Multitemporal C-band radar measurements on wheat fields

Inst. di Radioastronomia, Consiglio Nazionale delle Ricerche, Matera, Italy
IEEE Transactions on Geoscience and Remote Sensing (Impact Factor: 2.93). 08/2003; DOI: 10.1109/TGRS.2003.813531
Source: IEEE Xplore

ABSTRACT This paper investigates the relationship between C-band backscatter measurements and wheat biomass and the underlying soil moisture content. It aims to define strategies for retrieval algorithms with a view to using satellite C-band synthetic aperture radar (SAR) data to monitor wheat growth. The study is based on a ground-based scatterometer experiment conducted on a wheat field at the Matera site in Italy during the 2001 growing season. From March to June 2001, eight C-band scatterometer acquisitions at horizontal-horizontal and vertical-vertical polarization, with incidence angles ranging from 23° to 60°, were taken. At the same time, soil moisture, wheat biomass, and canopy structure were collected. The paper describes the experiment and investigates the radar sensitivity to biophysical parameters at different polarizations and incidence angles, and at different wheat phenological stages. Based on the experimental results, the retrieval of wheat biomass and soil moisture content using Advanced Synthetic Aperture Radar data is discussed.

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    ABSTRACT: The objective of this paper is to investigate the use of HH/VV backscatter ratio, derived from data acquired by the Advanced Synthetic Aperture Radar (ASAR) system at high incidence angles (i.e. swaths I5-I7), to discriminate wheat from other crops. The wheat classification is obtained by applying an optimal threshold derived from the statistical distribution of the co-polarized backscatter ratio. The classification is firstly applied to fields monitored during the experimental campaign, then it is extended to the entire study area and compared with a classification obtained from multi-temporal SPOT images. The experimental data set consists of a temporal series of 7 ASAR AP and 3 SPOT images acquired in 2006 over an agricultural site located in the Capitanata plain, close to the Foggia town (Southern Italy). The analysis shows that it is possible to obtain classification accuracies in the wheat and non-wheat discrimination higher than 85% under two conditions: 1) ASAR AP data must be acquired during the heading phenological stage (e.g. from the end of April to end of May); 2) the HH and VV backscatter need to be estimated at field scale (corresponding to an estimated number of looks higher than 65).
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    ABSTRACT: 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°).
    Remote Sensing 01/2015; 6(10):10002-10032. DOI:10.3390/rs61010002 · 2.62 Impact Factor


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Oct 28, 2014