The most important product of the USGS Geomagnetism Program is time series of stable magnetometer data having high accuracy and resolution. In this section we briefly describe how these data are collected, transported, processed, managed, and disseminated -- the primary tasks of Program staff.
Data Transport and Distribution
Much of the geomagnetic acquisition, transport and dissemination system is based upon the earthworm system developed by the seismology group. Some of the basic earthworm modules are used as-is, in particular the importer-exporter data transport modules and the waveserver storage module. Some modules were developed to adopt the earthworm system for geomagnetism. This system is referred to as the magworm.
Magnetic data and diagnostic housekeeping data are acquired at each USGS observatory by magworm modules linking the computers to the acquisition instruments. Data are transferred to Golden in via three different methods to improve redundancy and reliability. This includes a near real-time feed of 1-minute and 1-second data via magworm, a transmission of 1-minute data via satellite and a daily ftp of text files. Intermittent manual calibration measurements made at each observatory are recorded in text files and included in the ftp transfers. Additionally, each observatory provides a magworm connection for direct data transmission to the NOAA Space Weather Prediction Center.
At the USGS the data layer is based on virtual machines, which can easily be duplicated and moved to new physical machines when necessary to provide another level of redundancy to ensure we have data collecting, moving and storing as much as possible. Web-based modules are also being developed to eliminate dependencies on particular operating systems and hardware. This will also centralize the data so that processing for Data & Products can occur more quickly.
Data Processing, Management, and Dissemination
Data that are received in Golden in near-real time are ‘variational ’ or ‘preliminary’; they are arbitrary to within a baseline offset, which itself may have a slow drift. For many applications, such preliminary data are more than sufficient, particularly for investigators concerned with relatively rapid changes in the magnetic field occurring over time windows of less than a few days. Studies involving longer windows of time usually require absolute data time series. These are obtained through data processing, with adjustments made for baseline drift using the periodic absolute measurements made at each observatory. Specialized data-processing software, namely ‘MagProc’ has been developed in-house, making the production of absolute, so-called‘definitive’, data relatively efficient. Moreover, since the processing software allows for quick systematic inspection of large quantities of data, it can be used for troubleshooting and quality control. The Program is also developing an Oracle database, which will serve as an interface between the data-collection systems and processing software, as well as help facilitate the dissemination of both new and old observatory data. Data are disseminated in two forms: variational data, available in near-real time, and definitive data, available after processing and within a year of their collection. There are several near-real-time preliminary data displays and a location for downloading data here on the Program's website. Definitive data are disseminated through the production of CDs. These are produced in cooperation with Intermagnet, which also helps promote the dissemination of other nations' magnetometer data.