Automated optical sensing of the dynamics in vegetation fluorescence, reflectance and temperature, indicative of ecosystem function and carbon assimilation

Petya Krasteva Entcheva Campbell, NASA GSFC/JCET/UMBC, petya.campbell@nasa.gov (Presenter)
Elizabeth M. Middleton, NASA GSFC, elizabeth.m.middleton@nasa.gov
Karl Fred Huemmrich, NASA GSFC/UMBC, karl.f.huemmrich@nasa.gov
Lawrence A Corp, SSAI, lawrence.a.corp@nasa.gov
Qingyuan Zhang, GESTAR/USRA, qingyuan.zhang-1@nasa.gov
Sergio Bernardes, NASA, sbernard@uga.edu
David Landis, NASA GSFC, david.landis@nasa.gov

Current remote sensing techniques rely on reflectance (R) data to estimate vegetation vigor. While R has been related most successfully to Chl content, the emission of fluorescence from plant chlorophyll provides a more direct measure of photosynthesis that has not been fully exploited by remote sensing. Optical sampling of spectral reflectance and solar induced fluorescence (SIF) provides information on the physiological status of vegetation that can be used to infer stress responses and estimates of production. However, multiple repeated observations are required to observe the effects of changing environmental conditions on vegetation, to better understand the scaling of the reflectance and fluorescence parameters.

The goals of this study are to better understand the dynamic relationships between vegetation photosynthetic function and its spectral fluorescence and reflectance properties, at different light levels and at both leaf and canopy level.

This study evaluates the use of automatically collected optical measurements (SIF and R) for monitoring the photosynthetic function of corn (Zea mays, L.). Spectral reflectance and fluorescence were collected during the summer of 2014 at the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) fields (39.03°N, 76.85°W) USDA Beltsville Agricultural Research Center, where repeated observations of carbon flux are routinely obtained.

Automated optical measurements were collected from a tower using NASA's FUSION system (description at ftp://fusionftp.gsfc.nasa.gov/FUSION/ ). The FUSION system consists of two dual channel (upward and downward looking) spectrometers used to simultaneously collect high spectral resolution measurements of reflected and fluoresced light from vegetation canopies. FUSION collections were augmented with field measurements of canopy leaf area index, leaf pigments, chemical constituents, photosynthetic function and the associated fluorescence kinetic and steady state parameters.

FUSION solar induced canopy chlorophyll fluorescence (SIF) was retrieved at the atmospheric oxygen absorption bands centered at 688 and 760 nm bands using the Fraunhofer Line Depth method.

This study will present the analysis of FUSION data for three three days representative of the corn vegetative, reproductive and senescent growth stages.

Changes in magnitude of fluorescence were clearly seen throughout the day and with viewing geometry. We observed diurnal and seasonal changes in PRI, and in both SIF685 and SIF760. The differences associated with viewing illumination and geometry were more pronounced earlier in the season and with the advancement of senescence, the variation within the data declined. SIF685 was always lower as compared SIF 760. SIF increased from cold to hot spot, within the solar principle plane. The coefficient of variation (CV) for both SIF parameters was higher in the morning and increased throughout the season. The SIF688/760 ratio increased during the season, indicating a change in the proportion of SIF red and far-red emissions.

FUSION successfully collected multi-angular, high spectral resolution reflectance and solar induced fluorescence (SIF685 and SIF 760) measurements, which are useful for characterizing the bi-directional properties, diurnal and seasonal differences in PRI, SIF685 and SIF 760. During the summer of 2014 we simultaneously observed the seasonal and diurnal changes in corn Gross Ecosystem Production (GEP) from eddy covariance, the associated canopy SIF685, SIF760, and spectral reflectance PRI and NDVI from FUSION. FUSION parameters were useful in characterizing the dynamics in vegetation productivity, and strongly associated with short term canopy CO2 fluxes. The different diurnal and seasonal trends in PRI, SIF685, SIF760 and SIF685/760 indicate that they provide different information for the vegetation canopy, and that a combination of these measurements would likely provide an improved capability for monitoring vegetation function, than any of the parameters alone. In future research we will combine the leaf and canopy measurements within the SCOPE modeling to simulate leaf and canopy level photosynthetic function and the associated reflectance and fluorescence properties. This study will be expanded to corn under nitrogen and water deficiency/excess.

Presentation: 2015_Poster_Campbell_235_224.pdf (2474k)

Presentation Type:  Poster

Session:  Theme 2: Landscapes to coasts: understanding Earth system connections   (Mon 1:30 PM)

Associated Project(s): 

• Campbell, Petya: Assessing ecosystem diversity and urban boundaries using surface reflectance and emissivity at varying spectral and spatial scales ...details

Poster Location ID: 235