Evaluation of a Global Soil Moisture Product from Finer Spatial Resolution SAR Data and Ground Measurements at Irish Sites

In the framework of the European Space Agency Climate Change Initiative, a global, almost daily, soil moisture (SM) product is being developed from passive and active satellite microwave sensors, at a coarse spatial resolution. This study contributes to its validation by using finer spatial resolution ASAR Wide Swath and in situ soil moisture data taken over three sites in Ireland, from 2007 to 2009. This is the first time a comparison has been carried out between three sets of independent observations from different sensors at very different spatial resolutions for such a long time series. Furthermore, the SM spatial distribution has been investigated at the ASAR scale within each Essential Climate Variable (ECV) pixel, without adopting any particular model or using a densely distributed network of in situ stations. 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 in temperate grasslands. Temporal and spatial variability analysis provided high levels of correlation (p < 0.025) and low errors between the three datasets, leading to confidence in the new ECV SM global product, despite limitations in its ability to track the driest and wettest conditions.

[1]  Brian W. Barrett,et al.  Soil Moisture Retrieval from Active Spaceborne Microwave Observations: An Evaluation of Current Techniques , 2009, Remote. Sens..

[2]  Iliana Mladenova,et al.  Validation of the ASAR Global Monitoring Mode Soil Moisture Product Using the NAFE'05 Data Set , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[3]  Matthias Drusch,et al.  Observation operators for the direct assimilation of TRMM microwave imager retrieved soil moisture , 2005 .

[4]  W. Wagner,et al.  Soil moisture mapping in a semiarid region, based on ASAR/Wide Swath satellite data , 2014 .

[5]  W. Wagner,et al.  A Method for Estimating Soil Moisture from ERS Scatterometer and Soil Data , 1999 .

[6]  Mehrez Zribi,et al.  Operational performance of current synthetic aperture radar sensors in mapping soil surface characteristics in agricultural environments: application to hydrological and erosion modelling , 2008 .

[7]  Kamal Sarabandi,et al.  Preliminary analysis of ERS-1 SAR for forest ecosystem studies , 1992, IEEE Trans. Geosci. Remote. Sens..

[8]  T. Harter,et al.  Explaining soil moisture variability as a function of mean soil moisture: A stochastic unsaturated flow perspective , 2007 .

[9]  Albert I. J. M. van Dijk,et al.  TRMM‐TMI satellite observed soil moisture and vegetation density (1998–2005) show strong connection with El Niño in eastern Australia , 2007 .

[10]  W. Wagner,et al.  Fusion of active and passive microwave observations to create an Essential Climate Variable data record on soil moisture , 2012 .

[11]  Fabio Castelli,et al.  Mutual interaction of soil moisture state and atmospheric processes , 1996 .

[12]  J. Van doninck,et al.  Accounting for seasonality in a soil moisture change detection algorithm for ASAR Wide Swath time series , 2011 .

[13]  Günter Blöschl,et al.  Spatial correlation of soil moisture in small catchments and its relationship to dominant spatial hydrological processes , 2004 .

[14]  Emanuele Santi,et al.  A Comparison of Algorithms for Retrieving Soil Moisture from ENVISAT/ASAR Images , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[15]  David J. Goodman,et al.  Personal Communications , 1994, Mobile Communications.

[16]  A. Robock,et al.  The International Soil Moisture Network: a data hosting facility for global in situ soil moisture measurements , 2011 .

[17]  Ralf Ludwig,et al.  Derivation of surface soil moisture from ENVISAT ASAR wide swath and image mode data in agricultural areas , 2006, IEEE Transactions on Geoscience and Remote Sensing.

[18]  Malcolm Davidson,et al.  Dense Temporal Series of C- and L-band SAR Data for Soil Moisture Retrieval Over Agricultural Crops , 2011, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[19]  Yi Y. Liu,et al.  Developing an improved soil moisture dataset by blending passive and active microwave satellite-based retrievals , 2011 .

[20]  Niko E. C. Verhoest,et al.  Spatial and temporal characteristics of soil moisture in an intensively monitored agricultural field (OPE3) , 2006 .

[21]  Emanuele Santi,et al.  Comparison between SAR Soil Moisture Estimates and Hydrological Model Simulations over the Scrivia Test Site , 2013, Remote. Sens..

[22]  Jeffrey P. Walker,et al.  THE GLOBAL LAND DATA ASSIMILATION SYSTEM , 2004 .

[23]  Bojie Fu,et al.  Spatial variability of soil moisture content and its relation to environmental indices in a semi-arid gully catchment of the Loess Plateau, China , 2001 .

[24]  Fawwaz T. Ulaby,et al.  Effects of Vegetation Cover on the Radar Sensitivity to Soil Moisture , 1982, IEEE Transactions on Geoscience and Remote Sensing.

[25]  Marnik Vanclooster,et al.  Intraseasonal dynamics of soil moisture variability within a small agricultural maize cropped field , 2002 .

[26]  Jeffrey P. Walker,et al.  Upscaling sparse ground‐based soil moisture observations for the validation of coarse‐resolution satellite soil moisture products , 2012 .

[27]  Syukuro Manabe,et al.  The Influence of Soil Wetness on Near-Surface Atmospheric Variability , 1989 .

[28]  Hong Linh Truong,et al.  Potential for High Resolution Systematic Global Surface Soil Moisture Retrieval via Change Detection Using Sentinel-1 , 2012, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[29]  T. Schmugge,et al.  Passive microwave remote sensing system for soil moisture: some supporting research , 1989 .

