1. Quantifying Uncertainty and Biases in Automated Precipitation Measurements John Kochendorfer, Bruce Baker, Tilden Meyers and Mark Hall NOAA/ATDD Roy Rasmussen, Scott Landolt and Al Jachcik NCAR Michael Earl, Lawrence Wilson and Rodica Nitu Environment Canada Mareile Wolff Norwegian Meteorological Institute

2. WMO Solid Precipitation InterComparison Experiment (SPICE)

3. WMO-SPICE Objectives Define automated field references Address operational/network issues Derive transfer functions Quantify uncertainty Evaluate emerging technology CARE (Canada) Photos courtesty of Rodica Nitu, Environment Canada

4. WMO-SPICE Objectives Define automated field references Address operational/network issues Derive transfer functions Quantify uncertainty Evaluate emerging technology CARE (Canada) Photos courtesty of Rodica Nitu, Environment Canada

5. WMO-SPICE Objectives (3) Derive adjustments to be applied to measurements specific to individual automatic systems (gauge+shield) A function of variables available at an operational site: e.g., wind, temp, RH Courtesy: Craig Smith (EC)

6. WMO-SPICE Objectives (4)  Assess the measurement uncertainty of instruments included in WMO-SPICE:  sensitivity, uncertainty, bias, repeatability, and response time of automatic systems;  sources and magnitude of errors; (field experiments and CFD simulation);  Effects of snowflake characteristics (size, type) on gauge collection efficiency; Theriault et al. 10.1175/JAMC-D-11-0116.1 2011 Data from single Alter GEONOR gauge (box plots) Magenta: Model results from Fluent simulation of flow past single Alter GEONOR with snowflake trajectory modeling

7. Reference Measurement Uncertainty Dependent on meteorology Dependent on analysis techniques Difficult to quantify all sources of uncertainty “there are known knowns... We also know there are known unknowns… But there are also unknown unknowns...” -Donald Rumsfield

9. Shielding is irrelevant in rain

11. NOAA/NCAR/FAA Marshall, CO Site

12. Individual Geonor measurements compared to the average of all five gauges

15. Scatter index (s x ) estimated for every 30- min event from the standard deviation between the five gauges

16. Marshall Geonors and Wind Speed

17. Marshall Geonors and T air

18. Environment Canada CARE Site DFIR SA U DA SA U 6 x Geonor T-200B3 5 x OTT Pluvio 2 Shield legend: DFIR – double fence intercomparison reference shield DA – double-Alter SA – single-Alter U - unshielded

19. Pluvio NRT and Wind Speed

20. Pluvio NRT and T air

21. Average Scatter Index GaugeSxSx SiSi N Care Pluvio RT (5)0.03 mm3.1 %90 Care Pluvio NRT (5)0.04 mm4.6%87 Care Geonor (6)0.03 mm3.0%110 Marshall Geonor (5)0.07 mm7.5%490

22. Comparison of identical gauge/shield combinations Includes both snow and rain.

24. Possible Transfer Functions

25. Data from Haukeliseter, Finland

26. SSE: 19.53 R-square: 0.549 Adjusted R-square: 0.5473 RMSE: 0.1228

27. The end

28. Unshielded Geonor

29. Single-Alter Geonor

30. Double-Alter Geonor

31. Belfort Double Alter Geonor

32. Small DFIR Geonor