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Open AccessArticle

Irrigated Grassland Monitoring Using a Time Series of TerraSAR-X and COSMO-SkyMed X-Band SAR Data

IRSTEA, UMR TETIS, 500 rue François Breton, 34093 Montpellier cedex 5, France
SupAgro, UMR G-EAU, 2 place Pierre Viala, 34060 Montpellier, France
CESBIO, UMR 5126 CNES, CNRS, Université de Toulouse, IRD, 18 av. Edouard Belin, bpi 2801, 31401 Toulouse cedex 9, France
IRSTEA, UMR G-EAU, 361 rue François Breton, 34196 Montpellier cedex 5, France
INRA, UMR 1114 EMMAH, Domaine St. Paul, 84914, Avignon, France
Author to whom correspondence should be addressed.
Remote Sens. 2014, 6(10), 10002-10032;
Received: 16 June 2014 / Revised: 25 September 2014 / Accepted: 13 October 2014 / Published: 20 October 2014
PDF [6480 KB, uploaded 23 October 2014]


The objective of this study was to analyze the sensitivity of radar signals in the X-band in irrigated grassland conditions. The backscattered radar signals were analyzed according to soil moisture and vegetation parameters using linear regression models. A time series of radar (TerraSAR-X and COSMO-SkyMed) and optical (SPOT and LANDSAT) images was acquired at a high temporal frequency in 2013 over a small agricultural region in southeastern France. Ground measurements were conducted simultaneously with the satellite data acquisitions during several grassland growing cycles to monitor the evolution of the soil and vegetation characteristics. The comparison between the Normalized Difference Vegetation Index (NDVI) computed from optical images and the in situ Leaf Area Index (LAI) showed a logarithmic relationship with a greater scattering for the dates corresponding to vegetation well developed before the harvest. The correlation between the NDVI and the vegetation parameters (LAI, vegetation height, biomass, and vegetation water content) was high at the beginning of the growth cycle. This correlation became insensitive at a certain threshold corresponding to high vegetation (LAI ~2.5 m2/m2). Results showed that the radar signal depends on variations in soil moisture, with a higher sensitivity to soil moisture for biomass lower than 1 kg/m². HH and HV polarizations had approximately similar sensitivities to soil moisture. The penetration depth of the radar wave in the X-band was high, even for dense and high vegetation; flooded areas were visible in the images with higher detection potential in HH polarization than in HV polarization, even for vegetation heights reaching 1 m. Lower sensitivity was observed at the X-band between the radar signal and the vegetation parameters with very limited potential of the X-band to monitor grassland growth. These results showed that it is possible to track gravity irrigation and soil moisture variations from SAR X-band images acquired at high spatial resolution (an incidence angle near 30°). View Full-Text
Keywords: grassland; irrigation; TerraSAR-X; COSMO-SkyMed; SPOT-4; LANDSAT; soil moisture; vegetation parameters grassland; irrigation; TerraSAR-X; COSMO-SkyMed; SPOT-4; LANDSAT; soil moisture; vegetation parameters

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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MDPI and ACS Style

Hajj, M.E.; Baghdadi, N.; Belaud, G.; Zribi, M.; Cheviron, B.; Courault, D.; Hagolle, O.; Charron, F. Irrigated Grassland Monitoring Using a Time Series of TerraSAR-X and COSMO-SkyMed X-Band SAR Data. Remote Sens. 2014, 6, 10002-10032.

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