--------------------------------------------------------------------- DATASET OVERVIEW Dataset Title: Tower-based remote sensing data for understory vegetation at Delta Junction, Alaska 2019-2020 Investigators: Zoe Pierrat, zpierrat@g.ucla.edu, ORCID: 0000-0002-6726-2406, Troy Magney, tmagney@ucdavis.edu, ORCID: 0000-0002-9033-0024, Jochen Stutz, jochen@atmos.ucla.edu, ORCID: 0000-0001-6368-7629 Point of Contact: Zoe Pierrat, zpierrat@g.ucla.edu, University of California Los Angeles Summary: Data includes remote sensing products from PhotoSpec (a scanning spectrometer) from August 2019-December 2020. We provide daily averaged vegetation indices for a mix of understory lichen and moss species in a black spruce dominated forest. We compute near-infrared vegetation index (NIRv), normalized difference vegetation index (NDVI), photochemical reflectance index (PRI), and chlorophyll-carotenoid index (CCI) averaged for three understory targets at NEON Delta Junction. We also provide daily averaged photosynthetically active radiation (PAR) and solar zenith angle (SZA). Finally, we provide the average diurnal profiles of all the aforementioned metrics for 4 20-day windows in winter, spring, summer, and fall. Keywords: remote-sensing, vegetation reflectance, tundra ecosystems, timeseries, diurnal dynamics Acknowledgments: Earth Science Division grant numbers 80NSSC17K0108 and 80NSSC17K0110. ABoVE grant number 80NSSC19M0130. National Science Foundation Graduate Research Fellowship under Grant No. DGE-1650604 and DGE-2034835 Related Publication: Nelson, P., Maguire, A., Pierrat, Z., Orcutt, E., Yang, D., Serbin, S., Frost, G., Macander, M., Magney, T., Thompson, D., Wang, J., Oberbauer, S., Vargas Zesati, S., Davidson, S., Epstein, H., Unger, S., Campbell, P., Carmon, N., Velez,-Reyes, M., Huemmrigh, F. Remote Sensing of Tundra Ecosystems using High Spectral Resolution Reflectance: Issues and Opportunities. Journal of Geophysical Research: Biogeosciences. --------------------------------------------------------------------- DATASET CHARACTERISTICS Spatial Resolution: Instrument field of view is 0.7 degrees atop a 22m tower, resulting in a ground-instantaneous field-of view ~30-40 cm in diameter for the three understory targets. Temporal Resolution: PhotoSpec target measurements are made approximately every 20 seconds, and the revisit time for each understory target is approximately 1 hour so that all three understory targets are retrieved within the hour. For the timeseries data, we report daily averages which are calculated as the average of all three targets over the course of the day with SZA < 90. We also report hourly diurnal averages over 4 20-day time periods in winter, spring, summer, and fall. Temporal Coverage: 2019-Aug-22 to 2020-Dec-31 File Descriptions: JGRB_Tundra_Spec_Timeseries_Fig7.csv, JGRB_Tundra_Spec_Diurnals_Fig7.csv Data Dictionary for JGRB_Tundra_Spec_Timeseries_Fig7.csv: Time, Day of averaged measurements NDVI, daily average normalized difference vegetation index, unitless NDVI_STD, standard deviation of the diurnal variability in NDVI, unitless NIRv, daily average near-infrared reflectance from vegetation, unitless NIRv_STD, standard deviation of the diurnal variability in NIRv, unitless PRI, daily average photochemical reflectance index, unitless PRI_STD, standard deviation of the diurnal variability in PRI, unitless CCI, daily average chlorophyll-carotenoid index, unitless CCI_STD, standard deviation of the diurnal variability in CCI, unitless PAR, daily average photosynthetically active radiation in [micromol m^-2 s^-1] PAR_STD, standard deviation of the diurnal variability in PAR, [micromol m^-2 s^-1] SZA, daily average solar zenith angle SZA_STD, standard deviation of the diurnal variability in SZA Data Dictionary for JGRB_Tundra_Spec_Diurnals_Fig8.csv: Season_Flag, Indicator for the 20-day period for data collection, 1: Dec 1-20, 2: Mar 1-20, 3: Jul 1-20, 4: Sep 1-20 Hour, hour averaged over the 20-day period NDVI, hourly average normalized difference vegetation index over the 20-day period, unitless NDVI_STD, hourly standard deviation of NDVI