A) Global retrievals of fluorescence from space: GFZ

Global retrievals of fluorescence from space

Satellite-based spectrometers measuring in the 650-800 nm range with high spectral resolution and radiometric sensitivity are needed to measure (retrieve) fluorescence from space. The fundamental basis of the retrieval relies on the evaluation of the fractional depth of solar Fraunhofer lines. The fluorescence emission is a spectrally smooth signal superimposed to the solar radiation reflected and transmitted by the Earth’s surface and atmosphere. Due to the additive nature of fluorescence on the solar radiation, the fractional depth of the Fraunhofer lines in the solar spectrum decreases in the presence of fluorescence.

Spectrum of the radiation reflected by a green vegetation canopy and measured at the satellite level together with a spectrum of sun-induced chlorophyll fluorescence. The retrieval of chlorophyll fluorescence from space consists in the decoupling of the reflected radiance spectrum from the much less intense fluorescence signals. Global fluorescence retrievals have recently been achieved thanks to the high spectral and radiometric sensitivity of spaceborne atmospheric spectrometers such as GOSAT, SCIAMACHY and GOME-2 (figure by Luis Guanter).

Despite not been designed for land applications, studies by Joiner et al. and Frankenberg et al. in late 2011 demonstrated that spaceborne spectrometers can provide the necessary spectral and radiometric sensitivity for global fluorescence monitoring. Global fluorescence data sets are being derived from a number of instruments (namely, GOSAT, GOME-2, SCIAMACHY and OCO-2) since then. In GlobFluo we are contributing to the state-of-the-art of space-based fluorescence monitoring with the development of our own retrieval techniques and the production of new global data sets.