Using GPS multipath to measure soil moisture fluctuations: initial results   总被引：13，自引：2，他引：11  

Kristine M. Larson  Eric E. Small  Ethan Gutmann  Andria Bilich  Penina Axelrad  John Braun 《GPS Solutions》2008,12(3):173-177

Measurements of soil moisture are important for studies of climate and weather forecasting, flood prediction, and aquifer recharge studies. Although soil moisture measurement networks exist, most are sparsely distributed and lack standardized instrumentation. Measurements of soil moisture from satellites have extremely large spatial footprints (40–60 km). A methodology is described here that uses existing networks of continuously-operating GPS receivers to measure soil moisture fluctuations. In this technique, incoming signals are reflected off and attenuated by the ground before reception by the GPS receiver. These multipath reflections directly affect signal-to-noise ratio (SNR) data routinely collected by GPS receivers, creating amplitude variations that are a function of ground reflectivity and therefore soil moisture content. After describing this technique, multipath reflection amplitudes at a GPS site in Tashkent, Uzbekistan are compared to estimates of soil moisture from the Noah land surface model. Although the GPS multipath amplitudes and the land surface model are uncalibrated, over the 70-day period studied, they both rise sharply following each rainfall event and slowly decrease over a period of ∼10 days.  相似文献   

Estimation of flood damage functions for river basin planning: a case study in Bangladesh     

Y. C. Ethan Yang  Patrick A. Ray  Casey M. Brown  Abedalrazq F. Khalil  Winston H. Yu 《Natural Hazards》2015,75(3):2773-2791

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Sea-level rise impacts on longitudinal salinity for a low-gradient estuarine system     

Mulamba  Teddy  Bacopoulos  Peter  Kubatko  Ethan J.  Pinto  Gerard F. 《Climatic change》2019,152(3-4):533-550

Climatic Change - Salinity response to sea-level rise is evaluated for a low-gradient, tidally active estuary, the lower St. Johns River, Florida. A high-resolution numerical model is forced by...  相似文献   

Snow interception modelling: Isolated observations have led to many land surface models lacking appropriate temperature sensitivities     

Jessica D. Lundquist  Susan Dickerson-Lange  Ethan Gutmann  Tobias Jonas  Cassie Lumbrazo  Dylan Reynolds 《水文研究》2021,35(7):e14274

When formulating a hydrologic model, scientists rely on parameterizations of multiple processes based on field data, but literature review suggests that more frequently people select parameterizations that were included in pre-existing models rather than re-evaluating the underlying field experiments. Problems arise when limited field data exist, when “trusted” approaches do not get reevaluated, and when sensitivities fundamentally change in different environments. The physics and dynamics of snow interception by conifers is just such a case, and it is critical to simulation of the water budget and surface albedo. The most commonly used interception parameterization is based on data from four trees from one site, but results from this field study are not directly transferable to locations with relatively warmer winters, where the dominant processes differ dramatically. Here, we combine a literature review with model experiments to demonstrate needed improvements. Our results show that the choice of model form and parameters can vary the fraction of snow lost through interception by as much as 30%. In most simulations, the warming of mean winter temperatures from −7 to 0°C reduces the modelled fraction of snow under the canopy compared to the open, but the magnitude of simulated decrease varies from about 10% to 40%. The range of results is even larger when considering models that neglect the melting of in-canopy snow in higher-humidity environments where canopy sublimation plays less of a role. Thus, we recommend that all models represent canopy snowmelt and include representation of increased loading due to increased adhesion and cohesion when temperatures rise from −3 to 0°C. In addition to model improvements, field experiments across climates and forest types are needed to investigate how to best model the combination of dynamically changing forest cover and snow cover to better understand and predict changes to albedo and water supplies.  相似文献   

Quantification of the factors controlling the presence of excess Ar or He     

Ethan F. Baxter 《Earth and Planetary Science Letters》2003,216(4):619-634

A quantitative physical model is presented which includes the factors that control the presence, or absence, of internally derived excess ⁴⁰Ar or excess ⁴He in geological systems. In particular, the model incorporates the transport and partitioning properties of the rock surrounding the mineral of thermochronologic interest and illuminates the related effects on the amount of excess ⁴⁰Ar or ⁴He preserved in the system. Modeling of a simplified 1-D rock column bounded by an external sink for ⁴⁰Ar or ⁴He shows that a steady-state excess ⁴⁰Ar or ⁴He profile develops, the magnitude of which is determined by a system parameter called the ‘transmissive timescale’, τ_T. The characteristic time required to reach this steady state depends upon τ_T and the ‘total local sink capacity’, TLSC, wherein the important role of local matrix mineral and fluid phases is incorporated. Together, these two system parameters (τ_T and TLSC) determine the evolution of excess ⁴⁰Ar or ⁴He buildup within a system above the closure temperatures of all minerals involved. An analytical expression for the 1-D system describing the evolution of excess ⁴⁰Ar (or by analogy ⁴He) in a particular potassium-bearing (or U-Th-bearing) mineral located at a distance, L, from an external sink has been derived empirically from model results: