Investigating the influence of BRDF on airborne Solar Induced Fluorescence (SIF) retrieval
Abstract
Solar induced fluorescence (SIF) is closely related to plant photosynthesis and has been used to estimate vegetation productivity and monitor plant stress (e.g., water deficit). A number of satellites now provide SIF retrievals, and the proposed European Space Agency FLEX mission is designed to monitor terrestrial photosynthesis directly from space through combined SIF and reflectance products to improve our understanding on Earth carbon cycle and vegetation health. Airborne data can help bridge the gap between ground SIF measurements and satellite products and serve as a validation for satellite data. To better interpret the SIF signal, there is a need for studies of BRDF effects on remote SIF products.
In this study, we explored the BRDF effects on airborne SIF of different species (mainly maize and soybeans). We collected airborne images using a hyperspectral imaging spectrometer with very high spectral resolution (AISA IBIS, Specim, Finland) for maize (corn) and soybeans in Nebraska during the growing seasons, 2017 and 2018. We calculated the solar zenith, solar azimuth, view zenith and view azimuth angles for each pixel using in-flight GPS and IMU data. We collected three flights (morning, mid-day and afternoon) on a single day (July 20, 2018) providing a diurnal data set with different solar and view angles. The phenology of different vegetation (maize, soybeans and winter wheat) clearly varied in our time series of SIF images. SIF images also revealed spatial patterns not readily visible in the NDVI data. The BRDF effects on SIF products of Maize and soybeans were different and varied with the vegetation growth stages. We also noticed that minor instrumental issues could be amplified in the O2A absorption band, which might confound the SIF retrieval.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B31N2677W
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0480 Remote sensing;
- BIOGEOSCIENCESDE: 1631 Land/atmosphere interactions;
- GLOBAL CHANGE