Contains research objectives and summary of research.U. S. Air Force - Electronic Systems Division (Contract F19628-73-C-0196)National Science Foundation (Grant 40484X)Joint Services Electronics Program (Contract DAAB07-71-C-0300)National Institutes of Health (Grant 1 RO1 GM20370-01)U. S. Air Force - Air Force Systems Command (Contract F33615-72-C-2129)California Institute of Technology (Contract 952568)National Aeronautics and Space Administration (Contract NAS1 -10693)National Science Foundation (Grant GP-40485X

Barrett, Alan H.

Bechis, K. P.

Ho, P. T.

Kebabian, P. L.

Kunzi, K. F.

Lam, Kai-Shue

Martin, R. N.

Myers, P. C.

Price, R. M.

Rosenkranz, P. W.

Staelin, David H.

Waters, J. W.

DSpace@MIT

VIII. RADIO ASTRONOMYAcademic and Research StaffProf. A. H. Barrett Dr. P. L. Kebabian Dr. P. W. RosenkrantzProf. B. F. Burke Dr. K. F. Kunzi Dr. J. W. WatersProf. R. M. Price Dr. P. C. Myers J. W. BarrettProf. D. H. Staelin Dr. G. D. Papadopoulos D. C. PapaGraduate StudentsO. Appiah A. O. Haschick R. N. MartinK. P. Bechis P. T. Ho R. L. PettyjohnP. C. Crane K-S. Lam R. K. L. PoonR. W. Freund W. H. Ledsham R. C. WalkerT. S. Giuffrida S. Lee R. W. WilcoxK-Y. LoRESEARCH OBJECTIVES AND SUMMARY OF RESEARCH1. Atmospheric Measurements with Passive Microwave TechniquesU. S. Air Force - Electronic Systems Division (Contract F19628-73-C-0 196)A. H. Barrett, D. H. Staelin, K-S. LamThe 118-GHz 02 resonance can be used for sounding atmospheric temperature pro-files to mesospheric altitudes because of it s great opacity. The same resonance alsoprovides an opportunity for measuring the water content of clouds. It can be doneby comparing either ground or satellite observations of spectral bands having com-parable absorption by 02 near 60 GHz and 118 GHz. In the absence of clouds the twobands appear identical. Since clouds absorb more strongly at 118 GHz, the 60-GHz and118-GHz intensities differ in proportion to the liquid water content of observed clouds.Such observations at various frequencies should permit the altitude distribution of heavyclouds to be deduced.A 118-GHz radiometer is being fabricated for this project, but funding limitationshave slowed purchase of certain necessary hardware.It is well known that the theory of microwave absorption is inadequate when appliedto overlapping spectral lines, i. e., when the widths of the lines are comparable to theirspacing. Detailed theories, which include the effect of overlap, have not been appliedto the microwave spectrum of molecular oxygen when broadened by oxygen-nitrogen,oxygen-oxygen, and oxygen-water collisions.We are attempting to apply these theories to microwave absorption by molecularoxygen in an atmospheric environment. We have made microwave observations ofoxygen emission from high-altitude balloons looking downward, and hope to test thesetheories using these data.2. Microwave Spectroscopy of the Interstellar MediumNational Science Foundation (Grant 40484X)A. H. Barrett, P. T. Ho, R. N. Martin, K. P. Bechis, P. C. MyersRadio spectroscopy of the interstellar medium has revealed that many moleculesare present in detectable amounts. In the majority of cases the population distributionQPR No. 112(VIII. RADIO ASTRONOMY)6.0 -4.0 -2.0 --FREQUENCY (kHz)300 200 100 0 -1004 5 6 7 8 9LSR VELOCITY (km/s)-200 -30010 1 12Fig. VIII-1. Sample spectra of the J = 6, J = 7 lines of CH 3OH.among the molecular energy levels is nonthermal, which makes it difficult to interpretthe observational data in terms of physical parameters of the interstellar environ-ment, such as temperature, gas density, radiation density, molecular composition, gas-to-dust ratio, and so forth. Our studies have focused on the emission of OH, H 2 0, CH30OH,and CH20 in galactic HII regions and in stellar sources that have an infrared excess.Temporal studies of OH and H2 0 emission are being conducted in coordination with infra-red observations of stellar sources. A program of CO observations has been initiatedto study emission