A balloon includes an envelope inflatable by a gas, in particular air, an anemometer for detection of the wind speed outside the envelope, and a control circuit to control a fan so as to make the internal inflation pressure of the envelope vary according to the wind speed. The upper part of the mast passes vertically through the envelope to give the latter a static rigidity at the level of the diametrically opposed bottom pole and top pole. The mast is hollow and includes at least one air outlet orifice in its upper part to perform inflation of the envelope.