Contains reports on eight research projects.National Science Foundation (Grant AST77-06052)Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Aeronautics and Space Administration (Contract NAS5-21980)U. S. Department of Commerce - National Oceanic and Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Contract NAS5-22929)National Aeronautics and Space Administration (Contract NAS5-23677)National Science Foundation (Grant AST77-12960)National Science Foundation (Grant AST77-26896

Barrett, Alan H.

Burke, Bernard F.

Garcia-Barreto, J. Antonio

Giuffrida, Thomas S.

Haschick, Aubrey D.

Melcher, James R.

Myers, Philip C.

Rosenkranz, Philip W.

Shao, Micheal

Staelin, David H.

Walker, Robert C.

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XIV. RADIO ASTRONOMYAcademic and Research StaffProf. Alan H. BarrettProf. Bernard F. BurkeProf. James R. MelcherProf. Philip C. MyersAli D. AliBarry R. AllenYaneer Bar-YamWilliam T. BaumannCharles L. BennettPriscilla J. BensonTimothy S. BigelowRichard L. BuxtonAlan L. CasselProf. David H. StaelinProf. Edward L. WrightDr. Alan ParrishDr. David H. RobertsDr. Philip W. RosenkranzGraduate StudentsRowley L. ChengJohn J. DalyEmilio E. FalcoJ. Antonio Garcia-BarettoJohn R. GershPerry E. GreenfieldAubrey D. HaschickSteven T. KirschJeffrey H. LangCharles R. LawrenceDr. Michael ShaoJohn W. BarrettJohn D. KiersteadD. Cosmo PapaWilliam H. LedshamStephen LeibovicTerence H. MarshallDavid F. McDonoughBruce R. RosenMatthew H. SchnepsDiane C. SimmonsDaniel D. StancilPaul Toldalagi1. LONG-BASELINE ASTROMETRIC INTERFEROMETERNational Science Foundation (Grant AST77-06052)Michael Shao, David H. StaelinThis year the one-inch interferometer facility was completed and transported tothe Mt. Wilson Observatory in California, where initial experiments were performed.This system has a baseline of ~2 meters and tracks Polaris. The purpose of the systemis to demonstrate the basic concept of two-color fringe tracking, which should eventu-ally enable relative stellar positions to be measured with ~10-4 arc-sec accuracy. Suchaccuracy is sufficient to detect any Jovian planets orbiting nearby stars.1These initial experiments have been successful. Using one-half inch aperturesPolaris was tracked continuously with 2 arc-sec seeing, and intermittently with 3.5 arc-sec seeing.Future work will include two-color tracking experiments with a 10-meter baseline,and use of siderostats so that stars other than Polaris can be observed. Such experi-ments would be a prelude to establishment of a permanent four-inch observatory capableof measuring positions of 1 0 th -magnitude stars.References1. M. Shao and D. H. Staelin, "Long-Baseline Optical Interferometer for Astrometry,"J. Opt. Soc. Am. 67, 81-86 (1977).PR No. 121(XIV. RADIO ASTRONOMY)2. CONTROLLED THIN-FILM ANTENNAJoint Services Electronics Program (Contract DAAG29-78-C-0020)David H. Staelin, James R. MelcherThe use of a scanning electron beam for rapidly manipulating the charge distribu-tion on a thin membrane is being studied as a method for precisely controlling the shapeof very large (30- to 1000-m) reflector antennas in space.1The work progressed on three fronts in 1978. First, the theoretical effort hasfocused on the issues of electrostatic instabilities and algorithms for control. Second,to test these theories a 1-meter square membrane has been stretched on a frame betweenplates, the potentials of which are controlled at nine points independently. To date thebasic modes have been observed, together with their stability and cross coupling. Also,the 1, 1 mode has been biased to instability and then controlled. Third, an apparatus isnearly constructed which will enable the front and back-side secondary-emission char-acteristics of various metals and insulators to be studied as a function of beam energyand surface contaminants.References1. J. Lang, J. Gersh, and D. H. Staelin, "Electrostatically Controlled Wire-MeshAntenna, " Electronics Letters 14, 665-666 (1978).3. SCANNING MICROWAVE SPECTRO-METER EXPERIMENTNational Aeronautics and Space Administration (Contract NAS5-21980)David H. Staelin, Philip W. RosenkranzThe five-channel Scanning Microwave Spectrometer (SCAMS) yielded 10 months ofalmost continuous data from the Nimbus-6 satellite, launched in June, 1975.1Analysis of Typhoon June (1975) has shown that passive microwave soundings canyield wind information in two ways, by virtue of the enhanced surface emissivity due tofoam and rough seas, and by means of the observed horizontal temperature gradientswhich are related to winds by the thermal wind equation.2 These studies also demon-strated that such soundings can yield reasonable water vapor and liquid water estimatesin these intense storms. 