GRIB Keys

GRIB 格式

见第一章的介绍。

GRIB 1 消息

#==============   MESSAGE 1 ( length=130404 )              ==============
1-4       identifier = GRIB
5-7       totalLength = 130404
8         editionNumber = 1
======================   SECTION_1 ( length=28, padding=0 )    ======================
1-3       section1Length = 28
4         table2Version = 2
5         centre = 38 [Beijing  (RSMC)  (common/c-1.table) ]
6         generatingProcessIdentifier = 15
7         gridDefinition = 255
8         section1Flags = 128 [10000000]
9         indicatorOfParameter = 11 [T Temperature K (grib1/2.0.2.table) ]
10        indicatorOfTypeOfLevel = 100 [Isobaric level pressure in hectoPascals  (hPa)  (grib1/3.table) ]
11-12     level = 1000
13        yearOfCentury = 18
14        month = 1
15        day = 13
16        hour = 0
17        minute = 0
18        unitOfTimeRange = 1 [Hour (grib1/4.table) ]
19        P1 = 0
20        P2 = 0
21        timeRangeIndicator = 0 [Forecast product valid at reference time + P1  (P1>0)  (grib1/5.table) ]
22-23     numberIncludedInAverage = 0
24        numberMissingFromAveragesOrAccumulations = 0
25        centuryOfReferenceTimeOfData = 21
26        subCentre = 0 [Unknown code table entry () ]
27-28     decimalScaleFactor = 0
======================   SECTION_2 ( length=32, padding=0 )    ======================
1-3       section2Length = 32
4         numberOfVerticalCoordinateValues = 0
5         pvlLocation = 255
6         dataRepresentationType = 0 [Latitude/Longitude Grid (grib1/6.table) ]
7-8       Ni = 360
9-10      Nj = 181
11-13     latitudeOfFirstGridPoint = 90000
14-16     longitudeOfFirstGridPoint = 0
17        resolutionAndComponentFlags = 128 [10000000]
18-20     latitudeOfLastGridPoint = -90000
21-23     longitudeOfLastGridPoint = 359000
24-25     iDirectionIncrement = 1000
26-27     jDirectionIncrement = 1000
28        scanningMode = 0 [00000000]
29-32     zero =
======================   SECTION_4 ( length=130332, padding=0 )   ======================
1-3       section4Length = 130332
4         dataFlag = 8 [00001000]
5-6       binaryScaleFactor = -9
7-10      referenceValue = 223.079
11        bitsPerValue = 16
12-130332 values = (65160,130321) {
2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02, 2.4710023499e+02,
...
} # data_g1simple_packing values
======================   SECTION_5 ( length=4, padding=0 )     ======================
1-4       7777 = 7777

