ASCAT Wind Product User Manual
Contents
1. Description BUFR bit Fortran bit Not enough good sigma 0 available for wind retrieval 1 22 Poor azimuth diversity among sigma 0 for wind retrieval 2 21 Any beam noise content above threshold 3 20 Product monitoring not used 4 19 Product monitoring flag 5 18 KNMI quality control fails 6 17 Variational quality control fails 7 16 Some portion of wind vector cell is over land 8 15 Some portion of wind vector cell is over ice 9 14 Wind inversion not successful for wind vector cell 10 13 Reported wind speed is greater than 30 m s 11 12 Reported wind speed is less than or equal to 3 m s 12 11 Rain flag for the wind vector cell is not usable 13 10 Rain flag algorithm detects rain 14 9 No meteorological background used 15 8 Data are redundant 16 7 Distance to GMF too large 17 6 Reserved 18 23 5 0 Missing value All 24 set All 24 set In Fortran if the Wind Vector Cell Quality is stored in an integer I then use BTEST I NDW NB 1 to test BUFR bit NB where NDW 24 is the width in bits of the data element in BUFR If the monitoring not used bit BUFR bit 4 is set to zero the product is monitored If the product is monitored and the monitoring flag bit BUFR bit 5 is set to zero the product is valid otherwise it is rejected by the monitoring see Ref 1 The monitoring bits are set to the same value in all WVCs in one BUFR output file If the KNMI QC flag BUFR bit 62. KNMI De Bilt the Netherlands Reference SAF OSI CDOP KNMI TEC MA 1 26 OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 2 SAF OSI CDOP KNMI TEC MA 126 Cover illustration ASCAT winds over the Atlantic on 7 February 2007 around 21 hour UTC red arrows In this picture only half of the ASCAT wind vectors with 25 km cell spacing are plotted The blue and purple arrows show a 3 hour forecast of the winds by the KNMI High Resolution Limited Area Model HiIRLAM In the background a METEOSAT infrared image is shown in black and white OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 3 SAF OSI CDOP KNMI TEC MA 126 Contents Ta O 5 ds OM OIG Wis a as A ten sa dd 5 Tees DI e AAE A E 6 id S EEEE E E E E 6 1 4 Useful INS coi atado A e Todor 6 1 5 Limitations of the ASCAT windS recteoisit a odos 7 1 6 History of product Changos cspii lid 7 Die TINGS GACT TAS TUS ico dea aaa hed A Eo EAE SE atte ance 9 Gus Processing Scheme isen a a e ees aa EAEN et Ate EAn AEAEE iS 10 3 1 Backscatter averaging piscceses secsesnrsvnorsuarneageeacess sauedntsedetencausaaieeueoeenseceatusaerdeoededntays 10 3 2 Backscatter Calibration nss pio ios 10 3 3 NWP collocalOn cnica 10 3 4 Quality control and MoONItOTINO mocomiiccisncnicone salinidad 11 4 Helpdesk product dissemination and archive oooooooccccn nnccccconancnnnnnnnnnnnnnananoncnnnnnnnnannnnnns 12 Be Data descripta 13 91 Wind product Chara
3. Scatterometer wind speed m s so Scatterometer wind direction deg oL 1 1 1 1 i ob 1 1 1 a 0 5 20 25 o 360 10 15 180 Buoy wind speed m s Buoy wind direction deg Collocation result u 6280 wind vectors Collocation result v 6280 wind vectors T T T r A E r T T T 20E P 4 S Scatterometer u component m s o T Scatterometer v component m s o 3 i n rmm 3 AAA rm S T alii lira titty me Sa T E 20 10 o 20 20 10 o 20 Buoy u component m s Buoy v component m s Figure 3 shows the results of collocations of ASCAT winds from Metop A and Metop B with buoy winds These results cover the period of November 2012 to January 2013 3 months For more details about the collocation method please see Ref 4 and Ref 5 We find a wind speed bias of 0 02 m s for Metop A and 0 05 m s for Metop B Standard deviations of u and v wind components are 1 72 m s and 1 76 m s for Metop A and 1 78 m s and 1 80 m s for Metop B respectively These figures are all well within the OSI SAF requirements More validation information can be found in Ref 4 and Ref 5 OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 18 SAF OSI CDOP KNMI TEC MA 126 AR ASCAT BUFR EARS EPS ERS EUMETCast EUMETSAT HDF JPL KNMI Metop NASA NetCDF NOAA NSCAT NWP OSI SAF PO DAAC QC QuikSCAT RMDCN SAF SeaWinds SM SOS SST u V WVC 7 Glossa
4. ascat_ YYYYMMDD_HHMMSS_SAT_ORBIT_SRV_T_SMPL _CONT 12_bufr where ascat denotes the instrument YYYYMMDD denotes the date of the first data in the file HHMMSS denotes the time UTC of the first data in the file SAT denotes the satellite name metopa or metopb ORBIT is the orbit number 00000 99999 SRV is the service eps for global OSI SAF or ear for regional EARS Tis the processing type o for operational t for test SMPL is the WVC sampling cell spacing 250 or 125 or coa for the coastal product which has a WVC spacing of 12 5 km as well CONT optional field refers to the product contents ovw for a product containing only Ocean Vector Winds and no soil moisture information CONT is omitted if the product contains both winds and soil moisture 2 bufr l is the lowercase L denotes Level 2 product in BUFR Examples of file names are ascat_20070213_021503_metopa_01653 eps t 250 12 bufr for a global test product containing soil moisture information or ascat_20070213_021503_metopa_01653_ear_o 125 ovw 2 bufr for a regional operational product containing no soil moisture information The wind product is stored in the BUFR format as proposed for ASCAT and described in Ref 8 a list of descriptors fields contained in each WVC is provided in section 8 The BUFR data contain three main sections level 1 information fields 1 62 level 2 Soil Moisture information fields 63 82 and level 2 wind in
