## NOAA KLM User's Guide## Section 9.8.2 |

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An aerosol optical thickness 100 km analyzed field file consists of a specific set of information pertaining to global latitude and longitude intersections. The 1 degree resolution file, includes the area from -180 degrees to +179 degrees longitude and from -70 degrees to +70 degrees latitude.

The file consists of one documentation record (record number one), followed by one record for each latitude or row of the field. Record 2 or the first latitude row is the southernmost row or the 70 degrees South row. Each row consists of seven words (28 bytes) of information for each longitude column forming a grid intersection plus one seven-word unit containing the row number identification and the date and time of the last analysis made for the field. The first grid intersection of each row is the 180 degree west meridian or the date line. Grid points proceed to the east across the record from left to right ending with the 179 degree East meridian. The documentation record is created from a namelist dataset and is displayed in namelist format, although it is stored as a binary record. The record size is 10,108 bytes.

Word # | Parameter | Description |
---|---|---|

1 | LDBGN | Record number of the first row of the field (currently 2 for all fields since the documentation record requires only one record). |

2 | SMGLAT | Minimum latitude included in field which is the bottom edge and first row of field |

3 | AXLAT | Maximum latitude included in field which is the top edge and last row of field. |

4 | SMLONG | Minimum longitude included in field which is the left edge and first column of field. |

5 | AXLONG | Maximum longitude included in field which is the right edge and last column of field (excluding the I.D. column). |

6 | RES | Number of latitude/longitude degrees between each grid point |

7 | SMHOUR | Youngest time, in hours of the year, of observations used during last analysis, which becomes the oldest time allowed for the next analysis. If the difference between this time and time of next analysis is greater than the maximum time gap allowed, SMHOUR for the beginning of the next analysis is reduced to make the difference equal to the maximum time gap. |

8 | HOURS | Oldest time, in hours of the year, of observations used during last analysis. |

9 | TIMGAP | Number of hours between youngest and oldest times of observations used in analysis. |

10 | MAXDAT | Maximum number of hours allowed in time period for observation times to be included in analysis. |

11 | SMREL | Minimum reliability of observations to be used in analysis. |

12 | AXREL | Maximum reliability of observations to be used in analysis. |

13-22 | SORC(10) | List of source codes of observations to be used in analysis. |

23-32 | OBTYPE (10) | List of observation types allowed to be used in analysis. |

33 | NROWS | Number of rows (latitudinal parallels) included in field, excluding documentation record. |

34 | NCOLS | Number of columns (longitudinal meridians) in field, inclduing the I.D. column. |

35 | IBLK | Number of rows or logical records per physical block. |

36 | NWRDS | Number of fullwords (32 bits) allocated to each grid point. |

37 | ISZ | Number of rows to be maintained in an array in core for optical thickness and analysis and calculation of gradients. |

38 | ICENT | Center line within the array upon which calculations will be performed. |

39-41 | LWT, LNT, LBT | Word number, length in bits, and starting bit location of optical thickness within a grid intersection information unit of an SST Field. |

42-44 | LWG, LNG, LBG | Word number, length in bits, and starting bit location of Average Gradient. |

45-47 | LWGXP, LNGXP, LBGXP | Word number, length in bits, and starting bit location of Gradient X+direction. |

48-50 | LWGXN, WNGXN, LBGXN | Word number, length in bits, and starting bit location of Gradient X+direction. |

51-53 | LWGYP, LNGYP, LBGYP | Word number, length in bits, and starting bit location of Gradient Y+direction. |

54-56 | LWGYN, LNGYN, LBGYN | Word number, length in bits, and starting bit location of Gradient Y- direction. |

57-59 | LWPD, LNPD, LBPD | Word number, length in bits, and starting bit location of Physiographic Descriptor. |

60-62 | LWNO, LNNO, LBNO | Word number, length in bits, and starting bit location of Number Observations. |

63-65 | LWAGE, LNAGE, LBAGE | Word number, length in bits, and starting bit location of Age Recent Observation |

