Downloaded 10/08/21 11:38 PM UTC 402 BULLETIN AMERICAN METEOROLOGICAL SOCIETY on a Metal Plate

BULLETIN of the American Meteorological Society

Assistant Editor Editor Assistant to the Editor THOMAS A. GLEESON WERNER A. BAUM WHEATON M. COWARD, JR. Florida State University Florida State University American Meteorological Society Tallahassee, Florida Tallahassee, Florida Boston 8, Massachusetts

VOL. 39 AUGUST, 1958 No. 8

Meteorological Sounding Systems

THOMAS O. HAIG, MAJOR, TJSAF, AND VINCENT E. LALLY 1

Geophysics Research Directorate, Air Force Cambridge Research Center

(Manuscript received 10 January 1958)

ABSTRACT

A survey is presented of past and present systems for obtaining direct measurements of atmospheric wind, pressure, temperature, and water vapor. Estimates are included of the types of horizontal- and vertical-sounding systems which will be in field use within the next decade.

1. Introduction There are literally hundreds of techniques for In this paper we shall not attempt to cover all obtaining indirect soundings of the atmosphere, the systems for measuring all meteorological pa- ranging from cloud watching (preferably from a rameters. We shall limit ourselves to the classi- reclining position) to wind determination by cal parameters of pressure, temperature, wind measurement of the scintillation of stars. We field, and water vapor, and specifically exclude shall not even attempt to list all the optical, acous- aircraft sounding systems from the discussion to tical, and electromagnetic phenomena which can keep within a reasonable space limitation. be used to obtain atmospheric data, but will attempt only a descriptive presentation of vertical- Meteorological sounding systems may be cate- and horizontal-sounding techniques. gorized in three classes : (1) Vertical-sounding systems where an object is made to ascend over- 2. Vertical-sounding systems head and information is obtained on meteorological The best known vertical sounding that we read conditions essentially in the vertical; (2) hori- of in literature is H. W. Longfellow's friend who zontal-sounding systems where measurements are "shot an arrow into the air, it fell to earth, I knew made of objects moving essentially at constant not where." Can we not surmise that his intent altitudes; and (3) indirect-sounding systems in was to probe the wind field in the upper air and which information is obtained on the pressure, that his difficulties in recovery were due to a temperature, water vapor, and wind fields with- "busted" forecast? The technique is not without out the use of any device or object ascending merit—only recently the U. S. Army announced through or floating in the air. a similar procedure for firing a bullet into the air 1 Now associated with Teledynamics Corp. at an angle so that the spent bullet will fall back

Published monthly at Prince and Lemon Streets, Lancaster, Pa. Entered as second class matter September 24, 1945, at the Post Office at Lancaster, Pa., under the Act of August 24, 1912. Acceptance for mailing at special rate of postage provided for in paragraph (d-2), section 34.40, P. L. and R. of 1948, authorized September 24, 1945. Address all business communications, purchase orders and inquiries regarding the Society to the Executive Sec- retary, 3 Joy Street, Boston 8, Mass. 401

