Adaptive density estimation for directional data using needlets
  This paper is concerned with density estimation of directional data on the sphere. We introduce a procedure based on thresholding on a new type of spherical wavelets called {\it needlets}. We establish a minimax result and prove its optimality. We are motivated by astrophysical applications, in particular in connection with the analysis of ultra high energy cosmic rays. 
P. Baldi, G. Kerkyacharian, D. Marinucci, D. Picard