66-68 | LWREL, LNREL, LBREL | Word number, length in bits, and starting bit location of Reliability. |

69-71 | LWCLS, LNCLS, LBCLS | Word number, length in bits, and starting bit location of Class 1 Coverage. |

72-74 | LWSXP, LNSXP, LBSXP | Word number, length in bits, and starting bit location of Spatial Covariance in the positive X direction. |

75-77 | LWSXN, LNSXN, LBSXN | Word number, length in bits, and starting bit location of Spatial Covariance in the negative X direction |

78-80 | LWSYP, LNSYP, LBSYP | Word number, length in bits, and starting bit location of Spatial Covariance in the positive Y direction. |

81-83 | LWSYN, LNSYN, LBSYN | Word number, length in bits, and starting bit location of Spatial Covariance in the negative Y direction. |

84-86 | LWIND, LNIND, LBIND | Word number, length in bits, and starting bit location of Independent Temperature. |

87-96 | GRDWTS (10) | Weight assigned to each grid unit, according to its distance from the grid intersection for which gradients are being calculated |

97 | NP | Number of grid points to be used in calculation of gradients. |

98-117 | KMDST (10,2) | Look up table of gradient values and corresponding distances to be used in determining the search area for analysis. |

118 | MKM | Number of paired entries in KMDST. |

119-138 | H(10,2) | Look up table of gradient values and corresponding factors to be used in determining the new weight assigned to the observation temperature for analysis. |

139 | MH | Number of paired entries in H. |

140 | EXP | Exponent used in temperature analysis. |

141 | FDX | Factor used in determining new weight assigned to the optical thickness observation for analysis. |

142 | XCLASS | Factor used to place gradients into a class for Gradient Class Summary |

143 | DEL | Maximum number of optical thickness units that the new analysis temperature may differ from the previous optical thickness field value. |

144 | MF | Factor applied to the previous optical thickness and reliability to determine the final optical thickeness and its reliability. |

145 | MSTAR | Factor applied to the combined observations temperature and weight in determining the new analysis optical thickness |

146 | MNSRCH | Minimum distance in kilometers to be searched for analysis observations. |

147 | MXSRCH | Maximum distance in kilometers to be searched for analysis observations. |

148 | BDEL | Maximum difference allowed between new analysis optical thickness and the previous one for the Class 1 Coverage Bit to be set to 1. |

149 | FCWT | Maximum value that can be assigned as the reliability of the new analysis optical thickness. |

150 | IYYY | Year of youngest time of observation data used (0-99). |

151 | IYMM | Month of youngest time of observation data used (1-12). |

152 | IYDD | Day of youngest time of observation data used (1-31). |

153 | IYHH | Hour of youngest time of observation data used (0-23). |

154 | IOYY | Year of oldest time of observation data used (0-99). |

155 | IOMM | Month of oldest time of observation data used (1-12). |

156 | IODD | Day of oldest time of observation data used (1-31). |

157 | IOHH | Hour of oldest time of observation data used (0-23). |

158 | ICURTM | Last time used in analysis |

Values are stored as real (IBM floating-point) or integer according to the format implied by the first letter of their label. (Parameters beginning with I,J,K,L,M,N are integer values.)

Each data record (latitudinal row) consists of a series of grid intersection points. These points are 28 bytes in length. Each longitude (column) reflects one grid intersection. At the end of the data record (i.e., immediately following the last column) is a 28 byte row identifier. All parameters are stored as integer values.

