Trend enhancement in aeromagnetic maps using constrained coherence-enhancing diffusion filtering

Geophysical data have to be modeled on a regular grid for various numerical procedures. However, airborne data tend to be collected with fine spacing along traverses but with much coarser spacing between traverses. Gridding only honors flight-line data when the mesh size is close to the sample spacing; otherwise, high-frequency information is always lost, which creates aliasing artifacts. For example, linear trends at an acute angle with respect to flight lines are imaged as “bull’s-eyes,” which resemble a boudinage at line intersections. The presence of boudinage artifacts can significantly distort anomalies of interest and thus lead to incorrect interpretation of shapes or sizes of causative bodies. We evaluated a method called constrained coherence-enhancing diffusion filtering that only diffuses the image in specific areas where strong anisotropy is detected. This method was tested on synthetic and field data set. Results indicated that the method can be efficiently used to enhance linear structure in multiple local directions. The images derived from this grid, such as the vertical gradient map, are also significantly improved. The original line data are honored by the constraints applied. We also used a field data set to compare the proposed approach with the approach used when diffusion is applied uniformly in all areas, irrespective of anisotropy. The proposed method was proven to produce better results with fewer artifacts.

Memory Mechanisms and the Psychophysical Scaling of Duration

Two experiments were performed to examine the suggestion that underlying memory mechanisms may be revealed in the form of the psychophysical function for duration. In experiment 1 a broad range of durations, with fine spacing at the lower end, was employed to bring out any transition in function that might reflect a change from ‘iconic’ memory to short-term memory. Estimation in conventional time-units (Verbal Estimation) was also compared with unit-free estimation (Magnitude Estimation). In experiment 2 Verbal Estimation was compared with the Production method, for a different range of stimulus values, and with varying interval content. Contrary to earlier claims, memory mechanisms were not found to be reflected in the values of power exponents for subjective duration. The value of the search for such functions is questioned, as simple linear plots fit the data at least as well.