GENERAL INFORMATION
Data Source and Processing
MODIS: The nature of each polar wind product depends on the data source. The primary MODIS wind products are based on 1 km MODIS Level 1B (MOD021KM) HDF files are obtained through the NOAA Real-Time System, or bent pipe, located at NASA Goddard Space Flight Center. This dataset is used to produce single-satellite (Terra and Aqua separately) and mixed-satellite (Terra and Aqua combined) wind products. Two to four 5-minute granules from each orbit are remapped into a polar stereographic projection at 2 km resolution and composited using the McIDAS software. The resulting images are 2800x2800 pixels. The figure on the right shows the coverage from 3 granules.
MODIS
winds are also generated at a number of direct broadcast (DB) sites. For those
products, the MOD021KM MODIS product is used, with the coverage depending on
the position of the satellite relative to the receiving station in each
overpass. There are no 5-minute granules to piece together for the DB products.
As with the bent-pipe winds, 1 km data are remapped to 2 km pixels. Cloud-track
winds are generated using the 11 micron channel. Using the 6.7 micron water
vapor channel, winds are produced in both clear and cloudy areas.
AVHRR: Polar wind products are
generated using AVHRR Global Area Coverage (GAC) data, High Resolution Picture
Transmission (HRPT) direct readout data, and MetOP AVHRR data. The GAC pixel
size is 4 km; HRPT and MetOP AVHRR data are 1 km but remapped to 2 km as is
done for the MODIS winds. AVHRR does not have a water vapor channel, so only
cloud-track (IR) wind data are produced. The information below applies to all
products.
Period and Coverage
Real-time, with new data available as frequently as every 100 minutes.
There are 13-15 bent-pipe MODIS, AVHRR GAC, and MetOP AVHRR datasets per day
per satellite. The number of direct broadcast MODIS and HRPT AVHRR datasets
depends on the receiving station schedule, usually 6-10 per day per satellite.
All products generally cover the area poleward of +/-60 degrees
latitude. Bent pipe, GAC, and MetOP AVHRR winds cover both polar regions over
the course of a day. Direct broadcast and HRPT products cover only part of the
Arctic or Antarctic, depending on the location of the receiving station.
OBTAINING THE DATA
Wind
data files are available at CIMSS and at NOAA NESDIS, depending on the product.
For most purposes we recommend obtaining the data files from the NESDIS
server, as that is an operational, 24/7 system. There are three file
formats for the wind data: plain text, McIDAS MD, and BUFR. Not all products
are available in all formats. NESDIS data are BUFR only. The availability of
products and file formats is given in the table below.
|
Product/Source |
CIMSS |
NESDIS |
Server |
|
MODIS
single-satellite, bent-pipe |
text,
MD |
1,
2, GTS |
|
|
MODIS
mixed-satellite, bent-pipe |
text
(experimental) |
-
(expected late 2011) |
3 |
|
MODIS
direct broadcast |
text,
MD, BUFR |
- |
4,
5, EUMETCast |
|
AVHRR
GAC |
text,
MD, BUFR |
BUFR,
text, MD |
6,
GTS |
|
AVHRR
HRPT |
text,
MD, BUFR |
- |
7 |
|
AVHRR
MetOp |
text,
MD, BUFR |
-
|
6,
GTS |
|
Historical
AVHRR |
text,
MD, BUFR |
- |
8 |
Servers
referenced in table above (all anonymous FTP):
1. MODIS Bent-pipe from
CIMSS: ftp.ssec.wisc.edu in velden/winds/terra
and velden/winds/aqua.
Mirrored on stratus.ssec.wisc.edu in pub/winds/rts/terra and
pub/winds/rts/aqua.
2.
MODIS Bent-pipe
from NESDIS operations: The BUFR files are on satepsanone.nesdis.noaa.gov in pub/bufr/modis_winds. The text and MD files are on ftp.ssec.wisc.edu in velden/winds/terra/NOAA and
velden/winds/aqua/NOAA, as well as on stratus.ssec.wisc.edu in
pub/winds/rts/terra/NOAA and pub/winds/rts/aqua/NOAA.
3.
MODIS mixed-satellite: (available on request)
4.
MODIS DB BUFR: stratus.ssec.wisc.edu
in pub/winds/bufr. The file name extensions
are: PBRW - Barrow (AVHRR), PAFA – Fairbanks, ENTC - Tromso, EFSO -
Sodankyla, MCMR – McMurdo, EGAR - Rothera.
5.
MODIS and AVHRR DB plain text and MD: stratus.ssec.wisc.edu
in pub/winds/mcmurdo, pub/winds/tromso,
pub/winds/sodanklya, pub/winds/fairbanks, pub/winds/barrow, pub/winds/rothera.
6. AVHRR GAC and MetOP from
NESDIS operations and CIMSS: The NESDIS operational BUFR files are on satepsanone.nesdis.noaa.gov in pub/bufr/avhrr_winds. The CIMSS winds are on ftp.ssec.wisc.edu in velden/winds/avhrr/<sat>, where
<sat> is N15, N16, N17, N18, or METOP. Mirrored on stratus.ssec.wisc.edu in pub/winds/avhrr/<sat>.