[30]  C. Willmott,et al.  Advantages of the mean absolute error (MAE) over the root mean square error (RMSE) in assessing average model performance , 2005 .

[31]  Frédéric Baup,et al.  Radar Signatures of Sahelian Surfaces in Mali Using ENVISAT-ASAR Data , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[32]  Mehrez Zribi,et al.  Multi-scale estimation of surface moisture in a semi-arid region using ENVISAT ASAR radar data , 2010 .

[33]  Wolfgang Wagner,et al.  Using ENVISAT ASAR Global Mode Data for Surface Soil Moisture Retrieval Over Oklahoma, USA , 2009, IEEE Transactions on Geoscience and Remote Sensing.

[34]  W. Schlesinger,et al.  The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate , 1992 .

[35]  W. Wagner,et al.  Soil moisture from operational meteorological satellites , 2007 .

[36]  Gerard Kiely,et al.  Spatial variability of remotely sensed soil moisture in a temperate‐humid grassland catchment , 2012 .

[37]  R. Koster,et al.  Global Soil Moisture from Satellite Observations, Land Surface Models, and Ground Data: Implications for Data Assimilation , 2004 .

[38]  S. Seneviratne,et al.  Contrasting response of European forest and grassland energy exchange to heatwaves , 2010 .

[39]  Y. Kerr,et al.  Operational readiness of microwave remote sensing of soil moisture for hydrologic applications , 2007 .

[40]  Erwin Zehe,et al.  Effects of climate change on the coupled dynamics of water and vegetation in drylands , 2009 .

[41]  Luca Brocca,et al.  Selection of Performance Metrics for Global Soil Moisture Products: The Case of ASCAT Product , 2013 .

[42]  Richard K. Moore,et al.  Microwave Remote Sensing, Active and Passive , 1982 .

[43]  W. Wagner,et al.  Soil moisture estimation through ASCAT and AMSR-E sensors: An intercomparison and validation study across Europe , 2011 .

[44]  Wilfried Brutsaert,et al.  Hydrology: An Introduction , 2005 .

[45]  G. Vachaud,et al.  Temporal Stability of Spatially Measured Soil Water Probability Density Function , 1985 .

[46]  Günter Blöschl,et al.  On the spatial scaling of soil moisture , 1999 .

[47]  R. Grayson,et al.  Scaling of Soil Moisture: A Hydrologic Perspective , 2002 .

[48]  Yi Y. Liu,et al.  Trend-preserving blending of passive and active microwave soil moisture retrievals , 2012 .

[49]  Paul Snoeij,et al.  A Global Backscatter Model for C-Band SAR , 2010 .

[50]  P. Rosnay,et al.  Surface soil moisture estimation over the AMMA Sahelian site in Mali using ENVISAT/ASAR data , 2007 .

[51]  Dennis P. Lettenmaier,et al.  Skill in streamflow forecasts derived from large-scale estimates of soil moisture and snow , 2010 .

[52]  D. Entekhabi,et al.  Soil Moisture Active/Passive (SMAP) Mission concept , 2008, Optical Engineering + Applications.

[53]  C. Albergel,et al.  An evaluation of ASCAT surface soil moisture products with in-situ observations in Southwestern France , 2008 .

[54]  Jennifer M. Jacobs,et al.  Soil moisture variability of root zone profiles within SMEX02 remote sensing footprints , 2007 .

[55]  W. Wagner,et al.  Skill and Global Trend Analysis of Soil Moisture from Reanalyses and Microwave Remote Sensing , 2013 .

[56]  Yi Y. Liu,et al.  Error characterisation of global active and passive microwave soil moisture datasets. , 2010 .

[57]  Francesco Viola,et al.  Climate changes' effects on vegetation water stress in Mediterranean areas , 2010 .

[58]  Thomas J. Jackson,et al.  Validation of Advanced Microwave Scanning Radiometer Soil Moisture Products , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[59]  Wolfgang Wagner,et al.  Evaluation of the predicted error of the soil moisture retrieval from C-band SAR by comparison against modelled soil moisture estimates over Australia , 2012, Remote sensing of environment.

[60]  Karl Schneider,et al.  Variability of Surface Soil Moisture Observed from Multitemporal C‐Band Synthetic Aperture Radar and Field Data , 2010 .

[61]  Yann Kerr,et al.  Clarifications on the “Comparison Between SMOS, VUA, ASCAT, and ECMWF Soil Moisture Products Over Four Watersheds in U.S.” , 2014, IEEE Transactions on Geoscience and Remote Sensing.

[62]  Claudia Notarnicola,et al.  Retrieval of soil moisture variations in agricultural fields through a new Bayesian change detection approach , 2012, 2012 IEEE International Geoscience and Remote Sensing Symposium.

[63]  Klaus Scipal,et al.  Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR) , 2008, Sensors.

[64]  Ahmad Al Bitar,et al.  Comparison Between SMOS, VUA, ASCAT, and ECMWF Soil Moisture Products Over Four Watersheds in U.S. , 2014, IEEE Transactions on Geoscience and Remote Sensing.

[65]  Y. Kerr,et al.  Soil moisture and temperature profile effects on microwave emission at low frequencies , 1995 .

[66]  Thomas R. H. Holmes,et al.  An evaluation of AMSR–E derived soil moisture over Australia , 2009 .