NOAA KLM User's Guide

Section 9.8.4

Blue line drawn across page to separate text from document title.
Introduction Page, NOAA KLM TOC, Acronyms
Previous Section, Next Section

9.8.4 Aerosol Optical Thickness 8-Day Observation File

The Aerosol Observation File contains eight days of Sea Surface Temperature (SST) retrievals containing a single-channel (AVHRR Channel 1) optical thickness parameter τA. The SSTs in these retrievals are "aerosol-corrected" SSTs, but the uncorrected SSTs are also contained within the observation. The layout of the file is identical to the SST 8-day observation file with the exception that the 2-bytes used to store a water vapor parameter in the SST retrieval are used for an aerosol optical thickness value and a spare area is used for the uncorrected SST. This data file consists of 4002 physical records each with a length of 13,024 bytes.

9.8.4.1 File Structure Description

The organization of the file is as follows: earth is divided into 5 degree by 5 degree blocks and by 1 degree by 1 degree subblocks within each block. The blocks are numbered from 1 to 2592 with the origin or first block at 180 degrees West or -180 and 90 degrees South or -90. Block numbers increase by 1 to the East and by 72 to the North. To locate information in an area, the block number is found which corresponds to the block encompassing the area. A table in the directory record points to the record which contains the desired block. After locating the record containing the block, another table at the beginning of the record locates the proper location of the desired subblock.

The file has overflow records and as such expands and contracts as data are available.

The first record is the directory record containing the block directory and other information. All other records are data records, each containing a subblock directory followed by observations.

9.8.4.2 Directory Record Format

This record describes the size, origin, and location of the blocks making up the file. To calculate the block number of a location (ILAT, ILON) use the following formula:

IBLOCK = ( (ILAT-LA)/LAO x INBC) + ( (ILON-LO)/LOO) + 1

Where:

INBC = Number of Column Blocks = 360/LOO
LA = Latitude origin of file = -90
LO = Longitude origin of file = -180
LAO = Size of block in latitudinal direction in degrees = 5
LOO = Size of block in longitudinal direction in degrees = 5
ILAT = Latitude (+N, -S)
ILON = Longitude (+E, -W)

NOTE: To find INTEGER ILAT and ILON, round up if positive and down if negative. Each block includes the minimum whole latitude and longitude and excludes the maximum whole latitude and longitude which border the block.

For example: The limits of block 1 are:

-90.0 to -85.01 and -180.0 to -175.01

Table 9.8.4.2-1 contains the format of the directory record.

Table 9.8.4.2-1. Format of Directory Record.
Halfword Description Comments
1 Latitude Origin -90
2 Longitude Origin -180
3 Size of block in latitudinal direction in degrees (currently 5)
4 Size of block in longitudinal direction in degrees (currently 5)
5 First free record pointer Points to first available record
6 Number of records in file Currently 4002
7 Halfword number of start of block directory table Currently 11
8 Day of year of latest data 1-366
9 File availability 0=available
1=unavailable update in progress
10 Year of century of latest data 0-99
11 Record number for block 1 2-4002
12 Record number for block 2 0 if no data in block

9.8.4.3 Data Record Format

Table 9.8.4.3-1 contains the format of the data record.

Table 9.8.4.3-1. Data Record Format.
Halfword Description Comments
1 Record number 2 to 4002
2 Block number 1 to 2592
3 Extent number (# of records) removed from primary 0 if primary
4 Pointer to succeeding overflow record. Last overflow record points to primary. 0 if no overflow.
5 Pointer to halfword position of start of observation data currently 61
6 Pointer to start of subblock directory currently 11
7 Lower left latitude of block degrees
8 Lower left longitude of block degrees
9 Pointer to last halfword containing data If no data in the record, this pointer points to the start position of observation data -1
10 Unused .
11 Halfword of start of data for subblock #1 0 if no data for this subblock in this record
12 Halfword of end of data for subblock #1 0 if no data for this subblock in this record. Other extents may or may not contain data for this subblock.
13-60 Similar to halfwords 11 and 12 for remaining subblocks. .
61-6512 Observation data .

If the observations for a block cannot fit on one record, as many additional records (extents) are allocated as needed. Each additional record having the subdirectory and subdocumentation included. If the subblock is known to be empty for the current record, the start and end position contain a zero. Subblocks may cross record boundaries. If an entire subblock cannot fit into one record, it will be split and a new record is allocated for the remainder of the subblock. Unused portions of the records containing no data are zero filled.

Given IX longitude and IY latitude, the subblock number (SBN) can be calculated as follows:

SBN = (IY-LLA) x LOO + IX - LLL + 1

This assumes all subblocks are 1 degree boxes. Here LLA and LLL are respectively the lower left latitude and longitude for the 5 degree blocks.

Simplifying the above:

SBN = IY x LOO + IX + C

Where C = -LLA x LOO - LLL + 1 is previously determined.

9.8.4.4 Satellite Aerosol/SST Observation Format

Satellite Aerosol/SST Observations are of variable lengths with a minimum length of 28 halfwords (2-byte integer) and a maximum of 48 halfwords. The observation length must be an even number of halfwords with no odd halfword except the first halfword being negative (i.e. the sign bit is 1). The first odd halfword of an observation is always negative. Table 9.8.4.4-1 gives the format for the observations.