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC 402 BULLETIN AMERICAN METEOROLOGICAL SOCIETY on a metal plate. The angle required to hit the balloons carying observers will explore the middle plate provides a low-altitude ballistic wind. regions, and the modern scientific kites will serve The first meteorological soundings were made to carry self-registering instruments to heights ap- by kite in 1749 in Glasgow with the raising of a proaching two miles [2] thermometer on a kite. In 1752 Franklin per- This forecast verified for about twenty years, formed his electrifying demonstration, but little but by the end of World War I manned balloons beyond the edification of small boys was accom- and kites had given way almost completely to the plished with kites until the invention of the box- airplane sounding with the pilot climbing slowly kite by Hargrove in 1893. These kites were able to 10,000 to 15,000 ft with a meteorograph and to carry meteorographs to heights in excess of returning quickly to the field to provide reasonably 10,000 ft, but several miles of trailing wire created synoptic data. This technique was much superior a considerable safety hazard. To quote Napier to the balloon-carried meteorograph, the record Shaw [ 1 ], "Teisserenc de Bort has some thrilling of which might not be recovered for several experiences about the effect of loose steel wire months. upon locomotives, steamboats, and rowing boats in We have seen how the art of vertical soundings the neighborhood of Paris." progressed from manned balloons to unmanned It was not until the invention of the balloon by balloons and kites equipped with meteorographs Montgolfier in 1783 that the meteorologist had a and, finally, to aircraft equipped with meteoro- useful tool for probing the atmosphere at any graphs. In 1917 the first telemetering of sound- great height. This first conquest of space was ing data was performed, using the kite-wire to hailed with even greater fanfare than Sputnik. transmit the meteorograph signals. It was not The stories of the intrepid pioneers who ascended until 1927 that the first balloon-borne device trans- in balloons to make measurements of temperature mitted signals back from the stratosphere. Such and pressure make wonderful reading. Gay-Lus- devices were named "radiosondes" to distinguish sac, the celebrated French chemist, ascended to them from "balloon-sondes" (French for "sound- 23,000 ft as early as 1804 and made accurate tem- ing balloon"). By 1940 radiosondes had almost perature and pressure measurements as well as completely replaced the aircraft meteorographs measurements of the electric field. He obtained for the daily soundings used for weather fore- air samples with evacuated glass bulbs and verified casting. Pilot-balloons tracked by theodolite still the fact that the composition of the air was uni- provided the only means of obtaining wind data form. above the surface—and still do in many parts of In the 1860's James Glaisher made measure- the world. ments of pressure, temperature, and humidity up During World War II excellent gun-laying to 29,000 ft. Using various hygrometers, the dew radar sets were used to track balloon-borne tar- point was measured as being lower than — 45C. gets, and they provided wind data of unsurpassed Even today we are not making much more ac- accuracy. In 1944 the U. S. Army introduced the curate measurements than Glaisher's data of 100 first "rawinsonde" set, the SCR-658, which pro- years ago. vided temperature, pressure, and humidity data The merits of the manned balloon as a platform which were used to compute altitude. The com- for meteorological measurements were forgotten puted altitude is then combined with azimuth and in the 20th century excitement over aeronautics. elevation data provided by manual direction-find- Only in the last few years has there been a swing ing on the radiosonde transmitter. Our presently back to this most excellent means of making both used system within the United States, the AN/ horizontal and vertical measurements. GMD-1, operates in the same fashion as the During the latter half of the nineteenth century, SCR-658 except that tracking is automatic and oxygen masks were used to increase the height of much more accurate. manned balloon ascents, but no systematic ascents were made on a synoptic basis. Free balloons 3. Radiosonde systems in use throughout the carrying self-registering meteorological instru- world ments without observers came into use in the Vertical soundings are made in over 20 coun- 1890's. In Germany Dr. Asmann sent balloons tries using radiosondes. Unfortunately, few to heights of 60,000 ft carrying meteorographs. countries have equipment which will measure By the turn of the century it was the general con- winds together with the other meteorological ele- clusion "that to the free balloon, meteorologists ments. Pibals are still the only means to obtain must trust for data concerning the highest air; wind data except where radar equipment is used