5. KNMI For the global product the delivery time between acquisition of the data and availability for the user ranges from 40 to 120 minutes The regional product is available within 25 minutes after data acquisition Timeliness statistics are available on the product visualisation websites after clicking on the Monitoring information link OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 13 SAF OSI CDOP KNMI TEC MA 126 Expected accuracy The expected accuracy is defined as the expected bias and standard deviation of the primary calculations The accuracy is validated against in situ wind measurements from buoys platforms or ship and against NWP data Even better the errors of all NWP model winds in situ data and scatterometer winds are computed in a triple collocation exercise Ref 7 The performance is pretty constant over the globe and depends mainly on the sub footprint wind variability The performance of the products issued by the OSI SAF and EARS is characterised by a wind component RMS error smaller than 2 m s and a bias of less than 0 5 m s in wind speed 5 2 File formats Wind products are in BUFR Edition 4 or in NetCDF format A complete description of BUFR can be found in WMO publication No 306 Manual on Codes The graphical displays of the wind products are available and explained on the web see the links on http www knmi nl scatterometer The file name convention for the Level 2 BUFR product is
6. MA 126 ice_prob units 1 short ice_age NUMROWS NUMCELLS ice_age long_name ice age a parameter ice_age units dB int wvc_quality_flag NUMROWS NUMCELLS wvc_quality_flag long_name wind vector cell quality wvc_quality_flag flag_masks 64 128 256 512 1024 2048 4096 8192 16384 32768 65536 131072 262144 524288 1048576 2097152 4194304 wvc_quality_flag flag_meanings distance_to_gmf_too_large data_are_redundant no_meteorological_background_used rain_detected rain_flag_not_usable small_wind_less_than_or_equal_to_3_m_s large_wind_greater_than_30_m_s wind_inversion_not_successful some_portion_of_wvc_is_over_ice some_portion_of_wvc_is_over_land variational_quality_control_fails knmi_quality_control_fails product_monitoring_event_flag product_monitoring_not_used any_beam_noise_content_above_threshold poor_azimuth_diversity not_enough_good_sigma0_for_wind_retrieval short wind_speed NUMROWS UMCELLS wind_speed long_name wind speed at 10 m wind_speed units m s 1 short wind_dir NUMROWS NUMCELLS wind_dir long_name wind direction at 10 m wind_dir units degree short bs _distance NUMROWS NUMCELLS bs_distance long_name backscatter distance bs_distance units 1 global attributes title MetOp A ASCAT Level 2 25 0 km Ocean Surface Wind Vector Product title_short_name ASCAT L2 25km Conventions CF 1 4 institutio
7. is set in a WVC this means that the backscatter information is of poor quality for various reasons such as a too large inversion residual or a too high noise value in the input product WVCs in which the KNMI QC flag is set are not used in the calculation of the analysis field in the ambiguity removal step However after the ambiguity removal the wind solution closest to the analysis field is chosen if wind solutions are present in the WVC This means that such a WVC may contain a selected wind solution but it is suspect Land presence flag is set if a land fraction see section 3 3 larger than zero is calculated for the WVC As long as the land fraction is below the limit value a reliable wind solution may however still be present so there is normally no reason to reject WVCs with the land flag set Ice presence flag is set if the Bayesian sea ice screening algorithm calculates ice for the WVC see Ref 1 Note that the products contain wind solutions also over sea ice regions These bogus winds are flagged both by the KNMI quality control flag and by the ice flag OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 15 SAF OSI CDOP KNMI TEC MA 126 Hence it is important that you reject any winds with the KNMI quality control flag set when ingesting the products Note that WVCs that are rejected due to a large inversion residual e g in case of rain only have the KNMI quality control flag set On the other hand WVCs t
8. 0 Deg Incidence Angle dB 69 021152 Slope At 40 Deg Incidence Angle dB Degree 70 021153 Estimated Error In Slope At 40 Deg Incidence Angle dB Degree 71 021154 Soil Moisture Sensitivity dB 72 021062 Backscatter dB 73 021088 Wet Backscatter dB 74 040003 Mean Surface Soil Moisture Numeric 75 040004 Rain Fall Detection Numeric 76 040005 Soil Moisture Correction Flag Flag Table 77 040006 Soil Moisture Processing Flag Flag Table 78 040007 Soil Moisture Quality 79 020065 Snow Cover 80 040008 Frozen Land Surface Fraction 81 040009 Inundation And Wetland Fraction 82 040010 Topographic Complexity 83 025060 Software Identification Numeric 84 001032 Generating Application Code Table 85 011082 Model Wind Speed At 10 m m s 86 011081 Model Wind Direction At 10 m Degree True 87 020095 Ice Probability Numeric 88 020096 Ice Age A Parameter dB 89 021155 Wind Vector Cell Quality Flag Table 90 021101 Number Of Vector Ambiguities Numeric 91 021102 Index Of Selected Wind Vector Numeric 92 031001 Delayed Descriptor Replication Factor Numeric 93 011012 Wind Speed At 10 m m s 94 011011 Wind Direction At 10 m Degree True 95 021156 Backscatter Distance Numeric 96 021104 Likelinood Computed For Solution Numeric 97 011012 Wind Speed At 10 m m s 98 011011 Wind Direction At 10 m Degree True 99 021156 Backscatter Distance Numeric 100 021104 Likelinood Computed For Solution Numeric Note that descriptor numbers 93 96 can be repeated 1 to 144 ti
9. 4 Scatterometer wind speed m s Scatterometer wind direction deg L 3 Ne i o 5 10 15 20 25 90 Model wind speed m s a T a T Scatterometer u component m s o T Scatterometer v component m s o T o T 1 e S T 3 7 20 10 o 10 20 20 10 o 10 20 Model u component m s Model v component m s Collocation result speed 966770 wind vectors Collocation result direction 811903 wind vectors T r T ca T rog Scatterometer wind speed m s Scatterometer wind direction deg 0 1 1 1 0 5 20 25 90 180 Model wind direction deg 10 15 Model wind speed m s Collocation result u 966859 wind vectors Collocation result v 966850 wind vectors 205 205 Scatterometer u component m s e T Scatterometer v component m s 3 o 3 o T oy S T L 1 L L L Ery L L i 1 20 10 0 10 20 20 10 0 10 20 Model u component m s Model v component m s Figure 2 shows two dimensional histograms of the retrieved winds versus ECMWF 10m wind background for the 25 km wind product with the backscatter calibration see section 3 2 applied The data for these plots are from consecutive Metop A and Metop B orbits from 1 and 2 November 2012 28 orbits from both satellites The top left plots correspond to wind speed bins of 0 5 m s and the top right plots to wind direction bins of 2 59 The latter are computed
