Speaker
Dr
Francesco Mattia
(CNR-ISSIA)
Description
The objective of this paper is to report on a first assessment of superficial soil moisture (SSM) products retrieved from Sentinel-1A (S-1A) data. The SSM retrieval is obtained by applying the SMOSAR algorithm [1-2], which has been devised to exploit the advanced observational capabilities of S-1 mission, particularly its frequent revisit (i.e. exact revisit with 1 satellite of 12 days & 6 days with 2 satellites). The algorithm inverts the temporal changes of radar backscatter rather than the “single-date” backscatter values, as it was usually performed on SAR data acquired by past spaceborne systems, whose revisit was too long to enable an effective time series approach. The rationale of SMOSAR is that temporal changes of surface parameters influencing the radar backscatter, apart from SSM, (e.g. soil roughness, canopy structure, vegetation water content, etc.) usually take place at longer temporal scales than SSM changes (excluding cultivation practices). Therefore, SAR time series with a sufficiently short repeat cycle are expected to track changes in SSM only, since other parameters affecting radar backscatter can be considered constant. In SMOSAR this approximation is made and this implies that the retrieval approach is extremely simplified and fast with respect to approaches based on the cumbersome inversion of scattering models depending on a large number of surface parameters. SMOSAR can be applied to bare and vegetated surfaces dominated by surface scattering as, for instance, cereal crops. This means that beforehand retrieval a masking process, obscuring those areas dominated by volume scattering, is required.
In this study, S-1A and ground data collected over the Apulian Tavoliere (southern Italy) from October 2014-onward are analyzed. The Apulian Tavoliere is the second largest plain in Italy and a crucial agricultural area, particularly for the durum wheat production. The site is in the Mediterranean semi-arid climatic zone and presents important challenges for the water management. A network of more than 40 agrometeorological stations is distributed across the plain and a high resolution X-band meteorological radar with a coverage radius of 30 km and spatial resolution of 60 m covers approximately a quarter of the area. A focus area of approximately 2x3 km2 is almost completely managed by three agricultural research Institutes, which conduct intensive crop and soil monitoring activities, with a particular emphasis on cereal crops. In this focus area, a hydrologic network, composed of 11 ground stations continuously recording soil moisture and soil temperature (at 0.025, 0.1, 0.2 and 0.4 m depths) at an average spacing of approximately 500 m has recently been set up [3].
The assessment of S-1A SSM products includes i) a comparison between SSM data retrieved and observed by the hydrologic network over almost a one-year period and ii) an analysis of SSM spatial patterns observed at regional scale over single-date and seasonal-averaged SSM maps. In addition, the error structure of SSM estimates derived from SMOSAR is discussed.
References
[1] A. Balenzano, F. Mattia, G. Satalino, M. Davidson, “Dense temporal series of C-and L-band SAR data for soil moisture retrieval over agricultural crops,” IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. vol. 4, no. 2, pp. 439-450, 2011.
[2] A. Balenzano, G. Satalino, F. Lovergine, M. Rinaldi, V. Iacobellis, N. Mastronardi, F. Mattia, “On the use of temporal series of L-and X-band SAR data for soil moisture retrieval. Capitanata plain case study,” European Jou. of Remote Sens., vol. 46, pp. 721-737, 2013.
[3] A. Balenzano et al, "A ground network for SAR-derived soil moisture product calibration, validation and exploitation in Southern Italy," Proc. of Geosci. and Remote Sens. Symp. (IGARSS), pp. 3382-3385, 2014.
Primary author
Dr
Francesco Mattia
(CNR-ISSIA)
Co-authors
Dr
Anna Balenzano
(CNR-ISSIA)
Dr
Giuseppe Satalino
(CNR-ISSIA)