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC VOL. 39, No. 8, AUGUST, 1958 403 or where directional receivers are coupled with the probably more accurate than our lithium-chloride radiosonde as in the AN/GMD-1 equipment. element. Rather than list the types of systems used through- Tests are now being conducted jointly by all out the world, it will be simpler to consider sepa- United States weather agencies on a carbon hu- rately the elements of the systems: the sensing midity element which has a better response and devices for temperature, pressure, and humidity; superior low-temperature characteristics than lith- methods of data telemetering; methods of compu- ium chloride. It is expected that this element tation; wind measurements; and the balloons. will be standardized for use within the United Information on equipment of other nations is de- States by 1959. Even the carbon element leaves rived from the tests in May 1956 at Payernne, much to be desired, and we must continue to Switzerland, in which fourteen countries com- search for a better element which can be produced pared their radiosondes [3]. at a low cost. Phosphorus-pentoxide elements Temperature measurements.—Bimetallic ele- provide an absolute measure of water vapor since ments are used in the radiosondes of all countries all the moisture passing through a channel is ab- with the exception of Holland and the United sorbed by the phosphorus pentoxide and then hy- States. These elements suffer from long-time drolized by an electric current. The total flow of constant and radiation effects. Poor shielding of current provides an exact measure of the ab- the element can magnify radiation errors. The sorbed water vapor. No suitable airborne ele- temperature element used in the radiosondes of ments have yet been produced. Holland and the United States is a ceramic rod Pressure measurements.—Aneroid elements are (thermistor). In the United States sonde the used as pressure transducers on all radiosondes thermistor is unshielded but is coated with a lead except the new Dutch sonde, which uses a hyp- carbonate pigment. It has a radiation error of less someter. These elements provide acceptable ac- than 0.5C at lower altitudes, but above 80,000 ft curacy from surface pressures to 50 mb. Stand- its accuracy is open to question. In the Payernne ard deviation on most radiosondes at this altitude tests of 1956 the thermistor and the West German is ±1.5 mb. This corresponds to a pressure- bimetallic element showed remarkable correspond- altitude of about 600 ft, which is good enough. ence, but other less efficiently shielded bimetallic At 10 mb, however, 1.5 mb corresponds to 3000 elements measured the warmer temperatures in- ft; therefore, if we concern ourselves with those 1 dicative of radiation errors. The United States per cent of pressure elements which have errors of thermistor exhibited wet-bulb effects after passing 5 mb, we find height errors in our 10-mb surface through a cloud. of 20,000 ft. By a simple extension it is seen that A temperature element which will be immune to a balloon which rises to 5 mb (120,000 ft) and radiation errors and have fast response at high has an aneroid with a 5-mb error can produce an altitudes is a very thin metal wire, but such an outer-space sounding. element has a resistance which is too low and a Since balloons are now regularly reaching temperature coefficient which is far too small for altitudes in excess of 100,000 ft, it is essential that accurate telemetering from a simple radiosonde. more-accurate pressure measurements be em- The ideal element is a rod thermistor which is no ployed above 80,000 ft than those provided by in- more than 0.001 inch in diameter and has a high expensive aneroids. A simple hypsometer (which temperature coefficient. Unfortunately, such an indicates height by the temperature of a boiling element is presently too fragile to fabricate. liquid) can provide measurements with an ac- Humidity measurements.—All nations which curacy of 500 ft of pressure altitude independent employ bimetallic elements for temperature meas- of the actual altitude. The U. S. Air Force is urements use either hair elements or goldbeater's considering the modification of its present radio- skin for humidity measurements. Thus each ele- sondes to provide hypsometer measurements of ment controls the mechanical movement of an arm pressure above 80,000 ft on all flights. and provides compatible inputs to the telemetering An even better technique for simplifying the system. Only the United States presently uses pressure measurement and increasing its accuracy an electrolytic element—a lithium-chloride strip is to eliminate it. This is what is planned for the which provides an improved speed of response radiosonde system now under development by the over the hair and skin elements, although not any U. S. Army Signal Engineering Laboratories for real increase in accuracy. The rolled hair as used Air Force use. The new "remitter-sounding sys- in the West German sonde has a higher speed of tem," the AN/GMD-2, measures range and ele- response than conventional hair elements and is vation angle from which height is computed. The

