[LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

[Finkleman, Dave]

I finally get a chance to look like I might know something.

Neiher Gravity nor the Geoid are "standardized."  Witness that maps from
some countries do not employ WGS-84.  (Korea was this way.  I am not
sure whether they still are.)  There are "best practices" documents,
including some issued by standards organizations, but they are not
"normative" standards.  Data exchange standards, which are normative,
require statement of the gravity model and its metadata employed.  They
also required statement of the time system and Earth Orientation
Parameters (including the epoch of the Earth rotation model).  

One reason that Gravity is no standardized is that different degrees of
gravitational modeling are best for different problems.  There is also a
matter of internal consistency.  When the data are sparse, high orders
of approximation to gravitation, the geoid, or the atmosphere alias the
sparse data, revealing numerical artifacts rather than real physics.  At
one point, I worked in a field that never grew much called
"phenomelogical discrimination,"  discerning numerical artifacts from
reality.  

It is precisely the ambiguity in definition, let alone application, that
led to my involvement in the leap second issue.  

Dave Finkleman
Senior Scientist
Center for Space Standards and Innovation
Analytical Graphics, Inc.
7150 Campus Drive
Colorado Springs, CO 80920
 
Phone:  719-510-8282 or 719-321-4780
Fax:  719-573-9079
 
Discover CSSI data downloads, technical webinars, publications, and
outreach events at www.CenterForSpace.com.

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