over the 20-day period, unitless NIRv, hourly average near-infrared reflectance from vegetation over the 20-day period, unitless NIRv_STD, hourly standard deviation of NIRv over the 20-day period, unitless PRI, hourly average photochemical reflectance index over the 20-day period, unitless PRI_STD, hourly standard deviation of PRI over the 20-day period, unitless CCI, hourly average chlorophyll-carotenoid index over the 20-day period, unitless CCI_STD, hourly standard deviation of CCI over the 20-day period, unitless PAR, hourly average photosynthetically active radiation over the 20-day period in [micromol m^-2 s^-1] PAR_STD, hourly standard deviation of PAR over the 20-day period, [micromol m^-2 s^-1] SZA, hourly average solar zenith angle over the 20-day period SZA_STD, hourly standard deviation of SZA over the 20-day period --------------------------------------------------------------------- APPLICATION & DERIVATION Data is used to understand challenges and opportunities for remote sensing of tundra ecosystems --------------------------------------------------------------------- QUALITY ASSESSMENT Estimate of Uncertainty: Data is reported as daily averages and uncertainty is estimated as the standard deviation of the diurnal variability of measurements. The standard deviation of the diurnal variability is significantly higher than the measurement uncertainty. Additional details of measurement uncertainty can be found in Grossmann, K., Frankenberg, C., Magney, T. S., Hurlock, S. C., Seibt, U., & Stutz, J. (2018). PhotoSpec: A new instrument to measure spatially distributed red and far-red Solar-Induced Chlorophyll Fluorescence. Remote Sensing of Environment, 216(November 2017), 311–327. https://doi.org/10.1016/j.rse.2018.07.002 --------------------------------------------------------------------- DATA ACQUISITION, MATERIALS & METHODS Delta Junction (DEJU) is a terrestrial NEON field site located in central Alaska, approximately 150 km (93 mi.) southeast of Fairbanks and 15 km (9 mi.) south of the community of Delta Junction. The 29.9 km2 (7390 acre) site is managed by the U.S. Bureau of Land Management. It sits within the Tanana Valley at an elevation of 440 - 485 m (1400 - 1600 ft.), 30 km (18 mi.) from the confluence of the Tanana and Delta Rivers. The location is bordered to the north by the White Mountains, to the southeast by the Granite Mountains, and to the southwest by the Alaska Range. DEJU is one of the four sites (three terrestrial and one aquatic) located in the NEON Taiga Domain (D19), which comprises Alaska’s interior and the Alaska Peninsula. Field Site Latitude/Longitude 63.88112, -145.75136 https://www.neonscience.org/field-sites/deju We collected co-located remotely sensed products (NDVI, NIRv, PRI, CCI) as well as PAR and SZA using PhotoSpec (see Grossmann et al. (2018) for detailed instrument description) from August 2019 to December 2020. PhotoSpec was installed at the top of the 22m scaffolding tower facing due north. It has a narrow field of view (0.7 degrees) and a 2-D scanning capability which permits independent measurements of three understory targets consisting of a mix of lichen and moss species. All three targets are measured within a scan strategy that repeats on a 1 hour loop. Instruments: PhotoSpec --------------------------------------------------------------------- REFERENCES: Nelson, P., Maguire, A., Pierrat, Z., Orcutt, E., Yang, D., Serbin, S., Frost, G., Macander, M., Magney, T., Thompson, D., Wang, J., Oberbauer, S., Vargas Zesati, S., Davidson, S., Epstein, H., Unger, S., Campbell, P., Carmon, N., Velez,-Reyes, M., Huemmrigh, F. Remote Sensing of Tundra Ecosystems using High Spectral Resolution Reflectance: Issues and Opportunities. Journal of Geophysical Research: Biogeosciences. (accepted with minor revisions). Grossmann, K., Frankenberg, C., Magney, T. S., Hurlock, S. C., Seibt, U., & Stutz, J. (2018). PhotoSpec: A new instrument to measure spatially distributed red and far-red Solar-Induced Chlorophyll Fluorescence. Remote Sensing of Environment, 216(November 2017), 311–327. https://doi.org/10.1016/j.rse.2018.07.002