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC 404 BULLETIN AMERICAN METEOROLOGICAL SOCIETY pressure is then computed from heights and tem- point. The Swiss, Indian, and French radiosondes perature data with a considerable improvement are of this type. in accuracy over either an aneroid or hypsometer There are, of course, other telemetering sys- system. tems possible. Holland has a system in which Data telemetering.—There are three basic meth- three audio oscillators are used to transmit all ele- ods of telemetering radiosonde data which have ments continuously. Such a desirable feature been in use for many years: will undoubtedly appear in future systems of a. Audio modulation or frequency modulation other countries, since it allows temperature and of a carrier by the sensing elements. The ele- humidity measurements to be recorded without in- ments are switched by a clock, a windmill, or a terruption in the lower levels of the atmosphere baroswitch. The data are unscrambled on the where sharp discontinuities are possible which are ground by assignment of frequency bands to the important in the analysis of index of refraction— elements or by identification of the switching se- an increasingly important meteorological parameter. quence. The Belgian, English, and U. S. radiosonde operate in this fashion. The Finnish radio- 4. Computation of pressure-height data sonde uses a variable radio frequency rather than In order to construct contour height charts for a modulation of the carrier with a considerable constant-pressure surfaces, it is the universal prac- saving in weight. tice to compute a mean virtual temperature be- b. Code-type radiosondes in which the sensing tween standard-pressure surfaces and then read elements engage segments of a commutator which from a set of tables the exact value of the height transmit characteristic codes. These codes may difference between levels. With a knowledge of be groupings of dots and dashes which modulate surface conditions, the heights of all desired stand- the carrier and can be identified on the ground. ard surfaces are obtained by addition. This man- The West German, Japanese, and Russian radio- ual method is tedious and requires careful selection sondes are of this type. of the mean temperatures. (An error of 1C in c. Chronometric radiosondes in which the po- temperature data will produce an error of about sition of the sensing element with respect to a 40 ft for a 10,000-ft layer.) reference element is sensed by the time between There have been several computers constructed transmission of a reference point and a sensing to perform the hydrostatic computation manually,

Diagrammatic representation of the AN/GMD-2 sounding system. As shown, input to the zone wind computer is manual.

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC VOL. 39, No. 8, AUGUST, 1958 405 but none have seen field use. The first computer loon capable of lifting a radiosonde to 100,000 ft that may be used is a data computer for the "re- are presently over five times the cost of a fabri- mitter-sounding system," the AN/GMD-2. This cated neoprene balloon of equivalent performance. computer provides a considerable reduction in The plastic balloon shows a marked superiority to complexity by computing only the differences, the neoprene balloon for vertical soundings only "D" values, from the standard atmosphere rather when it is desired to carry heavier loads than ra- than the absolute computation [4]. Even so, it diosonde equipment. is still an expensive device for universal use. What is the altitude limit for vertical-sounding Since the heights of pressure surfaces are valu- balloons? A plastic of the thinnest available ma- able only when collected on a synoptic basis, the terial, % mil, would have to contain a minimum possibility of centralized computation at the analy- of 50,000 sq ft of plastic to carry a radiosonde to sis center should not be overlooked. (The Joint 150,000 ft; thus, the cost of such a balloon would Numerical Weather Prediction Center is even be out of the question for routine use. However, now making hydrostatic checks on radiosonde we now have a 2-lb balloon which reaches 120,000 data on its IBM 704 computer.) Problems of ft on occasion. If we can develop a neoprene bal- rapidly transmitting the required amount of data loon weighing 20 lb which has the same initial to a central computer are not as yet resolved and thickness and the same elasticity as the 2-lb bal- will have to wait for the availability of more effi- loon and if we can make such balloons uniformly, cient communications links than our present tele- then we should be able to reach 150,000 ft con- type circuits. Such links should be available by sistently at a moderate price. 1963 within the United States at least. Wind measurements.—Wind measurements are Meteorological balloons.—Balloon capabilities still taken in most countries by tracking a pilot have shown continuing improvement. Present al- balloon with a theodolite. This method is of little titudes of neoprene balloons costing less than $5.00 are averaging above 80,000 ft. By 1959 these altitudes will average well above 100,000 ft, both day and night, for any agency willing to pay the slight additional cost of newly developed balloons of improved materials and somewhat increased size. Daytime balloons of 2 lb and nighttime balloons of about 3 lb have already been developed and tested which average above 100,000 ft. Plastic balloons have been proposed to replace neoprene balloons for radiosonde flights. How- ever, the cost of materials alone for a plastic bal-

Balloon Set, Meteorological, AN/DMQ-3. This standardized constant-level balloon carrier includes balloon, The control recorded (left) and zone wind computer parachute and safety system, high-frequency transmitter, recently developed as part of the AN/GMD-2 sounding and load harness. It is designed to carry about 100 lb for system. more than 60 hr.

