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Problems Associated with Problems Associated with Comparing Comparing In SituIn Situ Water Quality Water Quality Measurements to Pollution Model Measurements to Pollution Model Output for Geographic AnalysesOutput for Geographic Analyses
Presentation to the Annual Meeting of the Association of American Geographers
March 7-11 2006, Chicago, IL Michael P. Finn
[email protected]://carto-research.er.usgs.gov/
AuthorsAuthors
Michael P. Finn Michael P. Finn aa
David D. Bosch David D. Bosch bb
E. Lynn Usery E. Lynn Usery aa
Austin D. Hartman Austin D. Hartman aa
aa U. S. Geological Survey, National Geospatial U. S. Geological Survey, National Geospatial Technical Operation CenterTechnical Operation Center
bb U. S. D. A., Agricultural Research Service U. S. D. A., Agricultural Research Service (ARS),(ARS), Southeast Watershed Research Laboratory Southeast Watershed Research Laboratory
BackgroundBackground Agricultural Non-Point Source Agricultural Non-Point Source (AGNPS)(AGNPS) Pollution Pollution
ModelModel Usery Usery et alet al., ., (2004)(2004) showed utility of using GIS showed utility of using GIS
databases to automatically generate input databases to automatically generate input parameters for AGNPSparameters for AGNPS
Automated input and output visualization through Automated input and output visualization through the ADGen program the ADGen program (described in Finn (described in Finn et alet al., 2006)., 2006)
Current research is focused on quantifying model Current research is focused on quantifying model output as generated by ADGenoutput as generated by ADGen– Today’s topic is one of three parallel investigations of Today’s topic is one of three parallel investigations of
the current researchthe current research
ObjectiveObjective
Use output of previous research to Use output of previous research to quantify significance of various quantify significance of various resolutions of spatial parameters on resolutions of spatial parameters on the model output valuesthe model output values– More specifically, determine the More specifically, determine the
accuracy of output values relative to accuracy of output values relative to in in situsitu measurements over a range of measurements over a range of spatial resolutions and identify threshold spatial resolutions and identify threshold of diminishing returns of diminishing returns (shoulder in the (shoulder in the curve) curve)
Shoulder (or Knee) in Curve Example:Shoulder (or Knee) in Curve Example:Synthetic DataSynthetic Data
0.00
2.00
4.00
6.00
8.00
10.00
12.00
-2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00
Series1
Study AreaStudy AreaLittle River Watershed, GeorgiaLittle River Watershed, Georgia
ARS benchmark ARS benchmark watershed for tillage watershed for tillage management, pesticide management, pesticide management, and management, and riparian restoration issuesriparian restoration issues
Agricultural areas with Agricultural areas with some woodland, wetlands, some woodland, wetlands, and small urban areasand small urban areas
AGNPS OutputAGNPS Output
A non-A non-point point source source (“.nps”)(“.nps”) file file– ASCII file ASCII file
(tabular, (tabular, numeric)numeric)
ADGen OutputADGen Output
ADGen Image of Phosphorous Output for the Little River, Georgia. Single Band: band 4, Total soluble phosphorous
Resample Coeffient of DeterminationElevation -- Little River Watershed
60120
480
1920
960
210240
0.000.100.200.300.400.500.600.700.800.901.00
0 500 1000 1500 2000
Resampled Size(From 30 meters)
R2
Shoulder (or Knee) in Curve Example:Shoulder (or Knee) in Curve Example:Synthetic DataSynthetic Data
0.00
2.00
4.00
6.00
8.00
10.00
12.00
-2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00
Series1
0.16 9.84
0.20 9.80
0.25 9.75
4.00 9.00
5.00 5.00
6.00 1.00
9.75 0.25
9.80 0.20
9.84 0.16
XResolution
YAccuracy
In SituIn Situ Water Quality Measurements Water Quality MeasurementsHydrologic “field” dataHydrologic “field” data
Sources: literature, spreadsheets, websites, Sources: literature, spreadsheets, websites, archived files, tables in docs, etc.archived files, tables in docs, etc.
