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Tower-based PhotoSpec Products for the 2019 and 2020 Spring Transition Season, SK, CA

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Documentation Revision Date: 2021-12-21

Dataset Version: 1

Summary

This dataset includes daily averaged solar-induced chlorophyll fluorescence (SIF) in the red (680-686 nm) and far-red (745-758 nm) wavelength ranges, relative SIF (SIF/Intensity), chlorophyll-carotenoid index (CCI), photochemical reflectance index (PRI), near-infrared vegetation index (NIRv), and normalized difference vegetation index (NDVI) for both black spruce (Picea mariana) and larch (Larix laricina) targets. The study site (Southern Old Black Spruce, SOBS Fluxnet ID CA-Obs) is located near the southern limit of the boreal forest ecotone in Saskatchewan, Canada. Data were collected for the spring transition in both 2019 and 2020 using PhotoSpec. Species-specific averages were calculated over each 30-minute period, then averaged again to report daily averages of SIF relative and reflectance measurements for both black spruce and larch.

Measurements were removed where photosynthetically active radiation (PAR) conditions changed over the PhotoSpec integration time. In addition, all data points were filtered for NDVI >0.5 to remove points that were mostly obscured by snow or non-green vegetation (e.g., soil, branches, stems), although this process left some measurements with mixed pixels. Data were only considered where the solar zenith angle was <80 to remove data where low light conditions increase retrieval uncertainty.

There are two data files in comma-separated values (*.csv) format included in this dataset.

Figure 1. Diagram of the field set-up. This dataset provides the products (i.e., NDVI, NIRv, PRI, CCI, red SIF, far-red SIF) collected using PhotoSpec mounted at the top of the tower. Measurements collected from other instrumentation shown are not provided in this dataset. Source: Pierrat et al., 2021

Citation

Pierrat, Z., and J. Stutz. 2021. Tower-based PhotoSpec Products for the 2019 and 2020 Spring Transition Season, SK, CA. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1887

Table of Contents

  1. Dataset Overview
  2. Data Characteristics
  3. Application and Derivation
  4. Quality Assessment
  5. Data Acquisition, Materials, and Methods
  6. Data Access
  7. References

Dataset Overview

This dataset includes daily averaged solar-induced chlorophyll fluorescence (SIF) in the red (680–686 nm) and far-red (745–758 nm) wavelength ranges, relative SIF (SIF/Intensity), chlorophyll-carotenoid index (CCI), photochemical reflectance index (PRI), near-infrared vegetation index (NIRv), and normalized difference vegetation index (NDVI) for both black spruce (Picea mariana) and larch (Larix laricina) targets. The study site (Southern Old Black Spruce, SOBS Fluxnet ID CA-Obs) is located near the southern limit of the boreal forest ecotone in Saskatchewan, Canada. Data were collected for the spring transition in both 2019 and 2020 using PhotoSpec. Species-specific averages were calculated over each 30-minute period, then averaged again to report daily averages of SIF relative and reflectance measurements for both black spruce and larch.

Measurements were removed where photosynthetically active radiation (PAR) conditions changed over the PhotoSpec integration time. In addition, all data points were filtered for NDVI >0.5 to remove points that were mostly obscured by snow or non-green vegetation (e.g., soil, branches, stems), although this process left some measurements with mixed pixels. Data were only considered where the solar zenith angle was <80 to remove data where low light conditions increase retrieval uncertainty.

Project: Arctic-Boreal Vulnerability Experiment

The Arctic-Boreal Vulnerability Experiment (ABoVE) is a NASA Terrestrial Ecology Program field campaign being conducted in Alaska and western Canada, for 8 to 10 years, starting in 2015. Research for ABoVE links field-based, process-level studies with geospatial data products derived from airborne and satellite sensors, providing a foundation for improving the analysis, and modeling capabilities needed to understand and predict ecosystem responses to, and societal implications of, climate change in the Arctic and Boreal regions.

