A BSTRACT. This is the first paper in a two-part series whi ch d escribes the design, ope r a ti on, and tes ting of a su ccessful 5 MHz ra dio-ech o sounder for te mper a te gl aciers. This p a rt dea ls with the e lec tromagne ti c charac teristi cs of temper a te glaciers a t radio freque ncies. Ea rlier workers' problem s in sounding through temper a te ice are explain ed in terms of electroma gn etic sca ttering by wa ter-filled vo ids. The frequenc y d epe nd e n ce of the scattering indicates tha t returns from sca tterers diminish ra pidly a t frequencies bel ow a bout 10 MHz. A sys te m w ith the foll owing c harac teristics is reco mmend ed : a transmitted pulse with a ce nte r frequency of a bo ut 5 MHz, dura ti on o f a bout I cycl e, a nd a r eceiver which is untuned a nd which meas ures fi e ld intensity r a the r tha n power. Spectral m ethods for studying the size distributi on of sca ltere rs a re p resented . An actua l in strum ent a nd fi eld tri a ls w ill be described in a forthcom ing publicati on by R . S. V ickers a nd R . Boll en.R ESUME. SOlldages par echo-radio dalls les glaciers temjJCris: propriitis de la glace et critereJ pOllr la cOllstructioll des appareils de sOlldage. Ceci es t la premi ere pa rti e d ' un e serie en d eu x a rticl es qui d ecrit l'a ppareill age, la mise en oeu vr e e t le contra le d ' un a ppa reil effi cace a 5 lVIHz d e so nd age p a r rad io-echo pour d es gl ac iers temperes.Celle partie tra ite d es ca racteristiques elec tro m ag netiques cles g lacie rs tem peres a ux frequences radio . Les p ro bl e m es renco ntres p a r les precedents ch e r ch e urs pour lel sond ages da ns la glace te mpe ree s'exptique nt pa r la di sp ersion elcctromagn c tique cla ns les cavites rempties cl 'eau. L ' inAuenee cle la [req uence sur la dispersio n indique que le rayonnement re nvoye p a r les d isperse urs dimin ue ra pid em e nt a ux frequences infe ri eures a environ 10 lVIH z. O n recomm a nd e un a ppa reill age ayan t les ca rac tc ri stiques sui va ntes : une imp ul sion tra nsmise avec un e frequen ce centra le d 'en viron 5 MHz p end a nt en viron un cycle, avec un recepte ur qui est desaccord c e t mesure l' inte n site du cham p, pluta t que la puissa nce. On presente d es meth odes spectrom etriques p our etud ier la di stributi on en dim e n sio n des disperseurs. U n instrum ent recll em e nt co nstruit et d es essa is sur le terra in seront d ecrits en deuxi e m e p a rti e pa r R. S. Vi cke rs et R. Bolle n . ZUSAMM ENFASSUNG . Radar-Echolotullg temperierter Cletseller : Eiseigellschajlen 1lI/.d Kriterien jllr dell Ball des Lolgerdtes .Es handcl t sich hi e r um den ersten T eil ein er zweiteili ge n V ero ffentli chungsfo lge, d ie d en Ba u, cl en Einsa tz und di e Erprobung ein es bra u chba re n 5 MH z-R ada r-Echolotes fUr tem p eri erle Gle tsch e r beschre ib t. Diesel' T eil beh a n dclt die elektro m ag ne ti schen Cha ra kteristiken tempe ri erte n Eises im R a di owell e nbere ieh . Di e Sch w ierigkeiten, mit d ene n frUh e re Forsch e...

An expression derived for the compressibility of glass foams is the same as Mackenzie's expression for a body containing a low concentration of spherical pores, when carried to the limit of very high porosity. Simple analysis shows that Mackenzie's expression is also valid for slightly nonspherical pores but should underestimate the actual compressibility for porosities which are neither high nor low. Compressibilities measured on a series of porous glass samples to 70% porosity agree closely with the theoretical relation, except at intermediate porosities, where the departure shows the predicted effect of pore interaction.

The microwave radiometric temperature of heterogeneous materials is altered by internal scattering. Radiative transfer theory and a Rayleigh scattering model are used to obtain the microwave temperature and its polarization as a function of view angle for emission from a nonuniformly thick layer containing scatterers. The scatter-induced change in brightness tempera:tare is generally negative and may be many tens of degrees. There are situations, however, such as the emission from ice over freshwater, where the scatterers may increase the brightness temperature by as much as 30øC. Lunar microwave temperatures may be decreased from a few degrees to more than 50øC depending upon wavelength and upon the specific lunar target; the brightness temperature as a function of wavelength of a lava flow may be decreased from 1 øC to more than 30øC by near-surface vesicles; snow may appear from a few degrees to more than 60øC darker as it ages; and air bubbles in ice over freshwater may increase the brightness temperature by as much as 30øC or decrease it by as much as 50øC depending upon the thickness of the ice and the size and concentration of the bubbles.

No abstract