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Focus Area on Soil Moisture Product Validation

Michael Cosh, USDA, Agricultural Research Service, USA
Carsten Montzka, Jülich Research Centre, Germany


Soil Moisture Definition

Soil moisture is expressed as soil water content (mass or volume of water in the soil) or soil water potential (soil water energy status). The volumetric soil water content is defined as the volume of the water divided by the total volume (volume of dry soil, air, and water) of a soil sample. Conversion is possible if soil properties are known. (WMO, 2008, updated 2012.)

Units: Volumetric soil water content is expressed in units of m3m-3. Additionally, degree of saturation and gravimetric are used for some products, expressed as percent and g cm-3, respectively.

Highest Validation Stage Currently Reached for Satellite-Derived Soil Moisture Products

Validation stage 3 (LPV validation stage hierarchy) - The highest LPV validation stage reached for satellite-derived Soil Moisture products. Limitations to reach higher validation stage include gaps in spatial distribution of reference data and limited representativeness of point measurements at the satellite pixel resolution.

Validation Good Practice

Currently, most recent satellite product validation plan documents serve as best references for validation of soil moisture:

SMAP mission

SMAP launch, January 31, 2015

  • SMAP - The SMAP Handbook includes a description of the Cal/Val plan.
  • ASCAT - Brocca, L., F. Melone, T. Moramarco, W. Wagner, C. Albergel
    (2014) Scaling and filtering approaches for the use of satellite
    observations, Chapter 17 in Remote Sensing of Engergy Fluxes
    and Soil Moisture Content
    , G.P. Petropoulus (Ed), CRC Press,
    Boca Raton London New York, 411-425.
  • ESA CCI Product Validation Plan
  • GCOM W (AMSR2) Validation Protocol
  • SMOS - Cal/Val Plan
    Y.H. Kerr, et al., Overview of SMOS performance in terms of
    global soil moisture monitoring after six years in operation,
    Remote Sens. of Environment, Volume 180, July 2016,
    Pages 4063.

Soil Moisture Validation Reference Data Sets

Best currently available in situ reference data for satellite-derived soil moisture product validation are provided by in situ operational networks, most of which can be found at the International Soil Moisture Network web site.

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