diff --git a/ArduCopter/Copter.h b/ArduCopter/Copter.h
index 94f34af4e8..8352e3d32b 100644
--- a/ArduCopter/Copter.h
+++ b/ArduCopter/Copter.h
@@ -289,17 +289,17 @@ private:
         bool get_dist_for_logging(float &target_dist, float &actual_dist) const;
         void invalidate_for_logging() { valid_for_logging = false; }
 
-        // surface tracking states
-        enum class SurfaceTrackingState {
-            SURFACE_TRACKING_DISABLED = 0,
-            SURFACE_TRACKING_GROUND = 1,
-            SURFACE_TRACKING_CEILING = 2
+        // surface tracking surface
+        enum class Surface {
+            NONE = 0,
+            GROUND = 1,
+            CEILING = 2
         };
-        // set direction
-        void set_state(SurfaceTrackingState state);
+        // set surface to track
+        void set_surface(Surface new_surface);
 
     private:
-        SurfaceTrackingState tracking_state = SurfaceTrackingState::SURFACE_TRACKING_GROUND;
+        Surface surface = Surface::GROUND;
         float target_dist_cm;       // desired distance in cm from ground or ceiling
         uint32_t last_update_ms;    // system time of last update to target_alt_cm
         uint32_t last_glitch_cleared_ms;    // system time of last handle glitch recovery
diff --git a/ArduCopter/RC_Channel.cpp b/ArduCopter/RC_Channel.cpp
index 37cc054174..6394ec886e 100644
--- a/ArduCopter/RC_Channel.cpp
+++ b/ArduCopter/RC_Channel.cpp
@@ -562,13 +562,13 @@ void RC_Channel_Copter::do_aux_function(const aux_func_t ch_option, const aux_sw
         case AUX_FUNC::SURFACE_TRACKING:
             switch (ch_flag) {
             case LOW:
-                copter.surface_tracking.set_state(Copter::SurfaceTracking::SurfaceTrackingState::SURFACE_TRACKING_GROUND);
+                copter.surface_tracking.set_surface(Copter::SurfaceTracking::Surface::GROUND);
                 break;
             case MIDDLE:
-                copter.surface_tracking.set_state(Copter::SurfaceTracking::SurfaceTrackingState::SURFACE_TRACKING_DISABLED);
+                copter.surface_tracking.set_surface(Copter::SurfaceTracking::Surface::NONE);
                 break;
             case HIGH:
-                copter.surface_tracking.set_state(Copter::SurfaceTracking::SurfaceTrackingState::SURFACE_TRACKING_CEILING);
+                copter.surface_tracking.set_surface(Copter::SurfaceTracking::Surface::CEILING);
                 break;
             }
             break;
diff --git a/ArduCopter/surface_tracking.cpp b/ArduCopter/surface_tracking.cpp
index b31c18fdcf..3a490298e7 100644
--- a/ArduCopter/surface_tracking.cpp
+++ b/ArduCopter/surface_tracking.cpp
@@ -7,9 +7,9 @@ float Copter::SurfaceTracking::adjust_climb_rate(float target_rate)
 {
 #if RANGEFINDER_ENABLED == ENABLED
     // check tracking state and that range finders are healthy
-    if ((tracking_state == SurfaceTrackingState::SURFACE_TRACKING_DISABLED) ||
-        ((tracking_state == SurfaceTrackingState::SURFACE_TRACKING_GROUND) && (!copter.rangefinder_alt_ok() || (copter.rangefinder_state.glitch_count != 0))) ||
-        ((tracking_state == SurfaceTrackingState::SURFACE_TRACKING_CEILING) && !copter.rangefinder_up_ok()) || (copter.rangefinder_up_state.glitch_count != 0)) {
+    if ((surface == Surface::NONE) ||
+        ((surface == Surface::GROUND) && (!copter.rangefinder_alt_ok() || (copter.rangefinder_state.glitch_count != 0))) ||
+        ((surface == Surface::CEILING) && !copter.rangefinder_up_ok()) || (copter.rangefinder_up_state.glitch_count != 0)) {
         return target_rate;
     }
 
@@ -17,8 +17,8 @@ float Copter::SurfaceTracking::adjust_climb_rate(float target_rate)
     const float current_alt_error = copter.pos_control->get_alt_target() - copter.inertial_nav.get_altitude();
 