Word # | Length (bytes) | Description | Units | Comments |
---|---|---|---|---|

1 | 2 | Optical Thickness | x 1000 | 0 to 2440 |

1 | 2 | Average Gradient | units/100km (x 1000) | 0 to 300 |

2 | 2 | Gradient X+ | units/100km (x 1000) | 0 to 300 |

2 | 2 | Gradient X- | units/100km (x 1000) | 0 to 300 |

3 | 2 | Gradient Y+ | units/100km (x 1000) | 0 to 300 |

3 | 2 | Gradient Y- | units/100km (x 1000) | 0 to 300 |

4 | 1 | Physiographic Descriptor | 0=sea 1=land |
0 to 15 |

4 | 1 | Spare | Undefined | 0 to 255 |

4 | 1 | Number observations | Integer | 0 to 255 |

4 | 1 | Age Recent Observation | Hours | 0 to 255 |

5 | 2 | (Weight) Wxy | Integer | 0 to 32767 |

5 | 2 | Class 1 Coverage | Bits | 0 to 1 |

6 | 1 | Spatial Covariance X+ | Grid Units | 0 to 10 |

6 | 1 | Spatial Covariance X- | Grid Units | 0 to 10 |

6 | 1 | Spatial Covariance Y+ | Grid Units | 0 to 10 |

6 | 1 | Spatial Covariance Y- | Grid Units | 0 to 10 |

7 | 2 | Climatological Temperature | degrees C (x10) | -850 to +610 |

7 | 2 | Spare | Undefined | 0 to 32767 |

**DEFINITION OF TERMS IN GRID
INTERSECTION**

**Optical Thickness** - The latest Aerosol Optical Thickness calculated based on the previous analysis optical
thickness, weighted according to its reliability, combined with a weighted average of current observations within a surrounding area
which is determined according to the grid point's gradient.

**Average Gradient** - The average of the gradients in all four directions (N, S, E, W) from the grid intersection.

**Gradient in X+ Direction** - Change in optical thickness between the grid point and neighbor points within the
field in the positive direction along the X axis.

**Gradient in X- Direction** - Change in optical thickness in the negative direction along the X axis.

**Gradient in Y+ Direction** - Change in optical thickness in the positive direction along the Y axis.

**Gradient in Y- Direction** - Change in optical thickness in the negative direction along the Y axis.

**Physiographic Descriptor** - The land/sea tag inticating whether a grid intersection is a land or sea point.

**Spare** - Unused parameter.

**Number of Observations** - The total number of current observations used in the analysis of the new optical
thickness for the grid intersection.

**Age of Most Recent Observation** - The age, in hours from the time of last analysis, of the most recent
observation used to determine the new optical thickness for a grid intersection.

**Reliability** - New reliability associated with the new optical thickness, based on the previous reliability
combined with the weighted reliability of all observations used in the last analysis.

**Class 1 Temporal Coverage** - Set of bits (0-15) of which bit 1 is set to 1 for each analysis which included
observations with a reliability greater than or equal to a specific minimum reliability considered as class 1. Bit 0 always remains a
0, and all bits are shifted right during each analysis leaving bit 1 a 0 when no class 1 reliability observations are used for a grid
intersection.

**Spatial Covariance X+** - The distance in grid units from the grid intersection to the nearest land mass in the
positive direction along the X axis.

**Spatial Covariance X-** - The distance in grid units from the grid intersection to the nearest land mass in the
negative direction along the X axis.

**Spatial Covariance Y+** - The distance in grid units from the grid intersection to the nearest land mass in the
positive direction along the Y axis.

**Spatial Covariance Y-** - The distance in grid units from the grid intersection to the nearest land mass in the
negative direction along the Y axis.

**Independent Grid Temperature** - The average sea surface temperature of a grid intersection for a particular month
over a number of years, taken from the global climatology file.

Table 9.8.2.3-2 gives the row identification information. NOTE: All parameters are stored as integer values. Words 5 to 7 are the date and time at which analysis was performed.

Full Word |
Length(bytes) |
Description |
Units |
Comments |

1 | 4 | Row | Integer | 1-141 |

2 | 4 | Spare | Undefined | . |

3 | 4 | Spare | Undefined | . |

4 | 1 | Marker | Integer | Always 255 |

4 | 3 | Spare | Undefined | . |

5 | 4 | Hour of Day, Minutes of Hour | (100 x Hours) + Minutes | 0-2359 |

6 | 4 | Day of Year | Days | 1-366 |

7 | 4 | Year | Years | . |

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Last Updated Tuesday, 03-Mar-2009 10:29:33 EST

Please see the NCDC Contact Page if you have questions or comments.