from infrared stars and its correlation with the visual output of thesestars, and emission in the galactic plane with particular emphasis on the column den-sity of CO in the direction of x-ray sources.Studies of CH30H in the Orion Nebula have indicated detailed structure in the spec-tral lines when examined with a frequency resolution of 17 kHz. The structure appearsto be characteristic of the molecule because it shows a high degree of symmetry aboutthe center of the line and a systematic increase in line width as lines of higher and higherrotational quantum number are measured. The lines appear to be polarized, which,coupled with the symmetrical line structure, is indicative of Zeeman patterns. Fig-ure VIII-1 shows sample spectra of the J = 6 and J = 7 lines of CH30H.QPR No. 1126.04.002.0 x0-UFJI 1 i I I I ' I I i iRESOLUTIONJ= 7 0.2 km/s17 kHzj I I I I I I I II I I(VIII. RADIO ASTRONOMY)3. Sensing of Subsurface Body Tissue Temperatures with MicrowaveRadiometryJoint Services Electronics Program (Contract DAAB07 -71 -C -0300)National Institutes of Health (Grant 1 RO1 GM20370-01)A. H. Barrett, P. C. MyersIntroductionDuring the past year we have continued to work on a preliminary study of the abilityof microwave radiometry to detect localized subsurface temperature elevations in ani-mals and humans. As we have reported previously,1, 2 the rationale behind this workrests on the following factors:1. All objects emit thermal electromagnetic radiation, whose intensity depends onthe temperature of the object and the frequency of observation at microwave frequencies.Thermal radiation is readily detectable from humans with present microwave radiom-eters.2. In the 100 MHz -10 GHz band microwave radiation can penetrate, and thereforealso escape from, body tissue depths of several centimeters. This behavior is illus-trated in Fig. VIII-2. Radiation received from the body in this band can therefore indi-cate subsurface tissue temperatures. Microwave radiometry of this type is directlyanalogous to infrared thermography, except that the temperature information pertainsto depths of ~1 cm instead of ~0. 1 mm.3. Detection of spatial variations in the body's thermal patterns may provide valu-able medical diagnostic information in numerous applications, including early detectionof malignant tumors, especially in the breast, detection of cerebrovascular insuf-ficiency - a sign of an impending stroke - and detection of peripheral vascular insuffi-ciency and local inflammation. 3Equipment DevelopmentDevelopment of equipment has involved operation of radiometers at 1. 3 GHz and3. 3 GHz, and fabrication of antennas of various apertures and spatial resolution.Auxiliary temperature sensing equipment, including recording thermocouples and ther-mistors, has been developed and employed. Mechanical equipment for precise controlof antenna positioning has been designed and built; digital circuitry for signal calibra-tion, averaging, and recording has been constructed and is under test.Research ResultsRadiometric data have been taken at 3. 3 GHz, using cats and humans as subjectsin order to detect localized temperature elevations under various circumstances. Thiswork has served as a basis for more detailed clinical tests on humans, which willbegin next year in collaboration with physicians at local Boston hospitals. Theradiometer is a superheterodyne of the Dicke-switched type. A detection sensitivityof ~0. 2°K antenna temperature was achieved with an integration time of 3 seconds.The antenna was a straight section of WR-90 rectangular waveguide of 0. 4 X 0. 9 inchcross section, filled with a low-loss solid of dielectric constant E = 11, in order topropagate the dominant waveguide mode above its cutoff frequency. The antennaaperture was placed flush against the skin, to provide better impedance match andspatial resolution than could be obtained with an intervening air gap. The resul-tant spatial resolution across the antenna axis is essentially that of the antenna nearfield, or ~0.4 X 0. 