see the appendix of this paper for understanding haarHaar measure.."Determinantal point processes in the plane from products of random matrices" : http://www.imstat.org/aihp/accepted.htmlDeterminantal point processes in the plane from products of random matrices
intuition for haarHaar random orthogonal matrix: choose a vector randomly from the unit sphere in R^n${\mathbb R}^n$ ( uniformuniform distribution on the unit sphere). Thats urThat's the first column. Now for the second column, choose a vector randomly from the unit sphere in n-1the $n-1$ dimensional subspace orthogonal to the first column. similarlySimilarly for the third column, choose a vector randomly from the unit sphere in n-2the $n-2$ dimensional subspace orthogonal to the first two columns...and so on....