Sub: Update land mode to move up instead of down.

ArduSub/control_land.cpp

@@ -215,10 +215,10 @@ float Sub::get_land_descent_speed()
     bool sonar_ok = false;
 #endif
     // if we are above 10m and the sonar does not sense anything perform regular alt hold descent
-    if (pos_control.get_pos_target().z >= pv_alt_above_origin(LAND_START_ALT) && !(sonar_ok && sonar_alt_health >= SONAR_ALT_HEALTH_MAX)) {
-        return pos_control.get_speed_down();
+    if (pos_control.get_pos_target().z <= pv_alt_above_origin(LAND_START_ALT) && !(sonar_ok && sonar_alt_health >= SONAR_ALT_HEALTH_MAX)) {
+        return pos_control.get_speed_up();
     }else{
-        return -abs(g.land_speed);
+        return abs(g.land_speed);
     }
 }
 

ArduSub/land_detector.cpp

@@ -24,7 +24,7 @@ void Sub::update_land_and_crash_detectors()
 // called at MAIN_LOOP_RATE
 void Sub::update_land_detector()
 {
-	if(barometer.get_altitude() > SURFACE_END_DEPTH && ap.throttle_zero) {
+	if(barometer.num_instances() > 1 && barometer.get_altitude() > SURFACE_END_DEPTH && ap.throttle_zero) {
 		set_land_complete(true);
 	} else {
 		set_land_complete(false);