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NACP Woody Vegetation Characteristics of 1,039 Sites across North Slope, Alaska, V2

Documentation Revision Date: 2017-02-28

Data Set Version: V2

Summary

This data set provides the results of (1) field measurements of woody vegetation (shrubs) at 26 diverse sites across the North Slope of Alaska during 2010 and 2011, (2) field-based statistical estimates of site shrub structural characteristics, (3) high-resolution panchromatic satellite imagery-based estimates of field site shrub characteristics using the Canopy Analysis with Panchromatic Imagery (CANAPI) model, and (4) adjusted CANAPI estimates of shrub characteristics at 1,013 selected sites widely distributed across the North Slope.

A site characterization file is included with the assigned physiognomic vegetation class, which was one of the criteria for the selection of the 1,013 CANAPI sites, and with the sources of the high-resolution imagery used to obtain CANAPI estimates. The CANAPI crown detection algorithm (Chopping, 2011) is also provided as a companion file.

As part of a NASA-funded research project to map changes in tall shrub (taller than 0.5 m) abundance in Arctic tundra, a 3-week field campaign was carried out in 2010 and 2011 on the North Slope of Alaska to statistically survey shrub structural characteristics at 26 sites. The field data presented include genus, crown height, crown radius, and spatial coordinates of all shrubs sampled at each 250 x 250-m site. These measurements were correlated with raw CANAPI structural estimates and the derived regression coefficients were applied to adjust CANAPI estimates for the field sites and additional sites across the North Slope. Together, the field measurements and image-based CANAPI estimates allowed the construction of a robust and extensive data resource of tall shrub characteristics at 1,039 tundra sites (Duchesne et al., 2016).

User Note: This data set is an updated version of:

Duchesne, R.R., M.J. Chopping, and K.D. Tape. 2015. NACP Woody Vegetation Characteristics of 1,039 Sites across the North Slope, Alaska. ORNL DAAC, Oak Ridge, Tennessee, USA. http://dx.doi.org/10.3334/ORNLDAAC/1270 

Users of version 1 should download the updated data files. Changes and additions are described below in Section 8.

There are five *.csv files and one companion *.txt file included in the Version 2 data set.

Figure 1. Locations of the 26 field sites and the 1,013 selected CANAPI sites, North Slope, Alaska

Citation

Duchesne, R.R., M.J. Chopping, and K.D. Tape. 2017. NACP Woody Vegetation Characteristics of 1,039 Sites across North Slope, Alaska, V2. ORNL DAAC, Oak Ridge, Tennessee, USA. http://dx.doi.org/10.3334/ORNLDAAC/1365

Table of Contents

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

Data Set Overview

This data set provides the results of (1) field measurements of woody vegetation (shrubs) at 26 diverse sites across the North Slope of Alaska during 2010 and 2011, (2) field-based statistical estimates of site shrub structural characteristics, (3) high-resolution panchromatic satellite imagery-based estimates of field site shrub characteristics using the Canopy Analysis with Panchromatic Imagery (CANAPI) model, and (4) adjusted CANAPI estimates of shrub characteristics at 1,013 selected sites widely distributed across the North Slope.

A site characterization file is included with the assigned physiognomic vegetation class, which was one of the criteria for the selection of the 1,013 CANAPI sites, and with the sources of the high-resolution imagery used to obtain CANAPI estimates. The CANAPI crown detection algorithm (Chopping, 2011) is also provided as a companion file.

As part of a NASA-funded research project to map changes in tall shrub (taller than 0.5 m) abundance in Arctic tundra, a 3-week field campaign was carried out in 2010 and 2011 on the North Slope of Alaska to statistically survey shrub structural characteristics at 26 sites. The field data presented include genus, crown height, crown radius, and spatial coordinates of all shrubs sampled at each 250 x 250-m site. These measurements were correlated with raw CANAPI structural estimates and the derived regression coefficients were applied to adjust CANAPI estimates for the field sites and additional sites across the North Slope. Together, the field measurements and image-based CANAPI estimates allowed the construction of a robust and extensive data resource of tall shrub characteristics at 1,039 tundra sites (Duchesne et al., 2016) .

