Crustal constraint through complete model space screening for diverse geophysical datasets facilitated by emulation

Deep crustal constraint is often carried out using deterministic inverse methods, sometimes using seismic refraction, gravity and electromagnetic datasets in a complementary or “joint” scheme. With increasingly powerful parallel computer systems it is now possible to apply joint inversion schemes to derive an optimum model from diverse input data. These methods are highly effective where the uncertainty in the system is small. However, given the complex nature of these schemes it is often difficult to discern the uniqueness of the output model given the noise in the data, and the application of necessary regularization and weighting in the inversion process means that the extent of user prejudice pertaining to the final result may be unclear. We can rigorously address the subject of uncertainty using standard statistical tools but these methods also become less feasible if the prior model space is large or the forward simulations are computationally expensive. We present a simple Monte Carlo scheme to screen model space in a fully joint fashion, in which we replace the forward simulation with a fast and uncertainty-calibrated mathematical function, or emulator. This emulator is used as a proxy to run the very large number of models necessary to fully explore the plausible model space. We develop the method using a simple synthetic dataset then demonstrate its use on a joint data set comprising first-arrival seismic refraction, MT and scalar gravity data over a diapiric salt body. This study demonstrates both the value of a forward Monte Carlo approach (as distinct from a search-based or conventional inverse approach) in incorporating all kinds of uncertainty in the modelling process, exploring the entire model space, and shows the potential value of applying emulator technology throughout geophysics. Though the target here is relatively shallow, the methodology can be readily extended to address the whole crust

The acceptance of long-range weather forecasts: a question of perception?

These perceptions were examined by a survey of property managers across Queensland who were involved in a wide variety of agricultural activities. Results from the survey, which was conducted prior to the release of ENSO-based long-range forecasts in Australia, reveal that the acceptance and subsequent use of these forecasts as an effective planning tool may be initially limited by a number of factors. Desired levels of forecast reliability, forecast presentation style, use of terminology in forecasts and perceptions with regard to weather information services are discussed. -from Author

The acceptance of long-range weather forecasts: a question of perception?

These perceptions were examined by a survey of property managers across Queensland who were involved in a wide variety of agricultural activities. Results from the survey, which was conducted prior to the release of ENSO-based long-range forecasts in Australia, reveal that the acceptance and subsequent use of these forecasts as an effective planning tool may be initially limited by a number of factors. Desired levels of forecast reliability, forecast presentation style, use of terminology in forecasts and perceptions with regard to weather information services are discussed. -from Author

Neutron monitoring of plutonium at the ZPPR storage vault

We investigated a method for monitoring a typical large storage vault for unauthorized removal of plutonium. The method is based on the assumption that the neutron field in a vault produced by a particular geometric configuration of bulk plutonium remains constant in time and space as long as the configuration is undisturbed. To observe such a neutron field, we installed an array of 25 neutron detectors in the ceiling of a plutonium storage vault at Argonne National Laboratory West. Each neutron detector provided an independent spatial measurement of the vault neutron field. Data collected by each detector were processed to determine whether statistically significant changes had occurred in the neutron field. Continuous observation experiments measured the long-term stability of the system. Removal experiments were performed in which known quantities of plutonium were removed from the vault. Both types of experiments demonstrated that the neutron monitoring system can detect removal or addition of bulk plutonium (11% /sup 240/Pu) whose mass is as small as 0.04% of the total inventory