Need help with sensor selection

Looking for a sensor (or means or performing the following action):

Identifying an objects distance and position (location only need be lateral) within a 180degree field of view from the sensor. I have no experience with arduino or sensors and im just lost at where to begin. If anyone can provide any help i would be very grateful. Thanks

Perhaps you can give more information. How big are the objects you are trying to detect? Over what range of distances? What kind of power source is available?

Taking into consideration the application and environment in which the sensor will operate is important. Understanding the operational location, temperatures, mounting and proximity to other devices is important to selecting the proper size, orientation and installation of the sensor. Take into consideration your location (indoor, outdoor, operating temperature, salt spray, electrically noisy area, high vibration or shock, oil, gas or other fluids, etc…) as well.