NOAA-15, 16, 17, & 18, AVHRR, Level 1B Cloud Clearing and Processor Converter Change Ver. Num. Update, 25 January 2006 - Issued: 28 April 2006; 2000 UTC

Topic:
    Update to implement cloud clearing information and processing converter change - Level 1B Version number change

Date/Time(UTC) Message Issued:
    28 April 2006, 1930 UTC

Satellite(s) Involved:
     NOAA-15, 16, 17, and 18

Instrument(s) Involved:
     AVHRR

Product(s) Involved/Affected:
    All Products

Date/Time(UTC) of Initial Implementation:
    25 January 2006, Time 1930 UTC

Details/Specifics of Change:
On January 25, the level 1b processing was updated to include cloud mask information.  At that time the header record was updated to use a spare byte as a flag to indicate when CLAVRx processing was turned on.  The original message that follows, did not include the fact that this was considered a level 1b version change.  The version number contained in the header was updated from 3 to 4.  All level 1b documentation should reflect that as of January 25 the version number will read, version 4, until another change is made.  Several users have expressed concern that the change was unexpected and caused them processing problem.  We regret any problems that you may have experienced and will endeavor to be more detailed in future notices. 

****Original Message from January 25, 2006****
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

HRPT/LAC Data Record

GAC data Record

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
*
*******************************************