Kobayashi et al. (2026) Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Remote Sensing
• Year: 2026
• Date: 2026-04-01
• Authors: Daiki Kobayashi, Ryota Suzuki, Kosuke Noborio
• DOI: 10.3390/rs18071055

Research Groups

Information not provided in the text.

Short Summary

This study combined satellite synthetic aperture radar (SAR) and ground-based Global Navigation Satellite System (GNSS) interferometric reflectometry (GNSS-IR) to assess their sensitivities to water-level variations and rice phenology in paddy fields. It found that L-band SAR and GNSS-IR spectral peaks are sensitive to water level, while a GNSS Phenology Indicator (GPI) and SAR polarization ratio effectively track phenological stages, suggesting a consistent electromagnetic interpretation framework.

Objective

• To analyze the sensitivities of satellite synthetic aperture radar (SAR) observations and ground-based Global Navigation Satellite System (GNSS) interferometric reflectometry (GNSS-IR) to water-level variations and phenological dynamics over a paddy field.

Study Configuration

• Spatial Scale: Field scale (paddy field)
• Temporal Scale: Continuous monitoring over rice phenological progression (seasonal to multi-seasonal)

Methodology and Data

• Models used: Lomb–Scargle periodogram (LSP) analysis for GNSS-IR signal processing.
• Data sources:
  • Satellite Synthetic Aperture Radar (SAR): Sentinel-1 (C-band) and ALOS-2/PALSAR-2 (L-band) time series.
  • Ground-based Global Navigation Satellite System (GNSS) interferometric reflectometry (GNSS-IR) using geodetic-grade instrumentation.
  • In situ water level measurements (for comparison).

Main Results

• L-band SAR co-polarized backscatter (VV and HH) and the GNSS-IR spectral peak (fwater) exhibited comparable relationships with in situ water level variations.
• C-band SAR showed weaker sensitivity to water level variations compared to L-band SAR and GNSS-IR.
• The GNSS Phenology Indicator (GPI), derived from the normalized spectral integral of LSP, showed temporal behavior similar to the SAR polarization ratio (VH/VV).
• Both GPI and SAR polarization ratio demonstrated clear responses around key rice growth stages, such as heading and harvest.
• The temporal evolution of LSP spectra from GNSS-IR exhibited systematic changes with rice phenological progression, including peak broadening and the emergence of multiple peaks as vegetation developed.
• A consistent electromagnetic framework was proposed where co-polarized L-band SAR responses correspond to the water-surface-related GNSS-IR peak, and cross-polarized indicators correspond to GPI.

Contributions

• Demonstrated the potential of GNSS-IR as complementary information for physically interpreting SAR scattering mechanisms in paddy fields.
• Highlighted a pathway toward more integrated microwave-based monitoring of land surface processes, specifically for water management and phenology.
• Established a consistent electromagnetic framework for interpreting the relationship between SAR polarization-based indicators and GNSS-IR spectral characteristics.

Funding

Information not provided in the text.

Citation

@article{Kobayashi2026Separating,
  author = {Kobayashi, Daiki and Suzuki, Ryota and Noborio, Kosuke},
  title = {Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations},
  journal = {Remote Sensing},
  year = {2026},
  doi = {10.3390/rs18071055},
  url = {https://doi.org/10.3390/rs18071055}
}