Project: North American Carbon Program (NACP)

The NACP (Denning et al., 2005; Wofsy and Harriss, 2002) is a multidisciplinary research program to obtain scientific understanding of North America's carbon sources and sinks and of changes in carbon stocks needed to meet societal concerns and to provide tools for decision makers. Successful execution of the NACP has required an unprecedented level of coordination among observational, experimental, and modeling efforts regarding terrestrial, oceanic, atmospheric, and human components. The project has relied upon a rich and diverse array of existing observational networks, monitoring sites, and experimental field studies in North America and its adjacent oceans. It is supported by a number of different federal agencies through a variety of intramural and extramural funding mechanisms and award instruments.

This data is an updated version of the following data set:

Duchesne, R.R., M.J. Chopping, and K.D. Tape. 2015. NACP Woody Vegetation Characteristics of 1,039 Sites across the North Slope, Alaska. ORNL DAAC, Oak Ridge, Tennessee, USA. http://dx.doi.org/10.3334/ORNLDAAC/1270 

Related Publication: 

Duchesne, R.R., Chopping, M.J. and Tape, K.D. 2016. Capability of the CANAPI algorithm to derive shrub structural parameters from satellite imagery in the Alaskan Arctic. Polar Record, 52(2), pp. 124–133. http://dx.doi.org/10.1017/S0032247415000509

 

Data Characteristics

Spatial Coverage: North Slope, Alaska

Spatial Resolution: Plots of 250 x 250-m are distributed across the North Slope. See Figure 1.

Temporal Coverage:

The field work was conducted during the summers of 2010 and 2011 -- beginning 2010-07-28 and ending 2011-08-04.

High resolution panchromatic images used for estimating shrub characteristics were from various dates between 2002-07-19 and 2012-06-21.

Temporal Resolution: one-time estimates

Site Boundaries: (All latitude and longitude given in decimal degrees)

Site (Region) Westernmost Longitude Easternmost Longitude Northernmost Latitude Southernmost Latitude
North Slope, Alaska -167 -145 71.4 65

 

Data File Information

Field Shrub Canopy Structure Data

The structural characteristics of woody vegetation (genus, height, crown radius, and geographic location) were surveyed at fourteen 250 x 250-m sites along the Chandler and Colville rivers and at twelve 250 x 250-m sites along the Dalton Highway.

Results are contained in the files:
   colville_shrub_data_V2.csv
   dalton_shrub_data_V2.csv

Projection Parameters

Projection Type: Universal Transverse Mercator Zone 5N
Spheroid Name: WGS 84
Datum: WGS 84
False Easting: 500000.00
False Northing: 0.00
Central Meridian: -153.00
Scale Factor: 0.999600000000000040
Latitude of Origin: 0.00

Table 1. Variable descriptions for colville_shrub_data_V2.csv and dalton_shrub_data_V2.csv data files.

Column Description Units/format
Site Unique identifier of site: The letters describe the name of the expedition, the following 4 digits are the collection year, and the last digits indicate the sites sequence north to south.  
Sp_genus Scientific genus name up to 25 characters  
Organization Indicates whether measurements represent an individual shrub or a cluster of shrubs  
Canopy_height Shrub height from ground to top most branch Meters
Crown_radius Shrub crown radius measured as half the distance from the left most branch to the right most branch Meters
X_coordinate Shrub location X coordinate Meters
Y_coordinate Shrub location Y coordinate Meters

Sample Data Records:

