Solar-induced chlorophyll fluorescence (SIF) is energy emitted by photosynthesizing plants. We can use this signal to measure the forest canopy scale light reactions of photosynthesis.
We take spectral measurements of incoming and outgoing light that we use to retrieve the SIF signal.
Our SIF system was custom designed and built at Oak Ridge National Laboratory. The system automatically adjusts measurement times depending on the brightness of background conditions. It also measures broadband radiation and other meteorological variables at the same instant as the spectra. The system was beta tested at MOFLUX and has now been licensed to Campbell Scientific Inc. for commercial sales.
In this figure, you can see examples of incoming and outgoing irradiance spectra (red and blue lines, respectively). These were directly measured by our SIF system. The black line represents apparent spectral reflectance, which is the ratio of outgoing to incoming irradiance. At a wavelength of around 761 nm, there are “wells” in the irradiance spectra. We see a corresponding bump in the apparent reflectance spectrum at this wavelength where there is less solar radiation. This makes it easier to detect the small SIF signal because there is less background solar radiation.
MOFLUX 