Two image segmentation techniques and a pixel classification were compared for mapping sagebrush in southern Montana. The SILC3 method used an image segmentation based on a 30m unsupervised classification of a July 2000 Landsat image. The eCognition method used an image segmentation based on a 15m bottom up region merging algorithm of a September 1999 Landsat image. The modified USFS Region Four principal components analysis (PCA) method used a pixel classification based on a 15m isodata analysis of the first 3 principle components of a September 1999 Landsat image. A study area was defined for the project based on the intersection of the July 2000 and September 1999 Landsat imagery. To reduce spectral and ecological differences, the study area was additionally restricted to the intersection of the two Landsat images within Montana and 24 miles south of the Montana border in Wyoming. Below is a detailed description of how the BLM3729SILC3 grid was created using the SILC3 image segmentation method.
BLM3729SILC3 Land Cover Type Classification using Sagebrush Canopy Classes Covertype Acres Description ------------------------------------------------ 1100 3937.1 Urban or Developed Lands 2010 82499.4 Agricultural - Dry 2020 171705.7 Agricultural - Irrigated 3130 542839.6 Very Low Cover Grasslands 3150 368958.0 Low / Moderate Cover Grasslands 3170 43581.6 Moderate / High Cover Grasslands 3370 416683.7 Sagebrush / Xeric Shrubs 05-14% Cover 3380 437902.4 Sagebrush / Xeric Shrubs 15-24% Cover 3390 130989.9 Sagebrush / Xeric Shrubs 25-34% Cover 3395 63706.3 Sagebrush / Xeric Shrubs >= 35% Cover 3610 134172.8 Mesic Shrublands / Willow 4101 18069.6 Aspen 4150 32303.1 Mixed Broadleaf / Cottonwood Forest 4203 29811.1 Lodgepole Pine 4204 108338.3 Whitebark Pine 4205 81662.1 Limber Pine 4206 38666.5 Ponderosa Pine 4212 143962.2 Douglas-fir 4216 175274.3 Utah Juniper 4223 5185.4 Douglas-fir/Lodgepole Pine 4237 115601.7 Subalpine Fir/Spruce 4241 74013.2 Mixed Upper Subalpine Conifer Forest 4242 31861.2 Mixed Lower Subalpine Conifer Forest 4244 25927.0 Mixed Xeric Conifer Forest 4400 342704.2 Burns 5000 30281.1 Water 7300 325728.8 Rock/Barren 7500 484.8 Mines/Quarries 9100 35524.5 SnowBLM3729SILC3 Sagebrush Species Classes (for regions classified as a sagebrush type above) Covertype Acres Description ------------------------------------------------ 3311 35802.5 Greasewood 3351 28977.4 Mountain Big Sagebrush 3352 861631.5 Wyoming Big Sagebrush 3353 9605.0 Basin Big Sagebrush 3354 113265.9 Black / Low Sagebrush
First, the Landsat image was run through a seven step isodata analysis to identify approximately 120 spectral classes. A potential natural vegetation (PVT) classification provided by Region One of the USDA Forest Service was included as a seed source in the isodata analysis. The Landsat image was then classified using the spectral class set, each of the approximately 56 million pixels were classified into one of the 120 spectral classes. The classified image was analyzed for areas with multiple ground features within a single spectral class. These spectral classes were removed from the spectral class set, split using an additional isodata analysis, and then added back to the original spectral class set. The Landsat image was reclassified using the new spectral class set and again analyzed for large spectral class regions. This process was repeated until a final spectral class set of 130-150 classes was created and then used to classify the pixels into spectral classes.
The classified pixels were then merged into regions (raster polygons) through a multi-stage merge algorithm using a variable minimum map unit based on heterogeneity of the surrounding pixels. Regions larger than 202.4 hectares were divided until all regions in the grid were less than 202.4 hectares (500 acres). The final unsupervised classification resulted in the creation of the P37R29Z grid with 751,176 regions ranging in size from 0.1 hectare to 202.2 hectares. Each region was assigned a set of attributes for TM channels 1-7 and panchromatic from the imagery, along with elevation, aspect, and slope from the 30 meter digital elevation model (DEM); these attribute values were calculated based on the mean values of the 30 meter pixels within each region. The original SILC3 P37R29Z grid was clipped to the study area described above, creating the BLM3729SILC3 region grid with 360,043 regions.
