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

mfinn@usgs.govhttp://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

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-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

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2.00

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-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

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2.00

4.00

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-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. Finnmfinn@usgs.govhttp://carto-research.er.usgs.gov/