<b> <i>In situ</i> measurement techniques </b> in remote sensing research over grasslands

Abstract Remote satellite observations have played a crucial role in monitoring vegetation since the 1970s, starting with the development of the Normalized Difference Vegetation Index (NDVI) by Rouse (1974) and Tucker (1979). Despite advances in satellite technology, validation with in situ measurements, which are often locally sparse, remains essential. Areas such as grasslands and wetlands, which are vital for CO 2 balance and water quality, require special attention. Within the GrasSAT project, in situ measurements were conducted in Poland and Norway, and included LAI, soil moisture, and biomass. This article focuses exclusively on in situ studies carried out in Poland, and presents results related to models operating under Polish environmental conditions, highlighting the importance of local factors in the context of comparing satellite and ground data. Different sampling methods, such as linear transect and quadrat methods, were considered. The research aimed to understand and improve the consistency between satellite and ground data, which is crucial for accurate vegetation models.