causing it to balance momentarily a brief interruption in the tension of the string may occur in such a case the tension is quickly reestablished and the descent continues the charge upon contacting the surface of snow often penetrates the snow by several decimeters furthermore the flexion of the carrier cable diminishes when it is relieved of the charge the apparatus according to the invention is however adapted to perform a pick up of the charge before effectively raising the charge above the surface of the snow to perform such a pick up the microprocessor commands a first wind up operation of string 4 on drum 27 of the winch for example over two turns which is 66 cm then verifies for example for five seconds if detectors 33 have signalled a rocking of the winch indicating a pick up of the charge if this is not the case it performs a second wind up operation over two turns and a third if necessary this method of operation makes it possible for winding up to two meters of the string until pick up of the charge which is sufficient in all cases to tension the string begins lifting the charges and compensates for a possible flexion in the carrier cable from this stage the microprocessor controls the winch in a manner so as to raise the charge to the preselected height as indicated by the coded wheel 53 then it stops the winch and waits for the explosion of charges 9 resulting from the completion of combustion of fuses 11 after explosion of the charges the tension in string 4 falls very low and the winch rocks the microprocessor commands the winch to remain in this state for a predetermined.