Application of remote sensing techniques to discriminate between conventional and organic vineyards in the Loire Valley, France

摘要

Aim: To test the use of Remote Sensing imagery and techniques to differentiate between conventional and organic vineyards.Methods and results: Conventional and organic vineyards were identified on three satellite images acquired by the ASTER sensor of the Loire Valley. A sample of 46 conventional and 12 organic plots was used; grape varieties were Chenin Blanc (33 plots) and Cabernet Franc (25 plots). Mean reflectances were extracted from pixels inside each plot for the nine spectral bands (visible and infrared) of ASTER. A statistical discriminant analysis was performed. The vegetation index NDVI was also analysed. Results showed that all 12 organic plots, and 41 out of 46 conventional plots were correctly separated, a 91.4% success rate. Also, 23 out of 25 Cabernet, and 30 out of 33 Chenin plots were also correctly identified, also a 91.4% success rate. Regarding NDVI, there are no differences between conventional and organic vineyards within a 5% significant level. Analyses focused on the influences of chemical treatments on vineyard colors and on the effects of light reflected by inter-row spaces, suggested that both processes introduce spectral changes in conventional vineyards, mainly in short-wave infrared. Results also indicate that infrared information is essential to spectral discrimination.Conclusion: The use of chemicals, typical to conventional viticulture, has an impact on leaf composition and cell structure, being an important factor to imprint a characteristic reflectance pattern to these vineyards; the contribution to the integrated reflectance from inter-row vegetation is probably also a differentiating factor. Both causes act synergistically to build a significant spectral difference between conventional and organic vineyards.Significance and impact of the study: Remote Sensing techniques can be used as a first approach to vineyard monitoring, producing relevant information on viticultural methods, which can be used as early indicators of the need for field inspection or conventional laboratory analysis. IntroductionViticultural methods based on eco-friendly approaches have been in steady expansion in the last decades (Brodt et al 2009) and are presently regulated by several organizations, either governmental (EEC 1991; DPI 2010; USDA 2013 and references therein) or private (Ecocert, Qualité France, and others). These methods and their products carry denominations like “biological”, “organic”, or “biodynamic”; in this paper we will refer to them as “organic”. Researches on wine consumers’ preferences reveal a growing interest for organic products (Mollá-Bauzá et al 2005; Jonis et al 2008; Remaud et al 2008). However, the certification procedures are complex and, once a producer is certified, periodical checking is necessary to ensure continuity of compliance to regulations. There are no viticultural regions in the world where all vineyards are organic, and the spatial mixing of conventional and organic vine plots adds logistical problems to an already complex verification system.Certification rules are strict, precise, and fundamental for granting the organic or biodynamic status, but some preliminary information can be helpful to monitoring the current situation of vineyards, either organic or else. Specifically, this paper reports how Remote Sensing techniques can be a complementary source of information, being used as an independent indicator of viticultural methods and as an early indicator of the need for field inspection.For the purposes of this paper, we will state that the basic information from Remote Sensing is the solar radiation reflected from the terrain, and in this case, the solar spectrum is altered by the nature of reflecting objects, which can be soil, vegetation, water, and other “classes”. Specific classes have quite different reflectance spectra (Swain and Davis 1978; Lillesand and Kiefer 1987), and even within a class, sub-classes carry characteristic spectra, making reliable identifications possible. This happens, for example, with vegetation reflectance spectra, and for vineyards it was demonstrated that they can be separated from other vegetation (Da Silva and Ducati 2009), while in another study, positive identifications of grape varieties were reported (Cemin and Ducati 2011).This paper was motivated by oral reports from organic vintners in the Loire Valley, made to the first author while in field trips in the region, stating that they could see by the naked eye the color differences between their vineyards and the neighboring conventional vineyards. Presently, this paper investigates this possibility, extending the spectral range to the infrared, using Remote Sensing techniques, being focused on vineyards, either conventional or organic, in the Loire Valley.If we accept that some viticultural practices (pruning, training systems, etc) are similar for both conventional and organic vineyards, then the differences between these systems will be due, basically, to