Can an airplane on an SVFR clearance land when visibility is less than 1 mile?
If the pilot is on an SVFR clearance, the weather inside the surface area deteriorates below 1 mile visibility, and the pilot has the airport in sight, he can inform the controller that he has the field in sight and will be cleared to land. The pilot is responsible for continuing to the airport or exiting the surface area in order to remain visual.


  NOTE− Clear an aircraft to land at an airport with an operating
  control tower, traffic permitting, if the pilot reports the airport in
  sight. The pilot is responsible to continue to the airport or exit the
  surface area. 14 CFR Section 91.157 prohibits VFR aircraft (other than
  helicopters) from landing at any airport within a surface area when
  flight visibility is less than 1 mile. A pilot could inadvertently
  encounter conditions that are below SVFR minimums after entering a
  surface area due to rapidly changing weather. The pilot is best suited
  to determine the action to be taken since pilots operating under SVFR
  between sunrise and sunset are not required to be instrument rated,
  and the possibility exists that flight visibility may not be the same
  as ground visibility. 14 CFR Section 91.3 authorizes a pilot
  encountering an inflight emergency requiring immediate action to
  deviate from any rule of 14 CFR Part 91 to the extent required to meet
  that emergency. Flight into adverse weather conditions may require the
  pilot to execute the emergency authority granted in 14 CFR Section
  91.3 and continue inbound to land. Air Traffic Control Handbook, 7−5−4