Photoproxy: The Nebraska SIF Campaign - a Multi-Scale Field Experiment
SIF – Eastern Nebraska Research and Extension Center (ENREC), Mead Nebraska
Primary Investigator, Collaborative Research, Jülich, Germany, & European Space Agency
With the advent of multiple global satellite Solar-Induced Fluorescence (SIF) products, experimental studies are needed to elucidate the factors controlling SIF emission from vegetation across temporal and spatial scales. Of particular interest is the functional link between SIF and pigment states, photosynthetic activity, and canopy structure, each of which are known to influence the SIF signal. Additional issues arise from multiple measurement approaches among the research community, which can include different instrumentation, fore-optics, measurement scales, and retrieval methods that affect the measured SIF signal, leading to uncertainty in estimates of gross primary productivity (GPP) from SIF.
To address these issues, we introduce an ongoing SIF field campaign at the University of Nebraska’s carbon sequestration research fields. The study is located at an AmeriFlux Core Site located at the Eastern Nebraska Research and Extension Center (ENREC) near Mead Nebraska. We present initial results of field experiments conducted in 2017 and 2018 over the research area. The study combines multiple automated and mobile ground-based instruments from several research institutions with airborne SIF and reflectance retrievals over irrigated and rain-fed maize and soybean fields, pastures, and shelterbelts, providing a valuable dataset for testing SIF instrumentation and methods. Initial results indicate general agreement with diurnal and seasonal GPP patterns in some cases. However, notable differences emerge between instruments, sampling scales, sampling geometry, and retrieval methods. Our research clearly indicates the importance of clearly defining SIF measurement protocols across research teams. SIF groups must work to standardize methods, normalize for stand structure and sampling protocols, and characterize sources of error and uncertainty for SIF retrievals.