Site,Sp_genus,Organization,Canopy_height,Crown_radius,X_coordinate,Y_coordinate
,Meters,Meters,Meters,Meters
Colville201001,Alnus sp.,Individual,1.32,0.73,558010,7729420
Colville201001,Alnus sp.,Individual,1.34,1.05,558010,7729420
Colville201001,Alnus sp.,Individual,1.27,0.7,558022,7729439
Colville201001,Alnus sp.,Individual,1.18,1.35,558055,7729407
...
Colville201014,Salix sp.,Individual,1.18,0.79,528109,7626599
Colville201014,Salix sp.,Individual,0.7,0.79,528127,7626600
Colville201014,Alnus sp.,Individual,1.05,0.49,528140,7626603
Colville201014,Alnus sp.,Individual,0.87,1.31,528161,7626608

 

Field Estimates Data

This data file contains estimates of mean crown radius, mean shrub height, total number of shrubs, and fractional cover for the 14 sites along the Chandler and Colville rivers and 12 sites along the Dalton Highway that were surveyed using the belt transect method.

Estimates of the structural characteristics of woody vegetation are contained in the file field_estimates_data.csv.

Projection Parameters

Projection Type: Alaska Albers Equal Area Conic
Spheroid Name: WGS 84
Datum: WGS 84
False Easting: 0.00
False Northing: 0.00
Central Meridian: -154.00
Standard Parallel 1: 55.00
Standard Parallel 2: 65.00
Latitude of Origin: 50.00
Linear Unit: Meter

Table 2. Variable descriptions for field_estimates_data_V2.csv.

Column Description Units/format
Site Unique identifier of site: The letters describe the name of the expedition, the following 4 digits are the collection year, and the last digits indicate the sites sequence north to south.  
Number_of_shrubs_per_unit_area Estimate of the total number of shrubs at each sampling site. Sites are 250 x 250 meters (6.25 ha). Count
Canopy_height_mean Shrub mean height estimated as the average height of all shrubs surveyed. Meters
Crown_radius_mean Shrub mean crown radius estimated as the average crown radius of all individual shrubs surveyed. Meters
Shrub_area_fraction Shrub fractional cover was estimated by dividing the “sum of all shrub crown area” by the area of the belt transects sampled at each site. Range 0 to 1
X_coordinate X_coordinate of site center point Meters
Y_coordinate Y_coordinate of site center point Meters

Sample Data Records:

Site,Number_of_shrubs_per_unit_area,Canopy_height_mean,Crown_radius_mean,Shrub_area_fraction,X_coordinate,Y_coordinate
,Meters,Meters,Range_0_to_1,Meters,Meters
Colville201001,18,1.22,1.142,0.001,98250,2190000
Colville201002,760,1.582,1.007,0.063,102500,2187250
Colville201003,365,1.231,0.986,0.026,97750,2172250
Colville201004,810,1.516,1.205,0.097,97750,2171000

Dalton201109,870,0.695,0.919,0.118,183000,2082250
Dalton201110,570,0.656,0.529,0.023,189000,2081250
Dalton201111,360,0.63,0.67,0.009,182750,2082000
Dalton201112,0,0,0,0,188500,2081250

 

CANAPI Estimates Data

The adjusted image-based estimates for the 26 field sites and the 1,013 selected sites, using the CANAPI (Canopy Analysis with Panchromatic Imagery) crown detection recognition algorithm (Chopping, 2011), are in the file canapi_estimates.csv.

Projection Parameters

Projection Type: Alaska Albers Equal Area Conic
Spheroid Name: WGS 84
Datum: WGS 84
False Easting: 0.00
False Northing: 0.00
Central Meridian: -154.00
Standard Parallel 1: 55.00
Standard Parallel 2: 65.00
Latitude of Origin: 50.00
Linear Unit: Meter

Table 3. Variable descriptions for canapi_estimates.csv.