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC 406 BULLETIN AMERICAN METEOROLOGICAL SOCIETY use for modern meteorological purposes beyond been tracked down from as high as 270,000 ft by obtaining gradient winds for surface charts. the U. S. Army. Metallized parachutes have been Systems such as the AN/GMD-1 are used in used instead of chaff to provide a more discrete the United States and Canada where wind data target, and successful wind tracks have been per- are obtained by combining angular measurements formed from heights of 150,000 ft using a para- of a tracking receiver with height information chute. from a pressure element. These systems are ex- Wind data have been acquired by measurement cellent under normal wind conditions. The trigo- of the acoustic propagation of sound waves from nometry of the wind computation is such, how- grenades fired from Aerobee rockets, but the tech- ever, that very serious wind errors are obtained nique is presently too complex for routine use under high wind conditions. Errors can be mini- [6]. It is possible to measure the wind field mized by determining the average winds over from vanes affixed directly to a rocket, but this greater height layers, but there is no way of ob- requires a stable platform within the rocket and taining accurate wind-shear data with this system. telemetering of yaw and pitch data for the rocket. Radar systems are used to track reflecting tar- Such measurements are clearly not amenable to gets by our Coast Guard weather ships, by U. S. synoptic use. Navy ships, and by several nations using com- The measurements of temperature, pressure, mercial or military-surplus radars. A recent and density are more easily made from rockets Navy development is a balloon with metal dipoles than is the wind field. The University of Michi- coated on the inside of the balloon, thereby elimi- gan has had success in such measurements di- nating the need for an external radar target. rectly from the rocket and by measurement of the Such devices are capable of giving excellent wind accelerations on a falling sphere. data, but maximum range is limited to distances The combining of temperature and wind meas- of 30,000 to 120,000 yd depending on the radar. urements on a single rocket for routine use is When we consider that the average winds be- a most formidable problem. Our only simple tween the ground and 40,000 ft can exceed 100 means of obtaining wind data is by tracking a fall- kn under jet stream conditions, even the best of ing object; but if the object released from the the present radars must abandon the target in less rocket is a balloon or parachute with a telemeter- than 40 min—or at approximately the 200 mb ing device to indicate temperature data, the object surface for a balloon rising at 1000 ft per min. will fall too rapidly at high altitudes to provide The AN/GMD-2 Rawinsonde System which adequate wind data. It can be shown that errors will be in general field use by 1960 or 1961 relies in wind data become excessive for any object on a device in the radiosonde which retransmits dropping faster than 15,000 ft per min [5] and it a modulating frequency back to the ground. does not appear feasible at this time to employ any Phase comparison of outgoing and incoming sig- device (except radar chaff) which will fall this nals provides accurate range data. This system is slowly above 200,000 ft. capable of providing not only accurate wind data Future vertical-sounding systems.—It is im- at any wind speed but also fine-scale shear data mediately assumed that future vertical-sounding over altitude intervals of less than 1000 ft. Radio- systems will necessarily be rockets. Proponents sondes have been tracked to distances in excess argue that rockets will give almost instantaneous of 300,000 yd with this system. data to any desired altitude and directly over the Systems similar to the AN/GMD-2 using trans- station. Balloons are slow and awkward and pro- ponder mechanisms are under development in vide data at points which may be over 100 mi England and Switzerland. from the station. We shall concede that rocket systems will be 5. Rocket and projectile sounding systems used for data above 120,000 ft and for special ap- plications such as aboard ship where space limita- The first recorded projectile-sounding system tions preclude use of adequate balloon systems. was tested in England in 1882. Wind currents Such systems are presently being designed, but were studied by track of shell-bursts. A height of it is too early to predict the detailed configurations. 9500 ft was reached with 6-lb shells [7]. Balloon-borne radiosondes will be with us for The U. S. Navy has recently used five-inch guns many, many years for the following reasons: to fire radar chaff to heights of 60,000 ft. The a. No rocket system will compete with a bal- chaff is then tracked back toward the surface by loon system on a cost basis. an accurate radar. The technique has been ex- b. The slow ascent rate of a balloon is a distinct tended to use of the LOKI rocket, and chaff has advantage since it tends to smooth out the smaller

