def depth(self):
        """Depth at grid centers (m)

        :getter:    Returns the points of axis ``'depth'`` if availible in the
                    process's domains.
        :type:      array
        :raises: :exc:`ValueError`
                    if no ``'depth'`` axis can be found.

        """
        try:
            for domname, dom in self.domains.items():
                try:
                    thisdepth = dom.axes['depth'].points
                except:
                    pass
            return thisdepth
        except:
            raise ValueError('Can\'t resolve a depth axis.')