Column Description Units/format
Site Unique identifier of site: Year of collection of high resolution imagery followed by four sequential digits.  
Adj_number_of_shrubs_per_unit_area Adjusted CANAPI total number of shrubs after applying regression coefficients based on calibrated field measurements. Sites are 250 x 250 meters (6.25 ha). Count
Adj_crown_radius_mean Adjusted CANAPI shrub mean crown radius estimate after applying regression coefficients based on calibrated field measurements. Meters
Adj_shrub_area_fraction Adjusted CANAPI shrub fractional cover estimate after applying regression coefficients based on calibrated field measurements. Range 0 to 1
X_coordinate Center point X coordinate in 250 x 250-m plot Meters
Y_coordinate Center point Y coordinate in 250 x 250-m plot Meters

Sample Data Records:

Site,Adj_number_of_shrubs_per_unit_area,Adj_crown_radius_mean,Adj_shrub_area_fraction,X_coordinate,Y_coordinate
,Count,Meters,Range_0_to_1,Meters,Meters
20100001,953,0.8583,0.0653,90000,2120000
20100002,739,0.7538,0.0351,90250,2120000
20100003,631,0.8377,0.0402,89750,2119500
20100004,535,0.9534,0.0523,90250,2119500

20101010,253,0.766,0.013,186500,2068000
20101011,278,0.789,0.016,187500,2068000
20101012,173,0.746,0.008,188000,2068000
20101013,486,0.699,0.02,189000,2068000

 

Vegetation Class and Imagery Source Data

All sites have been assigned a “Physiognomic vegetation class” according to the circumpolar vegetation map of the CAVM Team (2003). Vegetation class diversity was one of the criteria for the selection of the 1,013 sites for CANAPI estimates. Also included in this file is the source of the high resolution imagery used to obtain CANAPI estimates for all sites.

The file containing the physiognomic vegetation class and imagery source data is CAVM-class_sensor-info.csv.

Projection Parameters

Projection Type: Alaska Albers Equal Area Conic
Spheroid Name: WGS 84
Datum: WGS 84
False Easting: 0.00
False Northing: 0.00
Central Meridian: -154.00
Standard Parallel 1: 55.00
Standard Parallel 2: 65.00
Latitude of Origin: 50.00
Linear Unit: Meter

Table 4. Variable descriptions for CAVM-class_sensor-info.csv.

Column Description Units/format
Site Unique identifier of site: for field sites -- The letters describe the name of the expedition, the following 4 digits are the collection year, and the last digits indicate the sites sequence north to south. For selected and estimated sites -- Year of collection of high resolution imagery followed by four sequential digits.  
X_coordinate Center point X coordinate in 250 x 250-m plot Meters
Y_coordinate Center point Y coordinate in 250 x 250-m plot Meters
CAVM_class Physiognomic vegetation class of sampling sites according to the CAVM Team (B=Barrens, G=Graminoid tundra, S=Erect-shrub tundra, W=Wetland) (CAVM Team. 2003)  
Sensor Provenance of high resolution imagery used for obtaining CANAPI estimates for the entire reference database  
Acquisition_date Date of acquisition of high resolution imagery yyyy-mm-dd

Sample Data Records:

Site,X_coordinate,Y_coordinate,CAVM_class,Sensor,Acquisition_date
,Meters,Meters,yyyy-mm-dd
Colville201001,98250,2190000,W,,-999
Colville201002,102500,2187250,W,QuickBird,2009-09-05
Colville201003,97750,2172250,S,,-999
Colville201004,97750,2171000,S,,-999

20101010,186500,2068000,G,GeoEye,2010-06-21
20101011,187500,2068000,G,GeoEye,2010-06-21
20101012,188000,2068000,G,GeoEye,2010-06-21
20101013,189000,2068000,G,GeoEye,2010-06-21

Application and Derivation

The field data reported includes species name, crown height, crown radius, and spatial coordinates of all shrubs sampled at each site. The image-based estimates presented include mean height, mean crown radius, and fractional cover of shrubs at 1,013 sites. Only shrubs taller than 0.5 m were surveyed; the purpose of this data collection was to document the structural characteristics of the woody vegetation taller than 0.5 meters at the field sites, which were used for the training and validation of the empirical-boosted regression tree model that can retrieve shrub cover from bidirectional reflectance data (e.g., from the Earth-orbiting NASA Multiangle Imaging Spectro-Radiometer) and terrain variables.  See Duchesne et al. (2016) for details.

