Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations.
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| Title: | Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations. |
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| Authors: | Kobayashi, Daiki1 (AUTHOR) dk.kobayashi@ntt.com, Suzuki, Ryusuke2 (AUTHOR), Noborio, Kosuke3 (AUTHOR) |
| Source: | Remote Sensing. Apr2026, Vol. 18 Issue 7, p1055. 21p. |
| Subjects: | Paddy fields, Water levels, Vegetation dynamics, Phenology, Global Positioning System, Synthetic aperture radar |
| Abstract: | Highlights: What are the main findings? L-band co-polarized SAR (VV, HH) corresponds to the GNSS-IR LSP peak associated with water level variations in paddy fields. The L-band SAR cross-polarized ratio (VH/VV) corresponds to the GNSS-IR LSP normalized spectral integral, capturing rice phenological dynamics. What are the implications of the main findings? GNSS-IR provides complementary vertical structural information that supports the physical interpretation of SAR scattering mechanisms. Integrating SAR and GNSS-IR enables physically consistent and high-temporal-resolution monitoring of water and vegetation dynamics. Paddy field water management and rice phenology strongly affect crop productivity and environmental processes, requiring continuous and quantitative monitoring. This study combined satellite synthetic aperture radar (SAR) observations and ground-based Global Navigation Satellite System (GNSS) interferometric reflectometry (GNSS-IR) over a paddy field to analyze their sensitivities to water-level variations and phenological dynamics. Sentinel-1 (C-band) and ALOS-2/PALSAR-2 (L-band) SAR time series were compared with continuous GNSS-IR observations acquired using geodetic-grade instrumentation. For GNSS-IR, Lomb–Scargle periodogram (LSP) analysis of SNR data was applied to derive two indicators: (i) the dominant spectral peak (fwater) frequency associated with the effective reflecting surface, and (ii) a normalized spectral integral (GNSS Phenology Indicator, GPI) representing vegetation-induced scattering and attenuation effects. The temporal evolution of LSP spectra exhibited systematic changes with rice phenological progression, including peak broadening and the emergence of multiple peaks as vegetation developed. For water level variations, L-band SAR co-polarized backscatter (VV and HH) and the GNSS-IR spectral peak exhibited comparable relationships with in situ water level, whereas C-band SAR showed weaker sensitivity. For phenological dynamics, GPI showed temporal behavior similar to that of the SAR polarization ratio (VH/VV), with clear responses around key growth stages, such as heading and harvest. These results suggest that SAR polarization-based indicators and GNSS-IR spectral characteristics can be interpreted within a consistent electromagnetic framework: co-polarized L-band SAR responses correspond to the water-surface-related GNSS-IR peak, whereas cross-polarized indicators correspond to GPI. This study demonstrated the potential of GNSS-IR as complementary information for physically interpreting SAR scattering mechanisms, highlighting a pathway toward more integrated microwave-based monitoring of land surface processes. [ABSTRACT FROM AUTHOR] |
| Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
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| Header | DbId: egs DbLabel: Engineering Source An: 192958590 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Kobayashi%2C+Daiki%22">Kobayashi, Daiki</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> dk.kobayashi@ntt.com</i><br /><searchLink fieldCode="AR" term="%22Suzuki%2C+Ryusuke%22">Suzuki, Ryusuke</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Noborio%2C+Kosuke%22">Noborio, Kosuke</searchLink><relatesTo>3</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Remote+Sensing%22">Remote Sensing</searchLink>. Apr2026, Vol. 18 Issue 7, p1055. 21p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Paddy+fields%22">Paddy fields</searchLink><br /><searchLink fieldCode="DE" term="%22Water+levels%22">Water levels</searchLink><br /><searchLink fieldCode="DE" term="%22Vegetation+dynamics%22">Vegetation dynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Phenology%22">Phenology</searchLink><br /><searchLink fieldCode="DE" term="%22Global+Positioning+System%22">Global Positioning System</searchLink><br /><searchLink fieldCode="DE" term="%22Synthetic+aperture+radar%22">Synthetic aperture radar</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Highlights: What are the main findings? L-band co-polarized SAR (VV, HH) corresponds to the GNSS-IR LSP peak associated with water level variations in paddy fields. The L-band SAR cross-polarized ratio (VH/VV) corresponds to the GNSS-IR LSP normalized spectral integral, capturing rice phenological dynamics. What are the implications of the main findings? GNSS-IR provides complementary vertical structural information that supports the physical interpretation of SAR scattering mechanisms. Integrating SAR and GNSS-IR enables physically consistent and high-temporal-resolution monitoring of water and vegetation dynamics. Paddy field water management and rice phenology strongly affect crop productivity and environmental processes, requiring continuous and quantitative monitoring. This study combined satellite synthetic aperture radar (SAR) observations and ground-based Global Navigation Satellite System (GNSS) interferometric reflectometry (GNSS-IR) over a paddy field to analyze their sensitivities to water-level variations and phenological dynamics. Sentinel-1 (C-band) and ALOS-2/PALSAR-2 (L-band) SAR time series were compared with continuous GNSS-IR observations acquired using geodetic-grade instrumentation. For GNSS-IR, Lomb–Scargle periodogram (LSP) analysis of SNR data was applied to derive two indicators: (i) the dominant spectral peak (fwater) frequency associated with the effective reflecting surface, and (ii) a normalized spectral integral (GNSS Phenology Indicator, GPI) representing vegetation-induced scattering and attenuation effects. The temporal evolution of LSP spectra exhibited systematic changes with rice phenological progression, including peak broadening and the emergence of multiple peaks as vegetation developed. For water level variations, L-band SAR co-polarized backscatter (VV and HH) and the GNSS-IR spectral peak exhibited comparable relationships with in situ water level, whereas C-band SAR showed weaker sensitivity. For phenological dynamics, GPI showed temporal behavior similar to that of the SAR polarization ratio (VH/VV), with clear responses around key growth stages, such as heading and harvest. These results suggest that SAR polarization-based indicators and GNSS-IR spectral characteristics can be interpreted within a consistent electromagnetic framework: co-polarized L-band SAR responses correspond to the water-surface-related GNSS-IR peak, whereas cross-polarized indicators correspond to GPI. This study demonstrated the potential of GNSS-IR as complementary information for physically interpreting SAR scattering mechanisms, highlighting a pathway toward more integrated microwave-based monitoring of land surface processes. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.3390/rs18071055 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 21 StartPage: 1055 Subjects: – SubjectFull: Paddy fields Type: general – SubjectFull: Water levels Type: general – SubjectFull: Vegetation dynamics Type: general – SubjectFull: Phenology Type: general – SubjectFull: Global Positioning System Type: general – SubjectFull: Synthetic aperture radar Type: general Titles: – TitleFull: Separating Water-Level Variations and Phenological Changes in Rice Paddies: Integrating SAR with Ground-Based GNSS-IR Observations. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Kobayashi, Daiki – PersonEntity: Name: NameFull: Suzuki, Ryusuke – PersonEntity: Name: NameFull: Noborio, Kosuke IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 04 Text: Apr2026 Type: published Y: 2026 Identifiers: – Type: issn-print Value: 20724292 Numbering: – Type: volume Value: 18 – Type: issue Value: 7 Titles: – TitleFull: Remote Sensing Type: main |
| ResultId | 1 |
