Ocean & Sea Ice SAF. Validation of ice products January March Version 1.1. May 2005

Transcription

1 Ocean & Sea Ice SAF Validation of ice products January March 2005 Version 1.1 May 2005 Morten Lind, Keld Q. Hansen, Søren Andersen

2 1 INTRODUCTION PRODUCTS VALIDATION METHODS GENERAL CHARACTERISTICS OF THE GREENLAND SEA ICE COVER VALIDATION STATISTICS DAILY VALIDATION OF THE SAF PRODUCTS... 5 Ice concentration... 5 Ice edge... 6 Ice type WEEKLY COMPARISON OF SAF PRODUCT WITH THE DMI ICE ANALYSES... 7 Ice concentration... 7 Ice edge COMMENTS TO VALIDATION STATS APPENDIX A APPENDIX B APPENDIX C... 21

3 1 Introduction Validation takes a prominent position in the definition of the Ocean & Sea Ice SAF products. For the sea ice products, quality assurance involves the comparison of the automatic SAF sea ice analyses to navigational ice analyses as well as weekly overview ice charts issued by the ice centres in Denmark and Norway (DMI and DNMI). For the background and the technical specifications of these products, please see the sea ice product manual available at This report describes the quality of the O&SI SAF sea ice products covering the period 1. January April 2005 (51 months). 2 Products Validation methods For most advantageous utilisation of operational Ice Centre products and experience it was decided to validate the O&SI products west of 0º E/W in two separate ways: 1) Daily O&SI products compared visually / subjectively with the operationally prepared navigation ice charts or other relevant information using 3 categories, defined like: ICE CONCENTRATION: Good: SAF product average deviation better than 10%. Acceptable: Average deviation 10-30%. Bad: Average deviation more than 30% or major error ICE EDGE: Good: Acceptable: Bad: SAF product average deviation better than 10 km Average deviation km Average deviation more than 50 km or major error ICE TYPE: Good: Acceptable: Bad: Determines the correct ice type in most ice areas Correct ice type in about 35-65% of ice covered areas Correct ice type in less than 35% of ice covered areas or major error

4 An example of a scheme used through the operational validation period are shown in Appendix A. 2) Once a week the O&SI products compared statistically to the weekly DMI ice analysis for the entire Greenland area. The weekly ice analysis compile all available satellite data, including Radarsat SAR and NOAA-AVHRR for a weekly reference date at 12 UTC (± 24 hours). No additional ice products are believed to have a better accuracy compared with coverage. The Greenland weekly ice analysis for operational use is available at All ice analyses used for validation are available in the DMI archives. The resolution of the data grid extracted from the weekly analysis and the O&SI SAF products is 10 km. There were a few events of data errors and technical problems causing minor data delivery break downs, however these events did not disturb the overall results of the validation. 3 General characteristics of the Greenland sea ice cover Winter 2001/02 Greenland West Greenland South Greenland East Normal freeze-up (normal ice cover through the ice season) Late arrival of MY-ice from north Summer 2002 Early break-up (2-4 weeks) MY ice clearance in early August (normal) Winter 2002/03 Late Freeze-up (2-3 weeks) (less than normal ice cover through the ice season) Very late arrival of MY-ice from north Summer 2003 Early break-up (2-4 weeks) MY ice clearance in late June (5-6 weeks earlier than normal Winter 2003/04 Late Freeze-up (2-3 weeks) (less than normal ice cover through the ice season) Normal arrival of MY-ice from north Summer 2004 Early break-up (2-4 weeks) MY ice clearance in late August (3 weeks later than normal) Normal or slightly lighter than normal MY ice retreat to 79ºN (record low, normal 70ºN) Normal or slightly lighter than normal MY ice retreat to 74ºN (lighter than normal) Normal or slightly lighter than normal MY ice retreat to 74ºN (lighter than normal) Fall 2004 Freeze up close to normal No MY ice MY ice cover below normal Winter 2004/05 Less than normal ice cover throughout the ice season Very late arrival of MY-ice from north (app. 3 months) In general lighter ice cover than normal, but due to wind conditions ice cover above normal in the Denmark Strait inbetween Greenland and Iceland

