NOAA KLM User's Guide

Section 9.8.2

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9.8.2 Aerosol Weekly 100 km Analyzed Field File

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.

9.8.2.1 File Structure Description

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.

9.8.2.2 Documentation Record Format

Table 9.8.2.2-1. Documentation record format for Aerosol Weekly 100 km field file.
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.)

9.8.2.3 Data Record Format

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.

Table 9.8.2.3-1 Format of grid intersection in data record
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.

Table 9.8.2.3-2. Row Identification Information.
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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