Short Note
g_log4PDA: an application for continuous monitoring of gravity using LaCoste&Romberg Aliod 100 systems and Palm OS® run hand-held computers

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Introduction

Micro-gravity surveys are a widely applied geophysical technique to quantify time-dependent sub-surface mass and/or density changes. Applications include for example environmental studies and natural resource exploration (e.g., Murty and Raghavan, 2002) as well as the monitoring of active volcanoes (e.g., Rymer, 1994). Surveys are typically repeated at intervals of several days, weeks or years. Limitations to more frequent readings are predominantly financial, including the cost of instrumentation but more importantly the costs for trained personnel to operate the gravity meters and perform the readings. Not only to cut down the latter but also to limit exposure of gravity-meter operators to hazardous conditions found at active volcanoes, automated reading appears to be a sensible approach. In addition, it has become obvious particularly in the field of volcanology that continuous micro-gravity monitoring may provide valuable insights into sub-surface processes governing active volcanism (e.g., Budetta et al., 1999; Gottsmann et al., 2003; Carbone et al., 2003). Thus it has become desirable to resolve gravity changes at a significantly higher frequency (between one reading every 10 s to two readings per day) than practically attainable during conventional surveys using discrete measurements. An automated reading and storing procedure at defined time marks would provide a straightforward solution for continuous monitoring of gravity changes. Towards this end we have developed the software presented here.

Section snippets

Gravity-meter hardware

The gravity-meter manufacturer LaCoste&Romberg Inc. offers gravity meters equipped with an automatic beam nulling system (Aliod 100)1 that streams relative gravity readings at a frequency of 2 Hz in ASCII code via an external RS-232 port. The data stream may be accessed using computers capable of serial port communication. LaCoste&Romberg Inc. provide software, which enables the user to perform discrete readings directly onto a

Coding, computer platforms and differences from commercial software

g_log4PDA is written in MICROSOFT® VISUAL BASIC® using the commercial add-in software package MobileVBLite™ offered by APPFORGE™ which enables engaging GUI (graphical user interface) coding in VISUAL BASIC® for Palm OS® computer platforms. The software is designed to be operated on a Palm OS® (Version 3.0 or higher) run personal digital assistant (PDA) in order to read the data stream from Aliod 100 systems via serial port communication. We have chosen coding for PDA and Palm OS® for three main

Structure of the program

g_log4PDA (Version 1.0) consists of four different forms: a start-up form (‘g_log4PDA’), a form to access and read from the Palm OS® ‘memo’ database (‘main’), a form that creates a new entry into the database (‘memo’), and a form that provides information about the application itself (‘about’). Details on calling procedures of individual forms are shown in Fig. 1.

It is important to note that executing g_log4PDA automatically disables the ‘Auto-off’ settings of Palm OS®. The settings are

Conclusions

We have developed an application that allows the user to continuously log gravity data streamed from Aliod 100 equipped LaCoste&Romberg Inc. gravity meters onto a Palm OS® run PDA. The software enables automated data reading, storage and saving procedures at user-defined intervals. Standard data synchronisation procedures may be employed to upload saved data from PDA onto desktop or laptop computers for data post-processing. The software has scope to be further developed into a PC-based

Acknowledgments

This work was supported by the European Community Research and Training Network “Volcano Dynamics” (HPRN-CT-2000-00060). JG also acknowledges support from a European Community Marie Curie Individual Fellowship (HPMF-CT-2002-01969) and from the Spanish Ministry of Science (programa “Ramón y Cajal”). NF acknowledges funding from an Open University studentship. We thank an anonymous reviewer for constructive comments.

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