Robust sampling of natural Robust sampling of natural resources using a GIS resources using a GIS implementation of GRTS implementation of GRTS David Theobald Natural Resource Ecology Lab Dept of Recreation & Tourism Colorado State University Fort Collins, CO 80523 USA 23 September 2004
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Robust sampling of natural resources using a GIS implementation of GRTS
Robust sampling of natural resources using a GIS implementation of GRTS. David Theobald Natural Resource Ecology Lab Dept of Recreation & Tourism Colorado State University Fort Collins, CO 80523 USA 23 September 2004. CR - 829095. Funding/Disclaimer. - PowerPoint PPT Presentation
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Robust sampling of natural resources Robust sampling of natural resources using a GIS implementation of GRTSusing a GIS implementation of GRTS
David TheobaldNatural Resource Ecology Lab
Dept of Recreation & Tourism
Colorado State University
Fort Collins, CO 80523 USA23 September 2004
Funding/DisclaimerFunding/Disclaimer The work reported here was developed under the
STAR Research Assistance Agreement CR-829095 awarded by the U.S. Environmental Protection Agency (EPA) to Colorado State University. This presentation has not been formally reviewed by EPA. The views expressed here are solely those of the presenter and STARMAP, the Program (s)he represents. EPA does not endorse any products or commercial services mentioned in this presentation.
CR - 829095
Practical sampling needsPractical sampling needs Most information for least cost Sample some areas with higher probability than
others– Some features are more important than others– Higher uncertainty of knowing about particular
situations– Some locations are more difficult (time, $) to
access than others Flexibility
– In-the-field decisions (e.g., access denied, extra time)
– Changes in funding (+ or -) for current project– Subsequent projects (additional funding)
augment existing dataset (but often different study area)
GRTS algorithm (Stevens 1997; Stevens and Olsen 1999; Stevens and Olsen 2004)
Why GIS framework?Why GIS framework? Spatial data is needed to as input to describe population
(frame) Spatial data used to describe strata, to describe inclusion
probabilities, including continuous variables (e.g., terrain) Ability to sample point, line, and area-based ecological
resources Flexibility in adjusting input to alter sampling design Visualize sampling design in relation to other geographic
data: (e.g., accessibility, ownership) Large, broad user base of GIS technology
Sampling in ArcView v3, ArcGIS v8, v9– Typically simple random sampling (e.g., random x,
y constrained to polygon of study area) GStat (www.gstat.org): Pebesma and Wesseling. 1998.
Gstat, a program for geostatistical modeling, prediction and simulation. Computers and Geosciences 24(1):17-31.– Traditional: stratified, simple random sampling
Ecological resource types Ecological resource types Areas (e.g., lakes, land cover patches)
– Discrete – represent as point shapefile, GRID with single cell• Convert to centroid or labelpoint then to GRID• Tesselate surface: e.g., watersheds, 8-digit HUCs• Discontinuous: all lakes in Oregon
– Continuous – represent as polygon, GRID as zones• Patches of vegetation types• Variation of water clarity within selected lakes• Estuarine resources• Area bias?
Lines (e.g., streams, roads)– Discrete – represent as point shapefile, GRID with single cell
• Individual stream reaches• 100’ segments
– Continuous• All possible locations on stream network
Points (e.g., individual trees, lakes)– Discrete
• all lakes in Oregon
Population(MASK: 1/Nodata) Sample
Samples(point shapefile)
Inclusion Prob.(01)
Population(MASK: 1/Nodata) Sample
Samples(point shapefile)
Inclusion Prob.(01)
Strata(01)
Env. gradient(e.g., moisture)
Special resource(e.g., riparian areas)
Processing stepsProcessing steps 1. Input
– raster or GRID of frame, inclusion probabilities– get spatial extent, grain (resolution), study area (inside,
outside, holes) 2. compute number of quad-levels, L 3. generate random permuted 1-4 labels at each L 4. add levels together to create reverse-ordered
address 5. compute sequential list order 6. threshold against inclusion probabilities 7. convert raster to point shapefile
Level 1Level 1
111 113 131 133 311 313 331 333
112 114 132 134 312 314 332 334
121 123 141 143 321 323 341 343
122 124 142 144 322 324 342 344
211 213 231 233 411 413 431 433
212 214 232 234 412 414 432 434
221 223 241 243 421 423 441 443
222 224 242 244 422 424 442 444
1 3
2 4
Level 2Level 2
111 113 131 133 311 313 331 333
112 114 132 134 312 314 332 334
121 123 141 143 321 323 341 343
122 124 142 144 322 324 342 344
211 213 231 233 411 413 431 433
212 214 232 234 412 414 432 434
221 223 241 243 421 423 441 443
222 224 242 244 422 424 442 444
1 1
1 1
2 2
2 2
3 3
3 3
4 4
4 4
Level 3Level 3
111 113 131 133 311 313 331 333
112 114 132 134 312 314 332 334
121 123 141 143 321 323 341 343
122 124 142 144 322 324 342 344
211 213 231 233 411 413 431 433
212 214 232 234 412 414 432 434
221 223 241 243 421 423 441 443
222 224 242 244 422 424 442 444
Morton address to sequential listMorton address to sequential list
75
64
931
820
12 14 36 38 44 46
13 15 37 39 45 47
16 18 24 26 48 50 56 58
17
10
25 27 49 51 57 59
20 22 28 30 52 54 60 62
21 23 29 31 53 55 61 63
4341353311
42403432
19
Reverse-Morton address to listReverse-Morton address to list
111 311 131 331 113 313 133 333
211 411 231 431 213 413 233 433
121 321 141 341 123 323 143 343
221 421 241 441 223 423 243 443
112 312 132 332 114 314 134 334
212 412 232 432 214 414 234 434
122 322 142 342 124 324 144 344
222 422 242 442 224 424 244 444
75
391
64
280
50 26 58
36 12 44 38 14 46
20 52 28 60 22 54 30 62
33 41 35 11
32
17 49 25 57 19 51 27 59
37 13 45 39 15 47
21 53 29 61 23 55 31 63
1856244816
42103440
43
Random permutation of quad Random permutation of quad valuesvalues
2
68
04
7
13
5963 31 57 37
39 23 35 45 29 17
55 51 19 13 61 49 33
52 48 46 62
27
58
36 20 32 16 14 30 26 10
24 60 28 54 18 50
40 56 44 12 22 38 34
1143
21534125471559
42
Area frame for vegetation surveyArea frame for vegetation survey
““Continuous” listing of sequential Continuous” listing of sequential pointspoints