Related Publication

Pierrat, Z., M.F. Nehemy, A. Roy, T. Magney, N.C. Parazoo, C. Laroque, C. Pappas, O. Sonnentag, K. Grossmann, D.R. Bowling, U. Seibt, A. Ramirez, B. Johnson, W. Helgason, A. Barr, and J. Stutz. 2021. Tower-based remote sensing reveals mechanisms behind a two-phased spring transition in a mixed-species boreal forest. Journal of Geophysical Research: Biogeosciences 126. https://doi.org/10.1029/2020JG006191

Data Characteristics

Spatial Coverage: Saskatchewan, Canada

ABoVE Reference Locations

Domain: Core

RegionsState/Territory: Saskatchewan, Canada

Grid cells (5 m): Ch093v101, Ch93v102

Spatial Resolution: Approximately a 100 m radius around a 25 m tall flux tower

Temporal Coverage: 2019-03-20 to 2020-06-26

Temporal Resolution: Daily averages

Study Area: Latitude and longitude are given in decimal degrees.

Site North Latitude South Latitude East Longitude West Longitude
Saskatchewan, Canada 53.98 53.97 -105.11 -105.12

Data File Information

There are two data files in comma-separated values (*.csv) format included in this dataset that contain data for the 2019 (Photospec_SIF_CCI_NIRv_NDVI_Canada_Spring2019.csv) and 2020 (Photospec_SIF_CCI_NIRv_NDVI_Canada_Spring2020.csv) spring transition seasons. The variables are the same in both files.

Table 1. Variable names and descriptions in both data files. The prefixes "red" and "far" refer to red (680–686 nm) and far-red (745–758 nm) wavelengths.

Variable Units Description
latitude_north Decimal degrees Latitude of study site (north)
latitude_south Decimal degrees Latitude of study site (south)
longitude_east Decimal degrees Longitude of study site (east)
longitude_west Decimal degrees Longitude of study site (west)
date YYYY-MM-DD hh:mm:ss Date and time of measurements
far_sif_spruce

W m-2 sr-1 µm-1

 Daily averaged solar-induced chlorophyll fluorescence (SIF) between 745-758 nm
far_sif_spruce_stdev W m-2 sr-1 µm-1 Standard deviation of the diurnal variability of solar-induced chlorophyll fluorescence between 745-758 nm
far_sif_larch W m-2 sr-1 µm-1 Daily averaged solar-induced chlorophyll fluorescence between 745-758 nm
far_sif_larch_stdev W m-2 sr-1 µm-1 Standard deviation of the diurnal variability of solar-induced chlorophyll fluorescence between 745-758 nm
red_sif_spruce W m-2 sr-1 µm-1 Daily averaged solar-induced chlorophyll fluorescence between 680-686 nm
red_sif_spruce_stdev W m-2 sr-1 µm-1 Standard deviation of the diurnal variability of solar-induced chlorophyll fluorescence between 680-686 nm
red_sif_larch W m-2 sr-1 µm-1 Daily averaged solar-induced chlorophyll fluorescence between 680-686 nm
red_sif_larch_stdev W m-2 sr-1 µm-1 Standard deviation of the diurnal variability of solar-induced chlorophyll fluorescence between 680-686 nm
far_relative_sif_spruce 1 Daily averaged Far SIF/I where I is the near-infrared radiance in the retrieval window (745-758 nm)
far_relative_sif_spruce_stdev 1 Standard deviation of the diurnal variability of Far Relative SIF for spruce
far_relative_sif_larch 1 Daily averaged Far SIF/I where I is the near-infrared radiance in the retrieval window (745-758 nm) for larch
far_relative_sif_larch_stdev 1 Standard deviation of the diurnal variability of Far Relative SIF for larch
red_relative_sif_spruce 1 Daily averaged Far SIF/I where I is the near-infrared radiance in the retrieval window (680-686 nm) for spruce
red_relative_sif_spruce_stdev 1 Standard deviation of the diurnal variability of Far Relative SIF for spruce
red_relative_sif_larch 1 Daily averaged Far SIF/I where I is the near-infrared radiance in the retrieval window (680-686 nm) for larch
red_relative_sif_larch_stdev 1 Standard deviation of the diurnal variability of Far Relative SIF for larch
ndvi_spruce 1 Daily average normalized difference vegetation index (NDVI) for spruce
ndvi_spruce_stdev 1 Standard deviation of the diurnal variability in NDVI for spruce
ndvi_larch 1 Daily average normalized difference vegetation index (NDVI) for larch
nirv_spruce 1 Daily average near-infrared reflectance (NIRv) from vegetation for spruce
nirv_spruce_stdev 1 Standard deviation of the diurnal variability in NIRv for spruce
nirv_larch 1 Daily average near-infrared reflectance (NIRv) from vegetation for larch
nirv_larch_stdev 1 Standard deviation of the diurnal variability in NIRv for larch 
pri_spruce 1 Daily average photochemical reflectance (PRI) index for spruce
pri_spruce_stdev 1 Standard deviation of the diurnal variability in PRI for spruce
pri_larch 1 Daily average photochemical reflectance index (PRI) for larch
pri_larch_stdev 1 Standard deviation of the diurnal variability in PRI for larch
cci_spruce 1 Daily average chlorophyll-carotenoid index (CCI) for spruce
cci_spruce_stdev 1 Standard deviation of the diurnal variability in CCI for spruce
cci_larch 1 Daily average CCI for larch
cci_larch_stdev 1 Standard deviation of the diurnal variability in CCI for larch

