Collaborative Research: Development of GPS as a Soil Moisture Instrument

合作研究：开发 GPS 作为土壤湿度仪器

• 批准号: 0740498
• 负责人: John Braun
• 金额: $ 3.78万
• 依托单位: University Corporation For Atmospheric Res
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0740498&HistoricalAwards=false
• 关键词: Collaborative; Research; Development; GPS; Soil

NSF has supported the development of Global Positioning System (GPS) networks primarily for geophysical studies. In a broad collaboration with the international community, GPS data from these NSF-sponsored networks are freely available; they are being used for many non-geodetic applications including atmospheric and ionospheric studies. Engineering, telemetry systems, and archiving services already exist to support these continuously operating GPS networks.For this research, a technique that expands the use of existing continuously operating GPS networks to a new scientific community---the hydrologic community---will be employed. This technique uses signals that reflect off soil beneath continuously operating GPS sites. These reflections (multipath) are intrinsically related to the reflectance of the ground -- and thus soil moisture - and can be observed in GPS signal-to-noise-ratio (SNR) data. A potential advantage of this method is that it could provide an estimate of near-surface soil moisture across an area of ~100 m2 by explicitly measuring the variability of soil moisture that exists at finer scales. The PIs have compared multipath reflection amplitudes from a GPS site in Tashkent, Uzbekistan to soil moisture from a land surface model. Although the magnitudes of GPS multipath amplitudes and the land surface model soil moisture are not calibrated, they both rise sharply following each rainfall event and slowly decrease over the 70-day period studied. This research will further develop this technique and create a soil moisture calibration site near Boulder, CO. GPS receivers, antennas, and monumentation will be tested to determine which are optimal for soil moisture studies. The dependence of GPS multipath amplitudes on environmental conditions, including temperature, vegetation, soil texture, and vertical distribution of soil moisture, will be studied. Estimated reflectance coefficients will be compared with in situ measurements from volumetric sampling and water content reflectometers. Broader Impacts The research could potentially provide daily soil moisture estimates from a large number of existing geodetic GPS sites for continental to global scale climate and hydrologic studies. Soil moisture measurements are critical to study processes, test and calibrate models, and forecast availability of water resources. Although soil moisture networks exist (e.g. http://okmesonet.ocs.ou.edu/), most are still sparsely distributed; many regions in the world still lack standardized instrumentation. GPS SNR based studies could greatly increase the number of soil moisture measurements available to the hydrologic and atmospheric communities. The project will also enhance collaborations between the geodetic, atmospheric, and hydrologic communities in the U.S. These techniques could also be applied to international datasets. The geodetic techniques for this research will be developed by collaborating with hydrologists and transferred to the public domain. A graduate student will be involved in the research, working both with GPS and in situ soil moisture data.

NSF支持全球定位系统（GPS）网络的发展，主要用于地球物理研究。 在与国际社会的广泛合作中，可以免费获得这些NSF赞助网络的GPS数据；它们被用于许多非代理应用，包括大气和电离层研究。 工程，遥测系统和归档服务已经存在，可以支持这些不断运行的GPS网络。对于这项研究，将采用一种将现有的连续运行GPS网络扩展到新的科学界的技术 - 将采用水文社区。 该技术使用信号，这些信号在连续操作的GPS站点下方反射土壤。 这些反射（多径）与地面的反射率（因此是土壤水分）本质上相关，并且可以在GPS信噪比（SNR）数据中观察到。 这种方法的一个潜在优势是，它可以通过明确测量在更细的尺度上的土壤水分的可变性来提供近地表土壤水分的估计。 PI已将乌兹别克斯坦Tashkent GPS站点的多径反射幅度与土地表面模型的土壤水分进行了比较。 尽管GPS多径幅度的幅度和地表模型土壤水分的幅度未得到校准，但在每个降雨事件事件中，它们都急剧上升，并且在研究的70天期间逐渐减少。 这项研究将进一步开发该技术，并在GPS接收器，天线和纪念碑附近建立一个土壤水分校准地点，以确定哪些是最佳的土壤湿度研究。 将研究GPS多径幅度对环境条件的依赖性，包括温度，植被，土壤质地和土壤水分的垂直分布。 估计的反射率系数将与体积采样和水含量反射仪的原位测量值进行比较。更广泛的影响可能会从大量现有的大地GPS站点到全球规模的气候和水文研究，从而有可能提供每日的土壤水分水分估计值。 土壤水分测量对于研究过程，测试和校准模型以及预测水资源的可用性至关重要。 尽管存在土壤水分网络（例如http://okmesonet.ocs.ou.edu/），但大多数仍然分布稀少。世界上许多地区仍然缺乏标准化的仪器。 基于GPS SNR的研究可以大大增加可用于水文和大气群落可用的土壤水分测量的数量。 该项目还将增强美国的大地，大气和水文社区之间的合作，这些技术也可以应用于国际数据集。 这项研究的测量技术将通过与水文学家合作并转移到公共领域来开发。 研究生将参与研究，同时使用GP和原位土壤水分数据。