Quality Assessment

Accuracy of the regression equations used to adjust the CANAPI estimates for each vegetation parameter was assessed and reported in terms of the R-squared and the root mean square error (RMSE).

Table 5. R-squared and the root mean square error (RMSE)

Vegetation Characteristic R-squared RMSE
Total number of shrubs 0.54 446 shrubs
Mean crown radius 0.80 0.28 meters
Fractional cover 0.83 0.01

Data Acquisition, Materials, and Methods

Field Site Descriptions

The structural characteristics of woody vegetation were surveyed at fourteen 250 x 250-m sites along the Chandler and Colville rivers and at twelve 250 x 250-m sites along the Dalton Highway (Figure 2). Sampling sites are in an altitudinal and latitudinal climatic gradient with the southernmost sites at higher elevations and influenced by the continental climate coming from the Brook Range, and the northernmost sites at much lower elevations, where maritime climate conditions prevail. Details of sampling, image processing, and analyses may be found in Duchesne et al. (2016).

Sampling sites

Figure 2. Field Sites: Sampling sites along the Colville and Chandler Rivers (on the left) and sampling sites along the Dalton Highway (on the right). (Source: AlaskaMapped SDMI WCS layers [downloaded file]. Alaska Mapped, Statewide Digital Mapping Initiative. URL:http://www.alaskamapped.org/data/arcgis-layer-files: [20 February, 2015])

 

The coordinates and elevation were determined using a Global Positioning System (GPS). Elevation data are +/- 30 m, and horizontal locations +/- 10 m. The X and Y coordinates are the center point in a 250 x 250-m site in standard Albers Conical Equal Area grid for Alaska, Spheroid WGS 84, Datum WGS 84.

 

Table 6. Field site descriptions. Note that for Site Identifier, Colville and Dalton denote the names of the 2010 and 2011 expeditions, respectively. The following 4 digits are the collection year, and the last digits indicate the site sequence north to south. Site Feature values identify either the river or highway near the field site.

Site Identifier Site Feature X Coordinate Y Coordinate Elevation (m) Number of Transects Sampling Date Available Photo
Colville201001 Colville River 98250 2190000 94 Not applicable. Entire site surveyed. 08/11/2010-08/12/2010  
Colville201002 Colville River 102500 2187250 96 10 08/10/2010 Figure 6
Colville201003 Colville River 97750 2172250 96 10 08/09/2010  
Colville201004 Colville River 97750 2171000 96 5 08/09/2010  
Colville201005 Chandler River 87750 2128750 150 5 08/05/2010  
Colville201006 Chandler River 86750 2128250 145 10 08/05/2010  
Colville201007 Chandler River 89750 2120000 143 5 08/03/2010 Figure 3
Colville201008 Chandler River 89500 2119000 222 5 08/03/2010  
Colville201009 Chandler River 81500 2095500 249 10 08/02/2010  
Colville201010 Chandler River 81000 2092000 249 5 08/01/2010  
Colville201011 Chandler River 78000 2092500 297 10 07/30/2010-07/31/2010  
Colville201012 Chandler River 70000 2090500 287 5 07/29/2010  
Colville201013 Colville River 69750 2090000 289 10 07/28/2010  
Colville201014 Colville River 69250 2088250 290 10 07/29/2010 Figure 4
Dalton201101 Dalton Highway 203250 2216500 76 5 07/30/2011  
Dalton201102 Dalton Highway 203500 2216750 78 5 07/30/2011  
Dalton201103 Dalton Highway 213750 2178750 203 5 07/29/2011  
Dalton201104 Dalton Highway 214000 2179000 225 5 07/29/2011  
Dalton201105 Dalton Highway 207750 2128250 392 5 07/26/2011  
Dalton201106 Dalton Highway 208250 2128000 392 5 07/26/2011  
Dalton201107 Dalton Highway 209750 2110750 409 5 07/25/2011  
Dalton201108 Dalton Highway 209750 2110250 438 5 07/25/2011  
Dalton201109 Dalton Highway 183000 2082250 790 5 07/22/2011  
Dalton201110 Dalton Highway 189000 2081250 752 5 08/04/2011  
Dalton201111 Dalton Highway 182750 2082000 768 5 07/22/2011  
Dalton201112 Dalton Highway 188500 2081250 n/a 5 08/04/2011 Figure 5

