the snow around the cone. The latter three profiles are displayed on an LCD and stored in a 10MB PC memory card every 0.5 mm along the snow depth. The DSS can collect as many as 150 data sets in a series. KEYWORDS: Snow gages, Snow surveys, Snow property 1. NTRODUCTON To measure the snow property quantitatively some new probes that penetrate the snowpack from the surface have been developed (Dowd and Brown, 1986; Brown & Birkeland, 1990; Abe, 1991; Sensoy & Decker, 1992). These ram-type instruments via which a snow profile can be obtained without making a snowpit are very convenient for conducting snow surveys. Recently, a new generation rammsonde which measures the optical, mechanical and electrical. properties of snow simultaneously has been developed by Abe (1998). This rammsonde was renewed for commercial use as the Digital Snow Sonde (DSS). 2. DESCRPTON OF THE DSS 2.1 An Outline The DSS consists of a probe and a controller (Figure 1). The probe and controller are connected to each other by a 3 m cable. The probe includes a cone and a rod. Three sensors are built up around the cone and a position sensor of a depth meter in the rod. The controller displays three kinds of snow profiles * Corresponding auther address: Osamu ABE, Shinjo Branch of Snow and ce Studies, NED, Shinjo, Japan; tel: ; fax: ; oabe@shinjo. bosalgo.jp on a liquid crystal display, and stores these in a 10MB PC memory card. The DSS consists of four modules as shown in Table 1; a photo meter with optical. fibers, a penetrometer, an AC conductivity meter and a depth meter. Module Photo meter Penetrometer Conductivity meter Depth meter Table 1. Modules Function Penetration force Table 2. dentifications of snow Function Reflectivity Penetration force AC Conductivity Reflectivity AC Conductivity Depth of the cone Optical reflectivity, resistance of the cone to penetrate the snowpack and AC electrical conductivity are essential properties in the process of identifying all the snow layers of the snowpack (Table 2). dentification coarse or fine(+) soft or hard(+) dry or wet(+) (+) means large number of each function. 300

2 2.3 Structure of the cone Figure 2 shows a vertical section of the cone. To measure reflectivity one end of the optical fibers is opened at the end of the cone as shown in Figure 3, the other is connected to the photometer included at the top of the probe. For AC electrical conductivity there are two ringshape electrodes with a 1 mm distance along the cone axis. A space between the two electrodes is filled by Teflon ring as an insulator. For the penetration force the rod connected to the cone shaft is contacted with a small load-cell. Probe rod Cover 1-++-i---fl4-----!+-- Cable Case 1: Power plug 2: Battery charger 3: Charge cable 4: Controller 5: Power switch 6: Fuse-holder 7: Pilot LED 8: Probe switch 9: 20 sheet keyboard 10: Monochrome LCD 19 ~ 11: Memory card unit 12: Card access LED 13: Prove cable 14: Probe 15: Remote switch 16: Logging switch 17: Rod 18: Magnet ring 19: Cone 20: Spacer Attachment --l---l-+-- Load-cell Stopper Shaft Slider Wires Cone (<>30mm) Figure 1. Schematic configuration of the DSS. 2.2 Operation Operation of the DSS is very easy, first turn on the power switch, remote switch and logging switch, then penetrate the probe through the spacer vertically onto the snowpack. A penetration rate of approximately 0.5 mls is best for detecting thin snow layers. The DSS which has a total weight of 20 kg can be carried for snow surveys. Electrodes Optical fibers Figure 2. Vertical section of the cone. As shown in Figure 3, to shine the snowpack an optical fiber of 0.5 mm in diameter is used, and to measure reflected rays from the snow particles four optical fibers each of 0.25 mm in diameter are used. 301

3 1mm 3. SPECFCATONS 3.1 Functions ~ : For reflected rays Figure 3. Bottom view of the end of the optical fibers. 2.4 Definitions of the snow properties Reflectivity, the penetration force and AC electrical conductivity of snow are defined as follows. (a) Reflectivity The reflectivity R (in percent) obtained by the optical fibers is defined by R=(,lj) X 100(%) (1 ) where r and i are the total intensities of reflected rays and incident rays. light source is 660 nm. The wavelength of the (b) Penetration force The penetration force F (in N) refers to the total resistance force of the penetrating cone within the snowpack. A rod connected to the cone is contacted with a small load-cell (see Figure 2). The cone angle is 60 degrees, that is the same angle as that of the traditional rammsonde and its maximum diameter is 30 mm."g. (Haefeli, 1954). (c) AC Electrical conductivity Electrical conductivity of snow changes with the frequency of the current because of the dielectric dispersion of snow (Langham, 1981). To eliminate the effect of the penetration rate of the cone an alternating current was used in this study. The current frequency was set to be 12 khz. The AC conductivity E is defined as the inverse of the resistance, i.e., (2) where, rs is the AC electrical resistance between two electrodes of the snow. The DSS has three modes as follows. (a) Measurement mode The DSS will be in measurement mode when the power is switched on. Then after the remote switch and logging switch have been turned on, and penetrates the probe onto snowpack. (b) Display mode Three kinds of snow profiles; reflectivity, penetration force and AC electrical conductivity of the snowpack with depth are shown on the liquid crystal display of the controller. (c) Storage mode After displaying the data, the DSS stores all data sets of 150 points on a 10MB PC memory card. The data set addressed every 0.5 mm deep is readable by a computer, and can be analyzed by software such as Excel or Lotus Basic specifications The DSS has a high frequency response to detect thin snow layers. The basic specifications of the DSS are as follows. Frequency response Penetration rate Number of data storage Operating temperature Weight ;>1 khz ; mls ; > 150 points ;>-lo C ; 20 kg in total The range and resolution of each function were determined as shown in Table 3. Table 3. Specification of the function Function (unit) Range Resolution Reflectivity (%) X10-4 Penetration force (N) X10-3 Conductivity (mq-l) X1O-s Depth (m) X

