Abstract
Abstract. The newly-developed cosmic-ray method for measuring area-average soil moisture at the hectometer horizontal scale is being implemented in the COsmic-ray Soil Moisture Observing System (or the COSMOS). The stationary cosmic-ray soil moisture probe measures the neutrons that are generated by cosmic rays within air and soil and other materials, moderated by mainly hydrogen atoms located primarily in soil water, and emitted to the atmosphere where they mix instantaneously at a scale of hundreds of meters and whose density is inversely correlated with soil moisture. The COSMOS has already deployed more than 50 of the eventual 500 cosmic-ray probes, distributed mainly in the USA, each generating a time series of average soil moisture over its horizontal footprint, with similar networks coming into existence around the world. This paper is written to serve a community need to better understand this novel method and the COSMOS project. We describe the cosmic-ray soil moisture measurement method, the instrument and its calibration, the design, data processing and dissemination used in the COSMOS project, and give example time series of soil moisture obtained from COSMOS probes.
Highlights
The total amount of water stored in soil is much less than that stored in oceans, fluxes of water into and out of soils can be large, making soil water important in the exchange of matter and energy between the solid earth and the atmosphere
The critical gap between point measurements and satellite retrievals at the intermediate scale of meters to kilometers can be filled by recently-developed methods for measuring average soil moisture along lines (Steele-Dunne et al, 2010) and over areas using either a single instrument (Larson et al, 2008; Zreda et al, 2008) or a distributed-sensor network (Bogena et al, 2010)
Building on the short articles of Zreda et al (2008) and Desilets et al (2010), this paper presents a much more comprehensive discussion of scientific background and technical details at a level that is intended to be accessible to the diverse communities interested in this novel method and the data from the COSMOS project
Summary
The total amount of water stored in soil is much less than that stored in oceans, fluxes of water into and out of soils can be large, making soil water important in the exchange of matter and energy between the solid earth and the atmosphere. Point measurements share a critical shortcoming; they are not representative of the surrounding area because soil moisture is spatially heterogeneous over a range of length scales (e.g., Western and Bloschl, 1999; Entin et al, 2000; Famiglietti et al, 2008). The critical gap between point measurements and satellite retrievals at the intermediate scale of meters to kilometers can be filled by recently-developed methods for measuring average soil moisture along lines (Steele-Dunne et al, 2010) and over areas using either a single instrument (Larson et al, 2008; Zreda et al, 2008) or a distributed-sensor network (Bogena et al, 2010). Building on the short articles of Zreda et al (2008) and Desilets et al (2010), this paper presents a much more comprehensive discussion of scientific background and technical details at a level that is intended to be accessible to the diverse communities interested in this novel method and the data from the COSMOS project
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