9 inch.QPR No. 112100 1000FREQUENCY, MHz--,Microwave penetration depth in human tissue. These data aretaken from the literature on dielectric tissue properties.4-8The curves show the depth from which microwave radiation ofa given frequency will originate, if it is attenuated by e - I or37% when it reaches the surface. A I-GHz radiometer canthus see radiation from an e-1 depth of ~1. 4 cm in muscle, or~8 cm in fat.MICROWAVE6.0 ]3.0SURFACE300.0MICROWAVE MINUS SURFACEMICROWAVE MINUS SURFACE5.0I .0Fig. VIII-3.Temperature scans of locally heated cat thigh.Data were taken along a line on the surface ofthe thigh, whose interior was heated ultra-3sonically by ~3D C within a volume 1i cmEach scan shows the difference between tem-peratures measured while heating, and ~30minutes after heating was ended. The relativemicrowave temperature increase is greaterthan the relative surface temperature increase.This indicates microwave ability to sense sub-surface temperature elevation more effec-tively than a device which measures surfacetemperature. Measurement error: -0. 20 C.QPR No. 1121000.110FAT, BONE(LOW WATER CONTENT)MUSCLE, SKIN,INTERNAL ORGANS(HIGH WATER CONTENT)I I I I I 11 1 11100I00.1Fig. VIII-2.S0,000I I I I 1 I I I I-4 -2 0 2 4DISTANCE ALONG THIGH, cmI0(VIII. RADIO ASTRONOMY)In radiometric studies involving cats we employed focused ultrasound as a sourceof localized subsurface tissue heating. 9 A dead cat was studied first; these results,obtained in the absence of circulating blood, have been reported previously.2 Essen-tially the same techniques of heating, internal thermal sensing, and antenna scanningwere used in more recent studies of live anesthetized cats. Results obtained in onesuch study are shown in Fig. VIII-3. Here the local microwave antenna temperatureincrease is ~ 20 C, while the surface temperature increase is ~10 C. The microwavemethod is thus more capable of detecting subsurface temperature elevations than aninstrument that has the same temperature sensitivity but measures surface temperatureonly (e. g., an infrared thermograph).A study of a sterile abscess created in the thigh of a cat by injection of gum turpen-tine indicated a ~l'C subsurface temperature elevation but no surface temperaturerise immediately following injection, at the injection site. Subsequent measurements ofthe same cat during a 14-day period showed a migration of the "hot spot" and its declineat the end of this period.MICROWAVE SURFACE2.0-0 2 4 6 8 0 2 4 6 8DISTANCE TOWARD HAND (inches )Fig. VIII-4. Temperature scan of forearm heated by muscle contraction.Scans were taken along a line on the forearm, with the palmup. Muscles in the forearm were contracted by repeatedclenching of the fist. Each curve is the temperature differ-ence between the contracting and relaxed cases. A local in-crease is seen in a region including contracting muscles. Nocorresponding surface temperature increase is evident.Internal heating of the human forearm by muscular contraction was achieved byrepeated clenching of a fist. The microwave and surface temperature response wasmeasured (see Fig. VIII-4). Here each curve shows an average of two difference scansalong the arm, where temperatures measured before heating are subtracted from tem-peratures measured during heating. Again a region of subsurface temperature elevationis seen, while no corresponding surface temperature increase is noted. The region ofsubsurface heating corresponds to the location of the three forearm muscles employedin clenching the fist. This effect was observed in three subjects; the relative surfacetemperature increase was detectable in two cases not shown here. In all cases, how-ever, the microwave antenna temperature increase was greater than the surface tem-perature rise.References1. A. H. Barrett and P. C. Myers, "Investigation of Microwave Radiometry as aMedical Diagnostic Technique," Quarterly Progress Report No. 107, Research Lab-oratory of Electronics, M. I. T., October 