Vegetation overstory (land cover type) was labeled using a supervised classification. The land cover type supervised classification was performed using a combination of manual and training data classifications. The manual classification was performed by on screen analysis of the imagery and directly assigning cover type labels. The labels were filled into the MANLABEL attribute. The following classes were manually labeled:
COVERTYPE DESCRIPTION ------------------------------------------------ 1100 Urban or Developed Lands 2010 Agricultural - Dry 2020 Agricultural - Irrigated 4400 Burns 5000 Water 7500 Mines/Quarries 9100 Snow
Twenty land cover types were labeled using a training data classification. Canopy cover classes were used for both grassland and sagebrush/xeric shrub types because canopy classes provided significantly better separation between the two lifeforms than species classes did. A euclidian distance classifier based on TM band data and topographic variables with a nearest neighborhood of 15 was used in conjunction with a mean inverse spatial classifier to assign labels to the regions. The labels were filled into the COV_CODE_1 ATTRIBUTE. The following classes were used in the training data classification:
COVERTYPE DESCRIPTION ------------------------------------------------ 3130 Very Low Cover Grasslands 3150 Low / Moderate Cover Grasslands 3170 Moderate / High Cover Grasslands 3370 Sagebrush / Xeric Shrubs 05-14% Cover 3380 Sagebrush / Xeric Shrubs 15-24% Cover 3390 Sagebrush / Xeric Shrubs 25-34% Cover 3395 Sagebrush / Xeric Shrubs >= 35% Cover 3610 Mesic Shrublands / Willow 4101 Aspen 4150 Mixed Broadleaf / Cottonwood Forest 4203 Lodgepole Pine 4204 Whitebark Pine 4205 Limber Pine 4206 Ponderosa Pine 4212 Douglas-fir 4216 Utah Juniper 4223 Douglas-fir/Lodgepole Pine 4237 Subalpine Fir/Spruce 4240 Mixed Conifer Forest 7300 Rock/Barren
After the training data classification, regions labeled as Mixed Conifer Forest (4240) were assigned to one of three mixed conifer types using a ruleset based on elevation and PVT type for the region (see mixcon_recode.aml).
4241 Mixed Upper Subalpine Conifer Forest 4242 Mixed Lower Subalpine Conifer Forest 4244 Mixed Xeric Conifer Forest
A second training data classification was used to assign sagebrush species to regions classified as sagebrush/xeric shrub types in the first train data classification. A euclidian distance classifier based on TM band data and topographic variables with a nearest neighborhood of 15 was used in conjunction with a mean inverse spatial classifier to assign labels to the regions. The labels were filled into the SAGESPP1 ATTRIBUTE. The following classes were used in the sagebrush species classification:
SAGESPECIES DESCRIPTION ------------------------------------------------ 3311 Greasewood 3351 Mountain Big Sagebrush 3352 Wyoming Big Sagebrush 3353 Basin Big Sagebrush 3354 Black / Low Sagebrush
An accuracy assessment was performed on the land cover type and sagebrush species labels assigned from the training data classifications. A cross validation (leave-one-out) accuracy assessment was performed using the entire training data set.
To help track similarities and differences in map legends between this classification and previous ones (SILC1 and MT-GAP) cover type names and codes numbers were not changed if the actual types were mapped using similar training data.
Users Accuracies of Land Cover Types were: Acc% Covertype Definition ------------------------------------------- 86.9 3130 Very Low Cover Grasslands 82.4 3150 Low / Moderate Cover Grasslands 81.4 3170 Moderate / High Cover Grasslands 61.7 3370 Sagebrush / Xeric Shrubs 05-14% Cover 52.6 3380 Sagebrush / Xeric Shrubs 15-24% Cover 50.5 3390 Sagebrush / Xeric Shrubs 25-34% Cover 83.6 3395 Sagebrush / Xeric Shrubs >= 35% Cover 75.7 3610 Mesic Shrublands / Willow 69.1 4101 Aspen 79.4 4150 Mixed Broadleaf / Cottonwood Forest 62.5 4203 Lodgepole Pine 83.3 4204 Whitebark Pine 75.5 4205 Limber Pine 72.7 4206 Ponderosa Pine 80.6 4212 Douglas-fir 66.6 4216 Utah Juniper 46.3 4223 Douglas-fir/Lodgepole Pine 58.5 4237 Subalpine Fir/Spruce 65.4 4240 Mixed Conifer Forest 96.4 7300 Rock/Barren
Users Accuracies of Sagebrush Species were: Acc% SAGESPECIES DESCRIPTION ------------------------------------------------ 82.1 3311 Greasewood 89.3 3351 Mountain Big Sagebrush 96.6 3352 Wyoming Big Sagebrush 16.6 3353 Basin Big Sagebrush 83.7 3354 Black / Low Sagebrush
MAKE-DEM: extracted a digital elevation model (DEM) from the WSAL database for use during labeling.
MAKE-HYDROGRAPHY: extracted a hydrography coverage from the WSAL hydrography database for use during labeling.
REGIONGROUP: Used GRID regiongroup command to region group the final spectral class groups from the merge. Built an ArcInfo value attribute table (VAT) to hold all items (fields) for which descriptive data could be developed for each region. Filled in VALUE, COUNT, LINK, HECTARES, PERIMETER, TM1, TM2, TM3, TM4, TM5, TM6, TM7, PAN, TM1STD, TM2STD, TM3STD, TM4STD, TM5STD, TM6STD, TM7STD, PANSTD, MNDVI, ELE, SLP, ASP, and SLPASP fields.
PROCESS-GT: filled in spectral, topographic, and hydrologic information in ground-truth training data for use in supervised classification.
