This directory contains access to Remote Sensing Systems' SeaWinds on Midori-II (SeaWinds) or SeaWinds on QuikSCAT (QuikSCAT) Orbit Wind Vector Data (swath data) and Ocean Wind Bytemaps(0.25 degree gridded data). !!This note has been updated on December 30,2006 !!! *****Geophysical Model Function***** The SeaWinds on Midori-II and SeaWinds on QuikSCAT radar returns have been processed using the Ku-2001 geophysical model function. This is referred to as version-3 data (_v3). The data were reprocessed in October 2006 using the same model function and are referred to as version-3a (_v3a). Both QuikScat and SeaWinds Ku-2001 winds agree extremely well with buoys typically showing a mean difference near 0 m/s with an rms below 1 m/s assuming no rain is present and the wind speeds are below 20 m/s. *****Data Files******* There are two types of SeaWinds data available at this ftp site for both the Midori-II and QuikSCAT platforms - Orbit files and Bytemap files. **************** **Orbit Files*** **************** Orbit files are also known as wind vector files. They are located in the seawinds_wind_vectors or qscat_wind_vectors directories. Each file consists of one orbit of data. The data are gridded into wind vector cells, 76 across the orbit and 1624 rows of cells along the orbit. Reading subroutines are available in the scat_orbit_support directory to assist in reading the orbit data files: get_scat_orbit_v03.pro IDL subroutine get_scat_orbit_v03.f Fortran subroutine get_scat_orbit_v03.m Matlab subroutine Some users have had trouble on other systems with different compilers. If you are having trouble reading the orbit files, check the specifics of how the file is opened and how the read is performed to make sure it matches the requirements of your compiler. The orbit data files, once decoded, contain: ATIME is the 21 character time string, format: YYYY-DDDTHH:MM:SS.sss PHI_TRACK is the direction of the subtrack velocity vector relative to north XLAT is the geodetic latitude XLON is the east geodetic longitude (0 - 360) ICLASS indicates the expected quality of the vector retrieval ICLASS=0 denotes no retrieval was done (either no observations or only one flavor of observation) ICLASS=1 denotes 2 flavors of observations in wind vector cell ICLASS=2 denotes 3 flavors of observations in wind vector cell ICLASS=3 denotes 4 flavors of observations in wind vector cell We suggest using just cases for which ICLASS.GE.2 NUM_AMBIG is the number of ambiguites (0 to 4) ISELECT is the selected ambiguity (0 to 4) IRAIN_SCAT is the rain flag derived from the scatterometer measurements IRAIN_SCAT=1 indicates rain WINAL is the 10 meter ocean wind speed for the various ambiguities PHIAL is the wind direction for the various ambiguties (oceanographic convention) SOSAL is the normalized rms after-the-fit residual of the observation minus model sigma-nought. Large SOSAL values indicate the observations did not fit the geophysical model function. We suggest discarding observations for which SOSAL.GT.1.9. WINDS is the smoothed version of the selected wind, WINAL(ISELECT) PHIWS is the smoothed version of the selected wind, PHIAL(ISELECT) WINGCM is the general circulation model wind speed used for nudging (either NCEP or ECMWF) DIRGCM is the general circulation model wind direction used for nudging (either NCEP or ECMWF) RAD_RAIN is the AMSR columar rain rate (rain rate times rain column height, km mm/hour) RAD_RAIN=-999 no AMSR rain avaliable RAD_RAIN=0 no rain RAD_RAIN=0.1 possible rain RAD_RAIN=0.2 through 25.4 definite rain and the given value is the columnar rain rate "no rain" means no rain was detected within +/- 50 km and +/- time given in MIN_DIFF. "possible rain" means some rain was detected within +/- 50 km and +/- time given in MIN_DIFF. "definite rain" means rain was detected within +/- 25 km and +/- time given in MIN_DIFF. We suggest discarding observations for which RAD_RAIN.GT.0.15 MIN_DIFF is the time difference in minutes between the scatterometer and the collocated radiometer. A value of 255 means that no radiometer observation was collocated with the scatterometer. NUDGE_NCEP NUDGE_ECWMF Each data file contains two INTEGER(1) variables at the end of the file. Both variables supply information on which GCM was used for the nudging field. The first variable shows if NCEP data were used (0=used, 1=not used),and the second shows if ECMWF data were used (0=used,1=not used). Since GCM data are tri-linearly interpolated to the scatterometer data, it is possible that one of each map was used. If both ECMWF and NCEP data were missing for the required