Abstract:
A ground-based system that provides quasi real-time measurement and collection of snow-water equivalent (SWE) data in remote settings is provided. The disclosed invention is significantly less expensive and easier to deploy than current methods and less susceptible to terrain and snow bridging effects. Embodiments of the invention include remote data recovery solutions. Compared to current infrastructure using existing SWE technology, the disclosed invention allows more SWE sites to be installed for similar cost and effort, in a greater variety of terrain; thus, enabling data collection at improved spatial resolutions. The invention integrates a novel computational architecture with new sensor technologies. The invention&#39;s computational architecture is based on wireless sensor networks, comprised of programmable, low-cost, low-powered nodes capable of sophisticated sensor control and remote data communication. The invention also includes measuring attenuation of electromagnetic radiation, an approach that is immune to snow bridging and significantly reduces sensor footprints.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to, claims the earliest available effective filing date(s) from (e.g., claims earliest available priority dates for other than provisional patent applications; claims benefits under 35 USC §119(e) for provisional patent applications), and incorporates by reference in its entirety all subject matter of the following listed application(s) (the “Related Applications”) to the extent such subject matter is not inconsistent herewith; the present application also claims the earliest available effective filing date(s) from, and also incorporates by reference in its entirety all subject matter of any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s) to the extent such subject matter is not inconsistent herewith.
         1. U.S. provisional patent application 61/208,654, entitled “DISTRIBUTIVE, NON-DESTRUCTIVE REAL-TIME SYSTEM AND METHOD FOR SNOWPACK MONITORING”, naming Jeff L. Frolik and Christian E. Skalka as inventors, filed 26 Feb. 2009.       

    
    
     REFERENCE TO U.S. GOVERNMENT INTEREST 
     “The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Vermont Space Grant NNG05GH16H awarded by NASA.” 
    
    
     BACKGROUND 
     1. Field of Use 
     These teachings relate generally to a system and method for snow pack monitoring and more particularly to a ground based system that provides real time measurement and collection of snow-water equivalent (SWE) data in remote settings. 
     2. Description of Prior Art (Background) 
     The importance of snow water equivalence (SWE) estimation and snowpack studies to science and society is well known. For example, snowpack studies are critical to water planning for agriculture, recreation, cities, military, etc. The importance of snowpack data is emphasized by the fact that SWE data is so fundamental to so many interests that NOAA publishes daily global SWE composites online. As suggested in the literature most snow studies are motivated by the need to estimate basin-wide runoff to provide operational forecasting for snow-affected industries or rivers subject to flooding, or to improve climate forecasting. These applications require knowledge about the spatial distribution of SWE over large spatial scales, often in basins characterized by complex terrain and heterogeneous land cover. Prior research has demonstrated that SWE exhibits extreme variability in space. This variability is a result of influences of and interactions between meteorology (wind speed and direction, radiation), topography (elevation gradients, slope and aspect), and vegetation cover. In temperate landscapes, forest vegetation exerts important controls on snow distribution through its role in intercepting snow, attenuating wind, and altering radiation at the snow surface. Therefore, to obtain accurate SWE profiles of topographically complex areas, especially mountainous terrain, good temporal and spatial resolution is needed, with techniques that are robust to the effects of vegetation cover. 
     While several approaches exist for measuring and quantitatively characterizing the spatial distribution of SWE, including manual surveys and airborne sensors, continuous, automated ground-based techniques allow for better spatial resolution, more frequent measurement, and are not affected by tree canopies. Emerging approaches exploit various technologies, including gamma ray detection and acoustics, but these are largely still in the development phase and have not been deployed remotely as continuous, unmanned stations. The most prevalent ground-based, continuous method of SWE measurement makes use of snow pillows, which measures now mass by measuring loads on liquid-filled bags (the pillow). In particular, the SNOTEL network run by the NRCS (Natural Resources Conservation Service) relies heavily on snow pillow technology. However, this method is susceptible to the phenomena of snow bridging (a gap forming between the snowpack and the ground). To mitigate (i.e., average out) the snow bridging effect, snow pillows are made large, approximately 50 to 100 square feet on average, and thus contain up to several hundred gallons of liquid, typically antifreeze. This means that snow pillows can only be installed in large, flat areas to accommodate their size, and near roads or well-established trails for transporting the apparatus. Large plate-style snow load sensors with multiple load nodes and associated analytic techniques to correct for snow bridging have been proposed to supplant snow pillows, but this technology is not yet extensively used in practice. The upshot of this is that in addition to inaccuracies due to snow bridging, predominant ground-based SWE measurement technologies do not provide effective resolution at the basin scale, due to their expense and difficulty of deployment. 
