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International Comprehensive Ocean-Atmosphere Data Set (ICOADS): Release 2.1
10-deg Box Assignment Conventions at Location Discontinuities 27 February 2004
=====================================================================<loc_disc>
Document Revision Information (previous version: 9 September 2002): Updates
for Release 2.1 and ICOADS.
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{1. Introduction}
Ordinarily, 10-degree box (B10) and Marsden Square (MSQ) assignments follow the
historical convention that the two inclusive boundaries of each box are those
that form the corner nearest the intersection of the equator and prime meridian
(0N; 0E). For example, a report (with location to the nearest tenth of degree)
from 110.0W through 119.9W and from 10.0N through 19.9N would be assigned B10=
274 (MSQ=048) (see Release 1, supp. G for more information).
However, reports falling directly on the Greenwich Meridian (0 longitude)
or 180 longitude, or along the Equator (0 latitude) or at either Pole (+90
or -90 latitude) are subject to special problems in assignment of B10 and
MSQ. We refer to these boundaries as "location discontinuities" because the
aforementioned historical convention does not explicitly accommodate them.
According to WMO conventions, reports along these location discontinuities
are assigned WMO quadrant, applicable to current International Maritime
Meteorological (IMM) logbook or Global Telecommunication System (GTS) data,
according to the "observer's choice." In IMM data prior to 1 July 1996, and
possibly in early GTS data, observer's choice (or a processing decision by
individual countries) applied also along the additional boundaries of WMO
octants enclosed within quadrants. Early ship logbook data prior to WMO's
1963 definition of the IMM exchange may have followed different or unknown
conventions. A further complication is that NCDC has employed a different
quadrant numbering system, for the same WMO-defined quadrant areas, for Tape
Deck-11 (TD-11) data. Figure 1 illustrates the quadrant and octant numbering
systems.
180W Western Hemisphere 0 Eastern Hemisphere 180E
I--------------I---------------I--------------I---------------I 90N
I NCDC quadrant=1 I NCDC quadrant=2 I
I WMO quadrant=7 I WMO quadrant=1 I
I octant=1 I octant=0 I octant=3 I octant=2 I
I--------------I---------------I--------------I---------------I 0 lat
I NCDC quadrant=3 I NCDC quadrant=4 I
I WMO quadrant=5 I WMO quadrant=3 I
I octant=6 I octant=5 I octant=8 I octant=7 I
I--------------I---------------I--------------I---------------I 90S
Figure 1. NCDC and WMO quadrant numbering, and WMO octant numbering.
Differences in the archiving and processing of logbook versus GTS data may
introduce problems along location discontinuities. For example, it appears
likely that reported quadrant was preserved in logbook data (although octant
choice within quadrant was not preserved in TD-11 data). In contrast, some
GTS data as gathered by Operational Centers retained only pure latitude and
longitude. Later ICOADS duplicate elimination processing, which currently
operates on a 10-degree/1-degree box sort, may therefore be unable to locate
GTS and logbook duplicates, or even logbook-logbook (or GTS-GTS) duplicates
processed according to different conventions.
Resolution of these problems will require a total re-sort of the database,
hopefully as part of future ICOADS processing, for which we propose utilizing
a new "Uniform Convention," defined in sec. 2. Reprocessing of old data should
also consider the practicality of regeneration, and retention in supplemental
data, of original quadrant/octant assignment. To gradually phase in the
Uniform Convention for new data receipts, we are implementing it for new format
translations, and hopefully as part of anticipated upcoming changes to NCDC's
marine processing systems.
Background is provided in sec. 3 on the conventions used for Release 1 and
in currently available data, for processing of reports at the location
discontinuities. Information is also provided on some past systematic
assignment problems that are known to exist.
