I'll limit my question to approach and departure.
There's an increasing number of GPS approach/landing procedures out there. But is there really a backup?
Here goes my question: IIRC most weather radars have a ground mapping function. Couldn't this be used to check the aircraft's position relative to a terrain database? I imagine this would be especially useful at airports located in mountainous terrain, where an ILS can't be installed. Lower weather minimums should be possible.
And maybe it's also useful for low-visibility departures or taxiing?
Is it possible to clearly distinguish the runway surface from other objects with the ground mapping function of a weather radar?