2Kalman filtering was applied successfully to the problem of temperature profileretrievals; the rms errors were reduced by as much as ~50 percent, with moderateimprovements being more typical. 3Snow and ice observations have been analyzed at some length, and three manuscriptsPR No. 121(XIV. RADIO ASTRONOMY)are now in preparation.References1. D. H. Staelin, P. W. Rosenkranz, F. T. Barath, E. J. Johnston, and J. W. Waters,"Microwave Spectroscopic Imagery of the Earth," Science 197, 991-993 (1977).2. P. W. Rosenkranz, D. H. Staelin, and N. C. Grody, "Typhoon June (1975) Viewed bya Scanning Microwave Spectrometer," J. Geophys. Res. 83, 1857-1868 (1978).3. W. H. Ledsham and D. H. Staelin, "An Extended Kalman-Bucy Filter for Atmo-spheric Temperature Profile Retrieval with a Passive Microwave Sounder," J. Appl.Meteorol. 17, 1023-1033 (1978).4. TIROS-N SATELLITE MICROWAVE SOUNDERU. S. Department of Commerce - National Oceanic and Atmospheric Administration(Grant 04-8-IM01-1)David H. Staelin, Philip W. RosenkranzThe first Tiros-N Satellite was launched October 13, 1978, and the second unit isscheduled for launch in 1979; these operational weather satellites each incorporate four-channel passive microwave spectrometers operating in the 50-58 GHz band. The result-ing microwave maps of atmospheric temperature profiles complement the maps by theother spacecraft sensors. This research program focuses on development of an im-proved understanding of the limits to performance of these microwave sensors and thedevelopment of high-performance estimation procedures appropriate for handling theeffects of precipitation, clouds, and the surface, as well as the nonlinear, non-Gaussian,and nonstationary character of the statistics.Initial analysis of the data has revealed that the instrument performance is excellent.Software to analyze the scientific results is now being prepared.5. SCANNING MULTICHANNEL MICROWAVE RADIOMETER (SMMR)EXPERIMENTNational Aeronautics and Space Administration (Contract NAS5-22929)David H. Staelin, Philip W. RosenkranzThe two SMMR passive microwave instruments were launched June 26, 1978 on theSeasat satellite, and October 24, 1978 on the Nimbus-7 satellite. The Nimbus-7 SMIMRscans the earth over a ~780-km swath with resolutions of ~20-150 km, depending onfrequency. The instruments view the earth at a constant incidence angle of 50 degrees, attwo orthogonal linear polarizations and five frequencies: 6.6, 10.7, 18, 21, and 37 GHz.PR No. 121(XIV. RADIO ASTRONOMY)Parameters that can be mapped for the first time by this instrument include seasurface temperature and roughness, and certain snow, rain, ice, and humidity param-eters. The effort to develop improved geophysical analysis techniques centers on thedevelopment of improved physical models for the phenomena and improved estimationtechniques that appropriately reflect the nonlinear and nonstationary character of theproblem.One of the critical issues in the data interpretation process arises from thefrequency-dependent angular resolution of the sensors. An approach to this problemhas been developed and described.1 This procedure takes proper account, in a least-squares sense, of the three-dimensional statistical behavior of the physical phenomenonand of the frequency-dependent character of the sensor.References1. P. W. Rosenkranz, "Inversion of Data from Diffraction-Limited MultiwavelengthRemote Sensors. I. Linear Case," Radio Sci. 13, 1003-1010 (1978).6. METEOROLOGICAL REMOTE SENSING NEAR 2-mm WAVELENGTHNational Aeronautics and Space Administration (Contract NAS5-23677)David H. Staelin, Philip W. RosenkranzThe 118-GHz radiometer system was operated aboard the CV-990 aircraft for theSummer Microwave Hurricane Program (SMHP) during the summer and fall of 1978.Brightness temperatures were measured looking downward at clear atmosphere andrain cells and also upward at rain cells.The clear air data were inverted using a linear statistical method of multidimen-sional regression. The inferred temperature profile was compared with the profilemeasured by a dropsonde released from the aircraft. Agreement between the twoprofiles was within the expected error in the retrieval procedure, -1 K. This is thefirst temperature profile retrieval to be obtained using the 118-GHz oxygen line.7. MICROWAVE SPECTROSCOPY OF THE INTERSTELLAR MEDIUMNational Science Foundation (Grant AST77-129 60)Alan H. Barrett, Philip C. MyersDuring the past year our studies of atomic and molecular interstellar gas cloudshave continued, with observations of microwave transitions of HI, CO, CS, NH 3 , H 2 CO,and HC5N, toward Bok globules, dark clouds, molecular clouds associated with H IIPR No. 121(XIV. RADIO ASTRONOMY)regions, and globular clusters. We have used radio telescopes of the National RadioAstronomy Observatory in Green Bank, West Virginia, and at Kitt Peak, Arizona; Na-tional Astronomy and Ionosphere Center in Arecibo, Puerto Rico; Millimeter WaveObservatory, Fort Davis, Texas; and of M. I. T. Haystack Observatory.Observations have been made of HC 5 N, NH 3 , and CO emission from a number ofsmall dense clouds in Taurus which form a streamer. The NH 3 emission was foundto exhibit a wide range of intensity variation from cloud to cloud, by a factor of -10.