10. 5 002019 Satellite Instruments Code Table 6 001012 Direction Of Motion Of Moving Observing Platform Degree True 7 004001 Year Year 8 004002 Month Month 9 004003 Day Day 10 004004 Hour Hour 11 004005 Minute Minute 12 004006 Second Second 13 005001 Latitude High Accuracy Degree 14 006001 Longitude High Accuracy Degree 15 005033 Pixel Size On Horizontal 1 m 16 005040 Orbit Number Numeric 17 006034 Cross Track Cell Number Numeric 18 010095 Height Of Atmosphere Used m 19 021157 Loss Per Unit Length Of Atmosphere Used dB m 20 021150 Beam Collocation Flag Table 21 008085 Beam Identifier Code Table 22 002111 Radar Incidence Angle Degree 23 002134 Antenna Beam Azimuth Degree 24 021062 Backscatter dB 25 021063 Radiometric Resolution Noise Value 26 021158 ASCAT Kp Estimate Quality Code Table 27 021159 ASCAT Sigma 0 Usability Code Table 28 021160 ASCAT Use Of Synthetic Data Numeric 29 021161 ASCAT Synthetic Data Quality Numeric 30 021162 ASCAT Satellite Orbit And Attitude Quality Numeric 31 021163 ASCAT Solar Array Reflection Contamination Numeric 32 021164 ASCAT Telemetry Presence And Quality Numeric 33 021165 ASCAT Extrapolated Reference Function Numeric 34 021166 ASCAT Land Fraction Numeric 35 008085 Beam Identifier Code Table 36 002111 Radar Incidence Angle Degree 37 002134 Antenna Beam Azimuth Degree 38 021062 Backscatter dB 39 021063 Radiometric Resolution Noise Value 40 021158 ASCAT Kp Estimate Quality Code
11. KX Royal Netherlands AS Meteorological Institute Facilities Ministry of Infrastructure and the Environment Ocean and Sea Ice SAF Global OSI SAF 25 km wind product OSI 102 and OSI 102b Global OSI SAF 12 5 km wind product OSI 103 Global OSI SAF coastal wind product OSI 104 and OSI 104b Regional EARS 25 km wind product Regional EARS 12 5 km wind product Version 1 13 May 2013 SAF OSI CDOP KNMI TEC MA 126 DOCUMENT SIGNATURE TABLE Prepargdby O amp SI SAF Project May 2013 Team Approved by 08 SI SAF Project May 2013 Manager DOCUMENTATION CHANGE RECORD Issue Revision Date Change Description Version 0 1 Draft version Version 1 0 First external version Version 1 1 Added release note sec 1 4 Version 1 2 Single transponder calibrated L1 data version 5 2 1 Version 1 3 Take some comments of ORR A part 1 into account Version 1 4 Three transponder calibrated L1 data version 5 5 0 Version 1 5 Change to neutral winds Version 1 6 Comments of 12 5 km DRI included Version 1 7 NetCDF product format included Version 1 8 Editorial changes included section 1 7 Version 1 9 Included coastal product and changes for merging of soil moisture and winds Version 1 10 Some editorial changes Version 1 11 Changes for timeliness and EARS coverage Version 1 12 Implementation of Bayesian ice screening Version 1 13 Removed information which is now in the ATBD include Metop B include comments from Metop B ORR
12. SAF wind product documentation on http www osi saf org Scientific documents Technical documents NWP SAF website http Awww nwpsaf org EUMETSAT ASCAT documentation http www eumetsat int Home Main Satellites Metop Instruments SP_2010053161611647 l en EUMETSAT ASCAT product guide http oiswww eumetsat org WEBOPS eps pg ASCAT ASCAT PG index htm 1 5 Limitations of the ASCAT winds The following restrictions and limitations hold 1 Although the Level 1 product is fully calibrated now using three transponders on the ground the backscatter values are corrected using a calibration table derived from a geophysical wind model The backscatter values in the Level 2 wind product are however plain copies of those in the Level 1 product The corrections are very small and expected to be incorporated into a new version of the Geophysical Model Function 2 The backscatter data and noise values Kp in the coastal product are computed as part of the level 2 wind processing and they are not scientifically validated other than by validation of the wind retrieval properties in the coastal products 3 The provision of the full resolution ASCAT backscatter product from EUMETSAT to KNMI which is necessary for the coastal wind product processing is not considered an operational process Hence the coastal wind product can not have a fully operational status These restrictions and limitations are subject to further study 1 6 History of pro
13. SAT meteorological satellite products or contact opsOeumetsat int The BUFR and NetCDF products are also made available on a password protected ftp site This password is provided to new users by Email request Please send your requests to scat knmi nl The Metop A ASCAT 25 km global winds in BUFR format are disseminated on the GTS The messages are distributed to the Exeter node and can be identified by header T1T2A1A2ii ISXX 01 06 CCCC EHDB The coastal winds are available on the GTS with identification header T1T2A1A2ii ISXX 11 16 CCCC EHDB The EARS Metop A ASCAT winds are also available on the GTS with identification header T1T2A1A2ii ISXN 01 06 CCCC EHDB 25 km and header T1T2A1A2ii ISXN 11 16 CCCC EHDB 12 5 km A BUFR reader is available at www knmi nl scatterometer bufr_reader The OSI SAF Metop A ASCAT data are archived in the EUMETSAT Data Centre Archive see http www eumetsat int Home Main DataAccess EUMETSAT DataCentre index htm l en BUFR and NetCDF For data not yet present in the EUMETSAT Data Centre KNMI also keeps an off line archive of the global products You can send a request to scatOknmi nl The OSI SAF Metop A ASCAT data in NetCDF are also archived in the NASA Physical Oceanography Distributed Active Archive Center PO DAAC archive see http podaac jpl nasa gov datasetlist ids Sensor amp values ASCAT amp search The ASCAT 25 km global winds can be explored through the E