 

aerial view of site

Figure 3. Aerial photograph of the Colville201007 field sampling site and surrounding landscape. The top of the image is north. Photo credit: Ken Tape (University of Alaska, Fairbanks).

 

Figure 4. Portion of Colville201014 site.

 

dalton landscape

Figure 5. Portion of Dalton201112 site.

 

Field Sampling and Measurements

The belt-transect method was used to survey 25 out of the 26 field sites. At site Chandler201001, all shrubs across the site were surveyed. Transects were 5-m wide and 250-m long and their number per site varied between 5 and 10 depending on the difficulty of access to the site. The belt transects ran parallel to each other and across the terrain altitudinal gradient (Figure 6).

 

transect site

Figure 6. Illustration of potential belt transects placement at field site Colville 201002 (250 m x 250 m). White dots represent shrubs observed in the QuickBird panchromatic subset. Belt transects are 5-m wide by 250-m long and run perpendicular to the terrain slope.

All shrubs taller than 0.5-m within the belt transects were surveyed by taking its photograph next to a measuring rod and recording its GPS coordinates (Figures 7-9). In the lab, the photographs were calibrated to estimate shrub height, defined as the vertical extent of the shrub and measured from its base to the top of its foliage, and crown radius, defined as the horizontal extent of the canopy and measured from the left-most branch to the right-most branch of the shrub.

 

vegetation site
vegetation
vegetation site

Figures 7-9. Photographs of surveyed shrubs next to the measuring rod at site Colville 201002. From top to bottom: Willow sp., Alder Sp., and Alder Sp.

 

Field Site Estimates

The total number of shrubs, mean crown radius, mean shrub height, and fractional cover were estimated for each field site from the survey measurements.

The total number of shrubs was estimated by counting all surveyed shrubs, within the belt transects, sampled at each site.

Mean crown radius was estimated using only those observations where individual shrubs were clearly delimited. For that estimate, clusters of shrubs where not included in the analysis because the boundaries of the shrubs could not be identified. Mean shrub height was estimated using all the observations, both individual and clusters of shrubs.

Fractional cover was estimated by dividing the “sum of all shrub crown area” by the area of the belt transects sampled at each site. To calculate the sum of all crown area, both surveyed individual shrubs and clusters of shrubs were included; a cluster was considered one observation. Since the belt width was 5 m, individual shrubs and clusters that exceeded 5-m wide were adjusted to the maximum width of the belt transect.

 

CANAPI Shrub Estimates for Field Sites

The high resolution image-based shrub estimates for the field sites were obtained using the CANAPI algorithm in conjunction with high resolution panchromatic scenes for the North Slope of Alaska. Some scenes were purchased for the project while others were accessed through the National Geospatial-Intelligence Agency Commercial Archive Data site (http://cad4nasa.gsfc.nasa.gov/) that provides access for NASA Earth Science Investigators. CANAPI is a user-tunable algorithm that uses high resolution panchromatic imagery to identify and trace tree or shrub crowns by locating its crescent-shaped sunlit portion (Chopping, 2011).

