ODU SO GLOBEC: Grid

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Sampling Grid Overview

While latitude and longitude provide a perfectly valid system for locating
points on the Earth, there are some problems with coastal studies on the
Antarctic Peninsula. Fine scale studies have many stations at only slightly
different locations making it difficult to refer to stations by lat, lon or
by some arbitrary code. Second, the latitude and longitude for the WAP are
almost the same giving rise to confusion about which value is latitude and which
is longitude. A simple system for refering to stations is to use distances
on a plane measured in kilometers so that two short numbers give the
station location.

The grid system for the Southern Ocean GLOBEC study on the western side of
the Antarctic Peninsula is based on the Universal Transverse Mercator (UTM)
projection, which converts locations on the globe in latitude, longitude
into meters from some base point. Global UTM is based on a series of defined
zones, each of which has its own central point. The only relevance to our
study is that the projection error becomes larger as a point is farther from
the central point for the given zone.

The basic desire for this SO GLOBEC study was to have a coordinate system
that is aligned with the shelf break, and by extension, the coastline. The
first two choices are the geoid and the UTM zone. Geoid number 9 is chosen
(need to find which one this is) along with UTM zone -20. Within this zone,
an origin is chosen (71S, 72W) and a rotation angle (60 degrees, counter
clockwise) to create an (x,y) Cartesian coordinate system which provides the
basis for all station positions. In truth, the base point is not the origin
of the coordinate system but is a point (xoff, yoff) to allow fine
adjustments of the resulting grid. For this grid, the base point is (0, -50).

Software is provided to convert between latitude and longitude and the
sampling grid.

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Written by J. Klinck

February, 2001

Send questions or comments by e-mail to
klinck@ccpo.odu.edu