14. Table 41 021159 ASCAT Sigma 0 Usability Code Table 42 021160 ASCAT Use Of Synthetic Data Numeric 43 021161 ASCAT Synthetic Data Quality Numeric 44 021162 ASCAT Satellite Orbit And Attitude Quality Numeric 45 021163 ASCAT Solar Array Reflection Contamination Numeric 46 021164 ASCAT Telemetry Presence And Quality Numeric 47 021165 ASCAT Extrapolated Reference Function Numeric 48 021166 ASCAT Land Fraction Numeric 49 008085 Beam Identifier Code Table 50 002111 Radar Incidence Angle Degree 51 002134 Antenna Beam Azimuth Degree OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 20 SAF OSI CDOP KNMI TEC MA 126 Number Descriptor Parameter Unit 52 021062 Backscatter dB 53 021063 Radiometric Resolution Noise Value 54 021158 ASCAT Kp Estimate Quality Code Table 55 021159 ASCAT Sigma 0 Usability Code Table 56 021160 ASCAT Use Of Synthetic Data Numeric 57 021161 ASCAT Synthetic Data Quality Numeric 58 021162 ASCAT Satellite Orbit And Attitude Quality Numeric 59 021163 ASCAT Solar Array Reflection Contamination Numeric 60 021164 ASCAT Telemetry Presence And Quality Numeric 61 021165 ASCAT Extrapolated Reference Function Numeric 62 021166 ASCAT Land Fraction Numeric 63 025060 Software Identification Numeric 64 025062 Database Identification Numeric 65 040001 Surface Soil Moisture Ms 66 040002 Estimated Error In Surface Soil Moisture 67 021062 Backscatter dB 68 021151 Estimated Error In Sigma0 At 4
15. YMMDD_HHMMSS_SAT_ORBIT_SRV_T_SMPL_VERS _CONT I2 nc gz where the meaning of the fields is identical to those in the BUFR file names see section 5 2 Note that in NetCDF the SRV is always eps global data and the CONT is always ovw Ocean Vector Winds The VERS part of the file name denotes the software version A file name example is ascat_20090826_ 051502 metopa_14797 eps o 250 1018 ovw l2 nc gz Below are some meta data contained in the NetCDF data files dimensions NUMROWS 1581 NUMCELLS 42 variables int time NUMROWS UMCELLS time long_name time time units seconds since 1990 01 01 00 00 00 int lat NUMROWS NUMCELLS lat long_name latitude lat units degrees_north int lon NUMROWS NUMCELLS lon long_name longitude lon units degrees_east short wvc_index NUMROWS NUMCELLS wvc_index long_name cross track wind vector cell number wvc_index units 1 f short model_speed NUMROWS NUMCELLS model_speed long_name model wind speed at 10 m model_speed units m s 1 short model_dir NUMROWS NUMCELLS model_dir long_name model wind direction at 10 m model_dir units degree short ice_prob NUMROWS NUMCELLS ice_prob long_name ice probability OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 22 SAF OSI CDOP KNMI TEC
16. and A Stoffelen ASCAT B NWP Ocean Calibration and Validation OSI SAF Technical Report SAF OSI CDOP2 KNMI TEC RP 199 2013 Ref 6 EUMETSAT ASCAT Level 1 Product Generation Function Specification EUM EPS SYS SPE 990009 Ref 7 Thesis Scatterometry by Ad Stoffelen 1998 Ref 8 ADDITIONS TO BUFR CREX TABLES FOR PRE OPERATIONAL IMPLEMENTATION ENDORSED BY CBS for full operational status on 7 November 2007 updated 04 01 07 pp55 60 available on http www wmo intiweb www WMOCodes Updates BUFRCREX Preoperational050107 doc References marked with a are available on http www knmi nl scatterometer publications 1 4 Useful links KNMI scatterometer web site http www knmi nl scatterometer Information on OSI SAF activities at KNMI http www knmi nl scatterometer osisaf OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 6 SAF OSI CDOP KNMI TEC MA 126 Information on EARS activities at KNMI http www knmi nl scatterometer ears ASCAT visual products http www knmi nl scatterometer ascat_osi_25 prod http Awww knmi nl scatterometer ascat_osi_ 12 prod http www knmi nl scatterometer ascat_osi co prod http www knmi nl scatterometer ascat_ ear 25 prod http www knmi nl scatterometer ascat ear 12 prod http www knmi nl scatterometer ascat b osi 25 prod http www knmi nl scatterometer ascat b osi co prod Information on EARS and EUMET Cast http www eumetsat int O amp SI
17. cteristics estada 13 5 2 SFIS TONMAtS vic ia stavaavig devas a Dveusya dase sd du bles a e a a aa es 14 6 Data Quality S unta a Aa iaaa Ea psat 17 a O E attests 19 8 ASCAT BUFR data descriptors arcaicos coso case suas Nana danesa DeCS 20 9 NetCDF data foma eii ao rbd 22 OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 4 SAF OSI CDOP KNMI TEC MA 126 1 Introduction 1 1 Overview The EUMETSAT Ocean and Sea Ice Satellite Application Facility OSI SAF produces a range of air sea interface products namely wind sea ice characteristics Sea Surface Temperatures SST and radiative fluxes Surface Solar Irradiance SSI and Downward Long wave Irradiance DLI KNMI is involved in the OSI SAF and the EUMETSAT Advanced Retransmission Service EARS ASCAT service as the centre where the Level 1b to Level 2 wind processing is carried out This document is the Product User Manual to the ASCAT wind products Quality monitoring information on this product and more general information on the whole OSI SAF project is available on the OSI SAF web site http www osi saf org The user is strongly encouraged to register on this web site in order to receive the service messages and the latest information about the OSI SAF products The wind products are distributed in two resolutions a 50 km resolution product with 25 km cell spacing and a 25 km resolution product with 12 5 km cell spacing Both resolutions are available as a reg
18. duct changes Here is an historical overview of the changes in the ASCAT wind products 28 Mar 2007 OSI SAF ASCAT 25 km demonstration wind product available on EUMETCast ASCAT Wind Data Processor software version is 1_0i 23 May 2007 Processing transferred to operational KNMI server 10 Oct 2007 AWDP version 1_0k adapted to the improved calibration of the Level 1 product Wind product status is pre operational now 12 Dec 2007 AWDP version 1_0l OSI SAF ASCAT 25 km winds are available on the GTS 18 Mar 2008 AWDP version 1_0 13 adapted to the three transponder calibration of the Level 1 product OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 7 SAF OSI CDOP KNMI TEC MA 126 20 Nov 2008 03 Dec 2008 11 Dec 2008 03 Mar 2009 21 Apr 2009 01 Sep 2009 08 Sep 2009 12 Jan 2010 02 Feb 2010 28 Feb 2011 16 Aug 2011 23 Aug 2011 18 Sep 2012 14 Nov 2012 14 May 2013 OSI SAF EARS AWDP version 1_0 15 change to neutral winds 0 2 m s added to the wind speeds and improved calibration of the level 1 product activated at 2 December OSI SAF ASCAT 25 km wind product has the operational status EARS ASCAT 25 km and 12 5 km winds are available to all users OSI SAF ASCAT 12 5 km wind product is available with the operational status AWDP version 1_0_17 upgrades in BUFR encoding AWDP version 1_0 18 wind products are available in NetCDF now on the KNMI FTP server EARS ASCAT data are available
