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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