Vegetation growth is highly dynamic over space and time. Especially mountainous vegetation is regionally affected by climatic variability and human impacts. Tracking optical reflectance provides a unique possibility to analyze vegetation across scales from a small plot up to an extensive area. This study compares the NDVI index of grasslands across four different spatial scales during the growing period in 2017. These scales are covered by measurements from (i) ground spectrometer; (ii) station-based reflectance sensors; (iii) fixed installed Phenocam and (iv) Remote Sensing Sentinel-2 MSI images. We compared the reflectance on single points within a grassland and among different grassland sites in order to assess the strengths and weaknesses of each sensor. To this end we use multiple linear regression as well as in-situ collected biomass samples. First results show clear differences in the optical response among scales and in the detectability of management (e.g. fertilization, harvesting) activities.