{2. Uniform Convention for location discontinuities}
Part a) of the Convention discusses retention of original quadrant/octant
information, part b) defines a predictable box (B10 and MSQ) assignment for
data along the location discontinuities, and part c) deals with assignment
of NCDC quadrant in the event original quadrant/octant information is not
available.
a) Retention of originally reported quadrant/octant information:
i) TD-11 formats (containing quadrant and MSQ): If original information
is available (e.g., in IMMT data), it should be preserved by assignment
of the corresponding NCDC quadrant (octant choice may not be fully
preserved, because each quadrant encloses two octants). NCDC quadrant
assignment therefore may or may not agree with MSQ assignment as defined
in item b). (Note that future revisions of TD-11 conversion programs
will thus need to accommodate matching and mismatching of quadrant and
MSQ along the location discontinuities.)
ii) LMR format (containing B10 and pure latitude and longitude): The
LMR format lacks quadrant/octant so this information should henceforth
be preserved in the supplemental attachment (as programs are written to
convert new formats, or at the time of revision of existing conversion
programs as appropriate).
iii) For future re-conversion of already processed LMR data from formats
that possessed original quadrant/octant information, we should consider
the practicality of using existing B10 and any available supplemental
data to reconstruct quadrant/octant for retention in a redefined
supplemental attachment. However, questions of practicality arises
because if the supplemental attachment for a given format is redefined,
every report would need to be reconfigured (not just those along the
location discontinuities). Also, for reports derived from TD-11, as
discussed in sec. 3, questions arise along 180 longitude of whether the
input MSQ or the mismatching quadrant reflects the original quadrant/
octant assignment.
b) Assignment of B10/MSQ:
i) If exactly on either 0 or 180 longitude, assign to the Western
Hemisphere, where B10 (MSQ) assignment is based on latitude.
ii) If exactly on the Equator, assign to the Northern Hemisphere, where
B10 (MSQ) assignment is based on longitude.
iii) If exactly +90 or -90 degrees latitude, use longitude to determine
B10 (MSQ) assignment, i.e., to B10=1-36 (MSQ=901-936) or to B10=613-648
(MSQ=588-623).
c) Assignment of NCDC quadrant without original quadrant/octant information
(in conformance with part b):
i) If exactly on either 0 or 180 longitude, assign to the Western
Hemisphere, where quadrant (1 or 3) is based on latitude.
ii) If exactly on the Equator, assign to the Northern Hemisphere, where
quadrant (1 or 2) is based on longitude.
iii) If exactly +90 or -90 degrees latitude, use longitude to determine
quadrant (1, 2, 3, or 4).
For technical and historical reasons, the Uniform Convention makes B10 or MSQ
assignment of data along the Equator into the Northern Hemisphere, and along
both the Greenwich Meridian and 180 longitude into the Western Hemisphere.
Full implementation of the Convention will ensure that duplicates along
the location discontinuities receive predictable B10 or MSQ assignments.
However, subsequent selections of data for users from a B10- or MSQ-sorted
archive will also require attention to the Convention. For example, a request
for global data covering 10S latitude up to and including the Equator must
include access to B10=289-342 (MSQ=001-036). Furthermore, generation of
1-degree or 2-degree latitude x longitude statistics may be impacted by the
Convention (assignments of data to 2-degree or 1-degree boxes have thus far
been determined by using the 2- or 1-degree box enclosed by the pre-assigned
B10).
Table 1 provides a set of representative examples illustrating the Uniform
Convention.
Table 1. Representative examples of the Uniform Convention for assignment of
B10, MSQ, and NCDC quadrant (Q), for data including, or not including, original
WMO quadrant information (or WMO octant information mapped into quadrant).