15, 1972, pp. 14-17.QPR No. 112(VIII. RADIO ASTRONOMY)2. P. C. Myers and A. H. Barrett, "Microwave Sensing of Subcutaneous Tempera-tures," Quarterly Progress Report No. 109, Research Laboratory of Electronics,M. I. T., April 15, 1973, pp. 1-6.3. J. Gershon-Cohen, Jo Ann D. Haberman-Brueschke, and E. E. Brueschke, Radi-ologic Clinics of North America 3, 403 (1965).4. T. S. England, Nature 166, 480 (1950).5. H. P. Schwan and K. Li, Proc. IRE 44, 1572 (1956).6. J. R. Mallard and D. G. Lawn, Nature 213, 28 (1967).7. S. J. Webb and A. D. Booth, Science 174, 72 (1971).8. H. P. Schwan, IEEE Trans., Vol. MTT-19, No. 2, pp. 146-152, February 1971.9. P. P. Lele, J. Physiol. 160, 494 (1962).4. Long-Baseline Optical InterferometerU. S. Air Force - Air Force Systems Command (Contract F33615-72-C-2129)D. H. Staelin, P. L. KebabianA coherent optical interferometer has been designed for measuring angular diam-eters of very small optical sources such as stars. Baselines up to ~100 ft are feasible.New devices developed include a diffracting beam splitter and chopper system and anefficient 3 -level chopper. Upper limits have been placed on the tracking capability andsensitivity of such systems when located on the terrestrial surface.5. Environmental Sensing with Nimbus Satellite PassiveMicrowave SpectrometersCalifornia Institute of Technology (Contract 952568)D. H. Staelin, K. F. Kunzi, P. W. Rosenkranz, J. W. WatersThe Nimbus-5 Earth-observatory satellite was launched in December, 1972, intoa nearly circular polar orbit at an altitude of 592 NM. The 5-channel microwave spec-trometer (NEMS) views the nadir with half-power 100 beamwidth. Individual chan-nels are located at a weak water-vapor resonance in a spectral window, and at3 positions on the edge of the oxygen absorption band (5-mm wavelength); the centerfrequencies are 22.235, 31.4, 53.65, 54.9, and 58.8 GHz.The passive observations of the thermal microwave radiation in these five bandshave yielded both the temperature profile and the vapor and liquid water content ofthe terrestrial atmosphere over ocean, even under overcast conditions. Informa-tion has also been obtained on geophysical parameters that affect the surface emis-sivity, such as ice type, sea roughness, and snow cover.In Fig. VIII-5 the rms discrepancies between the NEMS inferred atmospherictemperature profiles and those interpolated in time and space from the NationalMeteorological Center Oh and 1 2 h operational analysis grids are presented. Typi-cal rms errors are 20 K, with larger values near the surface and tropopause,approximately as expected. These data demonstrate the ability of microwave soundingsto yield acceptable temperature maps over the entire globe, even in the presence ofmost clouds, including some clouds that hamper similar infrared observations.QPR No. 112(VIII. RADIO ASTRONOMY)1 00300IO000 I I 5K30 "35*-60* N /E 100-0 --- N=13 180E300 N1000O 5K30 - 10 - 35 N" N=23E 100 ---- N=40300270 E1000O 5KREGIONS USED FOR COMPARISONRMS DISCREPANCY BETWEEN NEMSAND INTERPOLATED NMC GRIDTEMPERATURE PROFILESFOR 18. FEB. 1973- LAND SURFACEWATER SURFACEFig. VIII-5. Temperature profiles.The ability of microwaves to sense abundances of water vapor and liquid watercontent over ocean is also unique, and preliminary analyses yield reasonable agree-ment with operational radiosonde observations of water vapor. Studies of ice andsnow, deserts, and other surfaces are also furnishing new and unexpected results.The Nimbus-6 satellite, which will be launched in 1974, will carry a scannedversion of NEMS, and provide two complete global maps with 200-km resolution eachday. Preparations for this next experiment are under way.6. Experiments for Microwave Temperature Sounding of the Mesosphereand Upper StratosphereNational Aeronautics and Space Administration (Contract NAS1 -10693)P. W. Rosenkranz, D. H. Staelin, J. W. WatersThe extremely opaque 0 2 resonances near 60 GHz provide an opportunity forsatellite-borne microwave radiometers to measure