Topic:
Update to implement cloud clearing information and processing
converter change
Date/Time(UTC) Message Issued:
25 January 2006, 1930 UTC
Satellite(s) Involved:
NOAA-15, 16, 17, and 18
Instrument(s) Involved:
AVHRR
Product(s) Involved/Affected:
All Products/no impact
Date/Time(UTC) of Initial Implementation:
25 January 2006, Time 1930 UTC
Details/Specifics of Change:
On January 25, NOAA updated AVHRR level 1b processing
so that the reserved CLAVR-x (Clouds from AVHRR
Extended cloud mask) bytes are utilized and the
announced 1B
converter changes are in operation.
The changes became operational beginning with the passes listed below:
NSS.HRPT.NM.D06025.S1927.E1938.B1865252.GC NSS.HRPT.NM.D06025.S1933.E1946.B1865252.MO NSS.GHRR.NM.D06025.S1752.E1925.B1865152.GC NSS.GHRR.NM.D06025.S1603.E1758.B1865051.GC NSS.LHRR.NM.D06025.S1902.E1911.B1865252.GC NSS.LHRR.NM.D06025.S1721.E1730.B1865151.GC NSS.HRPT.NM.D06025.S2247.E2259.B1865454.GC NSS.GHRR.NM.D06025.S2108.E2245.B1865354.GC NSS.GHRR.NM.D06025.S1919.E2114.B1865253.GC NSS.LHRR.NM.D06025.S2117.E2125.B1865353.GC NSS.HRPT.NN.D06025.S1933.E1945.B0353030.WI NSS.GHRR.NN.D06025.S1744.E1932.B0352830.WI NSS.LHRR.NN.D06025.S1917.E1929.B0352930.WI NSS.LHRR.NN.D06025.S1747.E1753.B0352929.WI NSS.HRPT.NN.D06025.S2114.E2129.B0353131.MO NSS.HRPT.NN.D06025.S2124.E2138.B0353131.GC NSS.GHRR.NN.D06025.S1926.E2121.B0352931.GC NSS.HRPT.NK.D06025.S2052.E2103.B4004646.WI NSS.GHRR.NK.D06025.S1930.E2052.B4004546.WI NSS.GHRR.NK.D06025.S1741.E1936.B4004445.WI NSS.HRPT.NK.D06025.S2230.E2245.B4004747.WI NSS.GHRR.NK.D06025.S2046.E2229.B4004647.WI NSS.HRPT.NL.D06025.S2128.E2136.B2755050.WI NSS.GHRR.NL.D06025.S2001.E2127.B2754950.WI NSS.GHRR.NL.D06025.S1811.E2007.B2754849.WI NSS.HRPT.NL.D06025.S2316.E2330.B2755151.GC NSS.GHRR.NL.D06025.S2121.E2315.B2755051.GC
****** Information from previous announcement ******
A new flag was added to
the header record (utilizing spares) that indicates when the
CLAVR-x processing is
actually turned on or off. A brief explanation of the CLAVR-x is
provided
below along with a list of the affected level 1b bytes. Also, you will
find a brief explanation of the 1B converter change. Though we believe
this to be a no impact
change, we are asking that you please monitor your systems carefully
over the next few days. d89nav
The CLAVR-x provides the cloud
mask present in the AVHRR level 1b datasets. It was designed to operate
under all conditions including all orbital configurations. The goal of
the CLAVR-x cloud mask is to provide a useful first guess cloud mask
for all AVHRR applications that require it. It is constrained to
perform
this task in a timely manner to avoid delays in subsequent AVHRR
applications. The CLAVR-x cloud mask in level 1b data is stored as a
2-bit value for each pixel . The values of the cloud mask are 0=
clear,1 =probably clear, 2= probably cloudy and 3 = cloudy. The cloud
mask is a series of spectral and spatial tests based on a long heritage
of AVHRR cloud detection within NESDIS. In addition to providing the
2-bit cloud mask in the level 1b data, the results of each CLAVR-x test
are also available in HDF files to allow for application specific
optimization of the cloud mask. A draft of the CLAVR-x cloud mask
theoretical basis document can be found at
http://cimss.ssec.wisc.edu/clavr/clavrx_docs/clavrx_mask_atbd.pdf
.