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Lon Lat B10 MSQ Original WMO quadrant information: No information:
(deg (deg Original = Resultant Resultant
E) +N, -S) WMO-Q = NCDC-Q NCDC-Q
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0 90 33 901 7 = 1 1 = 2 1
0 0 321 001 7 = 1 1 = 2 5 = 3 3 = 4 1
0 -90 645 588 5 = 3 3 = 4 3
90 90 7 927 1 = 2 2
90 0 295 027 1 = 2 3 = 4 2
90 -90 619 614 3 = 4 4
180 90 16 918 7 = 1 1 = 2 1
180 0 304 018 7 = 1 1 = 2 5 = 3 3 = 4 1
180 -90 628 605 5 = 3 3 = 4 3
270 90 24 910 7 = 1 1
270 0 312 010 7 = 1 5 = 3 1
270 -90 636 597 5 = 3 3
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{3. Handling of location discontinuities for Releases 1 and 2.1}
Table 2 and Figure 2 show that different conventions were used for Release 1
and currently available delayed-mode (ICOADS.DM) data.
Table 2. Release 1 and ICOADS.DM conventions for assignment of B10 at location
discontinuities (a-f in Figure 2), depending on whether the input data were
with or without quadrant/octant (Q/O). Quadrant used here is NCDC quadrant
(see Figure 1).
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Release 1* ICOADS.DM**
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lat lon #1) with Q/O #2) without Q/O #3) with Q/O #4) without Q/O
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a) 90N any B10=1 B10=1 per lon per lon
b) any 0 B10 in Q/O larger B10 (q=2/4) B10 in Q/O B10 in Q=1/3
c) any 180 B10 in Q/O larger B10 (q=1/3) B10 across Q/O& B10 in Q=1/3&
d) 0 any B10 in Q/O larger B10 (q=3/4) B10 in Q/O B10 in Q=1/2
e) 0 0 B10 in Q/O larger B10=358 (q=4) B10 in Q/O B10 in Q=1
f) 0 180 B10 in Q/O larger B10=340 (q=3) B10 across Q/O& B10 in Q=1&
g) 90S any B10=648 B10=648 per lon per lon
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* Note that the input Q/O was not retained in Attm4, although this information
should have been retained indirectly (except at the poles) because of B10
selection in accordance with the stated rules (i.e., "in Q/O"). However, see
<conv_lmr5> for a discussion of the "field 104" problem. The HSST Exchange
format contained octant; all other Release 1 inputs were TD-11 formats
containing quadrant. Thus the "without Q/O" rules (Release 1, p. G1) probably
were never invoked.
** Note that any input Q/O was not retained in Attm4, although this information
should have been retained indirectly through B10 selection in accordance with
the stated rules.
& Only along 180 lon, the current NCDC algorithm for calculation of MSQ from
quadrant, lat, and lon automatically produces a mismatch between the input
quadrant and MSQ. To achieve better duplicate matching for Release 2.1 between
data processed by NCDC and data processed by Boulder (e.g., TD-11 versus IMMT),
the results of this algorithm were duplicated in calculation of B10. Thus
for reports possessing an input quadrant/octant, the algorithm selects the B10
across the dateline from the input Q/O (e.g., at 0 lat, 180 lon, B10=303, 304,
339, 340 when quadrant is 1, 2, 3, 4, respectively). For reports at 180 lon
lacking input Q/O, quadrant 2/4 was arbitrarily selected, resulting in actual
B10 selection in quadrant 1/3 (see Figure 2). It is not known whether NCDC
has followed this procedure for all past TD-11 data.
----------
180W Western Hemisphere 0 Eastern Hemisphere 180E
I------------------------------I----------------a-------------I 90N
I NCDC quadrant=1 I NCDC quadrant=2 I
I WMO quadrant=7 QMb* WMO quadrant=1 QcM*
I QM I I
I---d--------------------------e------------------------------f 0 lat
I * NCDC quadrant=3 I* NCDC quadrant=4 I*
I WMO quadrant=5 I WMO quadrant=3 I
I I I
I------------------------------I----------------g-------------I 90S
Figure 2. Table 2 lists B10 assignment for reports at North and South Poles
(a, g), 0 and 180 lon (b, c), and the equator (d, e, f). For original data
lacking quadrant/octant information, this figure illustrates the direction
of TD-11 quadrant (Q) and Marsden Square (M) assignment, or of (hypothetical,
since it may never have been applied) B10 assignment (*) according to Release
1, p. G1.