Section 1: Product definition section
|1-3||section1Length||unsigned||Length of section|
|4||table2Version||unsigned||GRIB tables Version No. (currently 3 for international exchange) Version numbers 128-254 are reserved for local use|
|5||centre||codetable||Identification of originating/generating centre (see Code table 0 = Common Code table C1 in Part C/c.)|
|6||generatingProcessIdentifier||unsigned||Generating process identification number (allocated by originating centre)|
|7||gridDefinition||unsigned||Grid definition (Number of grid used from catalogue defined by originating centre)|
|8||section1Flags||codeflag||Flag (see Regulation 92.3.2 and Code table 1)|
|9||indicatorOfParameter||codetable||Indicator of parameter (see Code table 2)|
|10||indicatorOfTypeOfLevel||codetable||Indicator of type of level (see Code table 3)|
|11-12||Height, pressure, etc. of levels (see Code table 3)|
|13||yearOfCentury||unsigned||Year of century|
|14||month||unsigned||Month Reference time of data date and time of|
|15||day||unsigned||Day start of averaging or accumulation period|
|18||unitOfTimeRange||codetable||Indicator of unit of time range (see Code table 4)|
|19||P1||unsigned||P1 Period of time (number of time units) (0 for analyses or initialized analyses). Units of time given by octet 18|
|20||P2||unsigned||P2 Period of time (number of time units); or Time interval between successive analyses, initialized analyses or forecasts, undergoing averaging or accumulation. Units of time given by octet 18|
|21||timeRangeIndicator||codetable||Time range indicator (see Code table 5)|
|22-23||numberIncludedInAverage||unsigned||Number included in average, when octet 21 (Code table 5) indicates an average or accumulation; otherwise set to zero|
|24||numberMissingFromAveragesOrAccumulations||unsigned||Number missing from averages or accumulations|
|25||centuryOfReferenceTimeOfData||unsigned||Century of reference time of data|
|26||subCentre||codetable||Sub-centre identification (see common Code table C1 in Part C/c., Note (3))|
|27-28||decimalScaleFactor||signed||Units decimal scale factor (D)|
|29-40||Reserved: need not be present|
|41-nn||Reserved for originating centre use|
( 1) Inclusion of the Section 2 Grid description section (GDS) is the preferred method of defining a grid.
( 2) Where octet 7 defines a catalogued grid, that grid should also be defined in Section 2, provided the flag in octet 8 indicates inclusion of Section 2.
( 3) Octet 7 must be set to 255 to indicate a non-catalogued grid, in which case the grid will be defined in Section 2.
( 4) A negative value of D shall be indicated by setting the high-order bit (bit 1) in the left-hand octet to 1 (on).
( 5) If a Grid description section is not included, then any u- or v-components of vector quantities in the message are to be resolved relative to the specified grid in the direction of increasing x and y (or i and j) coordinates respectively. If a Grid description section is included in the message, which is the preferred option, then octet 17 of the GDS and Code table 7 will contain component resolution information.
( 6) To specify year 2000, octet 13 of the section (year of the century) shall contain a value equal to 100 and octet 25 of the section (Century of reference time data) shall contain a value equal to 20. To specify year 2001, octet 13 of the section shall contain a value equal to 1 and octet 25 of the section shall contain a value equal to 21 (by International Convention, the date of 1 January 2000 is the first day of the hundredth year of the twentieth century and the date of 1 January 2001 is the first day of the first year of the twenty-first century); it is to be noted also that year 2000 is a leap year and that 29 February 2000 exists.