Directional Data - MATLAB Recipes for Earth Sciences - page 409

Fig. 10.1 Orthoceras fossils from an outcrop at Neptuni Acrar near Byxelkrok on Öland,
Sweden. Orthoceras is a cephalopod with a straight shell that lived in the Ordovician era, about
450 million years ago. Such elongated, asymmetric objects tend to orient themselves in the
hydrodynamically most stable position and therefore indicate paleocurrent directions. h e
statistical analysis of cephalopod orientations at Neptuni Acrar reveals a signii cant southerly
paleocurrent direction, which is in agreement with the paleogeographic reconstructions.
Jones (2006a, b) discuss the use of MATLAB® for the statistical analysis of
directional data. MATLAB is not the i rst choice for analyzing directional
data since it does not provide the relevant functions, such as algorithms to
compute the probability distribution function of a von Mises distribution,
or to run a Rayleigh's test for the signii cance of a mean direction. Earth
scientists have therefore developed numerous stand-alone programs with
which to analyze such data, e.g., the excellent sot ware developed by Rick
Allmendinger:
http://www.geo.cornell.edu/geology/faculty/RWA/programs.html
h e following tutorial on the analysis of directional data is independent of
these tools. It provides simple MATLAB codes to display directional data, to
compute the von Mises distribution, and to run simple statistical tests. h e
i rst section introduces rose diagrams as the most widely used method to
display directional data (Section 10.2). With a similar concept to Chapter