JOURNAL OF RESEARCH of the National Bureau of Standards-D. Radio Propagation Vol. 6SD. No.2, March- April 1961

Radio-Wave Propagation in the Earth1s Crusf'2 Harold A. Wheeler

(F ebruary 26, 1960)

There is a reasonable basis for post ulating t he existence of a useful waveguide deep in the earth's crust, of t he order of 2 t o 20 km below the surface. Its di electr ic is basem ent I'Oc], of very low conductivity. Its upper boundary is formed by the conductive layers ncar the surface. Its lower boundary is formed by a high-temperature condu ctive layer far below the surface, termed the "thermal ionosphere" by analogy to the well-known "radiation ionosphere" far above the surface.

The electrical conductivity of th e basem.ent rock has not been explored. An example based on reasonable estimates indicates that transmission at 1.5 kc/s might be possible for a distance of the order of 1500 km.

This waveguide is located under land and sea over t he entire surface of th e earth. It may be useful for radio transmission from t he shore to a submarine on the fl oor of t he ocean. The sending antenna might be a long conductor in a dri ll hole deep in the basement rock ; the receivi ng antenna might be a vertical loop in t he water .

In Lhe earth 's crust, there appears to be a deep waveguicleLhat has not yet been explored. This waveguide extends under all the surface area, so it suggests the possibility of wave propagation under the ocean floor. This might enable communication from land to a submarine located on or neal' the ocean floor. If below a certain depLh , j t happens that the excess radio noise from electric storms would become weaker than thermal noise, and no otber so urce of appreciable radio noise is recognized.

This waveguide comprises basemen t rock as a dielectrie between upper and lower conductive boundaries. The upper boundary is formed of the well-known geological straLa lo cated between the surface and the basement rock , with conduetivity provided by electrolytic solutions and semiconductive minerals. The lower boundary is provided by high­temperature conductivity in the basement rock.

In concept, Lhe lower boundary is similar to Lhe usual ionosphere , bein g formed by gradually increas­ing condu ctivity. In the usual ionosphere [Wait, 1957], caused by extratenestl'ial radiation, tbe con­ductivity increases with height. In the present case, however, the conduetivity increases with deptb and is caused by the increasing temperature in the dielectric material. Therefore it may be designated as the "inverted ionosphere" or "thermal iono­sphere."

Figure 1 shows how this waveguide may be used for eommunication from a shore sending station (8) to an underwater receiving station (R). The latter may be a submarine on the bottom of the ocean. The sender launches a vertically polarized tl'ansverse­electro-magnetic (TEM) wave by means of a vertical wire projecting into the basement rock. The wave is propagated in the deep waveguide between the surface conductor and the thermal ionosphere. Some power from the wave leaks out of the wave-

I Contribution from '~'heeler Laboratories, Great Neck, N.Y., and Develop­mental Engineerin~ Co rp., Leesburg, Va.

, Paper presented at Conference on tbe Propagation of ELF Radio Waves, Boulder, Colo ., January 27, 1960.

S

--::-~_:.-:J?C: __ ~ I --_ R OCEAN

--- - _ 0 -- -.;;;- --------- - ---- -

WAVEGUIDE

THERMAL IONOSPHERE

FIGURE 1. Communicati on tlwough the deep waveguide under the ocean.

guide into the ocean ju t above, and is sampled by an antenna at the receiver.

Figure 2 shows an arrangement for the sender antenna. It is a long conductor (pipe) sunk into a drill hole flIl ed with oil insulaLion. The example shown has conducting material down to a depth of about 1 km. Thl'ough this layer of earth, there is an outer pipe which forms the outcr conductor of a coaxial tran mission line. This pipe is in contact with a conducting surface slleh as water or radial wires in the ground. Below this layer of earth, the inner conductor extends further about 2 km into the basement-rock dielectric. This extension radiates into the waveguide in the usual manner.

S

WATER

~"~"'~ ~ : 1

189

WAVEGUIDE : ( TEM MODE ) :

I I I I I I , I I I

L_ -'

2 km

FIG U RE 2. Sender antenna in the deep waveguide.

o o

E u 0

-'"

10 200

I "-f- ::;;: "- w W f-0

20 400

x x 0 0 0:: 0:: "- "-"- "-<l <l

30 600

- 12

(J", CON DUCTIVITY (mhos/m)

log 10 IT

-6

UPPER BOUNDARY

o

~ ~ DIELECTRIC

k'6 CONDUCTOR

(TEM WAVE)

ELECTRI C

FIGURE 3. 11ariation of conductirity with depth to form the deep waveguide.

