Contains reports on five research projects.National Science Foundation (Grant AST82-14296)National Aeronautics and Space Administration (Grant NAG W-373)National Aeronautics and Space Administration (Grant NAG5-537)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)SM Systems and Research, Inc.Defense Advanced Research Project Agency (Contract MDA903-82-K-0521

Arias, Tomás A.

Barrett, John W.

Briançon, Alain C.

Burke, Bernard F.

Cassereau, Philippe M.

Clark, Lloyd D., Jr.

Colavita, M. Mark

de Jaeger, Gerhard

Dreher, John H.

Hammerschlag, Roeland V.

Holm, R. Walter

Kelly, Matthew J.

Rosenkranz, Philip W.

Shao, Michael

Staelin, David H.

Wornell, Gregory W.

DSpace@MIT

Radio Astronomy28. Radio AstronomyAcademic and Research StaffProf. B.F. Burke, Prof. J.W. Dreher, Prof. D.H. Staelin, Dr. G. de Jaeger, Dr.P. W. Rosenkranz, Dr. M. Shao, J. W. BarrettGraduate StudentsT.A. Arias, G.J. Bartlett, P.J. Bonanni, A.C. Briangon, C. Carilli, P.M. Cassereau,L.D. Clark, M.M. Colavita, V. Dhawan, A.J. Gasiewski, M. Heflin, J.N. Hewitt,R.W. Holm, M.J. Kelly, A.M. Kirkland, G.I. Langston, J. Lehar, H.S. Malvar, J.C.Preisig, J.M. Shapiro, B.I. Szabo, A.S. Tom, G.W. Wornell28.1 Galactic and Extragalactic ResearchNational Science Foundation (Grant AST82-14296)Bernard F. Burke, John DreherThe distribution of matter in galaxies and in the universe as a whole is being investigated. Theprimary methods are the study of the deflection of radio and light waves by the gravitational fieldsassociated with large-scale aggregation of matter, and by direct observations of the gravitationalinteractions of galactic systems.1) The VLA is being used for a continuum study of the original twin quasar, the gravitationallylensed source 0957 + 561. The principle emphases of the observational VLA monitoring programis to measure the time delay between the arrival of wave fronts of the two lensed images. Adetermination of the time delay could in principle constrain estimates of cosmologicalparameters, and such studies of many gravitational lens systems will certainly tell us a great dealabout cosmology and the distribution of matter on the largest scales.2) VLBI observations of a sample of radio sources showing subarcsecond structure are beinganalyzed for evidence of gravitational lensing on a subsecond scale. Theoretical calculationsindicate that lensing by single galaxies should produce many examples of multiple images withsuch small separations.3) The gravitational lens search program continues, with 1000 more observations at the VLA, ofsources selected from the MG survey. A total of 4000 sources have been observed, and a sampleof these will be observed optically. Optical observations at Kitt Peak have yielded severalcandidates for gravitational lensing. the most spectacular instance so far was revealed by opticalspectra of what appear to be a pair of quasars with apparently identical redshifts, notable for theRLE P.R. 128219Radio Astronomyimage separation of 2.6 a, cminutes, 30 times larger than the previous lenses found. the nature ofthe lens is not known yet, but speculation yields interesting possibilities: it could be a cosmicstring, a supermassive black hole, or an accumulation of matter in an unfamiliar state. Radioobservations are being planned that should eliminate or confirm the possibilities.4) Follow-up observations of VLA snaps for models of radio source evolution are complete. Thedata will be used to test models of radio sources powered by massive black holes.5) The M.I.T. Greenbank radio survey of the sky at 6 cm nears completion of the first half. Thesurvey will be complete for the brightest sources in the declination range 170 to 4706) We are also conducting a study of the powerful double-lobed radio galaxy, CygnusA. Multi-frequency, with high resolution VLA images have revealed a wealth of structures withinthe radio lobes, including a previously undetected Jet extending from the core source into thenorthern lobe, and many lower surface brightness "filaments" of emission threading the lobes. Ascreen of magnetized gas in front of the source has also been seen, which gives rise to extremevalues of Faraday rotation (IRMI > 2000 rad/m/m). We plan to extend these studies to the limits ofthe present VLA system, with further observations at frequencies ranging from 327MHz - 23 GHz.Using our radio data, along with previous optical and x-ray observations, we hope to investigatethe conditions within the Faraday screen, as well as to verify or constrain existing theoreticalmodels of extended extragalactic radio sources.7) A program to observe the fine-scale structure of the HII regions associated with active sitesof massive star formation is also underway. Early results using high resolution VLA imagessupport both "implosive" star formation models and the hierarchical "ring" formation scenario.Complementary to this continuum work, millimeter wavelength observations of molecular lines arebeing made at Hat Creek as well as recombination line observations at the VLA8) Work is also being performed on the analysis of a novel technique to remove the effects of"windowing" on irregularly sampled time series data. the technique is being applied to analyzethe short-time scale (<1 hr) variability of the B1Lac object OJ287.28.2 Jovian Decametric RadiationNational Aeronautics and Space Administration (Grants NAG W-373 and NAG5-537)David H. Staelin, Philip W. Rosenkranz, Tombs A. Arias, Roeland V. HammerschlagThe Planetary Radio Astronomy (PRA) experiment on the Voyager 1 and 2 spacecraft observedradio emission from Earth, Jupiter, Saturn, and Uranus in 198 channels distributed over the bandfrom 1.2 kHz to 40.5 MHz.RLE P.R. 128 220Radio AstronomyDuring 1985 the Voyager data was examined much more carefully with 6-second resolution atfrequencies below 1.2 MHz where the spectrometer has higher spectral resolution and is moreinsensitive to spacecraft-interference. The Jovian modulated spectral activity (MSA) which wasdiscovered last year was studied much more intensively. These studies suggest that thepolarization of this emission varies rapidly and without organization on the observed space-timescale. The occasional saw-tooth form of the emissions with respect to frequency has beenstudied further and theoretical work to explain this behavior was begun.The software that displays the Voyager PRA data as a function of frequency and time has beenlargely transferred to the Apollo computer, which can provide color imagery for study.28.3 Long-Baseline Astrometric InterferometerU.