function fieldStudyRandomImage() {
  var imageDir= new Array('lake1.jpg','lake2.jpg','lake3.jpg','lake4.jpg','lake5.jpg','lake6.jpg','lake7.jpg');
  var chosen = Math.floor(Math.random()*7);
  document.open();
  document.write('<img src="/images/cds/fieldstudy/' + imageDir[chosen] + '" width="400" />');
  document.close();
}