Development of GPS as a Snow Sensor

该资助支持开发一种技术，利用GPS接收机信噪比（SNR）天线对GPS卫星传输的多个频率（例如L1、L2、L2C）的地面反射（多径）进行观测，以估计GPS天线附近（约50米内）的积雪深度和密度。Larson和他的同事们已经证明了在原位测量的10厘米以上的土壤湿度和GPS信噪比观测之间的紧密相关性，并得到了NSF/ATM和EAR的资助。现在，基于在科罗拉多州博尔德的马歇尔板块边界观测站（PBO）的观测结果，在一次重大降雪事件发生前后，Larson和他的同事们已经证明了在降雪事件发生前后不同卫星仰角下GPS信噪比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比较。利用GSP信噪比频率方向图的正演模型计算天线附近的雪深预报，然后与现场观测结果进行比较，结果非常吻合。这笔拨款的支持将允许进一步评估技术和考虑误差来源。具体而言，pi将：1)建立基于GPS数据的雪效应电动力学模型和估算雪水当量（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)开发一个模型来标记受天线顶部冰雪影响的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GPS衍生的其他水文产品的实用性，如土壤湿度和水文负荷；5)开发低功耗、低成本的GPS系统来测量SWE。该项目涉及GPS测地线师、水文学家、雪和气候科学家以及电气工程师之间的合作。将在科罗拉多州的马歇尔（NCAR）、尼沃特岭（LTER）和USFS弗雷泽实验森林开发三个积雪校准站点，每个站点都有原位积雪观测传感器和GPS站点。全球定位系统的部署将涉及联阿援助团设施现场工程援助。如果GPS雪传感器技术在现有的连续运行的GPS站点上被证明是强大的，那么更广泛的影响将包括提高整个美国大陆的积雪观测密度，利用现有的EarthScope PBO站，对水资源管理和气候研究具有重要意义。观测将补充现有的原位积雪观测方案（noaa SNOTEL），并将为卫星运载的积雪光学观测提供额外的地面真相。＊＊＊

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. ***