19. e Metop A and B satellites through EUMETCast global data and through a private network regional data These products are used as basis for further processing at KNMI The OSI SAF and EARS products are delivered on request through the KNMI FTP server to all users and through the EUMETCast system See also http www knmi nl scatterometer for real time graphical examples of the products and up to date information and documentation This user manual outlines user information for the OSI SAF and EARS products based on the ASCAT scatterometer Section 2 presents a brief description of the ASCAT instrument and section 3 gives an overview of the data processing configuration Section 4 provides details on how to access the products Detailed information on the file content and format is given in section 5 while in section 6 the product quality is elaborated This manual covers the following products OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 5 SAF OSI CDOP KNMI TEC MA 126 OSI SAF ASCAT 25 km wind product OSI 102 acronym ASCAT25 for Metop A and B OSI SAF ASCAT 12 5 km wind product OSI 103 acronym ASCAT12 for Metop A OSI SAF ASCAT 12 5 km coastal wind product OSI 104 acronym ASCAT12 for Metop A and B EARS ASCAT 25 km wind product acronym EARS ASCAT 25 for Metop A EARS ASCAT 12 5 km wind product acronym EARS ASCAT 12 for Metop A Products OSI 102 and OSI 103 also contain soil moisture
20. e instrument operates at a frequency of 5 255 GHz C band which makes it rather insensitive to rain Figure 1 ASCAT wind scatterometer geometry source EUMETSAT web site OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 9 SAF OSI CDOP KNMI TEC MA 126 3 Processing scheme KNMI has a processing chain running in near real time with ASCAT data including visualisation on the internet This processor is based on the NWP SAF software and runs in the KNMI operational environment The processing includes monitoring and archiving functionalities A brief overview of the modules of the ASCAT scatterometer processor is given below General information about the scatterometer wind processing algorithms can be found in the ATBD Ref 1 3 1 Backscatter averaging In this step which is performed only for the coastal product the full resolution ASCAT level 1 product is used to re compute backscatter values oos in the Wind Vector Cells The full resolution backscatter data are averaged using a spatial box filter rather than the Hamming filter that is used in the spatial averaging of the cos of the nominal level 1 products All full resolution oos within 15 km from the Wind Vector Cell centre are used in the averaging Ref 2 Moreover in Wind Vector Cells close to the coast only those full resolution os are used that are entirely over sea As the position of the averaged oo is an averaged value of the positions of the full re
21. egrees inclination at approximately 800 km orbit height The two satellite swaths are located to the left and to the right of the satellite ground track The swath width is either 21 25 km size WVCs corresponding to 525 km or 41 12 5 km size WVCs corresponding to 512 5 km Products are organised in rows of 42 or 82 WVCs respectively Coverage The OSI SAF products have global coverage For the ascending Metop A tracks the EARS data correspond to the last 30 minutes of the X band data dump when the satellite passes the Svalbard ground station For the descending tracks also AHRPT data from several ground stations are used adding coverage in the European seas and Atlantic and Indian oceans An up to date list of ground stations in use is available on http Awww eumetsat int Home Main Satellites GroundNetwork EARSSystem EARS ASCAT index htm l en Actual wind coverage is available on the OSI SAF and EARS ASCAT product visualisation websites see http www knmi nl scatterometer Output product The input product in BUFR is processed into a BUFR output product including a unique wind solution chosen its corresponding ambiguous wind solutions and quality information distance to cone quality flag The products contain up to four wind solutions The products are also available in NetCDF format see section 9 for more details Delivery time A wind product is available for distribution within 10 minutes after the input product reception at
22. ening procedure may sometimes assign rainy WVCs erroneous as ice using the extra SST criterion WVCs in warmer areas will never be labelled as ice Due to its rather high threshold value the NWP SST ice screening will only be active in regions far away from the ice extents Land presence within each WVC is determined by using the land sea mask available from the model data The weighted mean value of the land fractions of all model grid points within 80 km of the WVC centre is calculated The weight of each grid point scales with 1 7 where r is the distance between the WVC centre and the model grid point If this mean land fraction value exceeds a threshold of 0 02 no wind retrieval is performed Also the land fractions present in the beam information in the level 1b product are considered if any land fraction in the fore mid or aft beam exceeds 0 02 no wind retrieval is performed OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 10 SAF OSI CDOP KNMI TEC MA 126 NWP forecast wind data are necessary in the ambiguity removal step of the processing Wind forecasts are available twice a day 00 and 12 GMT analysis time with forecast time steps of 3h 6h 36h The model wind data are linearly interpolated with respect to time and location and put into the level 2 information part of each WVC see section 5 2 Note that the ECMWF winds stored in the wind products are real winds rather than neutral winds 3 4 Quality con
