I started my astronomical career in radio astronomy, using the facilities of the NASA Deep Space Network at Goldstone, just outside of Barstow in the southern California desert. These are the facilities I used for the papers on Uranus & Jupiter. I finished my astronomical career primarily analyzing the image data from the Spitzer Space Telescope, although in 2006 I did venture to the high ground of the The Mauna Kea Observatories, to use the Caltech Submillimeter Observatory (CSO). And in the middle of my astronomy career, I took a "break" to work on atmospheric physics and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) project. I have had an opportunity to work with top class scientists from all over the world, in both Earth & space sciences, collaborating with teams from France, Italy & Japan. When I pursued my education in physics, I could hardly have hoped for this kind of opportunity, to spend 28 years working with the Grandmasters in their fields. It was a fascinating experience, which I will document here through the bibliography of my own published research. There are no Einstein breakthroughs here, but just my contributions to the steady progress of science, such as they are.
I came to the Jet Propulsion Laboratory in January 1981, as part of the Radio Astronomy Group, which later changed its name to the Radio/Submillimeter Astronomy Group, in order to emphasize our transition into the then newly available submillimeter wavelengths. Our main thrust in those days was to use observations characteristic of thermal emission, to probe the structure of the atmospheres of the giant planets: Jupiter, Saturn, Uranus, and Neptune. A number of papers had already come out of the group, on Jupiter and Saturn, before I joined. This paper was the first one I was to work on. Our group was the first to recognize the time variability of the Uranian microwave spectrum, and the first to suggest a cause.
Abstract: Radio astronomical observations of Uranus show that the radio emission spectrum is evolving in time. Ammonia vapor must be depleted in the Uranian atmosphere as Gulkis and his co-workers previously suggested. Since 1965, ammonia either has been decreasing in time or is a decreasing function of latitude, or both, provided that the radio emission is atmospheric in origin. If Uranus has an observable low-emissivity "surface," these trends may be reversed. The microwave observations made in 1965, at the time when the spin axis of Uranus was nearly perpendicular to the sun-Uranus line, are consistent with an atmospheric opacity profile that would be produced by saturated ammonia vapor in a predominately hydrogen atmosphere. At the present time, when the spin axis of Uranus is nearly aligned with the sun-Uranus line, the measurements require an opacity that would be produced by saturated water vapor. A large thermal gradient between the pole and equator is ruled out.
The other major project that I worked on was the Jupiter Patrol, a long term project of Mike Klein's that monitored the synchrotron emission from Jupiter at 2295 MHz, using the radio antennae of the Deep Space Network, for more than a full solar cycle. We were eventually able to draw direct correlations between the synchrotron emission, and the solar wind loading of the Jovian magnetosphere. This was a significant result, because we were monitoring emissions from deep within the Jovian magnetosphere. At the time, it was thought that low energy electrons from the solar wind could not diffuse into the inner magnetosphere on such short time scales as we were able to demonstrate. Scott Bolton eventually came up with a new theoretical model for electron diffusion that became his PhD thesis, and explained the observations nicely. The electrons come in the back door, diffusing through the weaker magnetic field at the tail of the magnetosphere.
Abstract: A long-term observational program to monitor the time variations of the microwave emission from Jupiter has been in progress since April 1971. The measurements are made several times each month with the NASA Deep Space Network (DSN) antennas operating at 2295 MHz (13.1 cm). The data set, when combined with measurements by other observers, provides a record that extends over two 11-year solar cycles. The combined data set shows considerable variability that may be directly related to the high-energy electron population of the inner magnetosphere. Preliminary results of a study to search for plausible correlations between the Jovian synchrotron emission and solar-related phenomena reveal that a positive correlation may exist with the ion number density in the solar wind.
Abstract: It is generally believed that the strong magnetic field of Jupiter insulates the inner magnetosphere from fluctuations in the solar wind, and that the high energy electrons (>1Mev) responsible for the synchrotron radio emission from the planet are produced by inward diffusion of electrons from regions of weak to strong magnetic field intensity. Both the driving force for the diffusion process and the source of the relativistic electrons are presently unknown. It is widely believed that the diffusion process is driven by winds in Jupiter's ionosphere rather than fluctuations in the solar wind. Possible sources for the electrons include the Jovian satellites, in particular Io, Jupiter's ionosphere, and the solar wind. Thus far, no unambiguous connection between the solar wind properties and the relativistic inner belt electrons has been established. Such correlations, if they exist, could help to understand the physical processes that lead to the radiation belts. This paper reports on a study aimed at searching for correlations between Jovian decimetric radio emission and various solar wind parameters described below. Measures of correlations of the solar wind parameters with the decimetric radio emission will be presented.
