Abstract
Abstract. Soil moisture plays a critical role in land surface processes and as such there has been a recent increase in the number and resolution of satellite soil moisture observations and the development of land surface process models with ever increasing resolution. Despite these developments, validation and calibration of these products has been limited because of a lack of observations on corresponding scales. A recently developed mobile soil moisture monitoring platform, known as the rover, offers opportunities to overcome this scale issue. This paper describes methods, results and testing of soil moisture estimates produced using rover surveys on a range of scales that are commensurate with model and satellite retrievals. Our investigation involved static cosmic-ray neutron sensors and rover surveys across both broad (36 × 36 km at 9 km resolution) and intensive (10 × 10 km at 1 km resolution) scales in a cropping district in the Mallee region of Victoria, Australia. We describe approaches for converting rover survey neutron counts to soil moisture and discuss the factors controlling soil moisture variability. We use independent gravimetric and modelled soil moisture estimates collected across both space and time to validate rover soil moisture products. Measurements revealed that temporal patterns in soil moisture were preserved through time and regression modelling approaches were utilised to produce time series of property-scale soil moisture which may also have applications in calibration and validation studies or local farm management. Intensive-scale rover surveys produced reliable soil moisture estimates at 1 km resolution while broad-scale surveys produced soil moisture estimates at 9 km resolution. We conclude that the multiscale soil moisture products produced in this study are well suited to future analysis of satellite soil moisture retrievals and finer-scale soil moisture models.
Highlights
Soil moisture has a strong influence on land–atmosphere interactions, hydrological processes, ecosystem functioning and agricultural productivity
Calibration of the two cosmic-ray neutron sensors (CRNSs) occurred under different soil moisture conditions; at Bennetts the depth-weighted soil moisture content was 0.13 m3 m−3, while at Bishes it was 0.08 m3 m−3
Calibration of the rover was undertaken through side-by-side comparison with the Bennetts CRNS and the Bishes CRNS on two separate occasions each
Summary
Soil moisture has a strong influence on land–atmosphere interactions, hydrological processes, ecosystem functioning and agricultural productivity The importance of this variable has led to an increase in the number and resolution of satellite soil moisture observations and the ongoing development of finer-resolution land surface process models (Ochsner et al, 2013). Satellite observations typically have resolutions in the order of 3 to 50 km, while broad-area modelling of soil moisture variability typically occurs at resolutions > 1 km The scale of these products are orders of magnitude larger than those of traditional in situ sensors, which creates an issue because of the well-documented small-scale variability in soil moisture (Vereecken et al, 2014; Western and Blöschl, 1999). Some researchers have overcome this issue by establishing soil moisture monitoring networks (Bogena et al, 2010; Smith et al, 2012), but the extent of sensor networks is still relatively small (< 1 km2)
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