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)David H. Staelin, Michael Shao, John W. Barrett, M. Mark Colavita, Lloyd D. Clark, R. Walter Holm,Mathew J. KellyDuring 1985 the Mark III optical astrometric interferometer entered the construction phase atthe Mount Wilson Observatory with the installation of a large concrete table flanked by sixreinforced concrete pedestals, each 4 ft x 4 ft at the base, 8 ft tall, and half buried. The outermostpedestals in the north-south direction are separated by 20 meters, whereas the inner pair areseparated by 10 meters; the two east-west pedestals are at similar distances from the beamcombiner. Two 18-ft vacuum tanks containing movable delay lines have been installed on theconcrete table, which now sits inside an insulated shed approximately 12 x 6 meters in size.An improved star-tracking mechanism based on a photon camera has been developed and willbe installed when the new photon camera becomes available. Remaining to be completed are themain beam combiner and the laser systems for monitoring the positions of the siderostat mirrorassemblies to the high precision required ( F 1000 A ).This two-color astrometric instrument, operated under a joint program involving theSmithsonian Astrophysical Observatory and M.I.T., is expected to demonstrate wide angle( 200 ) differential astrometry with accuracies on the order of 10- 3 arc seconds. Theastrometric measurements, expected to begin late in 1986 or early 1987, should illuminate thelimits to astrometric accuracy posed by the atmosphere and by other effects.Also during 1985 the initial analysis of the Mark II astrometric interferometer data wascompleted.' This experiment, also at Mount Wilson, demonstrated the success of the two-colormethod for removing much of the atmospheric error introduced by the atmosphere. The variousatmospheric effects were analyzed theoretically.RLE P.R. 128221Radio AstronomyReferences1. M.M. Colavita, "Atmospheric Limitations of a Two-Color Astrometric Interferometer," Ph.D.Thesis, Department of Electrical Engineering and Computer Science, M.I.T., May 1985.28.4 Tiros-N Satellite Microwave SounderSM Systems and Research, Inc.Philip W. Rosenkranz, David H. Staelin, Alain C. BriangonThe National Oceanic and Atmospheric Administration (NOAA) operates polar orbiting weathersatellites carrying 4-channel passive microwave spectrometers (MSU) which map thethree-dimensional temperature field of the atmosphere at 6- or 12-hour intervals. This researchprogram is directed toward improved utilization of this passive microwave data on present andfuture NOAA satellites.Much effort this year was directed toward the next-generation Advanced Microwave SoundingUnit (AMSU). The AMSU has 15 channels which image the Earth with 50-km resolution every 12hours at frequencies distributed from 23 to 90 GHz; twelve of these channels sound atmospherictemperature profiles from 0 to 41-km altitude. Five additional channels between 90 and 186 GHzwill sound atmospheric precipitation and humidity with 15-km resolution. Continued progresswas made on definition of an optimum architecture for operational data reduction systems forAMSU. The goal is to maximize algorithmic flexibility through creative use of data arrays providedat execution, rather than by altering program code.The utility of multi-dimensional temperature profile retrievals was studied further, and theperformance of various techniques was compared. It was found that these techniques yieldsuperior performance for MSU data, and relatively smaller improvement for AMSU. Because ofthe nonstationary character of atmospheric statistics, useful improvements in retrieval accuraciescan also be achieved by using adaptive retrieval techniques, and study of such techniques isbeing continued.28.5 Video Bandwidth Compression TechniquesDefense Advanced Research Project Agency (Contract MDA903-82-K-0521)David H. Staelin, Gerhard de Jaeger, Philippe M. Cassereau, Gregory W. WornellThis research effort focuses on techniques for coding at 9.6 - 56 kbps full-motion videosequences characteristic of videoconferencing. When block transform coding techniques areused at low data rates, unacceptable block noise can be produced at the boundaries of thoserectangular image subunits over which the transforms are computed. This problem can beRLE P.R. 128 222Radio Astronomymitigated by use of a new class of transforms, designated Lapped Orthogonal Transforms (LOT),which have basis functions that overlap the basis functions in adjacent blocks while retainingorthogonality. This transform was successfully used for motion-compensated video compressionand exhibited reduced block noise without excessive ringing near block edges or image.contours.' It is believed that improved versions of the LOT can be developed.Cluster techniques were applied to the energy distributions within an ensemble of blocktransforms in order to define categories of transforms for which quantization patterns could beeffectively tailored. It was found that coding performance continued to improve as the number oftransform categories reached 32. 2 Incorporation of these adaptive transform techniques should,in principle, noticeably improve the performance of present video coding algorithms.References1. P.M. Cassereau, "A New Class of Optimal Unitary Transforms for Image Processing," S.M.Thesis, Department of Electrical Engineering and Computer Science, M.I.T., May 1985.2. A.M. Kirkland, "Image Block Classification for Adaptive Transform Coding," S.M. Thesis,Department of Electrical Engineering and Computer Science, M.I.T., September 1985.RLE P.R. 128223Publications and ReportsRLE P.R. No. 128 224

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