Application and Derivation

Data are used to evaluate springtime phenological transitions in a mixed-species boreal forest and environmental drivers of phenological change.

Quality Assessment

Measurements were removed where PAR conditions changed over the PhotoSpec integration time. All data points were filtered for NDVI >0.5 to remove points that were mostly obscured by snow or non-green vegetation (e.g., soil, branches, stems), although this process left some measurements with mixed pixels. Low-quality retrievals were excluded where the SIF retrieval error was >0.1 W m-2 sr-1 µm-1 and where SIF <-0.1 W m-2 sr-1 µm-1 or SIF >10 W m-2 sr-1 µm-1. Finally, data were only considered where the solar zenith angle <80 to remove data where low light conditions increase retrieval uncertainty.

Estimate of Uncertainty

Data are 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 errors and uncertainties associated with SIF retrieval by the PhotoSpec system can be found in Grossmann et al. (2018).

Data Acquisition, Materials, and Methods

The study site (Southern Old Black Spruce, SOBS; Fluxnet ID CA-Obs) is located near the southern limit of the boreal forest ecotone in Saskatchewan, Canada (latitude 53.98º, longitude -105.12º). The site is a mixed forest stand with stem density predominantly (90%) black spruce (Picea mariana) and scattered (10%) larch (Larix laricina). The average canopy height at the site is 16 m for larch and 11 m for black spruce with a canopy leaf area index of 3.8 m2 m-2.

Co-located remotely sensed products (i.e., NDVI, NIRv, PRI, CCI, red SIF, far-red SIF) were collected using PhotoSpec (Grossman et al., 2018) in the spring of 2019 and 2020. PhotoSpec was installed at the top of the scaffolding tower (25 m AGL) facing due north. It has a narrow field of view (0.7 degrees) and a two-dimensional scanning capability which permits independent measurements of both black spruce and larch, giving it a unique advantage over spatially averaged satellite measurements. The scanning strategy had three "elevation scans" (i.e., scanning vertically) at 35 degrees west (n=10), 0 degrees north (n=24), and 35 degrees east (n=10) that observed predominantly black spruce, and three individual targets on a larch. Individual measurements take approximately 20 seconds and the complete scan cycle repeats on a 30-minute loop. SIF was retrieved in the red (680–686 nm) and far-red (745–758 nm) wavelengths. Refer to Grossman et al. (2018) for additional instrument details.

Species-specific averages were calculated over each 30-minute period, then averaged to report daily averages of relative SIF and reflectance measurements for both black spruce and larch in the spring of 2019 and 2020. Refer to Pierrat et al. (2021) for additional information.

Data Access

These data are available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Tower-based PhotoSpec Products for the 2019 and 2020 Spring Transition Season, SK, CA

Contact for Data Center Access Information:

References

Pierrat, Z., M.F. Nehemy, A. Roy, T. Magney, N.C. Parazoo, C. Laroque, C. Pappas, O. Sonnentag, K. Grossmann, D.R. Bowling, U. Seibt, A. Ramirez, B. Johnson, W. Helgason, A. Barr, and J. Stutz. 2021. Tower-based remote sensing reveals mechanisms behind a two-phased spring transition in a mixed-species boreal forest. Journal of Geophysical Research: Biogeosciences 126. https://doi.org/10.1029/2020JG006191

Grossmann, K., C. Frankenberg, T.S. Magney, S.C. Hurlock, U. Seibt, and J. Stutz. 2018. PhotoSpec: A new instrument to measure spatially distributed red and far-red Solar-Induced Chlorophyll Fluorescence. Remote Sensing of Environment 216:311–327. https://doi.org/10.1016/j.rse.2018.07.002