GRIB 2 消息

#==============   MESSAGE 1 ( length=156935 )              ==============
1-4       identifier = GRIB
5-6       reserved = MISSING
7         discipline = 0 [Meteorological products (grib2/tables/4/0.0.table) ]
8         editionNumber = 2
9-16      totalLength = 156935
======================   SECTION_1 ( length=21, padding=0 )    ======================
1-4       section1Length = 21
5         numberOfSection = 1
6-7       centre = 38 [Beijing  (RSMC)  (common/c-11.table) ]
8-9       subCentre = 0
10        tablesVersion = 4 [Version implemented on 7 November 2007 (grib2/tables/1.0.table) ]
11        localTablesVersion = 0 [Local tables not used  (grib2/tables/4/1.1.table) ]
12        significanceOfReferenceTime = 0 [Analysis (grib2/tables/4/1.2.table) ]
13-14     year = 2018
15        month = 1
16        day = 13
17        hour = 0
18        minute = 0
19        second = 0
20        productionStatusOfProcessedData = 0 [Operational products (grib2/tables/4/1.3.table) ]
21        typeOfProcessedData = 0 [Analysis products (grib2/tables/4/1.4.table) ]
======================   SECTION_3 ( length=72, padding=0 )    ======================
1-4       section3Length = 72
5         numberOfSection = 3
6         sourceOfGridDefinition = 0 [Specified in Code table 3.1 (grib2/tables/4/3.0.table) ]
7-10      numberOfDataPoints = 205761
11        numberOfOctectsForNumberOfPoints = 0
12        interpretationOfNumberOfPoints = 0 [There is no appended list (grib2/tables/4/3.11.table) ]
13-14     gridDefinitionTemplateNumber = 0 [Latitude/longitude  (Also called equidistant cylindrical, or Plate Carree)  (grib2/tables/4/3.1.table) ]
15        shapeOfTheEarth = 6 [Earth assumed spherical with radius of 6,371,229.0 m (grib2/tables/4/3.2.table) ]
16        scaleFactorOfRadiusOfSphericalEarth = 0
17-20     scaledValueOfRadiusOfSphericalEarth = 0
21        scaleFactorOfEarthMajorAxis = 0
22-25     scaledValueOfEarthMajorAxis = 0
26        scaleFactorOfEarthMinorAxis = 0
27-30     scaledValueOfEarthMinorAxis = 0
31-34     Ni = 641
35-38     Nj = 321
39-42     basicAngleOfTheInitialProductionDomain = 0
43-46     subdivisionsOfBasicAngle = 0
47-50     latitudeOfFirstGridPoint = 90000000
51-54     longitudeOfFirstGridPoint = 0
55        resolutionAndComponentFlags = 48 [00110000]
56-59     latitudeOfLastGridPoint = 0
60-63     longitudeOfLastGridPoint = 180000000
64-67     iDirectionIncrement = 281250
68-71     jDirectionIncrement = 281250
72        scanningMode = 0 [00000000]
======================   SECTION_4 ( length=34, padding=0 )    ======================
1-4       section4Length = 34
5         numberOfSection = 4
6-7       NV = 0
8-9       productDefinitionTemplateNumber = 0 [Analysis or forecast at a horizontal level or in a horizontal layer at a point in time (grib2/tables/4/4.0.table) ]
10        parameterCategory = 0 [Temperature (grib2/tables/4/4.1.0.table) ]
11        parameterNumber = 0 [Temperature  (K)  (grib2/tables/4/4.2.0.0.table) ]
12        typeOfGeneratingProcess = 0 [Analysis (grib2/tables/4/4.3.table) ]
13        backgroundProcess = 0
14        generatingProcessIdentifier = 15
15-16     hoursAfterDataCutoff = 0
17        minutesAfterDataCutoff = 0
18        indicatorOfUnitOfTimeRange = 1 [Hour (grib2/tables/4/4.4.table) ]
19-22     forecastTime = 0
23        typeOfFirstFixedSurface = 100 [Isobaric surface  (Pa)  (grib2/tables/4/4.5.table) ]
24        scaleFactorOfFirstFixedSurface = 0
25-28     scaledValueOfFirstFixedSurface = 100000
29        typeOfSecondFixedSurface = 255 [Missing (grib2/tables/4/4.5.table) ]
30        scaleFactorOfSecondFixedSurface = MISSING
31-34     scaledValueOfSecondFixedSurface = MISSING
======================   SECTION_5 ( length=23, padding=0 )    ======================
1-4       section5Length = 23
5         numberOfSection = 5
6-9       numberOfValues = 205761
10-11     dataRepresentationTemplateNumber = 40 [JPEG2000 Packing (grib2/tables/4/5.0.table) ]
12-15     referenceValue = 22305.5
16-17     binaryScaleFactor = 0
18-19     decimalScaleFactor = 2
20        bitsPerValue = 14
21        typeOfOriginalFieldValues = 0 [Floating point (grib2/tables/4/5.1.table) ]
22        typeOfCompressionUsed = 0 [Lossless (grib2/tables/4/5.40.table) ]
23        targetCompressionRatio = 255
======================   SECTION_6 ( length=6, padding=0 )     ======================
1-4       section6Length = 6
5         numberOfSection = 6
6         bitMapIndicator = 255 [A bit map does not apply to this product (grib2/tables/4/6.0.table) ]
======================   SECTION_7 ( length=156759, padding=0 )   ======================
1-4       section7Length = 156759
5         numberOfSection = 7
6-156759  codedValues = (205761,156754) {
2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02, 2.4710527344e+02,
...
} # data_jpeg2000_packing codedValues
======================   SECTION_8 ( length=4, padding=0 )     ======================
1-4       7777 = 7777

ecCodes 方式

ecCodes 使用 key/value 方式访问 GRIB 消息中的信息。

  • numberOfPointsAlongAParallel -> 沿赤道的格点个数
  • numberOfPointsAlongAMeridan -> 沿子午线的格点个数

每个 key 都有原生类型（real，integer，string）。 当从一个类型到其他类型的转换可行时，ecCodes 提供这种转换。

不同消息之间可用的 key 集合与下面的因素有关：

  • GRIB 版本号
  • 消息的内容

修改某个 key 可能导致某些其它 key 可用或不可用。

key 值并不总是编码在 GRIB 消息中，因为某些 key 是其它几个 key 通过指定的算法计算得到的，或者只是临时结果（短暂的）。 因此有如下两种类型的 key：

  • CODED keys （编码在消息中的 key）
  • COMPUTED keys （临时或从其它 key 计算得到）

某些 key 可以使用别名。

  • numberOfPointsAlongAParallel -> Ni 或 Nx 或 numberOfColumns
  • numberOfPointsAlongAMeridan -> Nj 或 Ny 或 numberOfRows

