Plants respond to changing environmental conditions with various biochemical reactions that influence the passive remote sensing signal in different domains. However, most studies in satellite EO of vegetation make use of only one single sensor. Multi-sensor or synergistic sensor use will provide a deeper insight into the relations between spectral features and associated plant conditions. This Working Group aims to help realize synergies between passive optical EO domains. As multi-sensor approaches are typically affected by associated differences in spatial and temporal characteristics and vice versa, the achievements in the closing of the scaling gap (WG1) and temporal gap (WG2) will be of fundamental importance to WG3.