Comparison of winter wheat NDVI data derived from Landsat 8 and active optical sensor at field scale

The Normalized Difference Vegetation Index (NDVI) is a commonly used vegetation index for a wide range of purposes. In crop production NDVI is applied, amongst others, to monitor crop status and vigour, predict yields and prescript doses of nitrogen fertilizers. The calculation of NDVI requires the reflectance in Near Infrared (NIR) and Red (RED) wavelength bands. These data may be obtained from several sources, e. g. ground sensors, unmanned aerial vehicles, airborne and satellite sensors. These sources differ not only in spatial resolution, but also in sensor design and the wavelength range, at which the NIR and RED reflectance is being registered. An important issue is, if the NDVI values derived from such different sources are comparable, or they produce similar maps. The aim of this study was to assess the relationship between NDVI derived from an active optical sensor used in the farm, and NDVI derived from Landsat 8 satellite on 7 winter wheat fields representing different regions and soils of Poland. According to the results of this study, the relationship between NDVIs from both data sources may be field and year specific, and varying for two adjacent fields on the same date. Consequently, the NDVI derived from ground and satellite sources are not directly comparable, but the NDVI maps produced from these sources are frequently similar, even for quite different days of data acquisition. The issue of a universal equation to convert ground NDVI into satellite NDVI or vice-versa is still an open-ended research question.