PhotoSpec solar-induced fluorescence and meteorological data: Soy, Iowa, 2017

Description

Eddy‐covariance (EC) data were collected at long‐term and well‐characterized USDA agricultural flux towers in C3 (soybeans, Glycine max L. Merr.) cropping systems in central Iowa. Specific sites are Brooks Field (41.974536°N, −93.693711°W). These farming systems are typical for those in the Upper Midwest corn belt (more details in Dold et al., 2017, 2019). Data were excluded under unfavorable weather conditions (e.g., rainfall, low wind turbu- lence, and high humidity) (Baker & Griffis, 2005), screened for outliers (Dold et al., 2017), and gap‐filled. Turbulent CO2 fluxes were computed using the EC method (Burba, 2013), and then net ecosystem exchange was partitioned into GPP and ecosystem respiration (Re). We installed a PhotoSpec instrument in a soybean (Brooks Field, 41.974203°N, −93.695839°W) in central Iowa following planting in late May 2017 and measured SIF until harvest in September 2017 (Magney, Frankenberg, et al., 2019). PhotoSpec consists of a 2D scanning telescope to guide reflected radiances into a set of high‐resolution spectrometers (Grossmann et al., 2018) to infer SIF using the solar Fraunhofer line in‐filling technique, similar to all current satellite retrievals. The scanning telescope was placed atop a 7‐m tower, and we calculate a "canopy average" of all viewing angles at a half-hourly time step to match the temporal resolution of flux tower data (following Magney, Frankenberg, et al., 2019). Because the scanning telescope revisits every measuring point within a half-hour, this canopy average is more representative of a hemispherical sensor with a footprint of a few meters around the tower (an average of all viewing directions). Notably, while the escape ratio and angular dependencies are an important consideration for tower‐based SIF measurements (Zeng et al., 2019), this makes little difference in our study for the canopy structure is relatively stable during the peaking growing season. More details on PhotoSpec retrievals and instrument specifications can be found in Grossmann et al. (2018) and Magney, Frankenberg, et al. (2019). Relevant publications: He, L., Magney, T., Dutta, D., Yin, Y., Köhler, P., Grossmann, K., … Frankenberg, C. (2020). From the ground to space: Using solar‐induced chlorophyll fluorescence (SIF) to estimate crop productivity. Geophysical Research Letters, 0–3. https://doi.org/10.1029/2020GL087474 Magney, T. S., Frankenberg, C., Köhler, P., North, G., Davis, T. S., Dold, C., … Porcar-Castell, A. (2019). Disentangling Changes in the Spectral Shape of Chlorophyll Fluorescence: Implications for Remote Sensing of Photosynthesis. Journal of Geophysical Research: Biogeosciences. https://doi.org/10.1029/2019JG005029 For more information or higher resolution data please contact Troy Magney: tmagney@ucdavis.edu

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