23. for ECMWF winds larger than 4 m s The bottom plots show the u and v wind component statistics bins of 0 5 m s OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 17 SAF OSI CDOP KNMI TEC MA 126 From these results it is clear that the spread in the distributions is small The wind speed biases are quite small 0 20 m s We obtain wind component standard deviations of 1 44 in u and 1 49 in vdirections both for Metop A and Metop B Note that the data in the plots do not include WVCs that are quality controlled i e have a too large inversion residual Collocation result speed 6256 wind vectors Collocation result direction 5531 wind vectors T T 7 T T T r asr 7 so Figure 3 E e Contoured a 3 histograms of the 7 f 25 km ASCAT wind 3 J 3 product from 1 2 yt Metop A top and Metop B bottom vs in situ buoy 10 15 90 180 27 i Buoy wind speed m s Buoy wind direction deg winds Collocation result u 6257 wind vectors Collocation result v 6257 wind vectors T T T r 4 r T T T 3 pa L Scatterometer u component m s o T 1 Scatterometer v component m s e T 1 3 nimm m 1 pS Sar 3 3 20 0 20 20 0 20 Buoy u component m s Buoy v component m s Collocation result speed 6278 wind vectors Collocation result direction 5559 wind vectors T T T T T T r 360 gt 20 gt 4 e PA 270 180
24. formation fields 83 and up The L1 information is simply copied into the L2 data except for the coastal product where the backscatter data are recalculated based on the data in the ASCAT full resolution level 1 product Ref 3 More information on the L1 data can be found in the EUMETSAT ASCAT Product Guide see the link in section 1 4 The Soil Moisture data are produced by and under the responsibility of the EUMETSAT central facilities The coastal product does not contain Soil Moisture information since it contains recalculated backscatter information which is not OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 14 SAF OSI CDOP KNMI TEC MA 126 input to the Soil Moisture computations In this way inconsistency between the backscatter data and Soil Moisture in one product is avoided Field 2 Identification of originating generating sub centre is set to 0 for OSI SAF products For EARS products a value of 1 refers to X band data dumps from Svalbard whereas other values refer to AHRPT ground stations For a list of ground stations see http Awww eumetsat int Home Main Satellites GroundNetwork EARSSystem EARS ASCAT index htm l en Field 84 Generating Application contains the value 91 which means that first guess model winds are used for ambiguity removal The interpolated model winds are in the fields 85 86 The Wind Vector Cell Quality Flag field 89 table 021155 has the following definitions
25. hat are rejected due to sea ice have both the KNMI quality control flag and the ice flag set If the variational QC flag is set the wind vector in the WVC is rejected during ambiguity removal due to spatial inconsistency A wind solution is present but it may be suspect It is recommended not to use WVCs with the monitoring flag the KNMI quality control flag or the variational quality control flag set See Ref 1 for more information on product reliability The likelihood computed for solution descriptor 021104 actually contains the logio of the calculated likelihood for the wind solution This is done since otherwise values close to zero will be rounded to zero in the BUFR encoding In order to recalculate the probability the user should compute 10 to the power lt value from BUFR gt OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 16 SAF OSI CDOP KNMI TEC MA 126 6 Data quality As introduced in section 5 1 the accuracy should be better than 2 m s in wind component RMS with a bias of less than 0 5 m s in wind speed Collocation result speed 977034 wind vectors Collocation result direction 821351 wind vectors T r r T a TP gt Figure 2 Contoured histograms of the 25 km ASCAT wind product from Metop A top and Metop B bottom E id vs ECMWF model cad adi forecast winds Collocation result u 977140 wind vectors Collocation result v 977104 wind vectors T T T T r T T T 15L
26. information over land OSI 102 both for Metop A and B the coastal and EARS products do not contain soil moisture information 1 2 Disclaimer All intellectual property rights of the OSI SAF and EARS products belong to EUMETSAT The use of these products is granted to every interested user free of charge If you wish to use these products EUMETSAT s copyright credit must be shown by displaying the words copyright year EUMETSAT on each of the products used The OSI SAF and EUMETSAT are much interested in receiving your feedback would appreciate your acknowledgment in using and publishing about the data and like to receive a copy of any publication about the application of the data Your feedback helps us in maintaining the resources for the OSI SAF wind services 1 3 References Ref 1 OSI SAF Algorithm Theoretical Basis Document for the OSI SAF wind products SAF OSI CDOP2 KNMI SCI MA 197 Ref 2 Verhoef A and A Stoffelen ASCAT coastal winds validation report OSI SAF Report SAF OSI CDOP KNMI TEC RP 176 2011 Ref 3 Verhoef A M Portabella and A Stoffelen High resolution ASCAT scatterometer winds near the coast IEEE Transactions on Geoscience and Remote Sensing 2012 50 7 2481 2487 doi 10 1109 TGRS 2011 2175001 Ref 4 Verspeek J M Portabella A Stoffelen and A Verhoef ASCAT Calibration and Validation OSI SAF Technical Report SAF OSI CDOP KNMI TEC TN 163 Ref 5 Verspeek J A Verhoef