Figure 3 shows how tll e temperature and th e resulting conductivity may vary with depth, espe­cially in the basement rock at depths exceeding a few kilometers. This diagram will b e used to explain the expected behavior of the deep waveguide. At depths of about 2 to 20 km, the basement rock is indicated to have su ch low conductivity that i t is a dielectric suitable for wave propagation. Above and below this dielectric, the conductivity is high eno ugh to serve the function of boundaries for th e waveguide.

The upper boundary is fairly weU defined, in a depth of the order of 1 km (perhaps down to several kilometers). Its conductivity, in the most common materials, ranges from a maximum of 4 mhos/m in sea water down to about 10- 4 in rather dry nonco n-ductive minerals. .

Tbe dielectric layer , shown between depths of abo ut 2 and 20 km, may have very low conductivity, of the order of 10- 6 to 10- 11 mho/m. The lowest conductivity is observed in fu sed quartz , but prob­ably is not found in nature. The present plan is useful if the conductivity is around 10- 8 or lower. The dielectric constant is about 6.

The lower boundary has some unusual properties. (These are also characteristic of the ionosphere at frequ encies below VLF.) The gradual increase of conductivity [Van Hippel, 1954] provides an effective boundary Jor each kind of field, that for the electric field being closer than that for the magnetic field. In each case, there is a sort of skin depth in the boundary [Wl1eeler, 1952]. Both of these boundaries make comparable contribu tions to tbe total dissipa­tion factor of the waveguid e, which determines the exponenti al attenuation rate.

The locatioll ot each boundary depends on the frequency, t he conductivit)T, and the rate of change of conductivi ty with depth. In th e example to be outlined, these boundaries occur at temperatures in the range of 300 to 600 °C.

As an example of the behavior that might be expected in this waveguide , the following numerical values arc suggested.

190

Frequ ency Dielectric constan t Wavelength (in dielectric) Efl'ective boundari es of E fi eld (depths) Effective boundari es of M fi eld (depths) S ki n depth for E fi eld (lower boundary) Skin depth for JIll field (lowe r boundary) L ength of radiator (ill waveguide) R eactance of radiator

Effective length of rad ia tor Radiation resistance (in wav eg uide) Ot her r esista ncc Radiation efficiencv A verage power fadm' of E and JIll fields, about Napier distance (for wav e atten uation) D ecibel distance (for wave attenuation) 100- db distance

1.5 kc/s 6 80 km 1- 18 km 1- 27 km 1.5km 4km 2km 1600

ohms 1 km 0.4 ohms 20 ohms 0.02 0.1 130 kill 15 km 1500 km

If these values are to be experienced , communica­tion ranges of the order of 1500 km will be possible under the surface of the earth .

The assumptions for this example are based on preliminary estimates of the best cond itions that are at all likely to be realized. The high-temperature conductivity needed for the lower boundary is typical of quartz and other similar minerals. The extrem ely low conductivity at lower temperatures is unlikel.Y, but need not be quite so low to provide a dielectric that could give the indicated performance.

As for the properties of the basement rock, it is very doubtful how low its conductivity may be. Its seismic properties are explored but not its electrical condu ctivity. Its principal chemical com­ponents are known, but apparently not its small content of " impurities" that may determine the conductivity. It seems that core samples have been made to only a sm.all depth (less th an 1 km) in the basement rock, presumably because there has been little prospect of valuable mineral products at a reasonable cost. It is notable that some tests show a trend toward lower conductivity (below 10- 6) in the transition from the surface layers in to the base­men t rock. A con tinuation of this trend may enable such performance as is indicated in the example.

Returning to the waveguide properties, the TEM mode (with vertical polarization) is t he one that has the greatest probabilit.v of enabling long-range communication . It is the only propagating mode at frequencies below abo ut 2 kc/s (i ncluding the above example) .

This preliminary study has indicated that the deep waveguide is probably a definite physical phenomenon. The properties of its dielectric and boundaries are not known quantitatively, so it is uncertain to what distances this waveguide may be useful for communication or related purposes. Some rather optimistic assumptions as to these properties

lead o ne to s pe(;uhtc 0 11 di sLnllccs of Lite order of 1500 kill . 'vVhile Lh c d eep wavcguid e exLend s under th e cn t il'c s urfacc o f la nd and sea, i t is most n eed ed for md io Lr,U1 SJlli ssion to a subm arill e on t ilC ocean floor , b ccfw se t his locat ioll is s bielded from the usual radio \Y ,lyeS above th e surfac C' .

Thi s con cep t occurred to tb e wri t er r ecen tly d uring di sc Ll ssions with L ester H . Carr a nd his assoc iates in D evelopmental Engineering Corpora­tion, Il ot" bly L . E. R a wls, G . F . L eidorf, and t heir geologic'Ll consultant , P . P arker. The opportunity

of workill g with this group is acknowledged wi Lh apprecia tion.

