Development of GPS as a Snow Sensor

0948957大型这笔拨款支持开发一项技术，利用全球定位系统卫星发射的多个频率(例如，L1、L2、L2C)对地面反射(多路径)的全球定位系统接收器信噪比天线观测，以估计全球定位系统天线附近(约50米范围内)的积雪深度和密度。拉森和他的同事已经证明了现场测量的土壤上层10厘米湿度与GPS SNR观测之间的密切关系，并得到了NSF/ATM和EAR的资助。现在，基于对位于科罗拉多州博尔德市的马歇尔板块边界天文台(PBO)GPS站的观测，Larson及其同事展示了在一次大雪事件前后不同卫星仰角下的GPS SNR频率模式的明显变化，这与基于电动力学理论的模型预测相吻合。GSP信噪比频率方向图的正演模型被用来计算天线近端的预测积雪深度，然后与现场观测进行比较，结果非常吻合。这笔赠款的支持将允许对该技术进行进一步评估并考虑误差源。具体地说，PIS将：1)开发雪对GPS数据影响的电动力学模型和估计雪水当量(SNE)的算法；2)评估美国目前使用的接收器和天线(例如，PBO GPS网络)对雪的敏感性；3)开发一个模型，在天线顶部标记被雪/冰影响破坏的GPS数据，并对这些影响进行建模，以改善火山、构造和大气研究的位置；4)提高从GPS衍生的其他水文产品的效用，如土壤水分和水文负荷；5)研制了一种低功耗、低成本的SWE测量系统。该项目涉及GPS测地仪、水文学家、雪和气候科学家以及电气工程师之间的合作。科罗拉多州将在马歇尔(NCAR)、尼沃特岭(LTER)和USFS弗雷泽实验森林开发三个雪校准点，每个都有现场积雪观测传感器和GPS站点。全球定位系统的部署将涉及联安部队设施的实地工程援助。如果事实证明GPS积雪传感器技术在现有连续运行的GPS站点广泛应用的算法是可靠的，那么更广泛的影响将包括利用现有的EarthScope PBO站点提高整个美国大陆的积雪观测密度，这将对水资源管理和气候研究产生重要影响。观测将补充现有的现场积雪观测计划(NOAAS SNOTEL)，并将为卫星上的积雪光学观测提供更多的地面真实情况。***

0948957 LarsonThis grant supports development of a technique to use GPS receiver signal to noise ratio (SNR) antenna observations of ground reflections (multipath) from multiple frequencies of GPS satellite transmissions (e.g., L1, L2, L2C) to estimate snow pack depth and perhaps density proximal to the GPS antenna (within about 50 m). Larson and colleagues have already demonstrated a tight correlation between the upper 10 cm of soil moisture as measured in situ and GPS SNR observations and have been funded by NSF/ATM and EAR for that work. Now, based on observations at the Marshall Plate Boundary Observatory (PBO) GPS station in Boulder, CO just before and just after a significant snow event, Larson and colleagues have demonstrated an obvious change in the GPS SNR frequency pattern at varying satellite elevation angles before and after a snow event that compares well with model predictions based on electrodynamic theory. Forward models of the GSP SNR frequency patterns were used to compute predicted snow depth proximal to the antenna and then compared to in situ observations with very good agreement. Support from this grant will allow for further evaluation of the technique and consideration of error sources. Specifically, the PIs will : 1) Develop an electrodynamic model of snow effects on GPS data and an algorithm to estimate snow water equivalent (SNE); 2) Evaluate the sensitivity to snow of the receivers and antennas currently used in the U.S. (e.g., PBO GPS network); 3) Develop a model to flag GPS data corrupted by snow/ice effects on top of antennas and model these effects to improve positions for volcano, tectonic and atmospheric studies; 4) Improve the utility of other hydrologic products derived from GPS, such as soil moisture and hydrologic loading; and 5) Develop a low-power and low-cost GPS system to measure SWE. The project involves collaborations between GPS geodesists, hydrologists, snow and climate scientists, and electrical engineers. Three snow calibration sites will be developed in Colorado at Marshall (NCAR), Niwot Ridge (LTER), and the USFS Fraser Experimental Forest, each with in situ snow pack observational sensors and GPS sites. The GPS deployments will involve UNAVCO Facility field engineering assistance. Should the GPS snow sensor technique prove robust for wide spread application of algorithms at existing continuously operated GPS sites the broader impacts will include improved density of snow pack observations across the continental U.S. as leveraged off existing EarthScope PBO stations with important implications to water resources management and climate studies. Observations would complement existing in situ snow pack observational programs (NOAAs SNOTEL) and would provide additional ground truth for satellite borne optical observations of snow cover. ***