ABSTRACT

Photosynthesis is the primary driver of all biospheric processes, the basis for life on Earth, and is a key to understanding how the carbon cycle will behave in a changing climate. Over the past four+ years, there have been several breakthroughs in our ability to detect the tiny solar-induced fluorescence signal emitted by chlorophyll in vegetation using satellites. This small signal is of interest because it is related to the instantaneous photosynthetic functioning within leaves. Spectral indices and derived vegetation parameters based on the reflectance of sunlight from vegetation, such as the Normalized Difference Vegetation Index (NDVI), are sensitive to the amount of green biomass and are related to potential photosynthesis. Together, these remotely sensed parameters tell us how plants respond to various types of stress. This knowledge is important for predicting how vegetation and the carbon cycle will respond to climate change. There are now multiple instruments in space capable of measuring fluorescence at varying temporal and spatial resolutions; they were all designed to measure gases in the atmosphere, so it was a surprise to many when they were used to measure plant fluorescence. Now that we have a data record spanning more than eight years, we can examine variations in fluorescence related to the growing season, drought and heat stress, and land-use changes. We can also examine relationships with gross and net primary productivity derived from flux tower carbon dioxide measurements and crop yield statistics. Vegetation fluorescence can be simulated in global vegetation models as well as with one dimensional canopy radiative transport models. I will show how satellite-based fluorescence data are being used to evaluate and improve these models.

About the Speaker:

Joanna Joiner received the S.B.(E.E.), S.M.(E.E.), and Ph.D.(E.E.) degrees from the Georgia Institute of Technology in 1987, 1988, and 1991, respectively. Her doctoral research concentrated on the millimeter-wave spectra of the Jovian planets and included radio astronomical observations of Jupiter. From 1991 to the present, her research at Goddard Space Flight Center has focused on the development of retrieval and data assimilation techniques for satellite Earth remote sensing instruments spanning the electromagnetic spectrum. This includes improving weather forecasts and deriving information about cloud structure using satellite data. She was part of a team that published the first global fluorescence maps from the Japanese GOSAT satellite. She is now focused on using satellite fluorescence to improve land surface models and to study the carbon cycle and vegetation phenology. She is a deputy project scientist for the EOS Aura satellite and the acting US science team leader for the Ozone Monitoring Instrument (OMI) on Aura. She is an executive and founding editor for the journal Atmospheric Measurement Techniques and has served as an associate editor for the Quarterly Journal of the Royal Meteorological Society.