Monthly Water Quality Averages- in spreadsheet
In SituIn Situ Water Quality Measurements Water Quality MeasurementsHydrologic “field” dataHydrologic “field” data
Sources: Sources: literature, literature, spreadsheets, spreadsheets, websites, websites, archived files, archived files, tables in docs, tables in docs, etc.etc.
Daily Output- by sub-basins- text file
In SituIn Situ Water Quality Measurements Water Quality MeasurementsHydrologic “field” dataHydrologic “field” data
Sources: literature, Sources: literature, spreadsheets, websites, spreadsheets, websites, archived files, tables in archived files, tables in docs, etc.docs, etc.
Streamflow archives- from webpage
In SituIn Situ Water Quality Measurements Water Quality MeasurementsHydrologic “field” dataHydrologic “field” data
Sources: literature, spreadsheets, websites, Sources: literature, spreadsheets, websites, archived files, tables in docs, etc.archived files, tables in docs, etc.
Verification runs- random point capture and comparison
Problems Comparing Field Data to Problems Comparing Field Data to Model OutputModel Output
Convoluted matching Convoluted matching of field and model of field and model valuesvalues
Wide, disparate sets Wide, disparate sets of data sourcesof data sources
Only two parameters Only two parameters match directly (with match directly (with unit conversions) unit conversions) and an additional 6 and an additional 6 indirectlyindirectly Direct match
Direct match
Measures of AccuracyMeasures of Accuracy
51 model output values of sediment, nitrogen, phosphorus, 51 model output values of sediment, nitrogen, phosphorus, and other nutrientsand other nutrients
Curves representing the accuracy via mathematical meansCurves representing the accuracy via mathematical means– NNthth order polynomials, cubic splines or logistic regression order polynomials, cubic splines or logistic regression
Identify shoulder in curve -> quantify spatial resolution Identify shoulder in curve -> quantify spatial resolution thresholdthreshold
Accuracy CurveAccuracy Curve66thth Order Polynomial Example Order Polynomial Example
y = -2E-11x6 - 0.0062x5 + 0.1552x4 - 1.2662x3 + 3.4774x2 - 2.2722x + 10.122
-4.00
-2.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
-2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00
Series1
Poly. (Series1)
1st:
y' = -1.2E-10x5 - 0.031x4 + 0.6208x3 - 3.7986x2 + 6.9548x - 2.2722
y' = 0 @ x = 9.68393, 7.48698, 2.44069, 0.414203
2nd:
y'' = -6E-10x4 - 0.124x3 + 1.8624x2 - 7.5972x + 6.9548
y'' = 0 @ x = 8.74971, 4.98332, 1.28632
3rd:
y''' = -2.4E-9x3 - 0.372x2 + 3.7248x - 7.5972
y''' = 0 @ x = 7.16098, 2.85193
Accuracy CurveAccuracy CurveCubic Splines ExampleCubic Splines Example
Accuracy CurveAccuracy CurveLogistic Regression ExampleLogistic Regression Example
Overcoming these problemsOvercoming these problems
Quantification of spatial thresholdQuantification of spatial threshold– Provide insight to the role of spatial Provide insight to the role of spatial
resolution on the variance of output resolution on the variance of output valuesvalues
– Ultimately, insight into geographic Ultimately, insight into geographic analyses of water-quality investigationsanalyses of water-quality investigations
ConclusionsConclusions
Resolution affects model resultsResolution affects model results Some promising techniques to Some promising techniques to
determine the accuracy of output values determine the accuracy of output values relative to relative to in situin situ measurements for the measurements for the purpose of identifying threshold of purpose of identifying threshold of diminishing returnsdiminishing returns
Issues remain in building “Accuracy Issues remain in building “Accuracy Graphs” for 51 model output parametersGraphs” for 51 model output parameters
Problems Associated with Problems Associated with Comparing Comparing In SituIn Situ Water Quality Water Quality Measurements to Pollution Model Measurements to Pollution Model Output for Geographic AnalysesOutput for Geographic Analyses
Presentation to the Annual Meeting of the Association of American Geographers
March 7-11 2006, Chicago, IL
Michael P. [email protected]://carto-research.er.usgs.gov/