Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2002-08-05
2004-12-21
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S718000
Reexamination Certificate
active
06832522
ABSTRACT:
BACKGROUND
The predominant conventional method of measuring snow water-equivalent (SWE) is the fluid-filled snow pillow. Beaumont, R. T.,
Mt. Hood Pressure Pillow Snow Gage
, Journal of Applied Meteorology, p. 626-631, October 1965. Engeset, R. V. et al.,
Snow Pillows: Use and Evaluation
, Snow Engineering: Recent Advances and Developments, Hjorth-Hansen et al. Eds., Proceedings of the Fourth International Conference on Snow Engineering, Trondheim, Norway, pp. 45-51, 19-21 June 2000. Palmer, Peter L.,
Estimating Snow Course Water Equivalent from SNOTEL Pillow Telemetry: An Analysis of Accuracy
, Western Snow Conference, Phoenix, Ariz., Phase Profilometry, 81-86, Apr. 15-17, 1986. Smith, T. W. and H. S. Boyne,
Snow Pillow Behavior under Controlled Laboratory Conditions
, 49
th
Western Snow Conference, Colorado State University, pp. 13-22, 1981.
Other methods of determining SWE include active and passive microwave techniques and measuring the attenuation of natural gamma rays that pass through the snow cover. Osterhuber, Randall et al.,
Snowpack Snow Water Equivalent Measurement Using the Attenuation of Cosmic Gamma Radiation
, Western Snow Conference, Snowbird, Utah, April 1998. Ulaby, Fawwaz T. and William H. Stiles,
The Active and Passive Microwave Response to Snow Parameters:
2
. Water Equivalent Dry Snow
, Journal of Geophysical Research, Vol. 85, No. C2, pp. 1045-1049, Feb. 20, 1980.
The gamma and microwave methods have limited use at present and even as their use expands they will not replace ground based measurement that can measure SWE in real time. Microwave methods are generally used from satellites, thus they are limited to the period of time that the satellite is over the area of interest. Further, gamma attenuation methods require integration periods of up to four hours. A preferred embodiment of the present invention is an improvement over the microwave and gamma attenuation methods as it can be used to measure real time variations of moisture content, such as SWE, that are needed to forecast flood or landslide potential. Further, to fully appreciate the advantages of a preferred embodiment of the present invention, it is instructive to review the operation of an accepted conventional method of measuring snow water equivalent using a device termed a snow pillow.
The fluid-filled snow pillow is a bladder that is placed on the ground and subsequently filled with fluid, nominally a water-antifreeze mix. The change in pressure as snow accumulates on the bladder is used to determine SWE. The standard snow pillow is about three meters (m) (10 ft) in diameter. Smaller pillows are also used, but introduce larger measurement errors. The snow pillow was developed through a trial and error process that found that snow pillows with diameters smaller than about 3 m were subject to unexplained and inconsistent errors. The snow pillow at times may exhibit inconsistency in measurement. Even the 3 m snow pillows may provide inaccurate SWE measurements, primarily at the beginning of winter or at the transition between winter and spring. The cause of these errors was unknown until recently.
The inventors of the present invention determined that these measurement errors are caused primarily by the difference in thermal properties between the SWE detector and the soil upon which the detector is placed. A secondary influence is the mechanical property of the snow, i.e., elastic modulus and viscosity. Snow pillow measurement errors occur when snow load is shifted from the pillow to the surrounding soil through bridging or from the surrounding soil to the snow pillow. The errors may also occur because the amount of snow on the snow pillow is different than on the surrounding soil.
When thermal properties of a snow pillow, such as thermal conductivity and heat capacity, are different from the soil under and around it, the heat flux through the snow pillow will be different than through the soil. Acknowledging this fact is especially important during periods when the snow/soil interface is at the melting temperature. This difference in heat flux produces a difference in the snowmelt rate on the snow pillow compared to the surrounding soil, causing the snow load to transfer between the detector and the surrounding soil. The snow load will transfer to the snow pillow when the snowmelt rate over the pillow is less than that of the surrounding soil. The resulting error in measurement is termed an SWE over measurement. Conversely, the snow load will transfer from the snow pillow to the surrounding soil, i.e., an SWE under measurement, when the snowmelt rate over the pillow is greater than over the surrounding soil. Errors have the highest probability of occurrence in a) regions of deep snow cover, b) during unusual warming temperatures, or c) during spring.
Deep snow conditions cause the snow/soil interface to increase to the melting temperature by insulating the soil, thus reducing the conduction rate of stored heat in the soil. Warm air temperatures can produce an isothermal snow cover that is uniformly at the melting temperature, thus preventing heat from conducting from the soil, increasing the snowmelt rate at the snow/soil and snow/snow pillow interfaces. In the spring, when the snow temperature is isothermal, i.e., 0° C., or active melting is occurring, the snow/soil interface will be at the melting temperature also.
Snow pillow measurement errors caused by an actual difference in the amount of snow on the pillow compared to the surrounding soil may occur because of a difference in heat flux between the detector and soil, i.e., analogous to the process that produces snow load shifting. Measurement errors may occur in the late autumn and early winter when falling snow melts at a different rate on the soil than on a snow pillow because the heat capacity of the soil is different from that of the snow pillow. The effects of differences in heat storage in the soil and snow pillow disappear once a stable snow cover forms and steady heat flux conditions are established.
A physical theory of SWE detector performance, developed by one of the inventors, indicates that increasing the diameter of an SWE detector decreases the errors caused by differences in heat flux through the detector as compared to the soil. Johnson, J. B.,
Interim Report on the
1997-98
and
1998-99
Field Test Performance of the CRREL
-
Electronic Snow Pressure Sensor and Proposal for Sensor Redesign
, Ft. Wainwright, Ak., 1999. This is why a snow pillow must have a relatively large diameter compared to a moisture or soil stress detector of the present invention to achieve reasonable accuracy. However, increasing the detector diameter does not decrease errors caused by differences in the amount of snow melted over the detector compared to the ground.
Refer to
FIG. 7
(Prior Art) depicting the SWE measurement performance of a 3 m snow pillow for a five-year period. The solid markers indicate manually measured SWE and the dashed curve represents snow pillow measurements. The snow pillow and manual measurements have a good agreement for most of the measurement period. However periods of disagreement between manual and snow pillow measurements occur in early Winter '98. Differences are also evident during Winter/Spring '01 and spring transition periods of 1998 and 2001. In general, the snow pillow accurately measures SWE. However, during 1998-99, the snow pillow over measures SWE during the early part. This may be the result of differences in heat capacity between the snow pillow and the soil as shown in FIG.
7
A. Also, there are a number of periods when the snow pillow under measures SWE as shown in
FIG. 7D
for Winter/Spring '01.
A number of U.S. patents propose various solutions to measuring SWE. U.S. Pat. No. 3,665,180
, Method and Apparatus for Measuring the Water Content of a Snowpack
, to Gullot et al., May 23, 1972 uses two vertical tubes to locate a standard &ggr;-ray source. The source and a detector are moved simultaneously by a step-by-step motor, each step occurring after a pre-specified nu
Holmgren Jonathan Alfred
Johnson Jerome B.
Schaefer Garry L.
Baugher Jr. Earl H.
Jenkins Jermaine
Lefkowitz Edward
The United States of America as represented by the Secretary of
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