thermal radiation originating fromlevels up to 75-km altitude. It appears possible to map on a global scale the atmospherictemperature profile from 0-75 km altitude with a vertical resolution of ~5-20 km and ahorizontal resolution of 100-400 km.QPR No. 112(VIII. RADIO ASTRONOMY)To explore the problem further, a 23-channel microwave spectrometer covering a40-MHz band and tunable over several gigahertz near 53 GHz has been developed.Observations of the strongest lines near 60 GHz will only be made from satellites. Thisinstrument was first used on the ground at various latitudes to observe the 23 , 25 ,27_, 29_, and 31 0 2 resonances. The 27 line was observed more intently duringFebruary and March, 1973, using the NASA Convair 990 observatory aircraft (whichcrashed subsequently). These observations reveal what may be a fairly serious discrep-ancy between theory and experiment; the lines appeared to be approximately 50%stronger than expected.Future work will be directed toward resolution of the apparent conflict between the-ory and experiment and final development of a satellite capability. An engineeringmodel of such an instrument (at 53 GHz) is now being fabricated at the California Insti-tute of Technology Jet Propulsion Laboratory.7. Radio Structure of GalaxiesNational Science Foundation (Grant GP-40485X)R. M. PriceInvestigations under this program include radio astronomical studies of the struc -ture of our Galaxy and extragalactic "normal" spiral galaxies. In the first area con-tinuum observations have been used to study the distribution of nonthermal radioemission regions in our Galaxy. These observations yield information on the distribu-tion of galactic cosmic-ray electrons and the strength and orientation of interstellarmagnetic fields.In the studies of our Galaxy we have included high galactic latitudes, the so-calledhalo region, low galactic latitudes, the galactic disk, and more recently the region ofthe galactic center. Recent results of these studies indicate that approximately one-halfof the total power emitted from the galactic disk at wavelengths near 1 meter originatesin spiral features.During the coming year, galactic structure studies will be directed toward an inter-pretation of the radio emission from the region of the galactic center and a further defi-nition of the nonthermal emission regions in the disk. A study of radio emissionfrom mass-loss nebulae associated with Wolf-Rayet stars will also be completed.In the area of extragalactic studies, a survey of normal spiral galaxies is being car-ried out (with P. C. Crane) using the three-element interferometer of the National RadioAstronomy Observatory. Preliminary observations at 3 cm and 11 cm have already beencompleted on a sample of 185 galaxies with angular diameters greater than 4 minutes ofarc. Observations of another sample of 200 galaxies are planned for Spring 1974.This study is designed to yield data on the radio structure of spiral galaxies. Ofparticular interest are sources of small diameter or source complexes associated withthe galactic nuclei, extended emission regions associated with the disks (includingspiral features), and sources in the vicinity of galaxies that might have been ejectedfrom a "parent" galaxy. As part of this survey, we are investigating galaxies noted bySersic as having abnormal optical properties associated with their nuclei.Preliminary reductions of our observations yield the following results. Sourcesare detected in the fields of approximately 60% of the galaxies surveyed thus far. Ofthese, 45 sources (25% of the total sample) have small diameters and their positionsindicate they are probably associated with the nuclei of the galaxies, 35 are extendedsources (20% of the sample) with less well-determined positions but indicative ofstructure associated with the galaxies, and 30 sources (15% of the sample) haveconfused fields that will require further observation.QPR No. 112

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