5 4 Validation statistics 4.1 Daily validation of the SAF products The following three figures summarise the result of the daily validation for the O&SI SAF ice concentration, ice edge and ice type products for the period of January March Ice concentration Ice concentration (daily validation) fraction of IA's (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Jan 2002 Mar 2002 May 2002 July 2002 Sep 2002 Nov 2002 Jan 2003 Mar 2003 May 2003 July 2003 Sep 2003 Nov 2003 Jan 2004 Mar 2004 May 2004 July 2004 Sep 2004 Nov 2004 Jan 2005 Mar 2005 Good (1/10) Acceptable (1-3/10) date Bad (>3/10) No data Figure Feil! Ukjent bryterargument.: Bar graph showing the daily validation of the SAF ice concentration product.

6 Ice edge Ice edge (daily validation) fraction of IA's (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Jan 2002 Mar 2002 May 2002 July 2002 Sep 2002 Nov 2002 Jan 2003 Mar 2003 May 2003 July 2003 Sep 2003 Nov 2003 Jan 2004 Mar 2004 May 2004 July 2004 Sep 2004 Nov 2004 Jan 2005 Mar 2005 date Good (1/10) Acceptable (1-3/10) Bad (>3/10) No data Figure Feil! Ukjent bryterargument.: Bar graph showing the daily validation of the SAF ice edge product. Ice type Ice type (daily validation) fraction of IA's (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Jan 2002 Mar 2002 May 2002 July 2002 Sep 2002 Nov 2002 Jan 2003 Mar 2003 May 2003 July 2003 Sep 2003 Nov 2003 Jan 2004 Mar 2004 May 2004 July 2004 Sep 2004 Nov 2004 Jan 2005 Mar 2005 Good Acceptable datebad No data

7 Figure Feil! Ukjent bryterargument.: Bar graph showing the daily validation of the SAF ice type product.

8 4.2 Weekly comparison of SAF product with the DMI ice analyses The following figures show the results of the weekly comparison between the SAF ice concentration/edge products and the weekly DMI ice analyses. The statistics that founds the basis for the following two figures can be found in appendix B. Ice concentration Sea Ice Concentration (weekly charts) fraction of grid points (%) Match +/- 20 % Match +/- 10 % Figure Feil! Ukjent bryterargument.: Comparison between ice concentrations from the weekly DMI ice analysis and the SAF concentration product. 'Match +/- 10 %' corresponds to those gridpoints where concentration deviates within the range of +/-10 %. Each vertical line indicates one comparison. Situations where vertical lines are missing indicates missing DMI ice analyses.

9 Bias of ice concentration bias (% ice concentration) Water Ice Total date Figure Feil! Ukjent bryterargument.: Bias of ice concentration for three categories, i.e. water, ice and both. No estimates are available before 1st January Std. dev. of ice concentration std. dev. (% ice concentration) 10 Water Ice Total date Figure Feil! Ukjent bryterargument.: Standard deviation of ice concentration for three categories: water, ice and total. No estimates available before 1st January 2005.

10 Ice edge Sea Ice Edge (weekly charts) fraction of grid points (%) Match (ice-ice) SAF underestimates (water-ice) SAF overestimates (ice-water) Figure Feil! Ukjent bryterargument.: Area graph showing the comparison between the weekly DMI ice analysis and the SAF edge product. 'SAF underestimates' means grid points where the SAF product indicated water and the DMI ice analysis indicated ice and vice versa for 'SAF overestimates'. Each vertical line indicates one weekly comparison.