References

Von ] I ippel , A. It ., Dielectric mate rials and ap p lica t iolls. F used q ua rtz at high te mperatures, p . 403 (John Wiley & So ns, New Yo rk, J'\ .Y ., 1954).

' Vait, J . R ., Th e mode t heo ry o f VLF ionosphere propagation fo r fini te groulld co nducLiviLy, Pl'oc. IRE 45, 760- 767 (Jun e 1957).

Wh eeler, E . A., Uni versa l sk in-cffect chart for condu cting materials, E lectro ni cs 25, No. 11 , 152- 4 (?\fov. 1952). (In cluding land a nd sea.)

(P ap er 65D2- 119)

191

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JOURNA L OF RESEARCH of the National Bureau of Standards-D. Radio Propagation Vol. 65D, No.2, March- April 1961

Publications of the National Bureau of Standards*

Selected Abstracts

Use of the incoherent scatte r techniqu e to obtain ionosph eric te mpera tures, T. E. Van Zandt and K. L. Bowles, J . Geophys. Research 65, No.9, 2627-2628 (S ep t. 1960). If t he ion-electron gas is in di ff usive equilibrium on t he top­side of t he F layer, t hen the electron density decreases exponent ially wit h heigh t, and its logarithmic dec rement is proportio nal to the neutral gas t emperature. From an electron density p rofile obta ined by the scatter radar tech­niq ue, it is shown that t ll is in terpretation is co nsistent. Moreover , t he ded uction of ionosphe ric temperatures in t his way from scatter radar electron density profiles has several advantages over other methods.

Corre la tion of a n auroral arc a nd a sub vis ible monochrom atic 6300 A Arc with ou ter- zon e radi a tion on Nove mber 28, 1959, B. J . O'B ri en, J. A. VanAll en, F . E. R oac h, and C. W. GarU ei n, J . Geophys. R esearch 65, No . 9, 2759- 2766 (S epl. 1960) . Dur ing a severe geomagnetic storm on Nove mber 28, 1959, two Geiger t ubes on satelli te Explorer VII (1959 iota) fou nd anomalies in the oute1: radiat ion zone at an a lt itude of about 1000 km whi ch appear to be correlatcd in space and t imc wit h optical emiss ions from t he atmosphere beneath. Very intense narrow zo nes of radiation were detected over a v isib le aurora during o ll e p ass. The rad i'l.tion in t lu-ee such zo nes was h arder t oward low latit udes. On t hree subsequent p asses t he rad iation zo ne was deduced to be over a subvisib le 6300 A arc, whose bri ghtness diminished as the radi ation zones became less intense. The correlation is discussed.

Sea sona l varia tion s in the twiligh t enhance me nt of [OT] 5577, L. ll. M egill , P. M. J amnick, a nd J . E. Cru z, J . Atmosphe1·ic and T en·est. Phys. 18, No . 4, 309- 314 (Aug. 1960). Meas urements of t he t wi light en han ce ment of [01] 5577 were obtained dur ing t he p eriod September 1957 to Dece mber 1958 at Rapid City, S.D. All these measurements wer e normali zed to t he intens ity at sun set or sunrise at a heigh t of 100 km . The res ults obtained indi cate t h at t here was a seaso na l dependen ce of t he twi light enhancement of [01] 5577 emission . The enhance ment occurred most freq uently in the a ut umn a nd winter m on t hs, t he max imum occurrin g about 1 November. The enha nceme nt alm ost never OCC UlTed during t he sp rin g a nd summ er months.

Some mag netoionic phenomena of th e Ar ctic E -region, J . W. Wright, J . A.l11lospheric and 'l'en·est. Phys. 18, No.4, 276-289 (A ng. 1960). Sever al unusual phenomena of E -region ionogram echoes obtained at Thule, Greenlaud (mag. d ip 85.5 °) are described. They ar e exp la ined as t he effects of electr on collisions on the propagat ion of radio waves at h igh-magnetic latit udes. The third magnetoionic compone nt (Z-echo) is expla ined in t his way a nd several of i ts d istin guishi ng features are explained a nd illustrated . New phe nomena demonstrate t he existence of a ll E-pause (vall ey a bo ve hm .. E), and permit t he measure­ment of electron densit ies and collision frequencies therein.

Wid ely separated clocks with microsecond synchronization and ind epende nt di stribution systems, T. L. D avis and R . H. Doher ty, IR E Wescon Conv. R ecord 4, pt. 5, 3-17 (1960). In a major ity of t iming applications, a problem exist s in setting two or more clocks to agree with one another . Presen t techniq ues using \VWV or ot her high frequency broadcasts all ow clocks to be sy nchronized within one mill isecond. This paper offers an i mprovement in synchroni­zat ion of t hree orders of mag nit ude.