     In the SNOTEL network this is exacerbated by the general reliance on traditional data logging platforms such as the Campbell Scientific CR1000, which are heavy, expensive, and power hungry. Indeed, most long-term continuously monitoring snow stations are located in clearings, representing a biased measurement of SWE. Thus, developing a system to cost effectively collect data to improve the spatial and temporal resolution of SWE monitoring would have important impacts on both the scientific study of snow and social infrastructures dependent on snow. Furthermore, a system that is compact and portable would have the advantage of being deployable in variety of settings including those presently not observable with remote sensing technologies (e.g., snow packs under forest canopies or on sloped terrain). A low cost SWE data collection system would allow more data points to be measured, further improving spatial resolution, and would bring this technology to a broader user base. 
     In light of the above, there exists a need for a relatively inexpensive and easily deployable sensor platform that can be wirelessly networked, remotely accessed, and is robust to harsh winter environments. 
     There is also a need for a novel SWE measurement instrument suite and control algorithms suitable for integration with a relatively inexpensive and easily deployable sensor platform that can be wirelessly networked, remotely accessed, and is robust to harsh winter environments. 
     BRIEF SUMMARY 
     The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings. 
     In accordance with one embodiment of the present invention an apparatus for determining snow-water equivalence for snow pack monitoring is provided. The apparatus includes a wireless mote having a processor; random access memory (RAM); flash memory; and a communicator for wirelessly communicating. The apparatus also includes a gamma ray detector for measuring ambient gamma ray attenuation due to snowpack water content. 
     The invention is also directed towards a method for distributive snowpack monitoring. The method includes determining a snow water equivalent data package, which includes: measuring in situ snowpack temperature data at a first location; determining if the measured in situ snowpack temperature data exceeds a predetermined temperature threshold; measuring in situ snowpack height data at the first location; and determining if the measured in situ snowpack height data exceeds a predetermined height threshold. If either threshold is exceeded the method measures snowpack in situ microwave attenuation at the first location and determines if the measured snowpack in situ microwave attenuation exceeds a predetermined microwave attenuation threshold. If the microwave attenuation threshold is exceeded the method measures the snowpack in situ gamma ray attenuation at the first location. 
     In accordance with another embodiment of the present invention an apparatus for determining snow-water equivalence for snow pack monitoring is provided. The apparatus includes a wireless mote having: a processor; random access memory (RAM); flash memory unit(s); and a communicator for wirelessly communicating. The wireless mote also includes a program storage device readable by the mote, tangibly embodying a program of instructions executable by the mote to perform a method for collecting sensor data, managing power requirements, wireless transmitting sensor data, and receiving control data. The apparatus sensors include: at least one gamma ray detector for measuring ambient gamma ray attenuation; a 2.4 GHz microwave source; a 2.4 GHz microwave detector paired with the 2.4 GHz microwave source; a 5.1 GHz microwave source; and a 5.1 GHz microwave detector paired with the 5.1 GHz microwave source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is pictorial illustration of one embodiment of the present non-destructive real-time system SWE measurement apparatus in accordance with an embodiment of the present invention; 
         FIG. 2  pictorial illustration of a distributive wireless sensor network, non-destructive real-time system in accordance with the invention shown in  FIG. 1 ; 
         FIG. 3  is a graph showing gamma absorption due to a snowpack as a function of SWE in accordance with the invention shown in  FIG. 1 ; 
         FIG. 4  is a graph showing microwave attenuation due to a snowpack at different frequencies as a function of SWE in accordance with the invention shown in  FIG. 1 ; 
         FIG. 5  is a flow chart illustrating one method for power conservation for the invention shown in  FIG. 1 ; and 
         FIG. 6  is a circuit schematic illustrating one circuit for power conservation for the invention shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1  there is shown a SWE mote based computational and communications platform  10  that enables instrumentation of environments with greater temporal and spatial resolutions than are presently possible in a relatively non-intrusive manner. It will be appreciated that the SWE platform  10  shown in  FIG. 1  may be more broadly deployed for a wide range of environmental monitoring applications. 
