AVHRR Files - record format
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, including
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 thickness and its
reliability.
- 145 ---- MSTAR
- Factor applied to the combined observations optical thickness
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.)
IBM360 Floating points
- This floating point representation is not compatible with the
IEEE floating point specification which is used by most modern
computers. The IBM360 float was native to the now obsolete IBM
360/370 series of computers, and a few others. Since documentation
of this representation is getting difficult to find, a summary is
provided here.
- The 4-byte floating point representation is divided into one
byte (SEXP) for sign and exponent, followed by a 3-byte MANTISSA.
The mantissa should be thought of as a six digit hexadecimal
number, with a radix point preceding the first digit. The numeric
value of the MANTISSA is the value of the integer with the same hex
representation, divided by 0x1000000, and ranges from 0.0 to just
less than 1.0. For a non-zero, normalized float, the first hex
digit will range from 0x1 to 0xf.
- In the SEXP byte, the high order bit is the sign of the number,
0 for plus and 1 for minus. The remaining seven bits are a biased
exponent. After subtracting 0x40, the result is the number of
hexidecimal digits (powers of 16) to shift the radix point right
(if positive) or left (if negative). This means the range of the
representation is from 16^63 to 16^(-64).
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