Mi cro~econ d sy nchronizati on is obtained by use of nhe Loran- C navigation syste m as the link betwee n a m aster clock at Bou lder , Colorado, a nd any s laved clock any where in t he Loran-C service area. T he t iming syste m a lso includes a un iqu e method for distribu­t ion of several t ime code form ats 0 11 a single UHF channel.

Comment on m odels of the ionosphere a bo ve h m ax F" J . W. Wright, J . Geophys. R esearch 65 , No.9, 2595- 2596 (Sept. 1960). Evidence for a grad ient of scale height in t he F r egion is shown , a nd discussed in relat ion to a simp le Chapman model of t he P r egion a bove hm ax F ,. It is suggest ed t hat a simi lar model, but a ll owing for a scale-heigh t gr ad ient, may give somewhat bette r agree ment 1\"ith recent obser vations.

I mprove ments in radio propagatio n prediction servi ce, 'vV. B. C hadw ick , Elec. Eng. 79, 721- 724 (Se pt . 1960). Data from world-w ide ionospheric a nd solar stations per mit close observatio n of t he changin g state of t he iOll osphere so t hat t he maximum usable frequen cy for radio co mmunications between a ny two points in t he world can be accurately predicted 3 months in advance.

Other NBS Publications

Journ a l of Research, Vol 65A, No.1 , J a nuary- Fe bruary 1961. 70 ce nts.

Faint lines in the arc spec trum of iron (F e I). C. C. Kiess, V. C. Rubin , a nd C. E. Moore.

Infrared a bsorpt ion of spectra of so me l-aceta mido pyra noid deri vatives a nd red ucin g, acety lated pyranose~. R . Stuart Tipso n and H . S. I sbell .

Monolayers of linear saturated s uccinate p olyester and a ir­li q uid in terfaces. 'vV . M . Lee, J . Leon Shercshefsky, a nd R. ll. Stromberg.

H eat of formation of beryllium chl oride. 'vY. H . Johnson a nd A. A. Gilliland .

H eat of deco mposit ion of potass ium perchlorate. 'vV. H. Johnso n and A. A. Gillil and .

H eats of formation of lit hium perchlorate, a mmonium perchlorate, and sodium perchlorate. A. A . G ill iland and W. H . Johnson.

H eat of formation of N -dim ethy la minodiborane. W. H. Johnson , I. J affe, and E. J . Prose n.

Sep aration of hafnium from zirconium by a nion excha nge. J . L. Hague a nd L . A. Machla11.

Reaction of sulfur , hy drogen sulfide, a nd accelerators with propylene and butadiene. F. J . L innig, ]I;. J . Parks, a nd L. A. Wall.

Journ al of Research , Vol. 65C, No.1, January- M arch 1961. 75 cents.

E lectronic scanning microscope for a spectrographic plate comparator. M. L. Kuder.

Viscoelastometer for measurement of flow and elastic recovery. R . J . Overbe rg and H. Leaderman.

An ultra low frequency bridge for di electric m eas urements . D. J. Scheiber.

The ephi system for VLF direction-finding . G. H efley, R. F. Linfield, and T. L. D avis .

F ast counting of alp ha particles in air ion ization cha mbers. Z. Bay, F. D. McLernon, a nd P . A. N ewm a n.

193

X-ray diffract ion measurement of intragranular misorientation ill alpha brass subj ected to reverse plastic strain. C. J. Newton and H. C. Vachcr.

Enthalpy and specifi c heat of ninc corrosion-resistant alloys a t high tem peratures. T. B. Douglas and A. C. Victor.

D et ermination of minor constit uents in low-alloy steels by X-ray fiuorescence. R . E. Michaelis, R. Alvarez, and B. A. Kilday .

Stand ard X-my diffraction powder patterns, H . E. Swanson, M . 1. Coo k, E. H. E vans, and J. H. deGroo t . NBS Circ. 539, Vol. 10 (1960) 40 cents.

Heat t reatment and properties of iron and s tee l, T. G. Digges an d S. J. Rosenberg. NBS Mono . 18 (1960) 35 cents. (S u persedes C495).

Specific heat and enthalpies of technical solids at low temper­atures. A compi lation from the literature, R . J. Corruccini and J . J. Gniewek. NBS Mono. 21 (1960) 20 cents.

The metric syste m of measurement, NBS Misc. Pub!. 232 (1 960) 50 cents.

Household weights and measures. NBS Misc. Publ. 234 (1960) (Supersedes M39) 5 cents.