GRIB key 和 parameter 的参考

GRIB Parameter Database，GRIB 参数数据库

http://apps.ecmwf.int/codes/grib/param-db

GRIB keys

免责声明：官方 FM-92 GRIB 文档由 WMO 负责维护，请访问如下网址获取公开的文档。

http://www.wmo.int/pages/prog/www/WMOCodes.html

GRIB 工具与 ecCodes keys

GRIB 工具是查看 GRIB 文件和查找 key 的最简便方式：

  • grib_ls 获取文件内容的简要信息
  • grib_dump 获取更详细的信息

在做些练习之后，就会对下面的描述有更清晰的认识。

Namespace

命名空间是一系列 key 的集合的名称。

命名空间中的某个 key 可以通过在 key 前面加上命名空间前缀而获取/设置，或者更简单地不使用任何前缀。

  • time.step == step
  • parameter.paramId == paramId

有多个命名空间可以使用，例如：

  • parameter
  • time
  • geography
  • vertical
  • statistics

key 介绍

下面介绍一些有代表性的 key。

与文件相关

key 名称 描述
count 文件中的消息序号
countTotal 一组文件中的消息序号
offset 消息在文件中的起始字节数

数据值

key 名称 描述
values 包括数据值和缺失值的所有数据的数组
numberOfCodedValues 数据段中的数据个数（包括缺失值）
numberOfPoints 格点数或数据数组的大小
numberOfMissing 缺失值个数
max, min, average… 要素场的统计信息
… …

参数

不同版本间的参数定义有很大的区别。

GRIB 1 keys GRIB 2 keys
centre discipline
table2Version parameterCategory
indicatorOfParameter parameterNumber
levelType typeOfFirstFixedSurface
level scaleFactorOfFirstFixedSurface
… scaledValueOfFirstFixedSurface
… typeOfSecondFixedSurface
… scaleFactorOfSecondFixedSurface
… scaledValueOfSecondFixedSurface
… productDefinitionTemplateNumber
… …

ecCodes 提供一些与版本无关的 key，用于定义参数。

key 名称 示例值
paramId 151
shortName msl
centre ecmf(or 98)
name Mean sea level pressure
unit Pa

这些值定义在 parameter 命名空间中。

时间

预报运行起始时间 示例值
dataDate 20160224(YYYYMMDD)
dataTime 0, 600, 1200, 1800
预报时效 示例值
stepType instant, accum, avg, max, min, …
stepUnits s, m, h, 3h, 6h, 12h, D, M, Y, 10Y, 30Y, C
startStep 0, 3, …
endStep(= step) 0, 3, ..
stepRange 3-6, 6 (“startStep-endStep” ,“endStep” )
Validity of the forecast 示例值
validityDate 20160224(YYYYMMDD)
validityTime 0, 300, 1200, 1800

垂直层次和地理信息

vertical 命名空间 示例值
typeOfLevel hybrid, surface, depthBelowLandLayer,isobaricInhPa,…
level 0, 1, 137, 1000, 850, …
geography 命名空间 示例值
Ni (Nx) 720
Nj(Ny) 361
gridType reduced_gg, regular_ll, sh, …
latitudeOfFirstGridPointInDegrees 90.0,55.5, …
longitudeOfFirstGridPointInDegrees 0.0,350.0, …
latitudeOfLastGridPointInDegrees -90.0,35.0, …
longitudeOfLastGridPointInDegrees 360.0,50.0, …
iDirectionIncrementInDegrees 0.5, …
jDirectionIncrementInDegrees 0.5, …
N 640, 320, …
… …

地理数组

latitudes（纬度），longitudes（经度）

保存网格中每个点的所有经纬度值的数组

latLonValues

保存网格中每个点的所有经纬度和数据值的数组

(lat1,lon1,value1,lat2,lon2,value2,…,latN,lonN,valueN)

gridTypes

版本 1 和 版本 2 均可以使用的网格种类：

– regular_ll – reduced_ll – mercator – lambert – polar_stereographic – UTM – simple_polyconic – albers – miller – rotated_ll – stretched_ll – stretched_rotated_ll – regular_gg – rotated_gg – stretched_gg – stretched_rotated_gg – reduced_gg – sh – rotated_sh – stretched_sh – stretched_rotated_sh – space_view

仅版本 2 可以使用的类型：

– triangular_grid – equatorial_azimuthal_equidistant – azimuth_range – cross_section – Hovmoller – time_section – lambert_azimuthal_equal_area

对于下面的网格类型，使用 grib_get_data 工具和 C/F90/Python 接口 grib_iterator 可以获取网格点的经纬度值。

gridType 说明
regular_ll regular latitude-longitude
reduced_ll reduced latitude-longitude
regular_gg regular gaussian
lambert lambert conformal
polar_stereographic polar stereographic
space_view space view perspective

packingType

GRIB 版本 1 和 2 通用：

– grid_simple – grid_simple_matrix – grid_second_order – spectral_complex – spectral_simple

仅 GRIB 版本 2 使用：

– grid_simple_log_preprocessing – grid_jpeg – grid_png – grid_ieee

MARS

该命名空间包含所有的 MARS 关键词。

key 名称 示例值
date 20160224 (YYYYMMDD)
time 0000,0600, 1200, 1800
step 3,6, 9, 12, …
class od, …
stream oper, enfo,…
expver 0001
type an, fc, cf, pf, …
levtype sfc, pl,ml
levelist 500, 850, …
param 151.128