     As used in this disclosure, the term “mote device” or “mote” ( FIG. 1 , item  104 ) typically indicates a autonomous or semi-autonomous computing, communication, actuating, and/or sensing device as described in the mote literature (e.g., Intel Corporation&#39;s, or Crossbow Inc.&#39;s mote literature). 
     Certain embodiments of the mote device(s)  104  can be fabricated to be relatively small (typically less than several inches in dimension, often a fraction of an inch). Certain embodiments of mote systems(s)  10  can also be relatively inexpensive to produce, and can be designed to stand up to relatively harsh and/or external environments. 
     Many embodiments of mote systems(s)  10 , or simply “motes”, as described in this disclosure can provide a wide variety of parameter sensing and/or actuating functionalities. Such parameter sensing may be controlled (and/or light or display devices actuated) using computer-based sensing, electro-mechanical sensing, magnetic sensing, and/or other sensing techniques. Certain embodiments of mote device(s) and networks can be located at remote, hostile, external, or inaccessible location(s); and can be wirelessly networked. 
     Motes  104  can be programmed with control algorithms for auxiliary circuitry managing activation of sources and sensors, to ensure that energy is expended in an efficient manner, and to dynamically adapt deployments to environmental conditions. 
     Still referring to  FIG. 1  there is shown a pictorial illustration of one embodiment of the present non-destructive real-time system SWE measurement apparatus  10  in accordance with an embodiment of the present invention. In  FIG. 1  there is shown a programmable mote device  104 , equipped with processor  104 A, RAM  104 B and Flash memory  104 C. Optionally, mote  104  can be augmented with external memory  104 D. Motes also have a communication device  102  capable of approximately 100 meter communication range, and can support a variety of data retrieval techniques. 
     It will be appreciated that the invention advantageously incorporates motes  104  to eliminate the wiring burdens and heavy enclosures often required of traditional data logging mechanisms, and significantly reduces power requirements. As shown in  FIG. 1 , communication device  102  may be any suitable communication device which supports other data acquisition and/or system control. The mote system ( FIG. 1 , item  10 ) establishes a standard protocol connection, for example, but not limited to, a TCP/IP connection with another mote system. (See  FIG. 2 ). This standard protocol allows an easy interface to data storage and visualization applications at the sink. Furthermore, this TCP/IP connection serves as an actuation channel, for controlling the deployment remotely at the sink, for example to modify sampling rates for power management. 
     Still referring to  FIG. 1  and  FIG. 2 , the mote network nodes (motes)  10  communicate with each other via their radio frequency (RF) antennas  102  (communicators), each with ˜100 M range, forming an on-site network  20 . It will be appreciated that any suitable mote communication protocol may be used. All the mote nodes  10  communicate their data to a distinguished node or data collector designated as the “gateway”  22  that buffers data on external storage (not shown) and can communicate data long distance to a remote location (i.e. the lab, or ultimate data sink). Communication options include radio modems and cell modems. Cell modem technology is particularly appealing since communication range is effectively unlimited for deployments in cell phone reception areas. Using any suitable modem or communication device at the deployment site and at the data sink communicating via GPRS. 
     Still referring to  FIG. 1 , the SWE measurement apparatus (SWEMA)  10  also includes a support structure  118 B, which may be any suitable support structure. The support structure  118 B supports: mote device  104 ; microwave source  106 A; optionally, a solar cell  107  for recharging SWEMA  10  power source, typically, but not limited to, one or more batteries (not shown); ultrasonic transducer  108  for measuring snow height, ambient air temperature device  110 , and gamma ray detector  112 A. 
     Still referring to  FIG. 1 , SWEMA  10  includes a vertical support structure  118 A. The vertical support structure  118 A supports microwave detectors  116 A,  116 B, and  1160 . Vertical support structure  118 A also supports snowpack temperature devices  110 A,  110 B. It will be understood any suitable number of temperature devices may be used. It will be appreciated that the vertical support structure  118 A may be any suitable calibrated or un-calibrated support structure. 
     SWEMA  10 , as shown in  FIG. 1 , includes anchoring system  114 . It will be understood that anchoring system  114  may be any suitable terrain adapted anchoring system. 
