A division of the national Swedish Institute for Building Research wants to estimate the average noise level in a specific area. The dependence between measurements,   at different locations is...

A division of the national Swedish Institute for Building Research wants to estimate the average noise level in a specific area. The dependence between measurements,
  at different locations is described by
  where d is the distance between the i:th and the j:th measurement point. They are restricted to estimate the noise level with the average of the sound level recorded by three microphones. They discuss two different placements, shown in Figure 2.18. Do some computations, and argue in favor of one of the alternatives.