4 R (%) F (N) E (1 /kn) GRAN SHAPE DENSTY(kg m-3) E w (a) (b) (c) W#~ Figure 4. Three snow profiles measured by the DSS and the grain shape and density observed manually in a dry snow block. (a), (b) and (c) refer to the surface, boundary and bottom of the snow block, respectively. 1 mm 0<... (a) - (b) Figure 5. Snow particles ofthetwo snow layers as shown in Rgure 4. R (%) F (N) E (1 /kn) GRAN SHAPE DENSTY(kg m-3) E W o (a) o Figure 6. Three snow profiles measured by the DSS and the grain shape and density observed manually in a wet snow block. (a), (b) and (c) refer to the surface, boundary and bottom of the snow block, respectively. 4. RESULTS 4.1 Drysnow Preliminary tests of the DSS using both dry and wet snow blocks were conducted. At the same time, grain shape and the density of the snow blocks were also observed manually. A snow block which consists of two kinds of snow layers was prepared in a cold room at -10 e. The DSS detected a boundary between the two snow layers which were merged artificially as 303

5 shown in Figure 4. Symbols of the grain shape in the figure are based on the international classification for seasonal snow on the ground (lash, 1990). Reflectivity keeps large values in the upper layer of new snow, however it decreases in the lower layer which contains coarse snow particles (see Figure 5). Penetration force increases in the same snow layer. AC electrical conductivity also increases slightly. 4.2 Wetsnow Rgure 6 shows three profiles measured by the DSS for the wet snow. This snow block was formed by wet granular snow, and includes a snow layer saturated by water at the bottom. Reflectivity is very low in the wet snow, especially in the snow saturated by water. On the other hand, AC electrical conductivity increases remarkably, and the penetration force also increases with depth. Thus AC electrical conductivity is useful for identifying the wet snow layer. 5. CONCLUSONS The Digital Snow Sonde (DSS) was designed and tested in this study. The DSS can simultaneously obtain three kinds of snow profiles, Le., the optical, mechanical and electrical properties of snow. This sonde can display the three kinds of profiles on an LCD and store them in a PC memory card in the field. n this study an AC current with a frequency of 12 "~_..khi was used to eliminate the effect of the ~. penetration rate on electrical conductivity. The study demonstrates that snow layers can be identified with mutual comparison of the three profiles obtained by the DSS. The DSS will improve snow surveys and avalanche forecastings in the near future. ACKNOWLEDGMENTS We would like to express many thanksto S. to and Y. Akuzawa for their technical supports. This study was supported by the Science and Technology Agency. REFERENCES. Abe, 0., 1991: A prototype of fiber optic snow layer sonde. Seppyo, J. Jpn. Soc. Snow & ce, 53, 1-10 (in Japanese with English abstract). Abe, 0., 1998: A new generation rammsonde having multiple sensors. Report of the National Research nstitute for Earth Science and Disaster Prevention, 59 (in printing). Brown, R.L. and Birkeland, K.,1990: A comparison of the digital resistograph with the ram penetrometer. Proc. nt. Snow Sci. Workshop '90, Dowd, T. and Brown, R.L., 1986: A new instrument for determining strength profiles in snow cover. J. G/aciol., 32, Haefeli, R" 1954: Measurement of the resistance to ramming and taking of ram profiles. n Snow and its metamorphism(der schnee und seine metamorphose), Corps of Engineers, U.S. Army, Translation 14, nternational Association of Scientific Hydrology, 1990: The international classification for seasonal snow on the ground. 23pp. Langham, E.J., 1981: Physics and properties of snowcover. n Gray,D.M. and Male, D.H., eds. Handbook of snow. Pergamon Press, Ontario, Sensoy, B. and Decker, R., 1992: A fiber optic probe for indexing snowpack properties. Proc. nt. Snow Sci. Workshop'90,

A FIBER OPTIC PROBE FOR INDEXING SNOWPACK PROPERTIES. Bulent Sensoy (a) and Rand Decker (b) (a) Research Assistant, (b) Assistant Professor

A FIBER OPTIC PROBE FOR INDEXING SNOWPACK PROPERTIES Bulent Sensoy (a) and Rand Decker (b) (a) Research Assistant, (b) Assistant Professor Department of Civil Engineering University of Utah, 3220 MEB,