Synthetic aperture radar polarised backscattering behaviour in partially inundated agricultural fields

ABSTRACT

A methodology for classifying rainfed paddy fields based on their hydrological conditions is lacking. This study analysed the behaviour of synthetic aperture radar (SAR) backscatter coefficients at each polarisation and cross-polarisation ratio index in a rainfed rice paddy field with a partially waterlogged surface. The SAR polarisations used were the VH and VV of the C-band SAR Sentinel-1 and the HV and HH of the L-band SAR Palsar-2. The relationship between backscatter coefficient and terrains including topographic categories and local relative elevation, which affect waterlogging conditions in rainfed paddy fields, were evaluated. The VV of C-band, and HH and HV of L-band showed different patterns in the time series variation according to the topographic categories. We observed that the combination of L-band HH and HV could be used to assess waterlogging conditions because they differ depending on variations in local elevation. The study results suggest that future studies can evaluate the microtopography and associated local hydrological environment using the combination of L-band HH and HV backscatter coefficient.

KEYWORDS:

• SAR
• backscatter coefficients
• polarisation
• soil moisture
• waterlogging
• rainfed paddy field

Acknowledgments

The authors thank the residents in the target area, university staff, and government officials who cooperated in the survey.

Disclosure statement

No potential conflict of interest was reported by the authors.

Author contributions

The first author was responsible for data analysis, construction of the theory, and the study design in detail. The second author was responsible for the field survey, data collection, and detailed information about the target area. The final author contributed to the selection of the target areas and the overall design of the study. All authors critically reviewed and revised the manuscript draft and approved the final version for submission.

Data availability statement

Sentinel-1 and −2 data are accessible free of charge from the European Space Agency website (https://scihub.copernicus.eu/). PALSAR-2 data were sold by JAXA through an external provider.

Ethical approval

This study was approved by the National Research Council of Thailand under Research Permit Project ID:2008/092.

Additional information

Funding

This study was supported by a Grant-in-Aid for Scientific Research by Japan Society for the Promotion of Science [17K02023 2017-04-01–2022-03-31].