Davidson K; Lamour J; Calderon O; Zambrano A; Wright C; Ely K
PA-BCI; PA-Gam; PA-PNM; PA-SLZ
Barro Colorado Island (BCI); Gamboa Area; Parque Natural Metropolitano; Bosque Protector San Lorenzo (Fort Sherman)
Leaf spectra; Solar Radiation
Jan. 18, 2022
April 8, 2022
Paired leaf reflectance and transmittance data measured in Panama, at the Parque Natural Metropolitano (PNM), on Barro Colorado Island (BCI), at the San Lorenzo canopy crane site (SLZ), and in Gamboa, Panama from January to April 2022. Measurements were made on leaves from 57 different tree, shrub and liana species, from sunlit canopy and understory locations. Bark reflectance was also measured on the trunks of common tree species at the PNM and SLZ sites. Also included are irradiance measurements and leaf area index (LAI) from eight vertical profiles at PNM. The aim of these data was to refine our understanding of vertical trait and environmental variation in tropical forests, and to improve models which can predict leaf traits from leaf contact spectral measurements. All spectral data and metadata are presented in .csv files and complete instrument output are included in .zip folders. Protocol details are provided as pdf documents. In addition to spectral data described here, some of these samples were also used for measurement of leaf gas exchange, carbon and nitrogen content, and leaf mass per unit leaf area (LMA) these data can be cross linked using the unique sample ID and are provided in separate related data packages.
Reflectance and transmittance of each leaf was measured successively using two spectroradiometers. Leaf reflectance was measured using a Spectra Vista Corporation (SVC) HR-1024i spectroradiometer (SVC, Poughkeepsie, NY, USA; spectral range: 350–2500 nm; spectral resolution: 3.5 nm at 700 nm, 9.5 nm at 1500 nm, and 6.5 nm at 2100 nm) together with an external light source mounted on a leaf clip with a black background (SVC LC-RP-Pro foreoptic). The integration time was set to 1 second with a low light intensity to reduce heat damage to the leaves. A white reference was taken before measuring the leaf reflectance using a white Spectralon.
Leaf transmittance was measured using a second SVC HR-1024i spectroradiometer mounted with an integrating sphere (SVC Spectra DC-R/T Sphere; Diameter 3”; aperture 1/2”). The integration time was set to 3 s.
Bark reflectance was measured in the same manner as leaf reflectance. However, for bark measurements the leaf clip was pressed against the trunk of the tree rather than clipped onto a sample. Transmittance was not measured on bark samples.
Several reflectance and transmittance spectra were taken for each leaf, avoiding the midrib when possible and those spectra were averaged. The reflectance and transmittance type (‘Relative’ or ‘Spectralon corrected’) is indicated in the data. ‘Relative’ is the reflectance or transmittance calculated as the ratio of the radiance or DN of the leaf divided by the radiance or DN of the Spectralon standard for each instrument channel. ‘Spectralon_corrected’ is the reflectance or transmittance calculated as the ratio of the radiance or DN of the leaf divided by the radiance or DN of the Spectralon standard for each instrument channel and then multiplied by the spectral response of the Spectralon standard.
Before each reflectance measurement the temperature of the leaf was measured using an Apogee MI-210 radiometer. Leaf temperatures were measured on the up-facing surface and the radiometer was held ~5 cm away from the leaf and the temperature recorded when the measurement stabilized.
Sky irradiance was measured using two SVC HR-1024i spectroradiometers,each with a sky irradiance sphere mounted as the foroptic (Full Sky Irradiance Sphere, Diameter 3.3”; aperture 1/2”). One instrument (the above sensor) was set up at the top of the crane with an open view to the sky and the second (below sensor) was used in the gondola of the crane to measure the irradiance inside the vertical profiles. The above sensor was set to automatically log every 5 seconds. At each level within each profile three measurements were taken with the below sensor in an upward facing direction (toward the sky), and three measurements were taken with the below sensor in a downward facing direction (toward the ground), labeled as UP and DW respectively. To process the data, raw outputs from the below sensor were matched with the above sensor measurement that was closest in time. Then at each waveband the raw radiance values of the below and above sensors were ratioed to estimate transmitted irradiance at each waveband. Each of the three duplicate measurements at each combination of profile, orientation, and level, were averaged together.
Brookhaven National Laboratory, Smithsonian Tropical Research Institute, Oak Ridge National Laboratory
U.S. Department of Energy Office of Science Office of Biological and Environmental Research
Serbin, Shawn - Brookhaven National Laboratory ([email protected])
Davidson K; Lamour J; Calderon O; Zambrano A; Wright C; Ely K (2023): Leaf reflectance, leaf transmittance and sky irradiance, at four sites in Panama, 2022. 1.0. NGEE Tropics Data Collection. (dataset). https://doi.org/10.15486/ngt/1896889
This research was supported as part of NGEE-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under contract no. DE-SC0012704.
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