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC VOL. 39, No. 8, AUGUST, 1958 407 scales of turbulence which should not be repre- called an error depends upon one's point of view sented on synoptic charts. and how the "representative" wind is defined. For c. The persistence of streamline patterns in the the most part, upper-air wind-field information is stratosphere is so great that no need exists for used to producc forecasts for 12- to 48-hr periods up-to-the-minute data. Changes in a one-hour and there is good evidence that in this scale the period are not usually significant. error is large [8]. d. The fact that the balloon is at a distance Rawinsonde stations are not, and never can be, from the station for the high levels can be readily evenly distributed throughout the globe. The lo- compensated by the centralized numerical weather cation of an upper-air sounding station is deter- prediction machine. mined more often by economic and political rea- Although it is difficult to hazard a guess as to sons than by meteorological requirements, and the configuration of future rocket sounding de- there are many countries which may never install vices, we can estimate the characteristics of our adequate sounding equipment. But even if the vertical-sounding balloon equipment of ten years ideal distribution were achieved on land there from now based on the inadequacies of present would still be big gaps in the net over the oceans. devices and a forecast of the needs of the future. In 1936 Professors Jean Piccard and John Ack- This system will have balloons which consistently erman tried using constant-level plastic balloons to reach 120,000 ft. The temperature sensor will not fill the gaps in upper-air data [9]. So far as we be radically different from today's thermistor, but have been able to discover, this is the original the humidity element will be completely changed— work in this field. The balloons they used were perhaps to an absolute measuring device such as cellophane bags stuck together with "Scotch" the phosphorus-pentoxide element. The height tapes. They were moderately successful as long and wind data will be obtained by either trans- as the cellophane stayed warm, moist, and flexible, ponder techniques or, possibly, a radar using new and they made flights up to ten hours long. detection techniques which will permit adequate The Japanese balloon-bomb effort of World ranging with modest power. The data will be dig- War II actually started in 1933 and so predated itally encoded, redundency reduced to the desired the above flights, but these early flights were of level, and transmitted on a high-speed pipeline to paper balloons designed to carry a bomb about the weather central where computation of standard 60 mi after being launched from a submarine. pressure levels will be accomplished. War conditions, however, made it necessary to employ an alternative whereby balloons could be 6. Horizontal-sounding systems flown over longer distances. The Japanese scien- The present vertical-sounding equipment is very tists did a remarkable job in developing and produc- good as compared to other telemetering systems. ing the world's first long-range, unmanned bombing It does an adequate job of measuring part of system in less than two years. Their balloons were what we would like to know about the atmosphere, mostly made of treated paper 33 ft in diameter, but there is a limit to the refinements of ground with an automatic ballast-dropping control to and flight equipments which can be economically maintain altitude between 33,000 and 37,000 ft. justified. In addition to this arbitrary limit, there They launched 9300 balloons between November are two characteristics of vertical-sounding sys- 1944 and April 1945, and their success rate was tems which amount to serious inherent limitations. a little better than the ten per cent they expected. The air motion at any level can be described as a Because the balloon armament was poor, very summation of eddy motions of various scales and little damage resulted to the United States; thus, a large-scale "representative" wind. A balloon the Fugo balloon-bomb fortunately was not ef- responds to the total wind, but the measurement fective as a weapon, but it certainly illustrated the that is wanted is the representative wind at any capabilities of constant level balloons. particular level. If a balloon stays at one level Throughout the world, and especially in the long enough, its displacement will describe the United States, meteorologists recognized the pos- representative wind because the smaller-scale ed- sibilities of a balloon that can float for days carry- dies or turbulences will average out to a very small ing a sizeable payload, and they began using them. part of the total. On the other hand, a rising bal- The University of Minnesota and New York loon will be exposed to the total wind at one level University ran programs for the Air Force and for only a brief period, and the turbulence compo- the Navy, and both services organized their own nent of its displacement will be a much larger part units to develop and fly the big plastic bags. of the total. Projects "Moby Dick" and "Transosonde" have been the largest efforts to date. Of course the extent to which the effect can be

