A comprehensive field study of agricultural crops using remote sensing techniques

摘要

An intensive study of the spectral behavior of reflectance and absorbed Photosynthetically Active Radiation of vegetation crops, together with pigment content, Leaf Area Index (LAI), vegetation cover, plant height, and density was carried out in irrigated agricultural fields in southern Israel. Data were collected during eleven experiments conducted from December 1997 till May 1998, using two high spectral resolution spectroradiometers: a Licor LI-1800 in the range 400-1,100 nm and an ASD FieldSpec FR in the range 400-2,400 nm. Four species of wheat ("Ariel", "Ayalon", Beit-Hashita", and "Yaniv") were studied. The experiments were carried out over the course of the growing period from sowing until harvesting at one to two week intervals. The vegetation fraction changed from 0 (bare soil) to 100% (full vegetation cover) and LAI varied from 0 to 9. Reflectance of soil varied widely from 5 to 35 per cent in the red range and from 7 to 40 percent in the near infra-red range. In order to assess the information content of the data, a correlation matrix between reflectance at different wavelengths was calculated for each species. it was found that the maximal sensitivity of reflectance to vegetation density was around 550 and 700 nm and in the NIR range. The use of the green channel for monitoring vegetation status was suggested. This study is the first stage of an effort to devise robust algorithms for remote estimation of crop conditions. It introduces some new results on reflectance spectral features of crops throughout the growing season.