     // init based on tracking direction/state
-    RangeFinderState &rf_state = (tracking_state == SurfaceTrackingState::SURFACE_TRACKING_GROUND) ? copter.rangefinder_state : copter.rangefinder_up_state;
-    const float dir = (tracking_state == SurfaceTrackingState::SURFACE_TRACKING_GROUND) ? 1.0f : -1.0f;
+    RangeFinderState &rf_state = (surface == Surface::GROUND) ? copter.rangefinder_state : copter.rangefinder_up_state;
+    const float dir = (surface == Surface::GROUND) ? 1.0f : -1.0f;
 
     // reset target altitude if this controller has just been engaged
     // target has been changed between upwards vs downwards
@@ -40,7 +40,7 @@ float Copter::SurfaceTracking::adjust_climb_rate(float target_rate)
     valid_for_logging = true;
 
     // upward facing terrain following never gets closer than avoidance margin
-    if (tracking_state == SurfaceTrackingState::SURFACE_TRACKING_CEILING) {
+    if (surface == Surface::CEILING) {
         const float margin_cm = copter.avoid.enabled() ? copter.avoid.get_margin() * 100.0f : 0.0f;
         target_dist_cm = MAX(target_dist_cm, margin_cm);
     }
@@ -62,7 +62,7 @@ float Copter::SurfaceTracking::adjust_climb_rate(float target_rate)
 bool Copter::SurfaceTracking::get_target_alt_cm(float &_target_alt_cm) const
 {
     // fail if we are not tracking downwards
-    if (tracking_state != SurfaceTrackingState::SURFACE_TRACKING_GROUND) {
+    if (surface != Surface::GROUND) {
         return false;
     }
     // check target has been updated recently
@@ -77,7 +77,7 @@ bool Copter::SurfaceTracking::get_target_alt_cm(float &_target_alt_cm) const
 void Copter::SurfaceTracking::set_target_alt_cm(float _target_alt_cm)
 {
     // fail if we are not tracking downwards
-    if (tracking_state != SurfaceTrackingState::SURFACE_TRACKING_GROUND) {
+    if (surface != Surface::GROUND) {
         return;
     }
     target_dist_cm = _target_alt_cm;
@@ -86,31 +86,31 @@ void Copter::SurfaceTracking::set_target_alt_cm(float _target_alt_cm)
 
 bool Copter::SurfaceTracking::get_dist_for_logging(float &target_dist, float &actual_dist) const
 {
-    if (!valid_for_logging || (tracking_state == SurfaceTrackingState::SURFACE_TRACKING_DISABLED)) {
+    if (!valid_for_logging || (surface == Surface::NONE)) {
         return false;
     }
     target_dist = target_dist_cm * 0.01f;
-    actual_dist = ((tracking_state == SurfaceTrackingState::SURFACE_TRACKING_GROUND) ? copter.rangefinder_state.alt_cm : copter.rangefinder_up_state.alt_cm) * 0.01f;
+    actual_dist = ((surface == Surface::GROUND) ? copter.rangefinder_state.alt_cm : copter.rangefinder_up_state.alt_cm) * 0.01f;
     return true;
 }
 
 // set direction
-void Copter::SurfaceTracking::set_state(SurfaceTrackingState state)
+void Copter::SurfaceTracking::set_surface(Surface new_surface)
 {
-    if (tracking_state == state) {
+    if (surface == new_surface) {
         return;
     }
     // check we have a range finder in the correct direction
-    if ((state == SurfaceTrackingState::SURFACE_TRACKING_GROUND) && !copter.rangefinder.has_orientation(ROTATION_PITCH_270)) {
+    if ((new_surface == Surface::GROUND) && !copter.rangefinder.has_orientation(ROTATION_PITCH_270)) {
         copter.gcs().send_text(MAV_SEVERITY_WARNING, "SurfaceTracking: no downward rangefinder");
         AP_Notify::events.user_mode_change_failed = 1;
         return;
     }
-    if ((state == SurfaceTrackingState::SURFACE_TRACKING_CEILING) && !copter.rangefinder.has_orientation(ROTATION_PITCH_90)) {
+    if ((new_surface == Surface::CEILING) && !copter.rangefinder.has_orientation(ROTATION_PITCH_90)) {
         copter.gcs().send_text(MAV_SEVERITY_WARNING, "SurfaceTracking: no upward rangefinder");
         AP_Notify::events.user_mode_change_failed = 1;
         return;
     }
-    tracking_state = state;
+    surface = new_surface;
     reset_target = true;
 }