Abstract
During the last decade, great progress has been made by the scientific community in generating satellite-derived global surface soil moisture products, as a valuable source of information to be used in a variety of applications, such as hydrology, meteorology and climatic modeling. Through the European Space Agency Climate Change Initiative (ESA CCI), the most complete and consistent global soil moisture (SM) data record based on active and passive microwaves sensors is being developed. However, the coarse spatial resolution characterizing such data may be not sufficient to accurately represent the moisture conditions. The objective of this work is to assess the quality of the CCI Essential Climate Variable (ECV) SM product by using finer spatial resolution Advanced Synthetic Aperture Radar (ASAR) Wide Swath and in situ soil moisture data taken over three regions in Europe. Ireland, Spain, and Finland have been selected with the aim of assessing the spatial and temporal representativeness of the ECV SM product over areas that differ in climate, topography, land cover and soil type. This approach facilitated an understanding of the extent to which geophysical factors, such as soil texture, terrain composition and altitude, affect the retrieved ECV SM product values. A good temporal and spatial agreement has been observed between the three soil moisture datasets for the Irish and Spanish sites, while poorer results have been found at the Finnish sites. Overall, the two different satellite derived products capture the soil moisture temporal variations well and are in good agreement with each other.
Highlights
The amount of water stored in the soil is a key parameter for the energy and mass fluxes at the land surface-atmosphere boundary and is of fundamental importance to many agricultural, meteorological, biological and biogeochemical processes [1,2,3]
Where multiple stations were located within the same cell, i.e., in the Essential Climate Variable (ECV)-A and ECV-C, the average of the daily ground soil moisture values has been plotted
Ground measurements highlight a typical periodical variation of soil moisture, with almost dry conditions in summer and wetter soil in winter. Such seasonal variability is less evident in the ECV-D, where despite the soil moisture, reaches the lowest values in summer; quite dry conditions persist in winter, when the highest in situ SM measurements do not exceed 0.12 m3·m−3
Summary
The amount of water stored in the soil is a key parameter for the energy and mass fluxes at the land surface-atmosphere boundary and is of fundamental importance to many agricultural, meteorological, biological and biogeochemical processes [1,2,3]. For these reasons, soil moisture (SM) has been identified as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). Since the late 1970s, coarse resolution (25–50 km) soil moisture products derived from past and present microwave radiometers
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