11 5 Comments to validation stats Each of the three parameters, ice type, ice concentration and ice edge were validated individually but the ice type parameter is hard to evaluate due to lack of direct measurements of the sea ice thickness. Sea ice concentration On a weekly basis the O&SI SAF grid was compared with the related weekly ice analysis grid and the quantitative ice concentration match (number of grid points) ± 10% and ± 20% was determined (see Appendix C for an example of the weekly statistics). Outside the melt season the match ± 10% is generally 60-80% and for ± 20% it is 80-90%, see Figure Feil! Ukjent bryterargument.. In melt season, Mid-June to Early September the match decreases dramatically. Average Match, Summary ± 10% ± 20% Concentration, Oct-May 72% 84% Concentration, June-Sept 54% 69% Table Feil! Ukjent bryterargument.: The average no. of grid points that match within +/- 10% and +/- 20% on a seasonal basis. Predominately the SAF product underestimates the sea ice concentration Through the operational validation it was found that the concentration of Baffin Bay / Davis Strait sea ice is estimated better than for sea ice at the Greenland East coast. Sea ice edge Through the entire period the ice edge product proved high quality and stability, see Feil! Ukjent bryterargument. and Feil! Ukjent bryterargument.. From Figure Feil! Ukjent bryterargument. it is evident that underestimation and overestimation is of the same magnitude during winter time (October - May). This indicates that the bias is insignificant. During summer there is a bias towards underestimation, i.e. the SAF product tends to estimate water when ice analysis estimates ice. The match between the weekly ice analysis grid and SAF product grid is calculated as a fraction Number of matching grid points (ice-ice) matching grid points (ice-ice) + grid points(ice-water) + grid points(water-ice) The summary of the weekly statistics is shown in the table below Average Match, Summary IA Ice SAF Ice edge, Oct-May 93%

12 Ice edge, June-Sept 79% Table Feil! Ukjent bryterargument.: No. of grid points that matches ice in both the SAF edge product and the DMI ice analysis. Sea ice type The SAF product is generally able to classify the sea ice type (first year ice) correctly in Baffin Bay / Davis Strait but it underestimates the amount of multi-year ice in the East Greenland Current. However, the general sense of this product is that it does not give operational information on top of basic sea ice climatic knowledge.

13 Appendix

14 APPENDIX A DMI SAF Ice edge validation Month Date Good Acc Bad Comments Report to SAF manager

15 30 31

16 APPENDIX B Ice edge IA SAF Concentration dato Ice_ice Ice-water water ice water water Match % Match ice >=20 exact10 exact20 <=20 Match 10% Match 20% ,0 94, ,1 74, ,5 85, ,9 86, ,1 95, ,9 89, ,2 95, ,0 83, ,5 96, ,9 84, ,7 94, ,5 86, ,0 93, ,0 83, ,5 92, ,9 82, ,7 92, ,4 87, ,0 95, ,0 90, ,1 95, ,0 89, ,3 96, ,3 87, ,4 96, ,6 89, ,3 95, ,4 88, ,6 94, ,2 92, ,2 95, ,8 86, ,7 92, ,3 86, ,6 93, ,5 91, ,7 94, ,0 87, ,6 94, ,9 81, ,2 92, ,9 85, ,9 91, ,1 80, ,2 89, ,5 76, ,2 89, ,9 70, ,5 86, ,8 67, ,2 79, ,6 49, #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T ,6 66, ,7 39,6

17 ,3 56, ,1 36, ,3 59, ,5 46, ,4 73, ,5 66, ,9 75, ,2 66, ,3 75, ,9 20, ,1 69, ,7 58, ,6 76, ,7 64, ,7 83, ,8 81, ,4 81, ,2 70, ,5 83, ,9 83, ,5 89, ,9 87, ,7 89, ,7 72, ,8 91, ,7 85, ,5 90, ,7 89, ,6 86, ,6 93, ,0 90, ,4 90, ,1 85, ,9 76, ,4 92, ,4 79, ,3 93, ,2 83, ,0 92, ,4 76, ,6 91, ,9 68, ,8 92, ,8 78, ,5 95, ,8 80, ,0 93, ,1 75, ,7 93, ,4 79, ,9 94, ,3 72, ,9 94, ,5 79, ,2 95, ,9 83, ,7 94, ,9 72, ,1 95, ,6 84, ,6 93, ,5 79, ,4 95, ,0 83, ,1 94, ,3 85,2

