Abstract
Remotely-sensed solar-induced chlorophyll fluorescence (SIF) provides a means to assess vegetation productivity in a more direct way than via the greenness of leaves. SIF is produced by plants alongside photosynthesis so it is generally thought to provide a more direct probe of plant status. We analyze inter-annual variations of SIF over the US Corn Belt using a seven-year time series (2010–2016) retrieved from measurements of short-wave IR radiation collected by the Japanese Greenhouse gases Observing SATellite (GOSAT). Using survey data and annual reports from the US Department of Agriculture (USDA) National Agricultural Statistics Service (NASS), we relate anomalies in the GOSAT SIF time series to meteorological and climatic events that affected planting or growing seasons. The events described in the USDA annual reports are confirmed using remote sensing-based data such as land surface temperature, precipitation, water storage anomalies and soil moisture. These datasets were carefully collocated with the GOSAT footprints on a sub-pixel basis to remove any effect that could occur due to different sampling. We find that cumulative SIF, integrated from April to June, tracks the planting progress established in the first half of the planting season (Pearson correlation r > 0.89). Similarly, we show that crop yields for corn (maize) and soybeans are equally well correlated to the integrated SIF from July to October (r > 0.86). Our results for SIF are consistent with reflectance-based vegetation indices, that have a longer established history of crop monitoring. Despite GOSAT’s sparse sampling, we were able to show the potential for using satellite-based SIF to study agriculturally-managed vegetation.
Highlights
The US Corn Belt is a major agricultural region and of great importance to US food security, the US livestock industry, and, through sales of agricultural products alone, contributes on the order of $134 bn to the US GDP (USDA, 2019a)
For collocation of the enhanced vegetation index (EVI), normalized differential vegetation index (NDVI), ESA CCI Land Cover, fractional vegetation cover (FVC) and leaf area index (LAI) datasets, the scenespecific gases Observing SATellite (GOSAT) footprint is fully taken into account
To show that solar-induced chlorophyll fluorescence (SIF) captures the delays in planting, we investigate US Department of Agriculture (USDA)-National Agricultural Statistics Service (NASS) survey data and compare relevant annual aggregates from the surveys with quantities derived from the SIF time series
Summary
The US Corn Belt is a major agricultural region and of great importance to US food security, the US livestock industry, and, through sales of agricultural products alone, contributes on the order of $134 bn (about a third of the US total agricultural sales) to the US GDP (USDA, 2019a). SIF is a weak radiation signal in the far-red wavelength range between 650 nm and 800 nm that is emitted by plants while they perform photosynthesis This radiance signal is directly linked to the photosynthetic apparatus of the plant and is seen as a more direct probe of carbon fixation than, for example, reflectance-based measurements; see Meroni et al (2009) for a detailed overview. Remote sensing of SIF on a global scale has been possible since the advent of hyperspectral, space-based measurements of the oxygen (O2) A-band near 760 nm. These remotely sensed data products were pioneered by Joiner et al (2011) and Frankenberg et al (2011), who showed that a global and consistent picture can be obtained from the high spectrally resolved GOSAT/TANSO-FTS instrument. We construct a multi-satellite perspective on the US Corn Belt in the 2010 to 2016 time period, focusing especially on the SIF record and its relationship to agricultural data
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