Pilot balloon
A pilot balloon is used by meteorologists to determine the height of the bottom of the clouds above the ground during the daytime hours. The balloon is filled in such a way that its rate of ascent is known. From the measured time span between the start of the balloon and its immersion in the cloud, one can infer the height of the cloud base. By tracking the trajectory, earlier with a theodolite , today with radar or GPS , the direction and speed of high-altitude winds can be determined.
history
The pilot balloon in its current form was introduced in 1901 by Richard Aßmann in Berlin. In contrast to the previously used balloons made of fabric, gold bat skin or paper, rubber balloons ensured a constant and previously known ascent speed.
handling
A pilot balloon is a small, usually red, rubber balloon that is generally 76 millimeters prior to inflation. The balloons and associated equipment are usually housed in a cabinet that is mounted on a wall close to the gas cylinders. The cabinet has three doors, one of which opens downwards and on which the filler stand is attached. An "L" -shaped tube with two rings is attached to the top of the filler at the stand, a small one on the lower and a larger one on the top of the filler nozzle. The rings prevent the tube from falling or rising too far through the stand when the balloon is inflated. The top ring has some grooves in it to help it grip the balloon that is attached to it.
At the bottom of the tube is a weight which, when the exact amount of gas has been added, lifts to indicate that the balloon is full. A rubber hose is attached to this pipe, thereby crossing the filler stand twice. The first hole is larger than the hose to allow movement of the hose while the second is used to hold the hose in place. The hose runs to a needle valve that controls the amount of gas flow to the balloon. A second hose then runs from the valve to a regulator valve that is attached to the gas cylinder. This valve has two pressure gauges attached . One that shows the total pressure in the gas cylinder and a second that shows the amount of gas that is flowing through the hose. Usually the cylinder is made of steel and weighs approximately 63.5 kg. It contains about 5.7 m³ of the gas with a pressure of 14 MPa and can inflate about 120 balloons. On the opposite side of the cabinet is the room for storing the balloons. Helium is normally used as the filling gas, but it can also be hydrogen .
The balloon is brought to the gas nozzle and a piece of tape is wrapped around the neck of the balloon. After putting on the safety glasses and hearing protection , a check is made to see whether the needle valve is completely closed. The main valve on the cylinder is then opened, followed by the opening of the regulator valve. First the needle valve is opened and the balloon begins to fill. When the balloon reaches the correct size, the inflation nozzle begins to lift. At this point the needle valve is closed along with the regulator valve and the cylinder valve. The tape is then used to tie the base of the balloon so that no gas can escape.
After the balloon has been inflated outside, it is released. The time from the start to reaching the cloud cover is measured. When properly inflated, the balloon will rise at a rate of 140 meters per minute (460 ft / min). The undersides of the clouds are very rarely flat and firm, so the height of the clouds is reached when the balloon begins to fade in color rather than when it disappears. The balloon can also be used to measure vertical vision in a blanket of fog . In this case, the balloon will begin to fade as soon as it is released, so when the balloon disappears, the vertical view becomes apparent. If the balloon is visible in the cloud layer for a considerable period of time, the observer should make a note because this is a value for the density of the clouds.
The pilot balloon is a reliable, safe and easy means of obtaining data on the height of the clouds. However, it has some drawbacks that the observer must be aware of. Rain and wet snow can slow down the ascent of the balloon, which leads to an incorrect reading for the cloud height, and in poor visibility the balloon can disappear before it reaches the cloud. If the balloon rises at a rate of 140 m per minute (460 ft / minute), it will take five minutes for the balloon to reach 700 m (2300 ft). It is difficult to follow the balloon beyond this height, for example with binoculars , as even a slight movement of the eye away from the balloon will result in losing visual contact.
It is not practical to use a balloon at night. Then the cloud projector is used. However, during twilight it may be impossible to use the cloud projector and then an illuminated pilot balloon can be used. This contains a simple flashlight bulb attached to a battery. To charge the battery, it is submerged in the water for three minutes and then tied to the balloon before inflating. These are rarely used today. Caution must be used during inflation because of the occasional malfunctioning balloon and its failure. If the person inflating the balloon does not wear eye protection or hearing protection, eye or ear damage may result in the event of a burst.