18 ,4 93, ,9 75, ,6 91, ,6 74, ,1 92, ,0 82, ,4 94, ,5 86, ,7 94, ,5 79, ,8 92, ,5 81, ,3 91, ,7 74, #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T ,2 86, ,8 89, ,8 88, ,7 89, ,1 88, ,6 86, ,3 91, ,0 74, ,6 93, ,9 79, ,2 90, ,1 70, ,6 85, ,3 69, ,4 80, ,7 61, ,1 75, ,6 61, ,7 78, ,1 62, ,9 83, ,1 73, ,5 68, ,7 58, ,8 76, ,8 57, ,4 73, ,2 44, ,0 69, ,5 46, ,4 68, ,3 40, ,2 62, ,2 69, ,6 74, ,5 68, ,2 76, ,6 73, ,2 76, ,2 68, ,9 81, ,1 73, ,2 84, ,7 77, ,8 87, ,9 75, ,7 87, ,6 84, ,1 90, ,0 89,1

19 ,6 89, ,5 90, ,3 89, ,3 79, ,8 91, ,6 70, ,7 91, ,1 75, ,7 91, ,8 77, ,1 93, ,7 79, ,0 88, ,1 83, ,8 94, ,0 87, ,8 93, ,3 85, ,1 92, ,2 84, ,7 94, ,3 86, ,1 95, ,4 85, ,0 94, ,5 86, ,2 92, ,8 87, ,7 94, ,7 87, ,8 94, ,5 87, ,9 95, ,8 81, ,3 93, ,9 74, ,0 95, ,0 86, ,4 96, ,4 89, ,0 93, ,5 82, ,1 91, ,8 80, ,4 92, ,2 71, ,5 91, ,7 79, ,2 90, ,3 87, ,2 90, ,6 89, ,0 92, ,2 88, ,1 92, ,5 89, ,8 91, ,6 88, ,5 90, ,2 83, ,5 86, ,1 90, ,8 87, ,8 86, ,6 87, ,1 87,4

20 ,5 86, ,5 80, ,5 86, ,2 77, ,8 89, ,9 82, ,6 88, ,0 71, ,5 84, ,6 73, ,7 73, ,4 65, ,9 68, ,0 64, ,0 64, ,6 60, ,0 67, ,9 81, ,1 68, ,2 77, ,2 74, ,1 81, ,7 81, ,6 79, ,6 74, ,7 79, ,9 83, ,2 85, ,6 87, ,9 92, ,3 85, ,5 96, ,9 90, ,4 90, ,3 88, ,3 92, ,4 90, ,7 87, ,0 89, ,5 84, ,1 89, ,9 91, ,1 92, ,8 74, ,1 89, ,4 93, ,1 93, ,6 91, ,4 95, ,5 90, ,2 94, ,8 90, ,5 92, ,0 85, ,1 94, ,8 89, ,9 91, ,0 85, ,4 93, ,0 89, ,2 95, ,2 91, ,4 95, ,7 92, ,4 95, ,0 92,6

21 ,7 92, ,8 83, ,5 93, ,4 88, ,9 94, ,8 84, ,9 95, ,3 76, #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T ,5 93, ,3 84, ,9 94, ,0 86, #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T #I/T ,1 95, ,5 86,4

22 APPENDIX C Example of the weekly statistics from the comparison of the SAF ice edge and ice concentration product with the DMI ice analysis. Reading IA Ice concentration comparison Importing SAF CT field Performing analysis Error from IA range IA NP <-20% >-20% >-10% exact <+10% <+20% >+20% Total: Ice edge comparison Importing SAF CT field Performing analysis Ice edge stats IA\SAF Ice Water Ice Water