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Title:   Author  item
                                            PARINUSSA, R - Vrije Universityitem
                                            YILMAZ, M - Science Systems, Incitem
                                            Anderson, Marthaitem
                                            HAIN, C - National Oceanic & Atmospheric Administration (NOAA)item
                                            DE JEU, R.A.M. - Vrije University
  Submitted to: Hydrological Processes
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 7/9/2013
                                    Publication  Date: 8/14/2013
                                    Publication URL: http://handle.nal.usda.gov/10113/59948Citation: Parinussa, R.M., Yilmaz, M.T., Anderson, M.C., Hain, C., De Jeu, R. 2013. An intercomparison of remotely sensed soil moisture products at various spatial scales over the Iberian penisula. Journal of Hydrological Processes. 28(18):4829–4988.Interpretive Summary: Soil moisture can be mapped using satellite information in multiple wavebands.  Passive microwave observations provide direct information about soil moisture in the top few centimeters of the soil profile under both clear and cloudy sky conditions, but at relatively low spatial resolution (generally more than 20 km).  Soil moisture status can also be mapped using thermal infrared imagery, providing relatively high spatial resolution (down to 100 m) information about total rootzone moisture content, but only under clear skies.  In this paper, passive microwave and thermal infrared soil moisture retrievals were compared over the Iberian Peninsula and evaluated with in-situ soil moisture observations.  The thermal soil moisture maps served as a means for evaluating a method for downscale passive microwave retrievals to 10 km resolution.  The products compared well with each other and with ground observations, suggesting these methods provide reasonable estimates of soil moisture condition at relatively high spatial resolution.  This information is very useful for monitoring crop stress and yield affected by water availability, particularly in regions with very little ground data.
                                Technical Abstract: Soil moisture (SM) can be retrieved from active microwave (AM)-, passive microwave (PM)- and thermal infrared (TIR)-observations, each having their unique spatial- and temporal-coverage. A limitation of TIR-based SM retrievals is its dependency on cloud-free conditions, while microwave retrievals are almost all weather proof. A downside of SM retrievals from PM is its coarse spatial resolution. While SM retrievals at such spatial resolution proved to be valuable for global- and continental-scale studies, their value for regional-scale studies remains limited. To increase the use of SM retrievals from PM observations, an existing method to enhance their spatial resolution was applied. We present an inter-comparison study over the Iberian Peninsula for three SM products at two different spatial sampling grids. The products were also compared to in situ observations from the Remedhus SM monitoring network. Variations between in situ data and satellite based SM are observed, though all three remotely sensed SM product show good agreement to the ground based observations. In general the comparison between the ground- and different satellite data as well as the inter-comparison of the various satellite products is consistent. The remotely sensed SM products were inter-compared after the sampling at 25x25 km2, and after applying the Smoothing Filter based Intensity Modulation (SFIM) downscaling technique at 10x10 km2. After the application of the SFIM technique, the SM retrievals from PM observations show better agreement with the other remotely sensed SM products over the study area. Agreement between SM retrievals from PM and TIR-observations is generally high (R=0.77 for semi-arid areas); however, these values drop when transitioning to anomalies. Additional analysis revealed that this is mainly caused by the different temporal sampling of the TIR-based SM compared to the two microwave products. This study enhances our understanding of the remotely sensed SM products for improvements of SM retrieval- and merging strategies.


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