CODE DESCRIPTION MNDVI ----------------------------------------------- 3130 very low cover grasslands < -10 3150 low / moderate cover grasslands -10 to 34.9 3170 moderate / high cover grasslands >= 35
The training data were run through a cross-validation test where each train data was removed and then classified using the remaining train data set. A Dudani distance-weighted euclidian distance classifier using variables: TM1, TM2, TM3, TM4, TM5, TM7, MNDVI, ELEV (scaled elevation), SLP, and SLPASP with a nearest neighborhood of 15 was used in conjunction with a mean inverse spatial classifier. Outlier train data were identified based on the cross-validation test and were removed from the train data set. After completing the train data evaluation, the final train data set was used to run a supervised classification of all regions in the BLM3729SILC3 grid. The euclidian distance and spatial classifiers described above were used to classify the regions. The top three most probable land cover types were filled into the COV_CODE_1, COV_CODE_2, and COV_CODE_3 fields.
The final land cover type label was filled into the COVERTYPE field from the MANLABEL field if it was > -1 else from the COV_CODE_1 field.
Regions classified as Mixed Conifer Forest (4240) were recoded to one of three types based on a ruleset using the pvt type and elevation of the region.
4241 Mixed Upper Subalpine Conifer Forest 4242 Mixed Lower Subalpine Conifer Forest 4244 Mixed Xeric Conifer Forest
The aml with the ruleset is available through the data contact.
COVERTYPE DESCRIPTION ------------------------------------------------ 1100 Urban or Developed Lands 2010 Agricultural - Dry 2020 Agricultural - Irrigated 3130 Very Low Cover Grasslands 3150 Low / Moderate Cover Grasslands 3170 Moderate / High Cover Grasslands 3370 Sagebrush / Xeric Shrubs 05-14% Cover 3380 Sagebrush / Xeric Shrubs 15-24% Cover 3390 Sagebrush / Xeric Shrubs 25-34% Cover 3395 Sagebrush / Xeric Shrubs >= 35% Cover 3610 Mesic Shrublands / Willow 4101 Aspen 4150 Mixed Broadleaf / Cottonwood Forest 4203 Lodgepole Pine 4204 Whitebark Pine 4205 Limber Pine 4206 Ponderosa Pine 4212 Douglas-fir 4216 Utah Juniper 4223 Douglas-fir/Lodgepole Pine 4237 Subalpine Fir/Spruce 4241 Mixed Upper Subalpine Forest 4242 Mixed Lower Subalpine Forest 4244 Mixed Xeric Conifer Forest 4400 Burns 5000 Water 7300 Rock/Barren 9100 Snow
COVERTYPE DESCRIPTION ------------------------------------------------ 3130 Very Low Cover Grasslands 3150 Low / Moderate Cover Grasslands 3170 Moderate / High Cover Grasslands 3370 Sagebrush / Xeric Shrubs 05-14% Cover 3380 Sagebrush / Xeric Shrubs 15-24% Cover 3390 Sagebrush / Xeric Shrubs 25-34% Cover 3395 Sagebrush / Xeric Shrubs >= 35% Cover 3610 Mesic Shrublands / Willow 4101 Aspen 4150 Mixed Broadleaf / Cottonwood Forest 4203 Lodgepole Pine 4204 Whitebark Pine 4205 Limber Pine 4206 Ponderosa Pine 4212 Douglas-fir 4216 Utah Juniper 4223 Douglas-fir/Lodgepole Pine 4237 Subalpine Fir/Spruce 4240 Mixed Conifer Forest 7300 Rock/Barren
Code Definition ---------------- -1 Not Manually Classified 1100 Urban or Developed Lands 2010 Agricultural - Dry 2020 Agricultural - Irrigated 4400 Burns 5000 Water 7500 Mines / Quarries 9100 Snow
Code Description ----------------- 0 Flat 1 North 2 Northeast 3 East 4 Southeast 5 South 6 Southwest 7 West 8 Northwest
Code Description ----------------- 3311 Greasewood 3351 Mountain Big Sagebrush 3352 Wyoming Big Sagebrush 3353 Basin Big Sagebrush 3354 Black / Low Sagebrush
Code Definition ---------------- 0 no pvt code assigned 1 abla1 (lower elevation subalpine fir type) 2 abla2 (high elevation subalpine fir type) 3 junipe 4 laly (alpine larch) 5 pial (whitebark pine type) 6 picea (spruce type) 7 pincon (lodgepole pine) 8 pifl (limber pine type) 9 pinpon (ponderosa pine) 11 psemen (Douglas-fir type) 12 agric (agriculture type) 13 agrsmi 14 alpgrass (alpine grasslands type) 15 drygrass (xeric, valley bottom or foothills grassland type) 16 fesida (Idaho fescue type) 18 ripgrass (riparian grass type) 19 rock (rock dominated type) 20 bigsage (big sagebrush type) 21 dryshrub (non-sagebrush xeric shrub type) 22 messhrub 23 potfru (shrubby cinquefoil type) 24 rhusx 25 ripshrub (riparian shrub type) 27 urban 28 water