NOAA-15, 16, 17, & 18, AVHRR, Level 1B Cloud Clearing and Processor Converter Change, 25 January 2006 - Issued: 25 January 2006; 1930 UTC

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

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