Table 9.8.4.4-1. Satellite Aerosol/SST Observation Format.
Halfword # Byte Quantity Range
1 1 Type of Observation (see Table 9.8.4.4-2) 129 to 255
1

2

Source of Observation (see Table 9.8.4.4-3) 0 to 255

2

3

Year of Century 0 to 99

2

4

Month of Year 1 to 12

3

5-6

Latitude (+N,-S) x 100 -9000 to 9000

4

7-8

Longitude (+E,-W) x 100 -18000 to 17900

5

9

Day of Month 1 to 31

5

10

Hour of Day 0 to 23

6

11

Minute of Hour 0 to 59

6

12

Second of Minute 0 to 59

7

13-14

Aerosol-corrected SST (degrees C x 10) -20 to 350

8

15-16

Reliability 0 to 32767

9

17-18

Solar Zenith Angle (degrees x 10) 0 to 1800

10

19-20

Satellite Zenith Angle (degrees x 100) (Negative to left of spacecraft track, positive to right.) -6000 to 6000

11

21-22

Analyzed Field SST (degrees C x 10) -20 to 350

12

23-24

Internal Error (RMS x 100) 0 to 1000

13

25-26

Relative Azimuth Angle (degrees x 10) 0 to 1800

14

27-28

Climatological SST (degrees C x 10) -20 to 350

15

29

Beginning Row of Unit Array 1 to 11

15

30

Beginning column of Unit Array 1 to 11

16

31-32

AVHRR Channel 1 Average (% x 100) 0 to 10000

17

33-34

AVHRR Channel 2 Average (% x 100) 0 to 10000

18

35-36

AVHRR Channel 3 Average (K x 100) 0 to 32767

19

37-38

AVHRR Channel 4 Average (K x 100) 0 to 32767

20

39-40

AVHRR Channel 5 Average (K x 100) 0 to 32767

21

41-42

Space View SDEV Channel 1 (% x 100) 0 to 10000

22

43-44

Space View SDEV Channel 2 (% x 100) 0 to 10000

23

45-46

Space View SDEV Channel 3 (K x 100) 0 to 32767

24

47-48

Channel 4 Blackbody Temperature (K x 100) 0 to 32767

25

49-50

Channel 5 Blackbody Temperature (K x 100) 0 to 32767

26

51-52

Algorithm Number 1011 to ?

27

53-54

Aerosol Optical Thickness x 1000 0 to 2440

28

55-56

Uncorrected SST (K x 100) 27116 to 30816

If HIRS Data is appended:

29

57-58

HIRS Channel 1 Temperature (K x 100) 0 to 32767

30

59-60

HIRS Channel 2 Temperature (K x 100) 0 to 32767

31

61-62

HIRS Channel 3 Temperature (K x 100) 0 to 32767

32

63-64

HIRS Channel 4 Temperature (K x 100) 0 to 32767

33

65-66

HIRS Channel 5 Temperature (K x 100) 0 to 32767

34

67-68

HIRS Channel 6 Temperature (K x 100) 0 to 32767

35

69-70

HIRS Channel 7 Temperature (K x 100) 0 to 32767

36

71-72

HIRS Channel 8 Temperature (K x 100) 0 to 32767

37

73-74

HIRS Channel 9 Temperature (K x 100) 0 to 32767

38

75-76

HIRS Channel 10 Temperature (K x 100) 0 to 32767

39

77-78

HIRS Channel 11 Temperature (K x 100) 0 to 32767

40

79-80

HIRS Channel 12 Temperature (K x 100) 0 to 32767

41

81-82

HIRS Channel 13 Temperature (K x 100) 0 to 32767

42

83-84

HIRS Channel 14 Temperature (K x 100) 0 to 32767

43

85-86

HIRS Channel 15 Temperature (K x 100) 0 to 32767

44

87-88

HIRS Channel 16 Temperature (K x 100) 0 to 32767

45

89-90

HIRS Channel 17 Temperature (K x 100) 0 to 32767

46

91-92

HIRS Channel 18 Temperature (K x 100) 0 to 32767

47

93-94

HIRS Channel 19 Temperature (K x 100) 0 to 32767

48

95-96

HIRS Channel 20 Temperature (% x 100) 0 to 1000

Table 9.8.4.4-2. Aerosol/SST Observation Type Codes.
Code Type
157 Day Operational Algorithm
align="center"158 Day Operational Algorithm in relaxed cloud mode
167 Day Test Algorithm
168 Day Test Algorithm in relaxed cloud mode

Table 9.8.4.4-3. Aerosol/SST Observation Source Codes.
Code Source
1 NOAA-11 AVHRR
3 NOAA-14 AVHRR
100 Ship data from Navy (FNMOC)
101 Buoy data from TIROS collection system
102 Fixed Weather Ship (from NCEP)
103 Moving Ship with Name (from NCEP)
104 Moving Ship without Name (from NCEP)
105 Fixed Buoy (from NCEP)
106 Drifting Buoy (from NCEP)
107 XBT (from NCEP)


Previous Section Top of Page Next Section