Screw-thread standards for federal se rvices, 1957. Amends in part H28 (1944) (and in parts its 1959 Supplement). NBS Handb. H28 (1957) Part III (1960) 60 cents.

Quarterly rad io noise data- June, July, August 1959, W. Q. Crichlow, R. D. Disney, and M. A. Jenkins. NBS TN18- 3 (PBI51377- 3) (1960) $1.00.

Quarterly radio noise data- September, October, N ovember 1959, W . Q. Crichlow, R. D. Disney, and M. A. Jenkins . NBS TN18- 4 (PB151377- 4) (1960) $1.50.

Investigation of bearing creep of two forged aluminum alloys, L. Mordfin, N. Halsey, P. J. Granum. NBS TN55 (PB161556) (1960) $1.00.

Rapid determination of the order of chemical reactions from time-radio tables, J . H. F lynn. NBS TN62 (PB161563) (1960) 75 cents.

Radio refractometry, J. W. H erbstreit. NBS TN66 (PB-161567) (1960) 50 cents.

Transistorized building blocks for data instrumentation, J. A. Cunn ingham and R. L. Hill. NBS TN68 (PB161569) (1960) $2.00.

Low- and very low-radiofrequency model ionosphere reflec­tion coefficients, J. R. Johler, L. C. Walters, J . D. Harpen, Jr. NBS TN69 (PBI61570) (1960) $2.00.

Calibration of five gamma-emitting nuclides for emission rate, J. M. R. Hutchinson. NBS TN71 (PB161572) (1960) 75 cents.

Table of magnitude of reflection coefficient versus return loss

(LR = 20 log 10 1!1} R. W . Beatty and W. J . Anson. NBS

TN72 (PB161573) (1960) $1.25. VHF and UHF power generators for RF instrumentation ,

A. H. Morgan and P. A. Hudson. NBS TN77 (PBI61578) (1960) 75 cents.

Halobenzenes as sensitizers for the radiation-induced poly­merization of styrene, D. W. Brown and L. A. Wall, J . Polymer Sci, 44, 325 (June 1960).

Some aspects of fluorine flame spectroscopy, D. E. Mann. Proc. Propellant Thermodynamics and Handling ConI. Special Rept . 12 (Ohio State University, Columbus, Ohio, June 1960) .

Optical constants of aluminum, H. Mendlowitz. Proc. Phys. Soc. (London, England) LXXV, 664 (1960) .

Current t hermodynamic research on light- element compounds at the national bureau of standards, T . B. Douglas . Proc. Propellant Thermodynamics and Handling Conf. Special R ept. 12 (Ohio State University, Columbus, Ohio, June 1960).

Free radical s in gamma, irradiated polystyrenes, R . E. Florin, L. A. Wall, and D. 'V. Brown, Trans, Faraday Soc. 56, No. 453, 1304- 1310 (Sept. 1960).

Sealed-off Hg198 atomic-beam light source, R . L. Barger and K. G. Kessler. J . Opt. Soc. Am. 50, No.7, 651 (July 1960).

T emperature dependence of Young's modulus of vitreous germania and silica, S. Spinner and G. W . Cleek. J. Appl. Phys. 31, No.8, 1407 (1960).

Atomic clocks for space experiments, P. L . Bender, Astro­nautics p . 69 (Jul y 1960).

Photolysis of ammonia in a solid matrix at low temperatures, O. Schnepp a nd 1(. Dressler. J . Chem. Phys. 32, No.6, 1682 (June 1960) .

Photochemical rates in the eq uato ri al F2 region from the 1958 eclipse, T . E. Van Zandt, R. B. Norton, and G. H. Stone­hocker, J . Geophys. R esearch (j5, No. 7, 2003 (July 1960) .

Influence of source distances on the impedance characteristics of ELF radio wa\' es, J . R . Wait, Proc. IRE 48, No.7, 1338 (J uly 1960).

Electroless plated contacts to silicon carbide, R . L. Raybold. R ev. Sci. Instr. 31, No.7, 781 (July 1960).

Statistical models for component agin g experiments, J . R . Rosenblatt . Inte rn. Conv. Record . Inst . Radio Engrs. 8, Pt. 6, l15 (1960) .

Isotope effect in th e hydrogen atom-formaldehyde reaction, J. R. M cN esby, M . D. Scheer, a nd R . Klein, J . Chem. Phys. 32, No.6, 1814 (Jun e 1960).

Electric current and fluid spin created by the passage of a magnetosonic wave, R. P. Kanawal and C. Truesdell, Arch. Rational Yrach. and Analysis, 5, No. 5, 432, (1960).

The nature of the i norganic phase in calcified tissues, A. S. Posner. Calcification in Biological Systems, p. 373 (American Assoc. Advancement of Sci., Washington, D.C., 1960) .

