This invention relates to compositions and methods for treating subterranean formations, in particular, oilfield stimulation compositions and methods using water-in-water polymer emulsions to uniformly dissolve a rheologically active polymer, such as a thickener or friction reducer, in the treatment fluid. The wire strand diameter of the monofilament steel wires is from 0. The plural detectors are arranged on a surface of a subject and configured to substantially vertically emit light from an emission surface of the light emission unit to the surface of the subject.