     Optionally, included with SWEMA  10  is base support  118 C. It will be understood that any suitable base support may be used and that natural ground cover may be used as base support  118 C. Base support  118 C supports a second microwave detector  106 B and a second gamma ray detector  112 B. It will be understood that the microwave sources  106 A,  106 B and microwave detectors  116 A,  1168 , and  116 C, may be any suitable microwave source and respective microwave detector. 
     It will be understood that all measurement devices, sensors, electronic devices, and power sources shown in  FIG. 1  are connected, or connectable, to mote device  104 . 
     In general, the mote device  104  can be considered a small processor-driven device that can be configured to perform a variety of functions. Many embodiments of mote device(s)  104  can include a power source, which can be configured to provide power or energy to the mote during its normal operations. Certain embodiments of mote systems(s)  10 , as described in this disclosure for example, can be configured to sense a variety of parameters, actuate a variety of other devices such as (but not limited to) turn on or off a power relay (See  FIG. 7 ). 
     Still referring to  FIG. 1  and also  FIG. 3 , there is shown a gamma ray attenuation detector  112 A,  112 E apparatus connectable to the deployed mote station. It will be appreciated that a gamma ray attenuation detector  112 A,  112 B, such as, but not limited to, a Cadmium Zinc Telluride (CZT) gamma ray detector may be used to measure water attenuation of ambient or background radiation.  FIG. 4  shows measured water attenuation of gamma energy using all energies between 100 keV to 300 keV. 
     Still referring to  FIG. 1  and also  FIG. 4 , there is shown the susceptibility of microwave radiation to snowpack accumulation having significant water content. The horizontal scale of  FIG. 4  is in days and the vertical scale is in relative attenuation in dB. It will be understood that any suitable microwave band or bands, such as a dual-band system (2.4 GHz and 5.1 GHz) may used in which signal strength is monitored at various heights. In general attenuation rates are expected to be 20-100 dB/m in these bands depending on snow properties, however measurements with large dynamic range, at various heights and at different frequencies, can be used to solve for SWE and as well as snow structure. Still referring to  FIG. 1  there is shown a microwave testing arrangement consisting of a microwave source  106 B placed on the ground support  112 B, a microwave source attached to support  118 B and at least three microwave detectors  116 A,  116 B, and  116 C attached to support  118 A. The microwave sources are operating at 2.4 GHz and at 5.1 GHz).  FIG. 4  illustrates that attenuation in both the 2.4 GHz and 5.1 GHz bands are susceptible to winter precipitation high in water content (e.g., from ice storms). 
     Data retrieval. Referring to  FIG. 2  there is shown a pictorial illustration of a distributive wireless sensor network (WSN)  20 , non-destructive real-time system in accordance with the invention shown in  FIG. 1 . As noted earlier, a mote-based platform as described herein supports a variety of data acquisition and retrieval techniques. The simplest is data logging, and subsequent retrieval over Ethernet connection with a laptop carried to the deployment site. However, off-the-shelf motes typically have only 1 MB flash memory available for data logging, which is generally not sufficient for a full season of SWE operation. It will be appreciated therefore, that the current invention employs a lightweight data muting option  22 . 
     Still referring to  FIG. 2 , for purposes of this disclosure data muling is defined as a site visitor carries a mule mote  22  with a program that automatically downloads data via a communications link  24  to the mule  22  when the mule mote  22  is in radio transceiver range of the deployed mote system  10 . This data retrieval option exploits native features of WSNs that are designed to dynamically integrate new mote nodes into their network  26 . Since the weight of a mote is negligible, this approach allows more frequent site visits. It will be understood that the mule mote  22  can be hand carried or affixed to a suitable remote controlled platform such as but not limited to unmanned aerial drones or remote terrain vehicles (not shown). It will be appreciated that the data muling option described herein can be used in practice for SWE measurements without data loss. For example, measurement data from approximately 1-hour sampling intervals over a month is suitably sized for on-mote flash memory. 
     Still referring to  FIG. 1 , it should be appreciated that the mote  10  may be suitably augmented with flash memory ( FIG. 1 ,  104 D). It will be further appreciated that the invention&#39;s low cost features of the individual stations  10  allow more stations  10  to be deployed to obtain better spatial resolution; and wireless networking  20  allow multiple sites in a given area to cooperate in routing data to a single gateway  22  for communication to the sink. Such an area can be any suitable number of acres, yielding an efficient technique for fine-grained monitoring at the basin scale. 