Effect of water-reducing a dmixtures and set-retarding ad­mixtures on properties of concrete, Introduction and Sum­mary, B. E. Foster. Am. Soc. T esting Materials Spec. T ech . Publ. 266, Introduction 1 & 2 and Summary 240 (J une 1960).

Absorption spectra of solid methane, ammonia, and ice in the vacuum ul traviolet, K. Dressler and O. Schnepp, J . Chem. Phys. 33, No . 1, 270 (July 1960).

The extent of H II regions, S. R. Pottasch, Astrophys. J. 132, No.1, 269 (Jul y 1960).

Nickel oxide thin film resistors for low pressure shock wave detection, Ie E. McCullon. R ev. Sci . Instr. 31, No.7, 780 (July 1960).

Casimir coefficients and minimum entropy production , R. E. Nettleton, J. Chern. Phys. 33, No . 1, 237 (July 1960).

Variations of surface tension calculated wi th improved approximation for activ ity coefficient, L. C. Shepley and A. B. Bestul. J . Am. Ceram. Soc. 43, No.7, 386 (Ju ly 1960).

Council adopts F. D. 1. specification for alloy for dental amalgam, Council on Dental Research, J . Am. Dental Assoc. 60, No.6, 773 (June 1960).

The foundations of mechanics and thermodynamics, E . A. Kearsley and M. S. Green, Phys. Today 13, No . 7, 22 (July 1960).

Optical m ethods for negativ e ion studies, S. J. Smith and L. \1. Branscomb, R ev. Sci. Instr. 31, No.7, 733 (July 1960).

On the theory of the slow-tail portion of atmosp heric wave­forms, J. R. Wait, J . Geophys. Research (i5, No.7, 1939 (July 1960) .

Statistical aspects of the cement testing program, "V. J. Youden. Am. Soc. T esting Materials Proc 59,1120 (1959).

Optical transmissivity and characteristic energy losses, H. Mendlowitz, J. Opt. Soc. Am. 50, No.7, 739 (July 1960) .

Pyrolysis of polyolefins, L. A. "Vall and S. Straus, J . Polymer Sci. 440, 313 (Jun e 1960).

A barium fluorid e film hygrometer element, F . E. Jon es, and A. Wexle r, J . Geophys. Research 65, No.7, 2087 (July 1960).

Low-encrgy photoproduction of neutral mesons from complex nuclei, R. A. Schr'ack, S. Penner, and J. E. Leiss, II Nuovo Cimento 16, Serie X , 759 (March 1960).

Adsorption spectra of solid xenon, krypton, and argon in the vacuum ultraviolet, O. Schnepp and K. Dressler, J. Chem. Phys. 33, No .1 , 49 (July 1960).

Radiation pattern s of finite-size corner-reflector antennas, A. C. ViTilso n, H . V. Cottony, IRE Trans, Ant. Prop. AP-8, No.2, 144 (Ma r. 1960).

Structure of sulfurous esters, H. Finegold, Proc. Chem. Soc. (London) 283 (Aug. 1960) .

VLF attenuation for east-west and west-east daytime propa­gation using atm~spherics. ViT. L. Taylor, J. Geophys . Rese'l rch 65, No. 7, 1933 (July 1960).

194

Mecha ni zed co nversion of colorim eLri e d,ILa to munsell l'enotations, W. Rheinboldt and J. P. Y enard. J . Opt. Soc. Am . 50, N o. ,802 (Aug. 1960).

The usc of geos tat ionary satellit es for t he s tud .v of ionospheri c electron co ntent a nd ionospheri c rad io-wave propagat ion , O. K . GarriolL and C. G. Li t tle, J . Geop hys. R esearch 65, No . 7, 2025 (Jul y 1960).

Our measurement system a nd nflt ional needs, A. V. Astin , Sprr l"yscope 15, No.6, 16 (1960) .

Standards of heat capaci ty a nd thermal co nduct ivity, D. C. Ginnings, Book, Thermoelect ri city, p. 320 (In clu d in g Proc. Co nf. Th ermoelectri city, Sponsored by t he Na vfll R esea rch Lab ., Sept. 1958) (1960).

N eutron-insens it ive proportio nal counte r for ga mm a-ra.v dosimet ry , R . S. Caswell , R ev. Sci. In str. 31, No.8, 869 (Au g. 1960).

A stud y of 2-"NIc/s ionospheri c absorption measurements at hi gh a lt it udes, K . D avies, J. Geophys. R esearch 65, 2285 (Aug. 1960).

