They had a lot of the right instruments in the right place.
Graph of position (3 meters!):
http://ivsopar.obspm.fr/earth/tigo
Description of the TIGO package:
http://cddis.gsfc.nasa.gov/lw12/docs/Riepl_Tigo.pdf
Letter from the director:
http://www.expres-eu.org/Chile_06032010.html
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