Contains reports on research objectives and eight research projects.National Science Foundation (Grant AST79-25075)National Science Foundation (Grant AST79-20984)National Science Foundation (Grant AST79-19553)U.S. Navy - Office of Naval Research (Contract N00014-80-C-0348)National Aeronautics and Space Administration (Grant NAG2-50)M.I.T. Sloan Fund for Basic ResearchJoint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104)National Aeronautics and Space Administration (Grant NAG5-10)National Aeronautics and Space Administration (Contract NAS5-25091)National Aeronautics and Space Administration (Contract NAS5-22929)U.S. Department of Commerce - National Oceanic and Atmospheric Administration (Grant 04-8-MOl-1

Ali, Ali D. S.

Barrett, Alan H.

Baumann, William T.

Bigelow, Timothy S.

Burke, Bernard F.

Jin, Jian-sheng

Johnson, Timothy L.

Komichak, Michael J.

Lang, Jeffrey H.

Myers, Philip C.

Rosenkranz, Philip W.

Shao, Michael

Staelin, David H.

Szabo, Bernard I.

Toldalagi, Paul

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XV. RADIO ASTRONOMYProf. A.H. BarrettProf. B.F. BurkeProf. J.R. MelcherProf. P.C. MyersProf. D.H. StaelinA.D. AliB.R. AllenJ.T. ArmstrongY. Bar-YamW.T. BaumannC.L. BennettP.J. BensonT.S. BigelowR.B. BuxtonAcademic and Research StaffProf. E.L. WrightDr. A. RifaiDr. D.H. RobertsDr. P.W. RosenkranzGraduate StudentsS.D. DagaaE.E. FalcoR.I. FeigenblattJ.A. Garcia-BarretoP.M. GarnavichP.E. GreenfieldJ-s. JinY. JinM.J. KomichakJ.H. LangDr. M. ShaoJ.W. BarrettJ.G. KangJ.D. KiersteadD.C. PapaC.R. LawrenceD.C. MurphyB.R. RosenM.H. SchnepsJ.C. SzczepanskiP. ToldalagiJ.V. VallergaW. WilliamsY. Yam1. MICROWAVE SPECTROSCOPY OF THE INTERSTELLAR MEDIUMNational Science Foundation (Grant AST79-25075)Alan H. Barrett, Philip C. MyersIn 1980 three main efforts were pursued: (1) a study of motions and physicalconditions in the galactic center, as indicated by emission in NH3 inversion lines;(2) observations in lines of CO and NH3 to analyze nearby reflection nebulae; and(3) studies of CO and NH3 emission from nearby regions of high extinction. In thislast study, about 15 regions have been identified as cold cloud cores, with den-sity %3 x 104 cm- , temperature %10 K, mass 1l M0, and velocity dispersion between1 and 2 times the thermal dispersion. These are good candidates to be future low-mass stars.PR No. 123(XV. RADIO ASTRONOMY)2. RESEARCH OBJECTIVESNational Science Foundation (Grant AST79-20984)B.F. BurkeThe research program in radio astronomy is primarily centered on the use ofinterferometric techniques, including hard-wired arrays and Very-Long-BaselineInterferometry (VLBI), to study phenomena on the galactic and extragalactic scale.The principal activities are as follows:1. Interstellar masers are being studied, using VLBI, to determine theirstructural, polarization, and time-variation properties.2. The VLBI technique is being pressed to lower frequencies (300 MHz, 600MHz, and 1400 MHz) to study the characteristics of quasars and galactic nuclei.3. The double quasar 0957+561, the first observational example of the gravi-tational lens phenomenon, will continue to be studied. We are particularly con-cerned with its time variations, which may provide an entirely new class of cos-mological information. Both VLA (Very Large Antenna of the NRAO) and VLBI obser-vations will be employed.4. A computing system for reducing VLA snapshot data is being developed.The basic instrument will be our NOVA 800 computer, with added disc and core mem-ory. The software development will be partly in collaboration with Dr. Hjellmingof the NRAO.5. Our survey of radio sources under way at the NRAO, using the 300-ft tran-sit telescope at 5 GHz, has been broadened to include a general survey of theentire strip -30 to +200, comprising 2 steradians of sky. The survey should becompleted by late 1981.6. A new project has been started to look for spatial fluctuations in bright-ness of the cosmic