An appraisal of the accuracy of operational soil moisture estimates from SMOS MIRAS using validated in situ observations acquired in a Mediterranean environment

Abstract

Acquiring information on the spatio-temporal variability of soil moisture is of key importance in extending our capability to understand the Earth system's physical processes, and is also required in many practical applications. Earth observation (EO) provides a promising avenue to observe the distribution of soil moisture at different observational scales, with a number of products distributed at present operationally. Validation of such products at a range of climate and environmental conditions across continents is a fundamental step related to their practical use. Various in situ soil moisture ground observational networks have been established globally providing suitable data for evaluating the accuracy of EO-based soil moisture products. This study aimed at evaluating the accuracy of soil moisture estimates provided from the Soil Moisture and Ocean Salinity Mission (SMOS) global operational product at test sites from the REMEDHUS International Soil Moisture Network (ISMN) in Spain. For this purpose, validated observations from in situ ground observations acquired nearly concurrent to SMOS overpass were utilized. Overall, results showed a generally reasonable agreement between the SMOS product and the in situ soil moisture measurements in the 0-5 cm soil moisture layer (root mean square error (RMSE) = 0.116 m 3 m −3 ). An improvement in product accuracy for the overall comparison was shown when days of high radio frequency interference were filtered out (RMSE = 0.110 m 3 m −3 ). Seasonal analysis showed highest agreement during autumn, followed by summer, winter, and spring seasons. A systematic soil moisture underestimation was also found for the overall comparison and during the four seasons. Overall, the result provides supportive evidence of the potential value of this operational product for meso-scale studies and practical applications.

Towards improved spatio-temporal resolution soil moisture retrievals from the synergy of SMOS and MSG SEVIRI spaceborne observations

“…It controls the partitioning of available energy at the ground surface into sensible and latent heat exchange through evaporation and transpiration processes and on the allocation of precipitation into runoff, subsurface flow and infiltration (Petropoulos, Ireland, Srivastava, & Ioannou-Katidis, 2014;GOSIC, 2015). Changes in soil moisture may also have a very serious impact on agricultural productivity, forestry, and ecosystem health.…”

Evaluation of the Soil Moisture Operational Estimates From SMOS in Europe: Results Over Diverse Ecosystems

“…SMOS's onboard instrument is the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS), which records emitted energy from the Earth's surface in the microwave L-band (1.4 GHz). It has a spatial resolution of 35-50 km and operates through a dusk-down orbit with a 3-day repeat cycle at the equator [27], [28]. The aim of the SMOS operational product has been to provide soil moisture at an accuracy better than 0.04 m 3 m −3 , which should be achievable over relatively uniform areas.…”

Investigating flash floods potential areas using ASCAT and TRMM satellites in the Western Cape Province, South Africa

“…Although this method has received notable attention, the approach does not account for the underlying hydro-meteorological conditions such as soil moisture (Petropoulos et al 2014;Srivastava et al 2014) and catchment geomorphological properties. Currently, knowledge on the utility of remote sensing technologies in identifying and mapping flash flood potential areas across Africa is still rudimentary.…”

“…In this study, we therefore assume that embracing robust, quick and efficient new cutting edge remote sensing techniques can help in understanding and monitoring flash floods variability and distribution across the South Africa. The literature portrays remote sensing technologies as capable of providing (i) a better mapping alternative, given the extensive and complex nature of catchments, especially where routine field surveys are physically impossible (Chawira et al 2013;Dube, Gumindoga, et al 2014;Dube, Mutanga, et al 2014;Petropoulos et al 2014) (ii) the method offers a practical, timely and economical means of understanding the trends of flash floods (iii) its digital format sanctions fast processing of large data volumes, whereas the repeated acquisitions offer archive data useful for the detection of changes in flash floods over time, and (iv) its digital data can be easily integrated with ancillary data in a Geographic Information System (GIS) for further analysis. Unlike remote sensing, although gauges give relatively accurate point measurements of rainfall, they are associated with sampling errors in representing the areal rainfall over large areas.…”