CANAPI estimates for the Arctic woody vegetation present some departures from the field site estimates which are based on the survey measurements. For instance, CANAPI tends to underestimate fractional cover when there are clusters of shrubs present in the scene because it is unable to identify individual shrubs. Where vegetation is sparse, CANAPI estimates are very close to field data. On the other hand, mean crown radius CANAPI estimates are often lower in comparison with the field estimates.

 

Adjustment of CANAPI Estimates

In order to adjust the CANAPI estimates of fractional cover, mean crown radius, and total number of shrubs, regression coefficients were derived by finding the relations between the CANAPI estimates and the corresponding field estimates via simple linear regressions, for 25 field sites. Outliers were omitted from the analysis.

  • High R-squared values for fractional cover and mean crown radius (0.83 and 0.80 respectively) suggest that it is appropriate to use the regression coefficients to adjust CANAPI estimates (Figures 10 a and b).
  • Since the regression for total number of shrubs had a medium R-squared (0.54), using the regression equation to adjust CANAPI estimates must be done with caution (Figure 10 c).

These regression coefficients were used to adjust new CANAPI estimates obtained for 1,013 sites across the North Slope of Alaska.

 

scatter plots

Figure 10. Scatter plots displaying relationships between CANAPI-derived and field estimates for 25 sampling sites: (a) correlation for fractional cover (R2 = 0.83), (b) correlation for mean crown radius (R2 = 0.80), (c) correlation for total number of shrubs (R2 = 0.54)

 

Expansion of Tall Shrub Characteristics Reference Database

A total of 1,013 sites of 250 x 250-m were selected across North Slope. Sites were explicitly chosen to include representatives from all four physiognomic vegetation classes present in the region (CAVM Team, 2003) and from across the broad latitudinal and longitudinal range of the North Slope (Figure 1). The selection depended first on the availability of high resolution imagery, and then, on a visual assessment of the area to select sites with different degrees of cover from each physiognomic vegetation class.

The CANAPI algorithm was used to obtain total number of shrubs, fractional cover, and mean crown radius estimates for the new 1,013 sites. The estimates were later adjusted using the regression equations obtained in the previous step above. Together, the field measurements and image-based CANAPI estimates allowed the construction a robust and extensive data resource of tall shrub characteristics at 1,039 tundra sites. The adjusted image-based estimates are in the canapi_estimates.csv data file.

For the 1,013 new sites, the distribution of the Total Number of Shrubs and the Fractional Cover CANAPI estimates is skewed to the left and therefore the five-number summary is a better measurement of center and spread. In the case of the Mean Crown Radius CANAPI estimates, the values follow a normal distribution and for that reason the mean and the standard deviation are better measurements of center and spread.

 

Table 7. Fractional Cover and Mean Crown Radius Summary Statistics

  Total Number of Shrubs Fractional Cover Mean Crown Radius
Minimum 58 0.000 n.a.
First Quartile 166 0.006 n.a.
Median 292 0.016 n.a.
Third Quartile 611 0.044 n.a.
Maximum 1794 0.399 n.a.
Mean n.a. n.a. 0.832 m
Standard Deviation n.a. n.a. 0.163 m

 

CANAPI Model and Software Requirements

A copy of the CANAPI model (Chopping, 2011) is also provided. The file is named CANAPI_AK.txt. This model was developed by Mark Chopping and requires significant user input to obtain reasonable results.

  • Any AK-specific modifications where done on a site by site basis. That means that the original code was the same, but the settings were adjusted for each site according to the needs.
  • In the particular case of identifying shrubs in the Arctic, CANAPI works best with sub-meter high resolution panchromatic imagery (i.e., GeoEye and QuickBird).