The CLAVR specific bytes in the level 1B file are outlined below. This
information can be found in the NOAA-KLM Users' Guide
(http://www2.ncdc.noaa.gov/docs/klm/html/c8/s83-1.htm)
under the
NOAA-N format information.
Header Record
Field Name |
Start Octet |
End Octet |
Data Type |
Word Size |
Number of Words |
Scale Factor |
Units |
CLOUDS FROM AVHRR
(CLAVR) |
|
|
|
|
|
|
|
CLAVR Status
Bit Field |
989 |
990 |
u |
2 |
1 |
0 |
|
bits 15-1: <zero
fill> bit 0: CLAVR processing
(0=off; 1=on) |
|
|
|
|
|
|
|
<Zero
Fill> |
991 |
992 |
i |
2 |
1 |
0 |
|
HRPT/LAC Data Record
Field Name |
Start Octet |
End Octet |
Data Type |
Word Size |
Number of Words |
Scale Factor |
Units |
CLAVR |
|
|
|
|
|
|
|
<Reserved>
[CLAVR Status Bit Field] |
14977 |
14980 |
u |
4 |
1 |
0 |
|
bits 31-1:
<undefined> |
|
|
|
|
|
|
|
<Reserved>
[CLAVR] |
14981 |
14984 |
u |
4 |
1 |
0 |
|
<Reserved> [CLAVR CCM (Clear/Cloudy/Mixed) Codes
(0=clear; 1=mixed clear; 2=mixed cloudy; 3=cloudy)] |
14985 |
15496 |
u |
2 |
256 |
0 |
|
Word 1 |
|
|
|
|
|
|
|
GAC data Record
Field Name |
Start Octet |
End Octet |
Data Type |
Word Size |
Number of Words |
Scale Factor |
Units |
CLAVR |
|
|
|
|
|
|
|
<Reserved>
[CLAVR Status Bit Field] |
4049 |
4052 |
u |
4 |
1 |
0 |
|
bits 31-1:
<undefined> |
|
|
|
|
|
|
|
<Reserved>
[CLAVR] |
4053 |
4056 |
u |
4 |
1 |
0 |
|
<Reserved> [CLAVR CCM (Clear/Cloudy/Mixed) Codes
(0=clear; 1=mixed clear; 2=mixed cloudy; 3=cloudy)] |
4057 |
4160 |
u |
2 |
52 |
0 |
|
Word 1 |
|
|
|
|
|
|
|
The following gives a description of the changes to the converter:
A problem with certain data values in 1b data sets has been reported by
users. This problem involves 1-, 2-byte or 4-byte data fields where a
valid data value has the most significant bit set, with all other bits
0. Therefore, values affected are 1-byte fields with a valid signed
integer value of –128, 2-byte fields with a valid signed integer value
of –32768, or 4-byte fields with a valid signed integer value of
–2147483648. These values may be erroneously stored as 0 in the 1b. The
1b fields which have been reported as occasionally erroneous are AMSU-B
and MHS radiometry values and HIRS minor frame bit flags and minor
frame header elements. See December 13 notice for more details.
Contact Person(s) Name/Email/Phone Number for Questions:
John.Sapper@noaa.gov
301-457-9014 ext 148 - CLAVR questions
Emily.Harrod@noaa.gov
301-457-5247 ext. 117 - ops questions
Web site(s) that contain other relevant information (where
applicable):
http://www.osdpd.noaa.gov/PSB/PPP/PPP.html
- History of level 1B notices
http://www.ssd.noaa.gov/PS/SATS/messages.html
- All user notices
http://www.oso.noaa.gov/poes/index.htm
- SOCC polar satellite status
http://www.oso.noaa.gov/goes/index.htm
- SOCC geostationary satellite status
http://www.oso.noaa.gov/daily-news/index.asp
- SOCC morning reports
-- ******************************************* * * Emily D. Harrod * NOAA/NESDIS/OSDPD/IPD * Computer Operations Branch * Pre-Product Processing Group * E/SP11, Federal Building #4, room 0318 * 5200 Auth Road * Suitland, Maryland 20746-4304 * USA * voice 301-457-5247 ext 117 * fax 301-457-5199 * email Emily.Harrod@noaa.gov * *******************************************