Limit camera RotateAround for an UAV game

Hi, i am building a mobile UAV game and i want to limit camera's rotation. What is the best way to do this perfectly? Here is my code for using rotate camera:

 public class CameraMove : MonoBehaviour 
 {
     //
     // VARIABLES
     //
     public Camera UAVCam;
     public float turnSpeed = 4.0f;        // Speed of camera turning when touch moves in along an axis
     private Vector2 mouseOrigin;    // Position of touch when touch dragging starts
     private bool isRotating;    // Is the camera being rotated?
 
     //
     // UPDATE
     //
 
     void Update () 
     {
         // Get the first touch
         if(Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began) {
             // Get touch origin
             mouseOrigin = Input.GetTouch(0).position;
             isRotating = true;
         }
 
         // Disable movements on touch release
         if ((Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Ended)) isRotating=false;
 
         // Rotate camera along X and Y axis
         if (isRotating) {
             
             Vector2 temp = Input.GetTouch (0).position - mouseOrigin;
             Vector3 pos =UAVCam.ScreenToViewportPoint(new Vector3(temp.x,temp.y,0.0f));
 
             UAVCam.transform.RotateAround(UAVCam.transform.position, UAVCam.transform.right, -pos.y * turnSpeed);
             UAVCam.transform.RotateAround(UAVCam.transform.position, Vector3.up, pos.x * turnSpeed);
         }
             
     }
 }
 

Thanks in advance!