The radio data used in our study are based primarily on a uniform set of observations carried out since April 1971 with the NASA Deep Space Network of antennas operating at 2295 MHz (13.1 cm) (Klein et al., 1972; Klein, 1976). This data set, when combined with measurements by other observers provides a record that extends over two 11-year solar cycles. The combined data set shows considerable variability that can be directly related to the high energy electron population (Hide and Stannard, 1976; Klein, 1976).
The data set of the solar wind parameters is composed of five quantities measured by numerous earth orbiting spacecraft along with Pioneer 10 and 11 and Voyager 1 and 2. These are 1) solar wind, 2) velocity, 3) proton density, 4) proton temperature, and the 5) strength and direction of the magnetic field. The data, provided by the NSSDC, encompasses the time frame from 1963 to 1985.
Hide, R. and D. Stannard, Jupiter's magnetism, observation and theory, Jupiter, ed. T. Gehrels,
University of Arizona Press, Tucson, 767-787, 1976.
Klein, M.J., The variability of the total flux density and polarization of Jupiter's decimetric radio emission Journal of Geophysical Research 81, 3380-3382, 1 July 1976.
Klein, M.J., S. Gulkis, and C.T. Stelzreid, Jupiter: New evidence of long term variations of its decimetric flux density
Astrophysical Journal 176, L85-L88, 1972.
Abstract: Results of a study comparing long-term time variations (years) in Jupiter's synchrotron radio emission with a variety of solar wind parameters and the 10.7-cm flux are reported. Data from 1963 through 1985 were analyzed, and the results suggest that many solar wind parameters are correlated with the intensity of the synchrotron emission produced by the relativistic electrons in the Jovian Van Allen radiation belts. Significant nonzero correlation coefficients appear to be associated with solar wind ion density, ram pressure, thermal pressure, flow velocity, momentum, and ion temperature. The highest correlation analysis suggests that the delay time between fluctuations in the solar wind and changes in the Jovian synchrotron emission is typically about 2 years. The delay time of the correlation places important constraints on the theoretical models describing the radiation belts. The implication of these results, if the correlations are real, is that the solar wind is influencing the supply and/or loss of electrons to Jupiter's inner magnetosphere. We note that the data for this work spans only about two periods of the solar activity cycle, and because of the long time scales of the observed variations, it is important to confirm these results with additional observations.
By this time the Radio Astronomy Group was heavily involved in the NASA SETI project, which began to grow rapidly in 1988. In 1992, on Columbus Day the NASA SETI project made its official start, amidst fanfare and publicity. Congress cancelled the program within a year. I left the Radio Astronomy Group at about that time as the money for astronomy and astrophysics became too scarce. However, we all received NASA Group Achievement Awards for what we were able to get done. All SETI is now in private hands, mostly The SETI Institute and The Planetary Society. Most of my work centered around planning a system for storing several hundred terabytes of data, which was a far more difficult task to accomplish or pay for in the early 1990s than it is today. I also worked on observation strategies and the problem of radio frequency interference (RFI; intelligent signals of terrestrial origin, which must be filtered out before we look for intelligent signals of extraterrestrial origin).
I also had minor a minor support role in the COBE project. But one other interesting project, which unfortunately had little support, was a project we dubbed Argus. This was an attempt to monitor the Milky Way for transient sources, especially including supernova explosions, which are quite visible in the radio, but not optically, because of the heavy dust burden in the plane of the Galaxy. We collaborated with Woody Sullivan, from the Astronomy Department at the University of Washington. Despite its apparent scientific value, the program did not get funded over the long term.
After working in the radio astronomy group from 1981 to 1993, I spent a year as an assistant network administrator for the Science Computing Network, in the Earth & Space Sciences Division at JPL. It was a mixed network of mostly Sun workstations, along with Digital miniVAX, and a few Apple Macs, designed to supply computer support for the division scientists. I handled all of the system maintenance tasks and customer support for the VAX & Apple systems, and much of the maintenance for the network cables scattered around a few buildings.