CANAPI requires input information from the high resolution imagery to be used with it including:

  • Spatial resolution in meters
  • Solar elevation angle in degrees at the time the image was acquired
  • Rotation angle so that the shadow cast by the objects faces south

Other settings that are necessary to define are:

  • Saturation percentage for image contrast stretch (usually set to 1 but can be larger)
  • Lower threshold for sunlit crown isolation (16-bit) (values can range from 50,000 to 65,535)
  • Iterations of the watershed algorithm (usually set to 1)
  • Particle Analyzer minimum size (usually set to 1)
  • Particle Analyzer maximum size (values can range from 75 to 100)
  • Radius for median filter (usually set to 1 or 2)
  • Limit crown radius maximum, in pixels (for shrubs, it is recommended values less than 5)
  • Limit crown area minimum in square pixels (usually set to 1)
  • Upper threshold for shadow isolation (usually set to 70 but it could be higher)
  • Limit shadow length in meters (for shrubs, a value of 4 works well)
  • Convolve matrix (3x3)

Software Requirements:

The CANAPI model runs as a macro in ImageJ v.1.44. The latter is a public domain Java image processing software developed by Wayne Rasband from the National Institute of Mental Health. It is downloadable from http://imagej.nih.gov/ij/index.html.

Data Access

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

NACP Woody Vegetation Characteristics of 1,039 Sites across North Slope, Alaska, V2

Contact for Data Center Access Information:

References

CAVM Team. 2003. Circumpolar Arctic Vegetation Map. (1:7,500,000 scale), Conservation of Arctic Flora and Fauna (CAFF) Map No. 1. U.S. Fish and Wildlife Service, Anchorage, Alaska. ISBN: 0-9767525-0-6, ISBN-13: 978-0-9767525-0-9

Chopping M. (2011). CANAPI: Canopy Analysis with Panchromatic Imagery. Remote Sensing Letters, 2(1): 21-29. http://dx.doi.org/10.1080/01431161.2010.486805

Denning, A.S., et al. 2005. Science implementation strategy for the North American Carbon Program: A Report of the NACP Implementation Strategy Group of the U.S. Carbon Cycle Interagency Working Group. U.S. Carbon Cycle Science Program, Washington, DC. 68 pp.

Duchesne, R.R., Chopping, M.J. and Tape, K.D. 2016. Capability of the CANAPI algorithm to derive shrub structural parameters from satellite imagery in the Alaskan Arctic. Polar Record, 52(2), pp. 124–133. http://dx.doi.org/10.1017/S0032247415000509

Duchesne, R.R., M.J. Chopping, and K.D. Tape. 2015. NACP Woody Vegetation Characteristics of 1,039 Sites across the North Slope, Alaska. Data set. ORNL DAAC, Oak Ridge, Tennessee, USA. http://dx.doi.org/10.3334/ORNLDAAC/1270 

Wofsy, S.C., and R.C. Harriss. 2002. The North American Carbon Program (NACP). Report of the NACP Committee of the U.S. Interagency Carbon Cycle Science Program. U.S. Global Change Research Program, Washington, DC. 56 pp.

Data Set Revisions

Changes between Versions 1 and 2 effective December 15, 2016.  Users should download the updated files and note the changes to documentation.

Data files:

colville_shrub_data_V2.csv

  • Now includes an "Organization" column indicating whether the reported measurement is of an individual shrub or a cluster of shrubs
  • 12 additional observations
  • Several corrections to previously reported data

dalton_shrub_data_V2.csv

  • Now includes an "Organization" column indicating whether the reported measurement is of an individual shrub or a cluster of shrubs
  • Site "Dalton201210" corrected to "Dalton201110"
  • No other additions or corrections

field_estimates_V2.csv

  • Number of shrubs for "Colville201002" site reduced from 1520 to 760
  • No other additions or corrections

No changes were made to canapi_estimates.csv or CAVM-class_sensor-info.csv.

Documentation:

In Table 6. (Section 5, above), the number of transects for "Colville201002" site was corrected from 5 to 10.