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC 408 BULLETIN AMERICAN METEOROLOGICAL SOCIETY

All of the constant-level meteorological flights possible to measure air temperature, lapse rate, have been made using almost identical equipment, humidity, and wind shear and other parameters so we will describe these in general rather than from these balloons, only a few flights so in- for a specific program. The balloons are made of strumented have actually been made and the qual- strips of thin polyethylene film, heat-sealed to- ity of such measurements is not known. The gether to form a plastic bag with an open bottom. most complete analysis of the value of constant- The film that is used is practically identical, even level balloon data to appear so far is the paper by in thickness, to that used for super-market car- Morris Neiburger and James Angell in the April rot bags. When launched, the balloons are only 1956 issue of the Journal of Meteorology [10]. partly filled with gas. As they ascend, the gas Perhaps it is wrong to talk about "'horizontal- expands to fill the bag and the excess gas which sounding systems" because this implies an or- gave the balloon free lift is expelled from the open ganized and equipped operational program, and, bottom. This exhaust port is usually closed then strictly speaking, none exists. The "Moby Dick" to decrease loss of lift by diffusive mixing of lift- and "Transosonde" capabilities are not sufficient ing gas and outside air. These balloons have a to meet the minimum requirements for daily syn- ceiling height above which they cannot rise, unlike optic use. This type of balloon system is too ex- a rubber balloon that keeps on rising until it bursts. pensive and cannot be flown at altitudes normally The balloon will stay at its ceiling until it loses used by aircraft. Horizontal sounding is still a lift by gas diffusion or leakage or until the gas research effort, but we have learned enough to cools and contracts. When it starts to come down, know it is a good technique and can describe, as it will continue to the ground unless more lifting follows, the major characteristics of an operational gas is put into the balloon, or the gas is heated, system: or the total weight of the balloon and load is re- 1. A horizontal-sounding system cannot reduced to match its lift. This problem has almost place vertical soundings. It is just as improper to always been solved by throwing out ballast of attempt to determine vertical distribution from liquid or fine metal particles or sand. Very small a system which senses and integrates horizontally iron shot is usually used now because it can be as it is to attempt to describe horizontal flow from controlled easily by a simple magnetic valve. vertical soundings. Temperature and humidity The valve is operated by a pressure switch actu- should continue to be measured by radiosonde, ated by an aneroid capsule so that the flight of but at most stations it should be possible to elimi- these balloons is approximately on a constant- nate vertical wind soundings. pressure surface. 2. The cost of the horizontal wind sounding A typical balloon might be 40 ft in diameter, must be competitive with vertical sounding. Ac- flying at a pressure altitude of 300 mb, with a total tually it appears possible to reduce costs and in- gross weight of about 680 lb. The balloon weighs crease data quality with a suitable constant-level about 80 lb, and the rest is divided between fixed system. pay load and ballast. The system will expend 3. It must measure wind fields in three dimen- nearly 20 per cent of its gross weight every 24 sions and with sufficient resolution in time and hr to remain aloft. If the payload weighs 200 lb, space to describe weather systems in all states then the 400 lb of ballast will give an average of development. flight duration of 92 hr. It is interesting to note 4. It must be free of national or regional limi- that, while these figures resemble those of the tations, whether political or geographical in Japanese Fugo balloon, the success rate of the nature. Transosonde type balloon is five to seven times 5. It must not constitute a hazard to any air- higher. craft operations. Wind information is derived from the plotted We think that a system to meet these require- trajectory of the balloon flight, the trajectory be- ments will have the following characteristics: ing obtained by periodically determining the posi- 1. The vehicle will be a sealed, slightly over- tion of the balloon. Most position information inflated spherical balloon made of extremely thin, comes from radio-direction-finding stations of strong, plastic film. The balloon will rise until it the Navy, Air Force, Civil Aeronautics Authority is in equilibrium in the atmosphere, and there and Federal Communications Commission. Posi- it will have an internal pressure of about 110 per tion accuracy varies with distance from tracking cent of ambient. Because it is super-pressured, a stations and communications conditions, but is change in temperature will cause only a change in usually within a 10-mi-rad circle. While it seems pressure while the density of the balloon remains

