102 



METEOROLOGICAL EQUIPMENT FOR SHORT WAVE 



The record ou the ground was taken by means of a 

 standard U. S. Army radiosonde receiver. 



It was pointed out in this report" that it miglit he 

 advantageous to nse a combination of two radiosondes 

 in tandem, such that in one instrument the contacts are 

 connected to the temperature device, in the other to 

 the humidity element. It would then be possible to ob- 

 tain simultaneous temperature and moisture readings 

 at the same elevation, instead of alternating ones, as 

 is the case when only one instrument is used. This 

 would, however, require the use of two receivers at 

 the ground with two slightly difEerent carrier fre- 

 quencies. 



Another adaptation of the standard Weather Bu- 

 reau radiosonde was made by WSC.^^ The ground in- 

 stallation was similar to that used by the Weather 

 Bureau in its full radiosonde measurements, but the 

 standard radiosonde was modified by replacing the 

 pressure- (altitude-) actuated switch by a clock-driven 

 commutator. The results obtained were quite satisfac- 

 tory, and the technique may be appropriate at stations 

 w-here standard radiosonde equipment is available. 



Wired Transmission Type 



The other captive balloon or kite instruments are 

 of the wired type with galvanometers or recorders at 

 the ground. They may be classified as light and heavy 

 types. The light instrument merely carries tempera- 

 ture and humidity elements aloft which together with 

 the radiation shield do not weigh more than a few 

 ounces. To this is added the weight of the cable or 

 string carrying the connecting wires. The heavy in- 

 strument carries its own aeration equipment in the 

 form of a fan driven by a small electric motor. The 

 fan and the heavier construction of the frame required 

 to accommodate it increase the weight of the airborne 

 unit to several pounds. In addition there must be at 

 least one more lead ou the cable to supply power to the 

 fan. 



The first captive balloon instrument was built in 

 England about 2 years ago." The balloon is anchored 

 by an electric cable and the instrument is provided 

 with a fan. The overall weight of the instrument with- 

 out cable is about 8 lb. Its main part is a piece of poly- 

 thene tubing in the shape of an inverted Y with the 

 fan placed on top of the tubing while the two legs of 

 the Y contain the dry and wet thermopiles. The latter 

 are four-junction copper-constantau combinations. 

 The cold junctions are enclosed in a small Dewar flask 

 filled with melting ice which is located about 10 in. 

 below the Y piece. 



The cable of this ijistrument has five leads, three 

 for the thermocouples and two for the fan (2 to 4 

 volts of direct current) ; the instrument is suspended 

 from the balloon proper by means of a 100-ft string 

 which minimizes the influence of irregular motions of 

 the balloon upon the instrument. The ground equip- 

 ment consists of potentiometers and a spot galvanom- 

 eter with a switch to alternate between the dry and 

 wet couples. 



The light type of balloon or kite sounding equip- 

 ment was first developed by WSC.""-'*'' The tempera- 

 ture and humidity elements are surrounded by a 

 double-walled aluminum radiation shield, and the 

 whole airborne assembly weighs only a few ounces. 

 Originally the standard Weather Bureau temperature 

 element was used; now they use the Sanborn element 

 together with the Bureau of Standards humidity ele- 

 ments in the circuit shown in Figure 1. 



The sounding procedure used with this instrument 

 consists in letting the balloon go rapidly up to a max- 

 imum altitude chosen so high that moisture and tem- 

 perature variations with height are comparatively slow. 

 The characteristic features of the atmosphei'ic stratifi- 

 cation lie below this level. A rough survey of this 

 stratification is made during the ascent. The instru- 

 ment is then reeled in and is stopped at a number of 

 predetermined levels, long enough to let the elements 

 reach equilibrium with the surrounding air. The levels 

 chosen are spaced at height intervals small enough so 

 that the readings taken reveal the atmosphere struc- 

 ture accui'ately. It has been found that rapid lowering 

 of the sonde Ijctween readings will provide sufficient 

 aeration of the elements to give quite accurate readings 

 even in completely calm weather. 



The balloon sonde of the Navy Eadio and Sound 

 Laboratory uses a dry and a wet Sanborn resistor 

 surrounded by a double-walled aluminum radiation 

 shield. Often wind aeration is found to be sufficient for 

 the wet bulb element, but in calm air the instrument 

 is aerated before readings by giving the cable a series 

 of rapid jerks of about 5-ft amplitude. The ground 

 equipment consists of a to 50 microammeter which 

 can be connected to the dry element, the wet element, 

 and a standard resistor in turn by means of a double- 

 pole triple-throw switch. Voltage is supplied by a dry 

 cell and potentiometer. 



The captive balloon sondes used by Eadiation Labo- 

 ratoi-y* employ dry and wet Sanborn resistors mounted 

 diagonally in a piece of Bakelite tubing surrounded 

 by an aluminum radiation shield. The circuit and am- 