7. AVHRR HRPT: stratus.ssec.wisc.edu in pub/winds/barrow, pub/winds/rothera (text
and MD), and pub/winds/bufr (BUFR).
8. Historical AVHRR: stratus.ssec.wisc.edu in pub/winds/histavhrr/<sat>/MD|asci|bufr.
Direct
broadcast MODIS winds from Tromso and McMurdo are also available on EUMETCast.
NESDIS MODIS and AVHRR winds are broadcast over the GTS.
Archived
Winds: Most
of the wind files are archived. They are available on stratus.ssec.wisc.edu in pub/winds/archive/<product>.
Unfortunately, the subdirectory structures are not internally consistent at
this time.
FILE FORMATS AND NAMES
At
CIMSS/SSEC, the text and MD files are organized by wind set number. Since there
are 14-15 orbits/day, we get 12-13 wind sets/day (overlapping triplets, but not
crossing the day boundary). If wind sets are reprocessed, the files are
overwritten.
The
text files are named:
QIyyyyddd.nn.pp.gz
where
yyyy = year
ddd = day of year
nn = 01 to 13 indicating wind set of the day
pp = NP or SP indicating north or south pole
For
example:
QI2002183.01.NP.gz
is
the first wind set from day 2002183 over the North Pole.
The
data contained in the text file are of the form:
type sat day hms lat lon pre spd dir rff qi temp
WV MODIS
20021113 1530 82.78 -101.92 450 19.8 164 59.25 .83 234.6
WV MODIS
20021113 1530 86.73 -127.92 450 24.0 220 73.81 .71 235.7
WV MODIS
20021113 1530 82.24 -98.92 462 14.9 153 54.79 .83 234.6
where
type: WV - water vapor (6.7 μm); IR - infrared (11 μm)
sat: MODIS [all from MODIS instrument]
day: yyyymmdd: yyyy - year, mm - month of year; dd - day
of month
hms: hhmm: hour and minute of the middle image [GMT]
lat: latitude (positive North)
lon: longitude (positive West) Note: East longitudes are negative.
pre: pressure level of wind [hPa]
spd: wind speed in m/s
dir: wind direction
rff: CIMSS
recursive filter quality control value
qi: EUMETSAT
control value
temp: IR
or WV brightness temperature
The
MD files are named:
MDXXxxnn.yyyyddd.pp.gz
where:
xxnn = 2001 to 2013 [NP]
xxnn = 2101 to 2113 [SP]
and the last 2 digits are the wind set number as
above.
For
example: MDXX2001.2002183.NP.gz is the first wind set from day 2002183 over the
North Pole.
The
MODIS direct broadcast and AVHRR winds are also available in BUFR format. The
MODIS bent pipe winds are not available in BUFR. Standard BUFR decoders may
work. Our BUFR decoder is available via anonymous FTP from
stratus.ssec.wisc.edu
in
the /pub/winds/bufr_software directory. Pre-compiled versions for Linux,
Mac OS X, and Windows are available.
The
NESDIS BUFR file naming convention is:
Aqua Files: satwnd.bufrxxxx.aqua.Dyyddd.Thh:mm:ssZ
where:
xxxx = cdft for IR cloud-drift winds
xxxx = wvap for water vapor winds
yy = year
ddd = julian day
hh,mm,ss = hour, minute, second (system time)
The
CIMSS BUFR file naming convention is similar:
satwnd.bufrxxxx.<sat>.Dyyddd.ThhmmZ.<site>
where:
xxxx = cdft for IR cloud-drift winds
xxxx = wvap for water vapor winds
<sat> = the satellite: aqua, terra, N18, etc.
yy = year
ddd = julian day
hhmm = hour, minute
<site> = optional (including the period)
direct broadcast site indicator: PBRW - Barrow (AVHRR), PAFA – Fairbanks,
ENTC - Tromso, EFSO - Sodankyla, MCMR – McMurdo, EGAR – Rothera.
GTS
As
indicated in the table above, some data are available on the GTS. Here is the WMO
header list of MODIS and AVHRR GAC winds:
AQUA_IR: JICX01 KNES YYGGgg
TERRA_IR: JBCX01 KNES YYGGgg
AQUA_WV: JLCX01 KNES YYGGgg
TERRA_WV:
JFCX01 KNES YYGGgg
NOAA-15: JCVX91 KNES YYGGgg
NOAA-16: JCVX92 KNES YYGGgg
NOAA-17: JCVX93 KNES YYGGgg
NOAA-18: JCVX94 KNES YYGGgg
NOAA-19: JCVX95 KNES YYGGgg
METOP:
JCVX97 KNES YYGGgg
USAGE POLICY
The
data are free, where "free" means that they are available at no cost.
"Free" does not mean unconditional use. In order to ensure that they
are being used as intended, please send us a note with a brief description of
your application. While we have tried to make clear their limitations, there
will almost certainly be some applications that we have not addressed, and for
which the data or programs are not well-suited. Additionally, if these data
will play a significant role in a journal publication, please consider
including the developers as co-authors.
CONTACTS
If
you have any questions about the data or project, contact:
Jeff
Key: jeff.key@ssec.wisc.edu
Dave Santek: dave.santek@ssec.wisc.edu
Chris Velden: chris.velden@ssec.wisc.edu