27. ional mainly covering the Northern Hemisphere EARS product with a timeliness of approximately 25 minutes from sensing time and as a global OSI SAF product with a timeliness of approximately 1 5 2 hours from sensing time Moreover a global OSI SAF coastal product is available with 12 5 km cell spacing The wind characteristics in full sea regions are comparable to those of the nominal 12 5 km product but additionally more wind data closer to the coast are available At the time of writing this manual not all products are available yet for Metop B The scatterometer is an instrument that provides information on the wind field near the ocean surface and scatterometry is the knowledge of extracting this information from the instrument s output Space based scatterometry has become of great benefit to meteorology and climate in the past years This is extensively described in the Algorithm Theoretical Basis Document see Ref 1 KNMI has a long experience in scatterometer processing and is developing generic software for this purpose Processing systems have been developed for the ERS NSCAT SeaWinds and ASCAT scatterometers Scatterometer processing software is developed in the EUMETSAT Numerical Weather Prediction Satellite Application Facility NWP SAF whereas wind processing is performed operationally in the Ocean and Sea Ice SAF OSI SAF and in the EARS project EUMETSAT makes available near real time Level 1b scatterometer products from th
28. larised antennas It transmits a long pulse with Linear Frequency Modulation chirp Ground echoes are received by the instrument and after de chirping the backscattered signal is spectrally analysed and detected In the power spectrum frequency can be mapped into slant range provided the chirp rate and the Doppler frequency are known The above processing is in effect a pulse compression which provides range resolution Two sets of three antennas are used to generate radar beams looking 45 degrees forward sideways and 45 degrees backwards with respect to the satellite s flight direction on both sides of the satellite ground track These beams illuminate approximately 550 km wide swaths separated by about 700 km as the satellite moves along its orbit and each provide measurements of radar backscatter from the sea surface on a 25 km or 12 5 km grid i e each swath is divided into 21 or 41 so called Wind Vector Cells WVCs This brings the effective swath width to 525 km 21x25 or 512 5 km 41x12 5 for the 25 km and 12 5 km products respectively For each WVC we obtain three independent backscatter measurements using the three different viewing directions and separated by a short time delay As the backscatter depends on the sea surface roughness as a function of the wind speed and direction at the ocean surface it is possible to calculate the surface wind speed and direction by using these triplets within a mathematical model Th
29. mes depending on the value of the Delayed Descriptor Replication Factor descriptor number 92 OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 21 SAF OSI CDOP KNMI TEC MA 126 9 NetCDF data format The ASCAT wind products are also available in the NetCDF format with the following characteristics The data are organised in full orbits rather than in 3 minute granules The data format meets the NetCDF Climate and Forecast Metadata Convention version 1 4 http cf pcmai In gov The data contain contrary to the BUFR data only Level 2 wind and sea ice information no sigma0 nor soil moisture information The aim was to create a compact and easy to handle product for oceanographic and climatological users The data contain only the selected wind solutions no ambiguity information The wind directions are in oceanographic rather than meteorological convention see section 5 1 The format is usable for ASCAT ERS QuikSCAT and any other scatterometer data The data has file sizes comparable to those of the corresponding BUFR data e g one orbit of ASCAT 25 km wind data is 2 6 MB in BUFR and 2 2 MB in NetCDF When compressed with gzip the size of one orbit in NetCDF reduces to 820 kB The NetCDF data in near real time are only available on the KNMI FTP server but EUMETCast dissemination can be considered on user request The file name convention for the gzipped NetCDF product is ascat_YYY
30. n EUMETSAT OSI SAF KNMI source MetOp A ASCAT software_identification _level_1 702 instrument_calibration version 0 software_identification_wind 1018 pixel_size_on_horizontal 25 0 km service_type eps processing_type o contents ovw granule_name ascat_20090826_051502_metopa_14797_eps_o_250_1018_ovw 12 nc processing_level L2 orbit_number 14797 2009 08 26 05 15 02 2009 08 26 062 53 2 5 6 equator_crossing_longitude 244 606 start_date start_time stop_date stop_time equator_crossing_date 2009 08 26 equator_crossing_time 05 12 26 rev_orbit_period 6081 7 orbit_inclination 98 7 shistory N A references ASCAT Wind Product User Manual http www osi saf org http www knmi nl scatterometer comment Orbit period and inclination are constant values All wind directions in oceanographic convention 0 deg flowing North 2009 08 26 creation_time 08 31 31 creation_date OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 23
31. nhanced Satellite Archive Dataminer Naiad http www naiad fr OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 12 SAF OSI CDOP KNMI TEC MA 126 5 Data description 5 1 Wind product characteristics Physical definition Horizontal equivalent neutral wind vector at 10 m height see Ref 1 Units and range Wind speed is measured in m s The wind speed range is from 0 50 m s but wind speeds over 25 m s are generally less reliable Ref 1 In the BUFR products the wind direction is in meteorological WMO convention relative to North O degrees corresponds to a wind flowing to the South with a clockwise increment In the NetCDF products the wind direction is in oceanographic convention O degrees corresponds to a wind flowing to the North with a clockwise increment Input satellite data The generation of ASCAT level 1b data by EUMETSAT is described in their technical documentation Ref 6 The global ASCAT data are acquired in Svalbard Norway and transmitted to the EUMETSAT central processing facilities in Darmstadt where they are processed up to level 1b Regional EARS data are acquired at Svalbard and other ground stations processed up to level 1b and then transmitted to KNMI via a dedicated private network The product contains geo located measurement triplets on a satellite swath WVC grid of 25 km or 12 5 km size Geographical definition The Metop satellite flies in a near polar sun synchronous orbit at 98 d
