How good is Brittany Spaniel sense of smell?

I'm no scientist but my grand-daughter has a Springer Spaniel which stays with me when she and her family are away from home. The dog has a favourite rubber ball and I have consistently used a nearby three-acre woodland clearing to exercise the dog; I throw the ball and he retrieves it. The wild grass and tangled weed can be anything up to 24 inches high and I can throw the ball a fair distance. Nose close to the ground, he casts around in long, fast sweeps until he's sniffed it out. We haven't lost the ball once during the entire three years, even when he doesn't see the direction of the throw.