There are many technologies being used today such as ultrasonic sensors, which provide non-contact for solution levels in liquid storage tanks. Using this technology the tanks can use non-corrosive methods to prevent failure of parts. For instance in a fuel tank the bacteria can eat through a 505 (2-inch) think piece of stainless steel in about a week or so. Even plastic, which is made from petroleum products becomes brittle in such environments. So the solution in the various industries is to use sound waves to control switches and float leveling systems. One company in our industry is Compac Engineering which makes all types of "Eracta Switches" like an erector set you build the desired structure or device out of plastic, insert their sensors, plug it in and you are completed. You can know soap levels, waster water levels, freshwater levels using devices, which do not corrode, rust or deteriorate quickly.

These same systems and other systems are used in car washes to guide the car and systems close without touching the car. In the previous decade electronic eyes were used, costly and often failed and each morning a ghost wash was needed to test the system and if the control mechanism failed the unit would touch the practice car and scratch it, ruining the paint. This newer technology is best suited in that it has less moving parts and works very easily with less mechanism for Murphyism and less weight of components a critical issue in UAV operations since payloads are critical.

The best little tiny UAVs which go by another term MAV- Micro Air Vehicles can only carry 9-11 lbs. not much really, but enough to get the job done. Every pound you save adds to the range of the craft for fuel or battery power in the case of many of the UAVs around. Electric MAVs and/or Small UAVs for military purposes are desired since they do not need fuel only setting a switch allowing the chemicals to mix and cause a reation and start the process of making electricity. GPS guided units by satellites are often best for UAV control in that the operator releases or hand launches the unit and lets it go and the satellite guides it by electronic pulses or pinging from satellite within way-points without any rhythm and therefore electronic pulses are not able to be blocked as signals. Without blocking an entire band of frequencies and that takes lots of power and directional awareness of UAV which if autonomous is nearly impossible to find or see and you cannot know where it is since it's signature is less than the smallest bird.

Also electric is nice if the using terrain following devices, which if ultrasound is used are really inexpensive in the car wash industry will cause a somewhat vertically unpredictable flight pattern of that of a bird, which moves with the currents and updrafts crossing roads or downdrafts crossing creeks and cooler air.

You see the simple instability of the relative wind along with the terrain ultrasonic control system pulling up when it gets close to the ground will look like the flight of a bird, one which you cannot see and you cannot hear if it is electric. For all practical purposes a small delivery system similar to the birds in Harry Potters Book five. The speed of sound is a factor of air temperature and of course air pressure and density but at slower speeds of a UAV is less of a consideration. A tree in the way would be a different signal bounce for sound than the ground, sensors can easily see the difference.

Right now much work is being done on pedestrian radars using sound, which are now available in Europe on cars and soon in US. Most major auto manufacturers have this and if you remember the last Terminator Movie out now the robots, which shoot rotating machine guns use sound to identify targets, the disruption of the returning of the sound waves is recognized by shape and therefore the object is identified. They call this technique windowing. The proximity sensors for car washes use a complex series of ultrasonic sound pulses using emitters and receivers. But the systems can be easily made very simply and relatively weightless. Many animals in nature use such signals to hunt; Bats for instance and Dolphins sonar. You see not too difficult to see why. Easy to use and light-weight. In cold conditions the units, which gather ice could have a bit of a problem however most of the enemies of the US are near the equator, where it is warmer. This system works day or night and in stormy weather when proper filters are used. Another even cooler new technology which has been recently adopted in the car wash industry is "passive ferrous object detection" this technology uses a very simplistic approach which identifies natural local magnetic disturbances in the Earth's natural magnetic field; another easy system, which can guide a UAV.

Ultrasonic sensors can be solid state or newer chip technology to work. UAVs, which can fly under radars and line of sight around and through trees, like birds and insects are the future of UAV technology. It's a bird, It's a plane, no its a UAV. Holly pilot-less RC modeling Batman.