     Still referring to  FIG. 2 , it will also be appreciated that the mule mote or gateway node  22  can be augmented with on-site massive flash memory storage (2 GB) for buffering an entire season&#39;s worth of data, as a backup in case remote reporting via cell or radio modem fails or is not possible. 
     Still referring to  FIG. 1  and  FIG. 2 , data can also be mirrored within the WSN  20 , meaning that mode deployments  10  can cooperate to data synchronize and log data redundantly to mitigate volatility of individual mote deployments. 
     Still referring to  FIG. 1  and  FIG. 5 , where  FIG. 5  shows a flow chart illustrating one method for power conservation for the invention shown in  FIG. 1 . It will be appreciated that gamma ray detection device(s)  112 A, 112 B, such as the CZT device, is the most accurate in terms of SWE measurements and least susceptible to inclusions in the snowpack (e.g., ice lenses, air/water pockets). However, as noted, due to the gamma ray detection device power requirements it is not, in terms of power consumption, feasible for this device to be utilized continually, therefore, a feature of the invention employs a multi-parameter, multi-tiered, adaptive sampling method as shown in  FIG. 5  to optimize a balance of measurement accuracy and energy usage. The sampling of a particular sensor is conditional on previous and current values found on other sensors. In the present invention, the sensors having the least energy draw (i.e., ultrasound) are the least accurate in determining SWE (i.e., only snow pack depth is measured). However, the ultrasonic depth sensor  106 A would be capable of capturing a new snow event. Conversely, the ‘best’ SWE (i.e., CZT) also requires a relatively large amount of energy. Also, temperature sensors ( FIG. 1. 110A ,  110 B) ( FIG. 5 ,  64 ) within the snow pack may be utilized to detect melt conditions  66 . That is, these simple and low energy modalities can run at higher sampling intervals and be used to trigger subsequent sensors that would provide new information (See  FIG. 5 ). For example, should a snow fall be detected via depth change (cost of ˜5 mA) the invention will trigger a microwave measurement ( FIG. 5 ,  202 ) (cost of ˜50 mA). Should the snow fall be very dry (i.e., little water content) there will be very little variation in signal strength ( FIG. 5 ,  602 ) However, snow events high in water content will show significant changes in microwave signal strength. Such measurements will then be used to trigger a CZT or gamma ray measurement (cost of ˜500 mA) ( FIG. 5 ,  606 ). Sampling rates, change thresholds (e.g., temperature, height, attenuation) may be correlated with available power. In other words, sampling rates may be higher and/or thresholds lower if more power is available, e.g., batteries are fully charged. It will be appreciated that this multi-tiered, event-driven approach can be readily implemented upon resource-constrained motes running TinyOS. 
     Still referring to  FIG. 1  and also to  FIG. 6  there is shown a circuit schematic illustrating one circuit  700  for power conservation for the invention shown in  FIG. 1 . To efficiently regulate the power source to the required voltage levels for each component of the system, dual DC-DC buck converters  701 ,  718  are used. The buck converters  701 ,  718  convert the 12 VDCsource down to 3.3 VDC, schematically represented as power source  710 , to power the mote  703  and the Ultrasonic depth sensor, and 5 VDC to power the load cell. It will be appreciated that the converters may be any suitable converters and that the load cell may be any suitable load. If the SWEMA  10  is programmed to take readings from the sensors hourly then there is substantial time between readings when the sensors are not in use. By utilizing the output pins on the mote  104  I/O, a digital trigger on a mote can be provide a signal to switch  707  a relay  708 A, 709 A. Switching the relay  708 A, 709 A powers down the 12-to-5V buck converter  716  when the load cell  718  is not required to be in use. Another relay  704 A,  705 A also allows the Ultrasonic Load  706  to be powered down by creating an open circuit. It will be appreciated that powering down the 12 to 5V buck converter  716  and turning off the Ultrasonic sensor load  706 , conserves otherwise wasted power which is important when dealing with a remote systems and limited battery life. It will be appreciated that any suitable energy optional energy harvesting devices may be used (e.g., photovoltaic technology) (e.g.,  FIG. 1 ,  107 ) to extend battery life. 
     It should be understood that the foregoing description is only illustrative of the invention. Thus, various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.