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Soil moisture active and passive microwave products: Intercomparison and evaluation over a Sahelian site

Hydrology and Earth System Sciences (2010) 14(1) 141-156
DOI: 10.5194/hess-14-141-2010
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Abstract

This paper presents a comparison and an evaluation of five soil moisture products based on satellite-based passive and active microwave measurements. Products are evaluated for 2005-2006 against ground measurements obtained from the soil moisture network deployed in Mali (Sahel) in the framework of the African Monsoon Multidisciplinary Analysis project. It is shown that the accuracy of the soil moisture products is sensitive to the retrieval approach as well as to the sensor type (active or passive) and to the signal frequency (from 5.6 GHz to 18.8 GHz). The spatial patterns of surface soil moisture are compared between the different products at meso-scale (14.5° N - 17.5° N and 2° W - 1° W). A general good consistency between the different satellite soil moisture products is shown in terms of meso-scale spatial distribution, in particular after convective rainfall occurrences. Comparison to ground measurement shows that although soil moisture products obtained from satellite generally over-estimate soil moisture values during the dry season, most of them capture soil moisture temporal variations in good agreement with ground station measurements.

Figures

  • Table 1. Soil moisture ground stations used for satellite products validation.
  • Fig. 1. (a) Localisation of study area inside Mali. (b) Land cover map from Landsat mosaic, green area are homogeneous gently undulating sandy dunes covered by annual herbaceous savanna (65%), pink is flat rocky-loam plain (30%), and very dark red is clay-forested areas (5%). (c) Stations location (black squares) over the Gourma-Mali meso-scale site (grey box) and satellite soil moisture products grids. Regular grids are represented by red and green boxes for AMSR-E/NSIDC and AMSR-E/VUA-TMI/VUA respectively. For irregular grids central points of the pixels are indicated by purple and blue crosses for ERS/CETP and ERS/TUW respectively.
  • Table 2. Radiometric characteristics and spatio-temporal resolutions of each soil moisture product.
  • Fig. 2. Temporal coverage for each soil moisture product, in day by month over the Gourma window (counted when at least one pixel is available). The five soil m isture products re represen ed by color lines (ASMR-E/NSIDC, AMSR-E/VUA, TMI/VUA, ERS/CETP, ERS/TUW) and the red dotted line correspond to the data used from the ASMR-E/NSIDC product.
  • Fig. 3. Volumetric Soil Moisture (in % m3/m3) from satellite products and ground measurements at the ZAK, EKI and AGT stations and averaged at the meso-scale. Minimum and maximum value and standard deviation are calculated for the time series 2005-2006. Minimal and maximal values for ERS/TUW are from converted original indexes values as indicated in section 2.3.
  • Fig. 4. Mean relative difference (MRD) value for each satellite product. Negative values of MRD indicate that the product under-estimates soil moisture compared to the products average, while positive values indicate an over-estimation.
  • Table 3. Mean values of spatial correlations shown in Fig. 7, for the entire 2005–2006 period (left), for 2005–2006 monsoon seasons (middle) and for 2005–2006 dry seasons (right).
  • Fig. 8. Time-Latitude diagrams of the five soil moisture products (AMSR-E/NSIDC, AMSR-E/VUA, ERS/CETP, ERS/TUW, TMI/VUA) for 2005–2006, represents averaged longitude over the Gourma site [2W-1W]. For purpose of clarity a 10-day average moving window was applied in this figure.

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CITATION STYLE

APA

Gruhier, C., De Rosnay, P., Hasenauer, S., Holmes, T., De Jeu, R., Kerr, Y., … Zribi, M. (2010). Soil moisture active and passive microwave products: Intercomparison and evaluation over a Sahelian site. Hydrology and Earth System Sciences, 14(1), 141–156. https://doi.org/10.5194/hess-14-141-2010

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