Unauthenticated | Downloaded 10/08/21 11:38 PM UTC VOL. 39, No. 8, AUGUST, 1958 409 the same. The balloon will stay at a constant- and also tends to supply the greatest amount of density level without any ballast requirement so data in areas of bad weather. long as it remains super-pressured. Laboratory This system provides six times the time density tests with mylar films indicate an average balloon and four times the spacial density of our present life of 60 to 90 days is reasonable. system in addition to filling gaps over oceans and 2. The balloon film is very thin and frangible land masses which have inadequate coverage. upon impact. Regardless of speed or type of air- While we know it will improve our ability to fore- craft, no damage will result from collision with cast weather, this system will give entirely new the balloon. All electronic and other instrumenta- data which will lead to advances in techniques tion is distributed over the balloon surface. Evap- which we cannot now foresee. orated metallic films replace wires, transistors the Those working on the program call it size of grains of sand replace tubes, solar batteries "GHOST," short for Global Horizontal Sound- of paper-thin silicon replace chemical batteries, ing Technique, not only to emphasize the pervasive etc. The whole balloon will present no more scope of the concept but to remind themselves serious hazard to aircraft than a cloud of gnats. that these balloons, which will fly in the airlanes, 3. These balloons will be manufactured and must be as evanescent as a ghost if struck. launched from three or four sites under United When the Commission on Aerology of the Nations auspices. They will float at 700-, 500-, World Meteorological Organization met in Paris 300-, 200-, 100-, 50- and 10-mb levels and be in June 1957, the American delegate discussed spaced about 375 mi apart at each level. To horizontal sounding and invited all nations to cover the Northern Hemisphere from 30 to 70 deg contribute to a program to develop a system as N lat, about 30 balloons need to be launched each outlined above. The Commission responded with day. They will report identity, temperature, and a strong indorsement and passed Draft Recom- position every two hours through an automatic mendation A-ll (CAe-II/Doc. 79-E, Annex II). ground communications network directly to com- This paper recommends ". . . that research in the puters of the Numerical Weather Predictions creation and development of horizontal-sounding Unit and other similar forecasting centers in techniques be encouraged. . . While the oc- Europe and Asia. No manual data handling or casional sighting of an artificial satellite may re- reduction will be required. mind the world of the power of a nation, the con- The balloons will tend to clump together in stant presence of thousands of airborne spheres areas of convergence and spread out in regions of can be a daily reminder of the strength of an in-' horizontal divergence. This is an ever changing ternational body dedicated to the welfare of the pattern, however, and over a long period the de- whole world. I'O r r lsi sired average spacing will be maintained. This REFERENCES clumping is actually an advantage because it dis- < . 1. Shaw, N., 1942: Manual of meteorology, VoL. "I> plays the horizontal-divergence field at a glance London, Cambridge Univ. Press, 229. . 2. Alexander, J., 1902: Conquest of the air. New York, A. Wessels Co., 121. 3. U. S. Army, Signal Corps Engineering Laboratories, 1957: International radiosonde comparison tests: Tech. Memo. No. M-1907. 4. Lally, V. E., 1954: Use of anomalies in the design!1 of a hydrostatic computer. Bull. Amer. meteor•.> Soc., 35, 478-480. 5. , and R. Leviton, 1957: Accuracy of wind determination from the track of a falling object. AF Surveys in Geophys., No. 93. 6. Weissner, A. G., 1954: Rocket exploration of the upper atmosphere. London, Pergamon Press Ltd., 133-143. 7. Royal Society, 1882: Report of the meteorological council to the Royal Society. London, 23. 8. Air Weather Service, 1956: Constant-pressure trajectories. AWS Manual 105-47. 9. Akerman, J. D., and J. F. Piccard, 1937: Upper air study by means of balloons and radio meteorograph. Artist's conception of the GHOST vehicle showing /. aero. Sci., 4, 332-337. 10. Neiburger, M., and J. F. Angell, 1956: Meteorological solar cells and electronic circuitry applied to the surface application of constant-pressure balloon trajectories. of the balloon. /. Meteor., 13, 166-194.

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