Cnrri er-f requ eney dependence of t he basic transmission loss in t rop osp heri c fo rward scatte r propagation, 1\:. A. No rto n, J . Geop hys. R esearch 65, 2029 (Jul y 1960) .

Th e ionization co nstants of 2-ch loro-4-ni troph enol a nd :2-ni tro-4-chlorop henol, V. E. Bower a nd R . A. R obinso n, J. Ph.vs. Chem. 64, 1078 (1960).

Closed circu it liq uid hydrogen ref ri geration ys tem. D. n. Chelto n, J. ' V. D ean, and B. ' V. Birmingham, R ev. Sci. Instr . 31,712 (.July 1960).

A qu a nt itative fo rmulation of Sylvester's law of in erti a, A. i\ l. Ost rowski , Na Li . Acad . Sci. Proc. 45, No . 5, 740 ( i\ ay ] 959).

Infra red tra nsm ission of clouds, D . :\'r. Ga tes and C. C. Shaw , J . Opt. Soc. Am . 50, 876 (Sept. 1960) .

Comparat ive fi xat ion of ca lcium a nd st ronti um by synthetic hydroxyapatite, R . C. Likins, rr. G. McCann , A. S. Posner, a nd D . B . Scott, J . Biolog. Chem. 235, No.7, 2152 (Jul y 1960).

, A co mp a rison of atom ic beam frequenc.v s tan dards, R. E . Beehle r, R. C. :vrock ler, a nd C. S. Sn id e r, Nature Lett er 187 681 , (Aug. 20, 1960).

VI. M icroscopic a nd macroscopic energy loss d ist ribul ions. 1. Theo retica l rcvie" 's: A summ a r.v, U. Fa no, Nat l. Acad . Sci., ~atl. R esearch Coun cil Publ. 752, Report 29, p. 24 (Aug. 1960) .

The mecha nica l properti es of cera mi cs a nd their mcasul'e­ment at eleva ted temperatu res, S. .I. Sch neid cr, Book, Therm oelect ri city , Chflpte r 21, 342 (1960).

A rating method fo r refri gera ter! t ra il er bodi es ha uling pe rish­ab le foods, C. W. Phi llips, W. F . Goddard , Jr., a nd P. H.. Achen bach , ASTI RAE J. 2, No . 5, 45 ( ~1ay ]960).

o

R epl y 10, On t he st ru cture of t rimethylamine- t rimethylboron , . D . H.. Li ciC', Jr ., J . Chem. Ph ys. 32, No.5 , 1570 (May 19GO).

Dimensio nal changcs occurring in dent ures dllring processing, J . B. Woelfcl, G. C. Pa ff enba rger, a nd "V. T. Sweeney, J . Am. D en ta l Assoc. 61, No.4, 413 (Oct. 1960).

T eet h, a rt ifi cia l, G. C. Pa f"f enbarger a nd G. B. D ento n, E ncy­clopcdif. Britan nica 21, 878 (J a n. 1960).

A method of improvin g isola t ion in multi-cha nn el waveguide systems, G. F . Engen, IR1£ T rans . lYIicrolyave Theory and T ech. Letter MTT-8, 460 (Jul y 1960).

Innuence of earth cur vature a nd t he terrest ri fl l magnetic fi eld on VLF propagat ion , .I . R. Wait a nd 1( . Spies, J . Geop hys. Research 65, 2325 (Aug . 1960) .

Ch arge transfe r and electron produ ction in H- + H collisio ns, D . G. Humm er, R. F . Stebbings, " '. L . Fite, a nd L . ~1. Bransco mb, Ph ys. Rev. 2, 668 (Jul y 19(0) .

The characteri stic energy losses of elect rons in carbon , L . B. Leder a nd J . A. Suddet h, .I. Appl. Ph ys. 8, 1422 (Aug. 1960) .

Note hi storique sur les p rem iercs a nnces de la microscop ie electro niqu e, L . Ma rto n, Extrait 131 111. Acad . R oy. Bclg. (Classr drs Sciences) 5, 119 (Mar. ] 959).

An optical study of t he boundary layer t ra ns ition p rocesses in a supersoni c a ir system, 'V. Spangenberg a nd 'V. R . ROII' la nd , Phys. of F luids 3, No. 5, 667 (Sept.- Oct . 1960).

Thermodyna mi c stru cture of t he outer solar a t mosphere. VI. Effect of dcpartul'cs from t hc Saha equat ion on infe rred properti es of loll' chromosphere, S. R . Pottasch a nd R . N. Thomas, As t rop hys. J. 132, 195 (Jil ly ] 960).

Pol y mer deco m posit ion: Therm ody nam ics, mecha nism., and energet ics, L . A. Wall , Soc. Plas t ic E ngrs. Pt. I, 810 (Aug. 1960); P t . II, 1031 (Sept . ] 960) .

