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Chadwell, CD.  1999.  Reliability analysis for design of stake networks to measure glacier surface velocity. Journal of Glaciology. 45:154-164. AbstractWebsite

Measurement of glacier surface velocity provides some constraint on glacier flow models used to date ice cores recovered near the flow divide of remote high-altitude ice caps. The surface velocity is inferred from the change in position of a network of stakes estimated from the least-squares adjustment of geodetic observations-terrestrial and/or spaced-based-collected approximately year apart. The lack of outliers in and the random distribution of the post-fit observation residuals are regarded as evidence that the observations contain no blunders. However, if the network lacks sufficient geometric redundancy the estimated stake positions san shift to fit erroneous observations. To determine the maximum size of these potential undetected shifts, given the covariance of the observations and the approximate network geometry expressions are developed to analyze a network for redundancy number and marginally detectable blunders (internal reliability), and the position shifts from marginally detectable blunders (external reliability). Two stake networks, one on the col of Huascaran (9 degrees 07' S, 77 degrees 37' W; 6050 m a.s.l.) in the north-central Andes of Peru and one on the Guliya ice cap (35 degrees 17' N, 81 degrees 29' E; 6200 ma.s.l.) on the Qinghai-Tibetan Plateau in China, are examined for precision and internal and external reliability.

Gagnon, KL, Chadwell CD.  2007.  Relocation of a seafloor transponder - Sustaining the GPS-Acoustic technique. Earth Planets and Space. 59:327-336. AbstractWebsite

Rigid seafloor arrays of three to four precision acoustic transponders have been repeatedly positioned with the GPS-Acoustic technique to measure horizontal plate motion. In the event that one transponder becomes inactive, a replacement transponder must be precisely located relative to the existing array. Here we present a technique to determine the geodetic azimuth and baseline between the inactive and replacement transponders. We include three examples of relocations between 2002 and 2003 on the Juan de Fuca plate and near the Peru-Chile trench, which add 16-29 mm uncertainty to the GPS-Acoustic estimated position. A simulation of optimal network geometry shows that the relocation's contribution to uncertainty can be as low as 10 mm.