orbit, the orbit is not processed since no nudging field would be available. It is important to not use the data if the quality is suspect. We recommend the following conditions be satisfied for the **very best** quality data: ICLASS(icel,iscan).ge. 2 (this would omit all outer swath data) SOSAL(1,icel,iscan).le. 1.9 (yes, we mean the SOS of the first ambiguity) IRAIN_SCAT(icel,iscan).ne. 1 MIN_DIFF(icel,iscan).le. 30 .and. RAD_RAIN(icel,iscan).le. 0.15 The SeaWinds on Midori-II dataset contains several gaps during the six months of data collection. Official information on gaps and the cause of missing data can be found at http://podaac.jpl.nasa.gov/seawinds/seawinds_prob.html#gaps The following are known gaps reported: revs 1724-1725 1895-1901 2241-2242 2396-2397 2774-2774 2877-2877 3173-3173 3382-3395 3471-3471 3476-3478 3647-3648 3786-3786 3871-3871 4453-4453 The SeaWinds on QuikSCAT dataset also contains gaps. Official information on gaps and the cause of missing data can be found at http://podaac.jpl.nasa.gov/quikscat/qscat_prob.html#gaps The following are known gaps as of December 30, 2006: revs 2146 2170 2793 2810 3068 3070 5627 5636 6217 6218 7357 7384 9859 9907 10667 10694 12573 12598 14307 14328 15832 15835 16492 16504 17789 17807 20385 20389 22028 22029 23411 23423 26722 26729 36418 36425 36821 36855 38524 38527 The date and time information for each rev# is provided for each instrument in the SEAWINDS_INFO.txt and QSCAT_INFO.txt files The columns in each file represent: Rev #, # of good WVC rows, EQCROSSDATE, EQCROSSTIME, EQCROSSLONG, ORBITPERIOD Due to the large number of files, we have subdivided them into directories of approximately 1000 files each. 01000to01999/ 02000to02999/ etc. ******************* ***Bytemap Files*** ******************* Bytemap files are similar to those available from Remote Sensing Systems for SSMI and TMI. They are located in the bmaps_v03a directory. Each file consists of one day of data. The data are gridded into 0.25 degree lat/lon cells, 1440 cells longitude by 720 cells latitude. File reading subroutines are available in the scat_bmap_support directory to assist in reading the bmap data files: get_scat_daily_v03.pro IDL subroutines get_scat_averaged_v03.pro get_scat_daily_v03.f Fortran subroutines get_scat_averaged_v03.f get_scat_daily_v03.m Matlab subroutines get_scat_averaged_v03.f Each of these subroutines have complementary main programs that show how to call the subroutine and are already set up to write out the data shown in the verification file. Use the verification file to confirm that your adapted program is still reading correctly after you have made any changes. The bytemap files are (1440x720x4x2 or lon,lat,paramter,asc/dsc), and contain four parameters each stored as a single byte: 1 Time (minutes of day GMT) : TIME = IVAL * 6 2 Wind Speed : WSPD = IVAL*0.2 3 Wind Direction : WDIR = IVAL*1.5 4 Combination Rain Data : use bit extraction to access all data The combination rain flag contains a stand-alone scatterometer rain flag and available collocated radiometer rain data bit pos 0 SCATEROMETER rainflag (0=no rain, 1=rain) bit pos 1 collocated SSMI, TMI observations(for QuikSCAT data) or AMSR observations (for Midori-II data) within 60 min=1, else=0 bit pos 2-7 0-63: radiometer rain where: 0= absolutely no rain 1= rain in one of the adjacent cells 2= Radiometer RR = 0.5 3= Radiometer RR = 1.0 4: Radiometer RR = 1.5 etc. Each subroutine (IDL,Fortran,Matlab) performs the bit extraction and provides the user with the rain information. It is important to remove rain contaminated data from your processing, especially at lower wind speeds typical of the tropics as this is where rain has the greatest effect. Rain causes SeaWinds to measure higher wind speeds than are present in low wind situations. If a day is missing from the data set it is because all orbits for that day are missing. Official information on gaps and the cause of missing data can be found at the podaac web site listed above. Orbit numbers can be related to day and month bytemaps by looking at the SEAWINDS_INFO.txt or QSCAT_INFO.txt files. The date and time information for each rev# is provided in these files. The columns represent: Rev #, # of good WVC rows, EQCROSSDATE, EQCROSSTIME, EQCROSSLONG, ORBITPERIOD The bytemap files are stored by year and month. File names are YYYYMMDD.gz Use any gzip compatible zip utility to uncompress the data prior to using the read subroutines provided. *****Contact Information***** If you have questions about RSS Scatterometer data, contact RSS support: http://www.remss.com/support