[Xtide-announce] annual data refresh

[David Flater]

Available from http://flaterco.com/xtide/files.html

harmonics-dwf-20180101

   Imported NOS data from snapshot 2017-12-17.  Most data this year were
   sourced from the CO-OPS Metadata API (MDAPI).

   The perennial issues with time zones and meridians in Alaska and around
   the Port St. Joe region of Florida have gotten worse all of a sudden.  The
   number of reference stations with local meridians in the wrong time zone
   has increased from 8 to 21.  Additionally, when local time predictions are
   obtained from the NOS web service, Alaskan stations that are expected to
   be 2 hours earlier than XTide's results (on UTC-11 instead of UTC-9)
   instead are 23 hours *later*, on the wrong day.  Predictions requested in
   GMT match as expected.

   Two more of the old current reference stations have expired.  AFAICT,
   harmonic constants for currents still have not been published on the NOAA
   web site.
     PCT1341  Strait of Juan de Fuca Entrance, Washington Current
     PCT1541  Admiralty Inlet (off Bush Point), Washington Current

   All remaining current stations now use "sidplus" station IDs, which is the
   station id followed by an underscore and the "bin number" that is used to
   separate depths.

   Abandoned the practice of including the periods in U.S.A., F.S.M., D.C.,
   and the like.

   Normalized the assignment of countries so that territories and
   commonwealths of the US are called USA.  Marshall Islands is now called
   RMI (Republic of the Marshall Islands).  Pending the conclusion of
   long-running territorial claims, Wake Island has been assigned the RMI
   country code, but its name is still "Wake Island, Pacific Ocean."

   Discontinued the last remaining meridian "erratum," for 9466153 Helmick
   Point.  Predictions are still not available for comparison, but there is a
   nearby station, 9466057 Popokamute (Kokokamute), which is consistent with
   the unadjusted data.

   Dropped the tables data_sets_2010, drops, and footnotes, which are no
   longer used by import, and all tables associated with the discontinued
   meridian errata check.

   Added 7 new constituent name aliases to support revised constants for
   Anchorage and constituent corrections as described below.

   The investigation into 3 questioned constituents (3KM5, RP1, and KJ2) that
   are used only by 9455920 Anchorage, Knik Arm, Cook Inlet, Alaska concluded
   the following:

   - Using this year's constants, which have amplitude for all 3 of the
   questioned constituents, RMS error for predicted heights versus the NOAA
   web site is indeed minimized when all 3 of those constituents are flipped
   180 degrees from their definitions in congen_input.txt 4154 2012-01-05
   (which is the same as congen_input.txt,v 1.3 2004/08/16).

   - Reaffirmed the decision made last year regarding 3KM5.  Although the
   superseded definition was consistent with IHO (2017), the new definition
   is the one that was used in the paper that introduced the use of many
   constituents for Anchorage (Bernard D. Zetler and Robert A. Cummings, A
   harmonic method for predicting shallow-water tides, J. Marine Res. 25(1),
   pp. 103-114, 1967) and is also the one used by IOS (2006).  The node
   factors are different for the two different formulations.

   - The definitions of RP1 and PSI1 (which are the same thing but flipped
   180 degrees) in congen_input.txt are consistent with IHO, with the SP98
   definition of PSI1, and with the IOS definition of PSI1.  Therefore, to
   reduce error for Anchorage, the RP1 constituent is just mapped to PSI1.

   - The definition of KJ2 in congen_input.txt is consistent with SP98 but
   inconsistent with IHO.  KJ2 and ETA2 in congen_input.txt are two different
   formulations of what IHO and IOS call ETA2, and the one apparently needed
   by Anchorage is not present.  Complicating matters, KJ2 is one of the
   constituents that is inferred by libtcd using an SP98 rule-of-thumb which
   assumes a consistent treatment of the constituents' phases; flipping KJ2
   from its SP98 definition would be more likely to break this inference than
   to fix it.  Therefore, to reduce error for Anchorage, KJ2 is mapped to a
   new constituent, KJ2-IHO, which is flipped from the SP98 definition.

   The new constants for Anchorage also refer to a mysterious constituent
   OO2, which has been mapped to OQ2-HORN based on its speed.  IHO defines
   OQ2 as both this constituent and its 180 degree reversal; however, error
   is minimized by sticking with the OQ2-HORN definition.

-- DWF