The ro le of surfa ce ten .. ion in dele rmining certain clay-water properties, ' V. C. Ormsby, Bu ll. Am. Cerami c Soc. 39, ~o . 8, 408 (Aug. 1960).

* Publications jor whi ch a price is indicated (except j 01' Tech­nical Notes) are available onl y jmm the S uperi ntendent oj D ocuments, U.S. Government P1'inting O.fJice, lVashin(fton 25, D. C. (J oreign postage, one-fourth additi onal). T he Technical N ews Bulletin and Basic Radio Propagation P redictions are available on a 1-, 2-, or 3-year subscription basis, although no 1'eduction in rates can be made. Reprints f rom outside .iou1"1~als and the NBS J ournal oj Resew'ch may ojlen be obtained directl y j rom the auth01·s.

195

The National Bureau of Standards

announces a three-week course In

Radio Propagation

July 31 to August 18, 1961

Central Radio Propagation Laboratory Boulder, Colorado

This course is designed to provide a discussion of the fundamentals of radio propagation, the latest advances in t he state of the art, and t he application of t his knowledge to the design and development of communication syste ms . Tropospheric Propagation and Ionspheri c Propagat ion will be considered in two separate sect ions which may be taken individually or in succession. Details of t his co urse may be obtained from t he Educational Director at t he address given below.

The course will consider communication via the entire range of useable radio frequencies and will extend into the modes of propagation whi ch are being explored for the future. In bot h sections the cont inuing emphasis will be on t hose elements of propagation which affect system design and freq uency a llocation.

In addition to t he subject matter mentioned above t he two sections will include disc ussion of the following :

Tropospheric Propagation (July 31-August 4, 1961)

The effect of atmospheric t urbulence, and of both normal and unusual atmospheric strati 5cation, upon the refrac t ion and attenuation of radio waves . .. Climatology of the atmospheric radio refractive index and its meas urement by refractometers or weather data ... Diffraction and refl ection from irreg­ular terrain and a bsorption b y t rees and buildings .. . The phase stabili ty of mi crowave signals and its effect upon systems of t racking, guidance, and geodetic measurement . .. Mechan isms of t ropospheric propagation . .. Variability of t ransmission loss and the theoretical basis for t ransmission loss predic­tion ... Modu lation st udies and techniques . .. Methods for pred icting t he probability of satisfactor y point-to-point co mnlllnicat ion , broadcast coverage, and comm unication via sa te lli tes.

Ionospheric Propagation (August 7-18, 1961)

Theory of radio wave propagation via t he ionosphere, from t he very lowest frequencies to micro­waves .. The distorting effects of ionospheric irregularities and dispersion on broad-band radio signals . . A description of the ionosphere-its spatial and temporal variat ions and their predictabil­ity . . Transmission loss and its varia bility as a function of frequency and other system parameters . . . Special problems of ear t h-space communication ... Statistical character and average power of atmos­pheric, cosmic, and artifi cial ra dio noise . .. Characterization of t he propagation med ium as a time­varian t comm uni cation channel ... Consideration of per t urbat ions of amplitude and phase, mu lt ipath propagation, and noise as factors affecting modulat ion techniques, and t he capacity and reliability of syste ms ... Prediction of performance of ionospheric radio syste ms fOT communication, detection an d pos itioning, navigat ion and timing.

Prerequisites: A bachelor 's degree in E lectrical Engineering, Ph ysics, or other suitable acade mi c or practical experie nce.

Tuit ion: Tropospheric Propagation- $100 Ionospheric Propagation-$200 Entire cOlll'se- $300

R egistrat ions will be limited and earl y application should be made to enSlll'e consideration. Further deta ils of t he course and registration forms w ill be available March 1, 1961, from : Edmund H . Brown, Educa­t ional Director , Bou lder Laboratories, National Bureau of Standards, Bou lder , Colorado.

196

Editorial Notice

Conference on Transmission Problems Related to High-Frequency Direction Finding

This issue includes a group of papers presented in June 1960 at a confer­ence sponsored by the University of California at Los Angeles in cooperation with the Office of Naval Research. Thc purpose of the conference was to discuss the aspects of long-range high-frequency radio propagation that affect radio location and direction finding, and the related problems of measurement and analysis.

A comprehensive bibliography of published work on direction finding and related ionospheric propagation topics for the period 1955- 1959 has been pre­pared by the Nume rical Analysis Research Staff of the University of Ca lifor­nia at Los Angeles. This bibliography wi ll be edited by the Radio Systems Divisioll of the NBS and published as a Technical Note of the NBS.

THOMAS N. GAUTIER, Associate Editor.