Second Test of Mixed (Single- & Dual-Frequency) GPS Receivers
on Papandayan, June-July 2001

In late June 2001 Craig Roberts and Volker Janssen went to West Java, Indonesia, again. They spent 3-5 weeks continuing their work on the mixed-mode GPS volcano deformation monitoring system. The single-frequency network was originally deployed by Craig in 1999, while first tests of the mixed-mode set-up were carried out in early 2000. The software and hardware problems, which gave Craig and Volker much grief in 2000, had been investigated and mostly solved, so the outlook was very optimistic. Processing of the 2000 data had indicated that the fiducial baselines used in 2000 were too long to generate reliable correction terms, so different sites were chosen this time around. With the valuable help of our collaborators at the Institute of Technology Bandung (ITB) and the Volcanological Survey of Indonesia (VSI), fiducial GPS sites were set-up at Guntur observatory, in Pangalengan and Pameungpeuk. This resulted in a 31km-53km-52km triangle around the deformation zone of Gunung Papandayan.

As before, the fiducial network consisted of three Leica CRS1000 dual-frequency GPS receivers surrounding the deformation zone around the volcano. It's purpose was to generate empirical correction terms to account for error sources such as orbit bias, tropospheric delay and ionospheric delay across this local area. These correction terms can then be applied to the inner single-frequency network to improve accuracy (a strategy that is being used on the Singapore multi-base station network).

On the volcano itself, a lot of work had to be done as well. The metal drums used to house the equipment were rusted beyond recognition and had to be replaced. Plastic drums, which will resist the sulphur gas attack much better, were installed. Some cables had to be repaired, wires had to be replaced, and a new solar panel frame and fence had to be built at Kawah.