32. on the GTS AWDP version 1_0 19 products in BUFR Edition 4 and up to four wind solutions present in 25 km BUFR products OSI SAF products disseminated on EUMETCast are also available to users in Africa and the Americas now Both wind and soil moisture information are available in a multi parameter BUFR product AWDP version 2 1_00 up to four wind solutions present in the 12 5 km and coastal BUFR products use of NWP Ocean Calibration for more uniform wind characteristics across the swath AHRPT data from a number of ground stations are now available in addition to the EARS ASCAT data acquired at Svalbard Implementation of Bayesian ice screening First development version of ASCAT B 25 km and coastal global wind products AWDP version is 2 1_01 AWDP version 2_2 00 preparation for level 1b data format change ASCAT Wind Product User Manual version 1 13 May 2013 8 SAF OSI CDOP KNMI TEC MA 126 2 The ASCAT instrument The Advanced SCATterometer ASCAT is one of the instruments carried on board the Meteorological Operational Metop polar satellites launched by the European Space Agency ESA and operated by the EUropean organisation for the exploitation of METeorological SATellites EUMETSAT Metop A the first in a series of three satellites was launched on 19 October 2006 Metop B was launched on 17 September 2012 Metop C is planned to be launched approximately in 2017 ASCAT is a real aperture radar using vertically po
33. ry Ambiguity Removal Advanced Scatterometer Binary Universal Format Representation EUMETSAT Advanced Retransmission Service EUMETSAT Polar System European Remote Sensing Satellite EUMETSAT s Digital Video Broadcast Data Distribution System European Organisation for the Exploitation of Meteorological Satellites Hierarchical Data Format Jet Propulsion Laboratory NASA Royal Netherlands Meteorological Institute Meteorological operational satellite National Aeronautics and Space Administration USA Network Common Data Form National Oceanic and Atmospheric Administration USA NASA Scatterometer Numerical Weather Prediction Ocean and Sea Ice SAF Physical Oceanography Distributed Active Archive Center Quality Control USA dedicated scatterometer mission Regional Meteorological Data Communication Network Satellite Application Facility Scatterometer on board QuikSCAT platform USA Soil Moisture Scatterometer Ocean Stress Sea Surface Temperature West to east wind component South to north wind component Wind Vector Cell OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 19 SAF OSI CDOP KNMI TEC MA 126 8 ASCAT BUFR data descriptors Number Descriptor Parameter Unit 1 001033 Identification Of Originating Generating Centre Code Table 2 001034 Identification Of Originating Generating Sub Centre Code Table 3 025060 Software Identification Numeric 4 001007 Satellite Identifier Code Table
34. solution os the coastal Wind Vector Cell is slightly displaced away from the coast On the other hand it is possible to compute winds as close as 15 km from the coast while in the nominal 12 5 km product Wind Vector Cells closer than 35 km from the coast are flagged because of land contamination See Ref 2 and Ref 3 for more information on the coastal product 3 2 Backscatter calibration The backscatter values in the Level 1 product are calibrated by adding a WVC and beam dependent bias in dB to the incoming oos The calibration table was obtained by fitting the actual measurements to the theoretical GMF function More details are provided in Ref 4 and Ref 5 Note that the calibrated backscatter values are only available within the wind processing software the oo data in the wind product are identical to those in the Level 1 product 3 3 NWP collocation KNMI receives NWP model data from ECMWF twice a day through the RMDCN NWP model sea surface temperature SST data are used to support the Bayesian sea ice discrimination Ref 1 The SST values of the four surrounding model grid points around the WVC location are bilinearly interpolated Note that the ECMWF model data do not contain SST values over land if one or more of the four surrounding grid points has missing SST data the SST value of the grid point closest to the WVC is taken WVCs with a sea surface temperature above 5 C are assumed to be always open water The ice scre
35. trol and monitoring In each WVC the oo data is checked for quality and completeness and the inversion residual see Ref 1 is checked Degraded WVCs are flagged see section 5 2 for more details An information file is made for each product The content of the file is identical whatever the product and results from a compilation of all the global information concerning this product From these files various graphs are produced to visually display the confidence levels of the products and their evolution with time These graphs are available in near real time if you click on the Monitoring information link on the product visualisation web pages Data quality is also available to the users within the products see section 5 and 6 for a description of quality flags OSI SAF EARS ASCAT Wind Product User Manual version 1 13 May 2013 11 SAF OSI CDOP KNMI TEC MA 126 4 Helpdesk product dissemination and archive For a swift resoonse management procedure user requests on the OSI SAF data products should be issued at the Ocean and Sea Ice SAF website htto www osi saf org User requests on the EARS products can be sent to scat knmi nl User requests on the Soil Moisture content in the products can be sent to opsOeumetsat int The ASCAT BUFR L2 products are disseminated on EUMETCast Please consult http Awww eumetsat int under Access to Data for more information on EUMETCast dissemination and how to receive these and other EUMET
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