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Harvard Forest Data Archive

HF135

Canopy Sky Factors in CRUI Land Use Project at Harvard Forest 1998

Related Publications

Data

Overview

  • Lead: Timothy Sipe, Richard Bowden, Charles McClaugherty
  • Investigators: Kirsten Bixler
  • Contact: Timothy Sipe
  • Start date: 1998
  • End date: 1998
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.53 to +42.55
  • Longitude: -72.20 to -72.17
  • Elevation: 335 to 357 meter
  • Taxa:
  • Release date: 2009
  • Revisions:
  • EML file: knb-lter-hfr.135.9
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: historical and retrospective studies; large experiments and permanent plot studies; physiological ecology, population dynamics and species interactions
  • LTER core area: disturbance
  • Keywords: canopy cover, imagery, land use, radiation
  • Abstract:

    Hemispherical photos were taken at 35 interior grid corners in each land use site’s 30 m x 50 m permanent plot on uniformly overcast days during summer 1998. A Canon A-1 35 mm camera with a 7.5 mm lens was mounted on a tripod, positioned so the film plane was 0.5 m above ground, oriented N-S with a compass, and leveled. Ektachrome 100 slide film was used. Two exposures were made for each location.

    The slides were processed and digitized in jpeg format by Kodak, Inc. at a resolution of 1536 x 1024 dpi. The jpeg images were screened for nearground obstructions. Fifteen of the 35 photo locations per site were used in subsequent analysis.

    Hemiview software (v. 2.0, Delta-T Devices Ltd., Cambridge, UK) was used to process the images and calculate indirect, direct, and global (= indirect + direct) sky factors for each sample location, plus the proportion of global sky factor represented by direct beam radiation. Several images spanning a wide range of canopy density were used to develop protocols for setting optimal thresholds in converting from color to black and white images. Each B/W image was then analyzed at three threshold levels, the optimum level plus 5 threshold units (~ 2.5%) above and below the optimum. The results were averaged across the three threshold levels to provide one set of sky factor data per sample location.

    Above-canopy incident radiation was calculated daily for the June-September growing season based on (1) latitude and longitude, (2) average atmospheric transmission, and (3) monthly averages for fractions of the day in diffuse radiation due to cloud cover for the Harvard Forest area. Data for 2 and 3 above were provided by researchers at the State University of New York at Albany. Below-canopy radiation was estimated daily across half-hour intervals as the sum of diffuse and direct beam components. Sky factors were then calculated from the above- and below-canopy radiation values and averaged both monthly and across the growing season.

  • Methods:

    Plot locations: Plow #1 Site: Prospect Hill Tract, Compartment # III, southern end. Plow #2 Site: Prospect Hill Tract, Compartment # III, southern end. Pasture #1 Site: Prospect Hill Tract, Compartment # I, southeastern edge. Pasture #2 Site: Prospect Hill Tract, Compartment # VIII, central edge. Woodlot #1 Site: Prospect Hill Tract, Compartment # VIII, northeastern edge. Woodlot #2 Site: Prospect Hill Tract, Compartment # VII, central.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Sipe T, Bowden R, McClaugherty C. 2009. Canopy Sky Factors in CRUI Land Use Project at Harvard Forest 1998. Harvard Forest Data Archive: HF135.

Detailed Metadata

hf135-01: canopy sky factors

  1. category: level of pooling
    • All Sites: all 6 sites combined
    • By Legacy: plow vs. pasture vs. woodlot, with data averaged across the two replicates of each legacy
    • By Site: by individual site
  2. sky.factor: sky factor
    • ISF: indirect sky factor
    • DSF: direct sky factor
    • GSF: global sky factor (ISF+DSF)
    • DSF/GSF: ratio of direct and global sky factors
  3. legacy.site: for legacy or site comparisons
    • P: plow
    • S: pasture
    • W: woodlot
    • P1: plow replicate 1
    • P2: plow replicate 2
    • S1: pasture replicate 1
    • S2: pasture replicate 2
    • W1: woodlot replicate 1
    • W2: woodlot replicate 2
  4. n: sample size, number of hemispherical photos analyzed for all sites combined, per legacy and per site (unit: number / missing value: NA)
  5. mean: mean for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  6. std.dev: standard deviation for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  7. std.error: standard error for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  8. range: range for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  9. max: maximum for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  10. min: minimum for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  11. median: median for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  12. ci.25: 25% CI for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)
  13. ci.75: 75% CI for photos analyzed across all sites, per legacy, and per site (unit: number / missing value: NA)