Adaptive constraints for feature tracking

In this paper extensions to an existing tracking algorithm are described. These extensions implement adaptive tracking constraints in the form of regional upper-bound displacements and an adaptive track smoothness constraint. Together, these constraints make the tracking algorithm more flexible than the original algorithm (which used fixed tracking parameters) and provide greater confidence in the tracking results. The result of applying the new algorithm to high-resolution ECMWF reanalysis data is shown as an example of its effectiveness.

Weak constraints in four-dimensional variational data assimilation

The formulation of four-dimensional variational data assimilation allows the incorporation of constraints into the cost function which need only be weakly satisfied. In this paper we investigate the value of imposing conservation properties as weak constraints. Using the example of the two-body problem of celestial mechanics we compare weak constraints based on conservation laws with a constraint on the background state.We show how the imposition of conservation-based weak constraints changes the nature of the gradient equation. Assimilation experiments demonstrate how this can add extra information to the assimilation process, even when the underlying numerical model is conserving.

Seeing things: perception, experience and the constraints of excavation

Recent attempts to problematize archaeological fieldwork concerned with excavation at the expense of surface survey, and with questions of procedure more than interpretations of the past. In fact these two kinds of fieldwork offer quite different possibilities and suffer from different constraints. Thought must be given to ways in which they can be combined if they are to make a real contribution to social archaeology. The argument is illustrated by a project carried out at a megalithic cemetery in Scotland.