Geometry‐specified troposphere decorrelation for subcentimeter real‐time kinematic solutions over long baselines

Real‐time kinematic (RTK) GPS techniques have been extensively developed for applications including surveying, structural monitoring, and machine automation. Limitations of the existing RTK techniques that hinder their applications for geodynamics purposes are twofold: (1) the achievable RTK accuracy is on the level of a few centimeters and the uncertainty of vertical component is 1.5–2 times worse than those of horizontal components and (2) the RTK position uncertainty grows in proportional to the base‐torover distances. The key limiting factor behind the problems is the significant effect of residual tropospheric errors on the positioning solutions, especially on the highly correlated height component. This paper develops the geometry‐specified troposphere decorrelation strategy to achieve the subcentimeter kinematic positioning accuracy in all three components. The key is to set up a relative zenith tropospheric delay (RZTD) parameter to absorb the residual tropospheric effects and to solve the established model as an ill‐posed problem using the regularization method. In order to compute a reasonable regularization parameter to obtain an optimal regularized solution, the covariance matrix of positional parameters estimated without the RZTD parameter, which is characterized by observation geometry, is used to replace the quadratic matrix of their “true” values. As a result, the regularization parameter is adaptively computed with variation of observation geometry. The experiment results show that new method can efficiently alleviate the model’s ill condition and stabilize the solution from a single data epoch. Compared to the results from the conventional least squares method, the new method can improve the longrange RTK solution precision from several centimeters to the subcentimeter in all components. More significantly, the precision of the height component is even higher. Several geosciences applications that require subcentimeter real‐time solutions can largely benefit from the proposed approach, such as monitoring of earthquakes and large dams in real‐time, high‐precision GPS leveling and refinement of the vertical datum. In addition, the high‐resolution RZTD solutions can contribute to effective recovery of tropospheric slant path delays in order to establish a 4‐D troposphere tomography.

African Gamer: Whose Story Is It Anyway?

New Video Gamer: Africa Needs More Technology (CNN 12/12/2011) In December 2011 CNN news service online edition (Sutter, 2011) posted a short item about Cwi Nqane, a Khoisan man who entered Samsung’s Namibian World Cyber Games (WCG) heats held at the 2011 the annual Windhoek Show. Cwi Nqane won a place on the Namibian WCG team playing a smartphone game called Asphalt 6: Adrena-line (Gameloft, 2011). Cwi was presented with a ‘top of the line’ Samsung Galaxy tablet and subsequently sent to compete in Korea. Later, other news and game news websites re-reported the incident, which inspired a variety of enthusiastic comment about tech-nology and ‘new knowledge’. Then Kotaku news service picked up the item (Narcisse, 2011) and took a very different slant. Kotaku proposed that Samsung was exploiting Cwi and had assumed the role of a Techno-Tarzan: “striding into Nqane’s homeland and swinging him off into the wonders of the modern world where they can trot him out as a curiosity”. These two perspectives on the story of Cwi’s WCG entry expose two dominant views on Indigenous knowledges and technologies: ICTs as progress for in-digenous peoples and ICTs as disruptive and exploitative. Neither position, however, allows for the claiming of digital technology by indigenous communities, indeed both views position indigenous cultures as being outsiders.