microwave background. A multichannel receiver is being built,for use with the 140-ft NRAO telescope, to improve statistics and to give betterdiscrimination against spurious effects such as atmospheric fluctuations.PR No. 123(XV. RADIO ASTRONOMY)3. LONG-BASELINE ASTROMETRIC INTERFEROMETERNational Science Foundation (Grant AST79-19553)U.S. Navy - Office of Naval Research (Contract N00014-80-C-0348)National Aeronautics and Space Administration (Grant NAG2-50)M.I.T. Sloan Fund for Basic ResearchMichael Shao, David H. StaelinInitial results from the Mark I one-inch aperture, 1.5-meter baseline inter-ferometer experiment at Mt. Wilson Observatory were published, 1 and further reduc-tion of the data continued during the year.Work began on the Mark II dual 5-cm aperture, 3-meter baseline interferometerintended to demonstrate a few milliarc sec day-to-day repeatability for measure-ment of angles between stars '1.50 apart, and <0.05 arc sec repeatability forstars 15-20' apart. The design sensitivity is %6-7 mag for 2 arc-sec seeing andlO0-msec averaging times. The system contains two parallel interferometers thatshare the same optics but view different stars (one is one magnitude more sensi-tive than the other).References1. M. Shao and D.H. Staelin, "First Fringe Measurements with a Phase-TrackingStellar Interferometer," Appl. Opt. 19, 1519-1522 (1980).4. CONTROLLED THIN-FILM ANTENNAJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)Jeffrey H. Lang, Timothy L. Johnson, David H. StaelinThe use of electrostatic charges for rapidly manipulating a thin membrane isbeing studied as a method for precisely controlling the shape of reflector anten-nas of lO0-300-meter diameter in space; beamwidths <l-10 arc sec are sought.This year we began the design of a 5-ft diameter rubber-membrane mirror with100 control elements. Theoretical studies have focused on finite-element repre-sentations for control and on formulations that can handle more effectively thespillover between sensors, actuators, and modes.PR No. 123(XV. RADIO ASTRONOMY)5. IMPROVED MICROWAVE RETRIEVAL TECHNIQUESNational Aeronautics and Space Administration (Grant NAG5-10)Philip W. Rosenkranz, Michael J. Komichak, David H. StaelinThis program, which began in 1980, is directed toward the development of im-proved techniques for retrievals of atmospheric temperature, wind, and humidityfields from passive microwave spectral images of the earth, as observed from sat-ellites. Linear statistical retrieval techniques were applied to data for whichthe temperature weighting functions varied in a systematic way with view angle.Improvements were obtained in the mean profile because of the increased number ofeffective temperature weighting functions, but the decorrelation between atmo-spheric temperatures in the horizontal direction was found to be too great topermit further benefits.Evaluations were also made of second-order nonlinear effects in optimum three-dimensional linear statistical retrievals employing Fourier transforms of the datafield. These procedures were successfully applied to atmospheric humidity, watercontent, and other parameters using microwave data from the Nimbus-7 satellite;these case studies were performed under another contract described separately here.Other studies were also performed. For example, regionalization of a prioristatistics was found to help primarily when retrieving tropical parameters, andprogress was made in developing retrieval techniques appropriate for species withopaque spectral lines, such as the 183-GHz resonance of atmospheric water vapor.6. COMMUNICATIONS SATELLITESNational Aeronautics and Space Administration (Contract NAS5-25091)David H. Staelin, Ali D.S. AliThis year a major study of future large broadband switched satellite communi-cation networks was completed and distributed; it was co-authored by David H.Staelin of the Research Laboratory of Electronics and Robert L. Harvey of LincolnLaboratory. It explored