Early in 1994 I joined the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) project, as a member of the Atmospheric Corrections Group, a part of the science team for the Thermal Infrared (TIR) detector on the ASTER instrument, which launched on the TERRA satellite of the Earth Observing System (EOS) on 18 December 1999. I designed the algorithms to compensate for the presence of Earth's atmosphere between the satellite and the ground. By removing the infrared signature of the atmosphere, we would then recover the infrared properties of the surface, which allows determination of both temperature and emissivity for the surface. Most of my time pre-launch was devoted to designing the algorithms to do that in an automated, data pipeline environment. After launch I took part in the vicarious calibration program, where we deployed on numerous occasions to specific targets, usually desert dry lake playas or lake surfaces, though we did once use the blacktop of the parking lot at Magic Mountain. The team would set up instruments to measure the physical & radiative properties of the target surface, and the atmosphere, coincident with the satellite overpass; I was responsible for the weather station, radiosonde (weather balloon) and solar radiometer. We would then use the data gathered in-situ to do the atmospheric compensation on ASTER TIR raw data, and compare with the results from the algorithms I had designed, to make sure they were doing what we all thought they would do. My algorithms passed the test, matching our calibration exercises within about 1%. The field work included a trip to Venice, Italy, in April 2001, where we were working with an Italian oceanography group studying the problem of Venice slowly sinking under its own weight. They were using ASTER data products, and we were there to help out with that. See my Venice page, and my ASTER page for more about my work on this project.
Abstract (first paragraph of introduction):
The objectives of the ASTER investigation in the thermal infrared include, among other things, providing estimates of the radiance leaving the land surface. The radiance, which is measured by the ASTER instrument, includes emission, absorption and scattering by the constituents of earth's atmosphere. The purpose of the atmospheric correction method, described in this document, is to remove these effects providing estimates of the radiation emitted and reflected at the surface. Atmospheric corrections are necessary to isolate the features of the observation, which are intrinsic to the surface, from those caused by the atmosphere. Only after accurate atmospheric correction can one proceed to study seasonal and annual surface changes and to attempt the extraction of surface kinetic temperatures and emissivities.
Abstract: Calibration of the five EOS ASTER instrument emission bands (90 m pixels at surface) is being checked during the operational life of the mission using field measurements simultaneous with the image acquisition. For water targets, radiometers, temperature measuring buoys and local radiosonde atmospheric profiles are used to determine the average water surface kinetic temperature over areas roughly 3 X 3 pixels in size. The in-band surface leaving radiance is then projected through the atmosphere using the MODTRAN radiation transfer code allowing an at sensor radiance comparison. The instrument at sensor radiance is also projected to the water surface allowing a comparison in terms of water surface kinetic temperature. Over the first year of operation, the field measurement derived at sensor radiance agrees with the image derived radiance to better than plus/minus 1% for all five bands indicating both stable and accurate operation.
In January, 2002, I joined the staff of the newly created Center for Long Wavelength Astrophysics, in the Earth & Space Sciences Division at JPL (which has since been renamed as simply The Science Division). I was initially involved in setting up the software for the center, supporting JPL astronomers in proposal preparation, and simulating data from the Space Infrared Telescope Facility (SIRTF), which was then expected to launch in January 2003. SIRTF eventually launched on August 25, 2003, and was renamed the Spitzer Space Telescope, in honor of Lyman Spitzer, Jr.. It was Spitzer who, in 1947, first pointed out the value of space based telescopes.
Since then I have been more heavily involved in super-resolution enhancement of Spitzer images. Spitzer makes observations by adding up individual frames that are dithered in half-pixel increments. That means there is information about structures smaller than one pixel in the collected images, and our software will extract that information, creating images that are enhanced in resolution by about a factor of 3. The first major result of this was the discovery of an asymmetry in the debris disk around the star Fomalhaut. Our resolution enhanced imagery was able to show that the observations were consistent with models which indicate that the asymmetry is caused by a planet embedded in the debris disk. Of course, this is only an indirect indication, but an exciting result, nonetheless. The disk models were created by Elizabeth K. Holmes, who sadly passed away suddenly in her office, while working on her models. The Fomalhaut paper is dedicated to her memory. The September 2004 issue of The Astrophysical Journal Supplement Series is exclusively devoted to the Spitzer Space Telescope. Although I retired from JPL in 2008, I returned as a consultant in 2012/2013 to work on another exercise in Spitzer imagery.
Abstract: We present Spitzer Space Telescope early release observations of Fomalhaut, a nearby A-type star with dusty circumstellar debris. The disk is spatially resolved at 24, 70, and 160 microns using the Multiband Imaging Photometer for Spitzer (MIPS). While the disk orientation and outer radius are comparable to values measured in the submillimeter, the disk inner radius cannot be precisely defined: the central hole in the submillimeter ring is at least partially filled with emission from warm dust, seen in Spitzer Infrared Spectrograph (IRS) 17.5-34 micron spectra and MIPS 24 micron images. The disk surface brightness becomes increasingly asymmetric toward shorter wavelengths, with the south-southeast ansa always brighter than the north-northwest one. This asymmetry may reflect perturbations on the disk by an unseen interior planet.