-1The velocity width is very small, typically ~0.5 km s . The HC 5 N emission was de--1tected only in one cloud, TMC-2, where the width is extremely narrow, ~0.2 km s .The CO observations indicate that the dense clouds have temperature 10-15 K. In TMC-2,the small size (~0. 1 pc) and linewidth of the HC 5 N region suggest that this dense clumpmay be a nearly stable prestellar condensation.8. RADIO ASTRONOMY STUDIES OF INTERSTELLAR MASERS,THE INTERGALACTIC MEDIUM, AND EXTRAGALACTICSOURCESNational Science Foundation (Grant AST77-26896)Bernard F. Burke, Robert C. Walker, Aubrey D. Haschick, Thomas S. Giuffrida,J. Antonio Garcia-BarretoThe principal aims of this research have centered on the properties of the inter-stellar medium. In our own galaxy, the emphasis was on the properties of interstellarmasers, which are closely related to stars in their earliest stages of formation. Theextragalactic studies concentrated on the properties of the interstellar gas in Seyfertgalaxies and in the intracluster medium in clusters of galaxies.The maser work emphasized the use of VLBI methods to.map the maser complexes,which consist of clusters of individual spot sources, each at its own velocity. As partof his Ph.D. thesis, Robert C. Walker showed that the apparent size of a given spotis a strongly varying function of the observing frequency within the line. Near the linecenter, the apparent size is smaller than in the wings of the line, and no model is infull agreement with the data. A saturated maser model is closer to the data, however,than an unsaturated model. A study of the OH maser in W3OH, the observations havingbeen taken two years previously in a 7-station VLBI experiment, finally neared comple-tion. Aubrey D. Haschick, working with M. Reid of the NRAO, produced a detailedmap of the region that strongly suggests multiple Zeeman pairs. Some work remainsto be done on the enormous quantity of data that had to be reduced, but the principal taskis now complete.A discovery was made in the W30H water maser of a strongly time-varying linethat was followed through its entire development, and three VLBI experiments werePR No. 121(XIV. RADIO ASTRONOMY)performed to clarify the results. The H20 complex is in the form of a well-defined arc,plus a few outlying sources. One of the sources in the arc came up from a low intensityover a one-week period, and then declined over the following month. The light curveappears to be fitted accurately by a simple phenomenological theory, but the implicationis that a large amount of pump energy, 1040 ergs or more, had to be released withinone or two days. Star-formation processes may well involve such unexpected irregular-ities, but the current state of cosmogonic models lacks predictive power fur such ir-regular phenomena, which may be caused by magnetic-field merging.The study of the intracluster medium resulted in stringent upper limits to the quan-tity of neutral hydrogen inside clusters of galaxies. A total of 15 nearby clusters werestudied by looking for hydrogen absorption lines against background radio sources. Theobserved upper limits on the density are several orders of magnitude below the densityneeded to bind the clusters or close the universe.Work with the Very Large Array (VLA) of the NRAO in Socorro, New Mexico hasbegun, and several programs have been carried out that were designed, in part, to helpwith development of the equipment. The x-ray source associated with the galaxyNGC 2110 was identified quickly, and the coincidence of the radio source with the nucleusof the galaxy was established. The source has a 3 arc-second size and a normal radiospectrum.The extensive program on hydrogen absorption lines in galaxies was completed byAubrey D. Haschick in his Ph.D. thesis. Several examples of absorption lines in quasar/galaxy pairs were studied, absorption lines in Seyfert galaxies were discovered, and anunusual example of an absorption line in the radio source 2C178 was also discovered.Absorption lines in Seyfert galaxies appear to be a moderately common phenomenon.The microwave aperture-synthesis interferometer was completed during the reportyear. The "debugging" operations are proceeding, and useful observations will be ex-pected after approximately one year of engineering studies. At the same time, we aredeveloping a cooled 7-mm mixer that should be useful for interferometric observations.PR No. 121

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