Near Real-Time Polarimetric C-Band SAR Observations of Vineyards: RADARSAT-2 watching the Italian Frascati wine area
Alessandro Burini(1), Giovanni Schiavon(2) and Domenico Solimini(2)
(1) Geo-K, Via del Politecnico 1, 00133, ROME, Italy
(2) Tor Vergata University, Via del Politecnico 1, 00133, ROME, Italy
The wine industry tends to enter a renewal phase, with a particular attention devoted to monitoring the end-to-end production
process, from farming practices to cellar operations. Presently, vinification and refinement have started exploiting advanced
technologies, while vine cultivation are more often left to the tradition, with overall results still heavily dependent on human
factors and natural events. Indeed, the state of vineyards is monitored by inspections carried out by agronomists, who sample
the fields at a necessarily limited spatial and temporal rate and at an overall cost that can be fairly high.
Some wine producing countries, such as the U.S.A. (especially in California), South Africa and Australia, have introduced
optical remote sensing to support and integrate the information acquisition on the vineyards, e.g., , , given the potential
of the Earth Observation technology in providing information crucial to ameliorate wine production at relatively reduced
costs. We add that satellite observations can also play a general role in agricultural landscape management, for instance
when planning new vineyards, or when the urban expansion conflicts with vineyard conservation, affects cultivation and can
result in degradation of wine quality or even of its safeness. On their side, radar images have been used mainly for vineyard
mapping . More recently, the sensitivity of backscattering to cultivation practices has been investigated, e.g. , , also
in the attempt of identifying the contribution of grapes to the backscattering. To this end, an airborne experiment supported
and organized by ESA within the BACCHUS-DOC project, was carried out in the fall 2005 , when L-band polarimetric
and C-band dual-pol images were acquired over Frascati by the DLR E-SAR. The experiment outlined a relation between
backscattering and biophysical vine parameters, but the poor time sampling (only two flights) and the peculiar climatic
conditions did not allow to demonstrate a sensitivity of backscattering to grapes. It is worth to point out that the problem of
measuring the grape parameters by radar is made difficult by the interfering scattering contributions from the stable woody
structure of the vines, from the concrete poles and metallic wires supporting the runners, and from the soil and weed which
add to the scattering from leaves and grapes.
This contribution reports on monitoring vineyards in the Frascati, Italy, D.O.C. (Protected Designation of Origin - PDO)
area by the new polarimetric C-band RADARSAT-2 during the grape ripening and harvest period, from August to October
RADARSAT-2 Dataset and Analisys of Vineyard Images
Within the Science and Operational Applications Research (SOAR) for RADARSAT-2 Program Project 1488, the Earth
Observation Laboratory of Tor Vergata University, Rome, Italy, is now being provided with at least two fully polarimetric
images per month and benefits from their prompt delivery (from few hours to 3 days). A total of 10 polarimetric acquisitions
is scheduled between August and December 2008, with a closer time sampling during the ripening and harvest period in
September and October. Images acquired on seven dates have been received up to now. All data have been calibrated,
co-registered, geocoded and integrated into a G.I.S..
The experiment is being carried out on a test site selected in the Frascati D.O.C. area, located within an ancient volcanic
complex South Est of Rome. The observed area has an overall surface of about 10 km2 and is characterized by sparse urban
land cover mixed to agricultural fields. The slopes are generally gentle with several flat areas. Nine different vineyards have
been selected, both with rows (oriented North - South and East - West) and with the spatially homogeneous tent structure. In
addition, three forest stands, three grass parcel and four plots of arable land have been chosen in the neighborhoods of the
vineyards. These regions of interest have been selected taking into account their slope, to reduce the effects of the different
viewing and incidence angles and to achieve a satisfactory co-registration. A suitably stable estimate of the backscattering is
achieved by averaging over at least 3 hectares.
Thanks to the fully polarimetric dataset, different polarization basis are under consideration. For the time being, time
series of the difference (in dB) between the linear cross-polar backscattering coefficient sigma_hv and the linear co-polar sigma_hh
averaged over the parcel, have been plotted for each field. This backscattering ratio shows time variations up to 3 dB in the
case of vineyards. The behavior in now under investigation to possibly understand the involved effects, also with the support
of the observed ground truth. Maps of the degree of interferometric and polarimetric coherence are also being generated,
as interferometric image pairs become availble, and the space-time variation of coherence is being studied in relation to the
conditions of the observed vineyards.
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