Abstract: We present a description of Hires, a super-resolution program based upon the Richardson-Lucy algorithm, generalized to the case of redundant coverage, with higher order optical image distortion, implemented for the Spitzer Space Telescope.
Abstract: Spitzer provides unprecedented sensitivity in the infrared (IR), but the spatial resolution is limited by a relatively small aperture (0.85 m) of the primary mirror. In order to maximize the scientific return it is desirable to use processing techniques which make the optimal use of the spatial information in the observations. We have developed a deconvolution technique for Spitzer images. The algorithm, "HiRes" and its implementation has been discussed by Backus et al. in 2005. Here we present examples of Spitzer IR images from the Infrared Array Camera (IRAC) and MIPS, reprocessed using this technique. Examples of HiRes processing include a variety of objects from point sources to complex extended regions. The examples include comparison of Spitzer deconvolved images with high-resolution Keck and Hubble Space Telescope images. HiRes deconvolution improves the visualization of spatial morphology by enhancing resolution (to sub-arcsecond levels in the IRAC bands) and removing the contaminating sidelobes from bright sources. The results thereby represent a significant improvement over previously published Spitzer images. The benefits of HiRes include (a) sub-arcsec resolution (~0".6 - 0".8 for IRAC channels); (b) the ability to detect sources below the diffraction limited confusion level; (c) the ability to separate blended sources, and thereby provide guidance to point-source extraction procedures; (d) an improved ability to show the spatial morphology of resolved sources. We suggest that it is a useful technique to identify features which are interesting enough for follow-up deeper analysis.
I retired from JPL in November 2008. I had worked with Steve Pravdo to find infrared counterparts in Spitzer images for some of his X-ray sources. That research was published a few months after I had retired.
Abstract: We report the discovery of a cluster of Class I protostars in GGD 27. One of these protostars is the previously known, centrally located, GGD 27-ILL, which powers a massive bipolar outflow. We show that GGD 27-ILL, which is known to be the bright infrared (IR) source, IRAS 18162-2048, and a compact radio continuum source, is also the newly discovered hard X-ray source, GGD 27-X. The observations were made with the ACIS instrument on the Chandra X-ray Observatory. The X-rays from GGD 27-X are variable when compared with 4 years earlier, with an unabsorbed 2-10 keV X-ray luminosity in this observation of 1.5-12 × 1031 erg sec-1 and a plasma temperature of >= 107 K. The X-rays are probably associated with the underlying B0 star (rather than outflowing material), providing a rare glimpse in hard X-rays of an optically obscured massive protostar with an outflow. The X-ray luminosity and spectrum appear to be consistent with stars of its type in other star formation regions. Several other variable X-ray sources are also detected in the IR cluster that contains GGD 27-X. We also discuss another nearby cluster. In each of the clusters there is an object that is X-ray hard, highly absorbed at low energies, in a blank optical/IR/radio field, and variable in X-ray intensity by a factor of >= 10 on a timescale of 4 years. These latter objects may arise from more recent episodes of star formation or may be "hidden" Class III sources.
In 2012/2013 I returned to JPL on a year long part-time consulting contract to produce a new data set of HiRes images of protostars in the Spitzer archives. We were particularly interested in the younger objects, and the primary goal was to create a library of enhanced resolution images for the research community.
To study the role of protostellar jets and outflows in the time evolution of the parent cores and the protostars, the astronomical community needs a large enough database of infrared images of protostars at the highest spatial resolution possible to reveal the details of their morphology. Spitzer provides unprecedented sensitivity in the infrared to study both the jet and outflow features, however, its spatial resolution is limited by its 0.85 m mirror. Here, we use a high-resolution deconvolution algorithm, "HiRes," to improve the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in the IRAC bands) and removing the contaminating side lobes from bright sources in a sample of 89 protostellar objects. These reprocessed images are useful for detecting (1) wide-angle outflows seen in scattered light, (2) morphological details of H2 emission in jets and bow shocks, and (3) compact features in MIPS 24 μm images as protostar/disk and atomic/ionic line emission associated with the jets. The HiRes FITS image data of such a large homogeneous sample presented here will be useful to the community in studying these protostellar objects. To illustrate the utility of this HiRes sample, we show how the opening angle of the wide-angle outflows in 31 sources, all observed in the HiRes-processed Spitzer images, correlates with age. Our data suggest a power-law fit to opening angle versus age with an exponent of ~0.32 and 0.02, respectively, for ages <=8000 yr and >=8000 yr.
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