Anaktuvuk River fire scar canopy reflectance spectra from the 2008-2014 growing seasons, North Slope Alaska.

Abstract: 

The Anaktuvuk River Fire occurred in 2007 on the North Slope of Alaska. In 2008, three eddy covariance towers were established at sites represent ing unburned tundra, moderately burned tundra, and severely burned tundra. During the 2008-2014 growing seasons, canopy vegetation within the footprint of each of these towers was scanned with a handheld spectrophotometer several times throughout the growing season. Average reflectance spectra per site and collection day are presented here.

Project Keywords: 

Data set ID: 

10116

EML revision ID: 

7
Published on EDI/LTER Data Portal

Citation Suggestion: 

Rocha, A., Shaver, G. 2015. Anaktuvuk River fire scar canopy reflectance spectra from the 2008-2014 growing seasons, North Slope Alaska. Environmental Data Initiative. http://dx.doi.org/10.6073/pasta/ce1f38604169aa052e288f9371a82e92
People
Dates

Date Range: 

Sunday, June 22, 2008 to Wednesday, August 6, 2014

Publication Date: 

2015

Methods: 

METHODS
The Anaktuvuk River Fire occurred in 2007 on the North Slope of Alaska. In 2008, three eddy covariance towers were established at sites representing unburned tundra, moderately burned tundra, and severely burned tundra. Vegetation within the footprint of each of these towers was scanned with a handheld spectrophotometer several times throughout the 2008-2014 growing seasons.

A spectrophotometer measures incoming irradiance and radiance reflected by the canopy vegetation. The ratio of these signals (irradiance to reflected radiance) is used to generate a reflectance spectrum. In 2008, a single channel spectrophotometer was used (Unispec  SC, see INSTRUMENTATION) to perform these measurements. In 2009 and 2010 either a single or a dual channel (Unispec DC, see INSTRUMENTATION) was used.

On each collection day, 80 replicate scans were performed at each site. These replicate scans were taken at approximately 1m intervals along eight transects that extend roughly 10 meters in eight compass directions the eddy covariance tower at each site. An aluminum "T" frame was used to position the spectrophotometer’s foreoptic cable at a consistent height and orientation relative to the vegetation. When using this frame, the foreoptic cable is 1.09m above the vegetation and has a field of view with a radius of approximately 40 cm.

Data was processed and interpolated to the nanometer using the program Multispec V.5 (available at http://specnet.info/specnet_toolkit.htm).  The replicate reflectance spectra were then averaged per site to generate the average reflectance spectra presented here.

INSTRUMENTATION 
2007-2010 - Single channel spectrophotometer:
A single channel spectrophotometer  (Unispec SC,  PP Systems, Amesbury, Massachusetts, USA) uses one foreoptic cable to measure first incoming irradiance and then radiance reflected by the vegetation canopy. The foreoptic cable (UNI-684) extends from the machine and is equipped with a ferrule over which a 100mm hypotube (UNI-688) is placed. This produces a field of view that extends at an angle of 20 degrees from the end of the hypotube.  The hypotube is held vertically over the target vegetation during a data scan. The foreoptic cable is connected to a miniature photodiode array detector  in the instrument that produce signals ranging from zero to 65,000 A/D counts for 256 wavebands. These wavebands represent 3.3 nm wide portions of the visible and near infrared spectrum from 310 to 1100 nm.  A scan is performed over a period of milliseconds with the exact integration time determined by the user based on current light conditions.

At the time of data collection, a reference scan is performed by positioning the foreoptic cable over a white standard (UNI-420). This reference scan represents the incoming irradiance due to the highly reflective nature of the white standard. A dark scan is also performed by covering the foreoptic with a dark cloth. The raw signal from the dark scan is used by the machine to correct for background noise. Canopy reflectance is calculated for each waveband as follows:
 
Reflectance= (Icanopy / Ireference)
 
Icanopy= signal from foreoptic during data scan (radiance reflected from target vegetation)
Ireference= signal from the foreoptic during reflectance scan (incoming irradiance)

2009-2010 - Dual channel spectrophotometer:
A dual channel spectrophotometer (Unispec DC, PP Systems, Amesbury, Massachusetts, USA) utilizes two foreoptic cables to simultaneously measure incoming irradiance and radiance reflected by the canopy vegetation. One foreoptic cable (UNI-684) is oriented downwards and is equipped with a ferrule over which a 100mm hypotube (UNI-688) is placed. This produces a field of view that extends at an angle of 20 degrees from the end of the hypotube. The other foreoptic cable (UNI-686) is oriented upwards and is fitted with a cosine receptor (UNI-435). The two foreoptic cables are connected to two miniature photodiode array detectors that produce signals ranging from zero to 65,000 A/D counts over 256 wavebands. These wavebands represent 3.3 nm wide portions of the visible and near infrared spectrum from 310 to 1100 nm. A scan is performed over a period of milliseconds with the exact integration time determined by the user based on current light conditions.
At the time of data collection, a dark scan is performed by covering the foreoptics with a dark cloth. The raw signals from the dark scan are used by the machine to correct for background noise. A reference scan is also performed by positioning the downward foreoptic cable over a white standard (UNI-420). Canopy reflectance is calculated for each waveband as follows:
 
Reflectance= (Idata down / Idata up) x (Ireference up/ Ireference down)
 
Idata down = signal from downward foreoptic during data scan (radiance reflected from target vegetation)
Idata up = signal from the upward foreoptic during data scan (incoming irradiance)
Ireference up= signal from the upward foreoptic during reflectance scan (incoming irradiance)
Ireference down= signal from the downward foreoptic during reflectance scan (radiance reflected from white standard)

2011-present - ASD Field Spec 3 spectrophotometer:

Measurements taken with an ASD Field Spec 3. This instrument measures reflectance from 300-2500 nm at 3 nm spectral resolution. Users should note that the data from this instrument are the raw measurements and include noisey values in the 1300-1500 nm, 1700-2000 nm, and  2300-2500 nm ranges because of sensor overlap.  This type of noise is typical of this instrument and people usually discard the values at these wavelengths.

FOR MORE INFORMATION CONTACT: Adrian Rocha, University of Notre Dame, Department of Biological Sciences 100 Galvin Life Sciences Center, Notre Dame, IN 46556

FORMAT OF DATA FILE: ASCII

References:
Rocha, A.V. and G.R. Shaver (2011) Burn severity influences post-fire CO2 exchange in arctic tundra. Ecological Applications. 21:477-489.

Rocha, A.V. and G.R. Shaver (2011) Postfire energy exchange in arctic tundra: the importance and climatic implications of burn severity. Global  Change Biology. doi:10.1111/j.1365-2486.2011.02441.x.
  

Version Changes: 

  • Data collection is ongoing. Data collection and processing through 2014 is complete. Version 1, May 2011:
  • Initial data release. Version 2 updated the excel file to .xlsx since there were not enough columns for the data. Jim L 11Dec2012
  • Version 3: Updated to newer metadata form (with sites sheet). CH March 2013.
  • Version4 corrected eml excel file name JimL 16May13
  • Version 5: Checked keywords against the LTER network preferred list and replaced non-preferred terms. Jim L 15Jan14
  • Version 6: Missing value code corrected: NAN should be NaN. Jim L 24Jan14
  • Version 7: Added data through 2014. AR and BK. 15May15; Transposed the data since with the ASD & spectra there are too many wave length columns. Jim L 9Apr2015

Sites sampled.

Download a comma delimited (csv) or Excel file (includes metadata and data sheets).

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