the future markets for communications services, technicalPR No. 123(XV. RADIO ASTRONOMY)means for providing the necessary communications systems, economic analyses andtradeoff studies, and a survey of many of the primary policy issues such expansionwould have. Novel technical concepts include an efficient multibeam antenna andsignal-switching configuration for satellites, and a concept for clusters of coop-erating but individually switched satellites that share a single orbital slot.Related analyses have been performed on the relative merits of FDMA and TDMAsystems and on the optimum relationship between terrestrial links employing opticalfibers or other low-cost technologies versus the use of satellites.7. VIDEO-BANDWIDTH COMPRESSION TECHNIQUESM.I.T. Sloan Fund for Basic ResearchDavid H. Staelin, Bernard I. SzaboExperiments were performed on adaptive-quantization picture-coding schemesthat were applied to two- and three-band images; the bands included (1) low-frequency images formed by 8 x 8-pel averages which were bilinearly interpolated,(2) medium-frequency images formed by the difference between bilinearly interpo-lated 2 x 2-pel averages and the low-frequency images, and (3) high-frequencyimages which were the difference between the total true images and either the low-frequency images or the sum of the low- and medium-frequency images. An image ofa cameraman was coded with 1.5-0.9 bits per pel to produce images that ranged fromexcellent to slightly annoying, respectively. Conditional replenishment video-coding schemes using these representations are estimated to require %0.4-4 Mbpsfor acceptable monochrome video images of 512 x 512 pels.8. SCANNING MULTICHANNEL MICROWAVE RADIOMETER (SMMR)National Aeronautics and Space Administration (Contract NAS5-22929)Philip W. Rosenkranz, Timothy S. Bigelow, William T. Baumann, David H. StaelinResearch under this contract has been in two areas:(1) Application of a linear spatial filtering to the problem of estimatingocean-surface temperature, near-surface wind speed, and atmospheric water vaporand liquid water from measurements made by the Scanning Multichannel MicrowavePR No. 123(XV. RADIO ASTRONOMY)Radiometer, an instrument which was launched on the experimental satellites1,2NIMBUS-7 and SEASAT.(2) Nonlinear techniques for remote sensing of atmospheric water vapor andmesospheric winds. 3References1. P.W. Rosenkranz and W.T. Baumann, "Inversion of Multiwavelength RadiometerMeasurements by Three-Dimensional Filtering," in A. Deepak (Ed.), Remote Sens-ing of Atmospheres and Oceans (Academic Press, New York, 1980), pp. 277-312.2. P.W. Rosenkranz, "Inference of Sea Surface Temperature, Near-Surface Wind, andAtmospheric Water by Fourier Analysis of Scanning Multichannel Microwave Radi-ometer Data," COSPAR/SCOR/IUCRM Symposium on Oceanography from Space, Venice,Italy, May 26-30, 1980.3. D.H. Staelin, "Progress in Passive Remote Sensing: Nonlinear Retrieval Tech-niques," in A. Deepak (Ed.), Remote Sensing of Atmospheres and Oceans (AcademicPress, New York, 1980), pp. 259-276.9. TIROS-N SATELLITE MICROWAVE SOUNDERU.S. Department of Commerce - National Oceanic and Atmospheric Administration(Grant 04-8-MOl-1)David H. Staelin, Philip W. Rosenkranz, Paul Toldalagi, Jian-sheng JinThe purpose of work under this contract is to develop improved methods ofestimating atmospheric parameters, especially temperature, using the MicrowaveSounding Unit, a four-channel scanning microwave radiometer which has been launchedon the operational weather satellites TIROS-N and NOAA-6. Adaptive Kalman filter-ing1 for temperature estimation and pattern recognition for cloud correction havebeen studied.References1. P.M. Toldalagi, "Some Adaptive Filtering Techniques Applied to the PassiveRemote Sensing Problem," in A. Deepak (Ed.), Remote Sensing of Atmospheresand Oceans (Academic Press, New York, 1980), pp. 19-44.PR No. 123

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