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General framework for features-based verification

Explore a general framework for verifying meteorological data using object-oriented methods, joint distributions of forecasts and observations, feature characterization, and object matching. Learn key terminology, methods for identifying, classifying, and comparing features, and measuring accuracy and reliability.

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General framework for features-based verification

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  1. General framework for features-based verification Mike Baldwin Purdue University

  2. General framework • Any verification method should be built upon the general framework for verification outlined by Murphy and Winkler (1987) • Object-oriented or features-based methods can be considered an extension or generalization of the original framework • Joint distribution of forecasts and observations: p(f,o)

  3. general joint distribution • p(f,o) : where f and o are vectors containing all variables, 3-D, same time • o could come from data assimilation o=first guess + weight*forward_model(obs) • p(fm,om) : fm and om are values of a single variable across the entire domain • traditional joint distribution

  4. general joint distribution • p(G(f),G(o)) : where G is some mapping/transformation/operator that is applied to the variable values • morphing • filter • convolution • deformation • fuzzy

  5. general joint distribution • p(Gm(f),Gm(o)) : where Gm is a specific aspect/attribute/characteristic that results from the mapping operator • distributions-oriented • measures-oriented • compute some error measure or score that is a function of Gm(f),Gm(o) • MSE

  6. Terminology that we might standardize • “feature” – a distinct or important physical object that can be identified within meteorological data • “attribute” – a characteristic or quality of a feature, an aspect that can be measured • “similarity” – the degree of resemblance between features • “distance” – the degree of difference between features • (others?)

  7. framework • follow Murphy (1993) and Murphy and Winkler (1987) terminology • joint distribution of forecast and observed features • goodness: consistency, quality, value

  8. aspects of quality • accuracy: correspondence between forecast and observed feature attributes • single and/or multiple? • bias: correspondence between mean forecast and mean observed attributes • resolution • reliability • discrimination • stratification

  9. Features-based process • Identify features FCST OBS

  10. Features-based process • Characterize features FCST OBS

  11. How to determine false alarms/missed events? How to measure differences between objects? Features-based process • Compare features FCST OBS

  12. Features-based process • Classify features FCST OBS

  13. feature identification • procedures for locating a feature within the meteorological data • will depend on the problem/phenomena/user of interest • a set of instructions that can (easily) be followed/programmed in order for features to be objectively identified in an automated fashion

  14. feature characterization • a set of attributes that describe important aspects of each feature • numerical values will be the most useful

  15. feature comparison • similarity or distance measures • systematic method of matching or pairing observed and forecast features • determination of false alarms? • determination of missed events?

  16. classification • a procedure to place similar features into groups or classes • reduces the dimensionality of the verification problem • similar to going from a scatter plot to a contingency table • not necessary/may not always be used

  17. SSEC MODIS archive 10 Apr 2003

  18. feature matching

  19. attributes

  20. How to match observed and forecast objects? = missed event dij = ‘distance’ between F i and O j O1 O3 Objects might “match” more than once… If d*j > dT : missed event O2 F1 …for each observed object, choose closest forecast object …for each forecast object, choose closest observed object If di* > dT then false alarm F2 = false alarm

  21. Example of object verf ARW 2km (CAPS) Radar mosaic Fcst_2 Obs_2 Fcst_1 Obs_1 Object identification procedure identifies 4 forecast objects and 5 observed objects

  22. ARW 2km (CAPS) Radar mosaic Distances between objects • Use dT = 4 as threshold • Match objects, find false alarms, missed events

  23. ARW4 ARW2 Df = .04 Dl = -.07 Df = .07 Dl = .08 median position errors matching obs object given a forecast object NMM4 Df = .04 Dl = .22

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