To supplement planetary study by the world's major observatories and planetary spacecraft - both of which are frequently imaging the planets in very specific wavelengths of light or through radio (i.e., Jupiter) wavelengths - the Arkansas Sky Observatory (ASO) has continued through the past 30 plus years to improve its rapid real-time patrol studies of Mars, Jupiter and Saturn to include visual high resolution studies of planetary clouds and surfaces, very fine bifilar micrometric measurements of planetary clouds and features, and now high-definition digital imaging that is presently available on an updated daily basis through the ASO Image Archives to astronomers worldwide.  It presently is being used by professional and advanced amateur astronomers worldwide in projects ranging from polarization studies to actual ground-based comparative studies for benchmark standards for sophisticated planetary spacecraft.

 

Likewise, the Patrol of the ASO has greatly assisted NASA-driven projects and major observatories worldwide in the study of variable stars, eruptive novae-type stars, actual early observation and confirmation and preliminary light curve collection of novae and extragalactic supernovae, and early comet verification and database collection on faint newly discovered comets.

 

This brief discussion provides a very concise summary of the history, development and actual implementation of the Arkansas Sky Observatory Patrol imaging project and demonstrates the great amount of dedicated manpower and instrument requirements to provide this archive of solar system imagery.

 

VISUAL CONFIRMATION / HIGH DEFINITION VISUAL VERIFICATION AND MONITORING

 

For very detailed imagery of developing areas, such as Martian dust storms, the major changes in and around the GRS on Jupiter or a new white oval seen in the equatorial regions of Saturn for example, the ASO team many times elects to do confirmation and/or early study work visually to detect as fine detail as possible of developing areas of interest.  Many times detail that will escape even the highest resolution imagery can be captured in momentary glimpses by the eye....and the eye can always be called to duty at a minute's notice.

 

As the highly detailed drawing of Jupiter's Great Red Spot (GRS) area shows, the very minute changes that can occur on a nightly - even hourly - basis can be quickly recorded and preserved in the ASO Image Archives for research reference.  Many times when reports are received of developing storms on Mars or cloud development on Jupiter/Saturn, visual work is the preferred method of recording, particularly if the suspect storm or development requires very finely delineated imaging at the spur of the moment and cannot wait for equipment preparation and calibration.

 

In addition to planetary patrols, the Observatory has been instrumental in visual, photographic and photoelectric confirmation and early data collection on hundreds of newly discovered comets, Apollo-type objects, eruptive and novae-type stars.

 

PHOTOELECTRIC DETERMINATION OF LIGHT CHANGES OF MINOR PLANETS and ERUPTIVE VARIABLE STARS

 

The ASO has a successful track record of very detailed determinations of sizes and shapes - as well as very accurate rotational periods - of several minor planets by recording carefully the changes in brightness of these objects over an extended period of time; utilizing the Optec UBV CCD photoelectric photometer and the larger telescope, imaging and successful studies have been done on 433 Eros (1974-75) , 134 Sophrosyne (1980) , 1580 Betulia (1976), 216 Kleopatra (1980) and 201 Penelope (1980).

In addition, detailed ground based support of the extensive International Ultraviolet Explorer (IUE) Experiment of 12 cataclysmic stars in the AAVSO catalog in September 1981 was also conducted by eight observers at the Observatory utilizing the same equipment and protocol developed for the minor planet patrol studies.  Similar "non-planetary" patrol monitoring of cataclysmic stars (79 of them) in the Yale Bright Star Catalog was conducted photoelectrically - monitoring 32 stars on any given night at repeated 45-minute intervals for rapid small scale outbursts - from a period of 1979 through 1981.  Among significant novae studied in earlier photoelectric ASO patrols were Nova Scuti (1975), Nova Cygni(1975), Nova Vulpeculae (a976) and Nova Cygni (1978) in addition to many lesser brilliant novae in recent years. 

 

In July, 1975 the Observatory was instrumental in obtaining ground-based photoelectric data  for the joint Soviet-USA NASA MA-083 Extreme Ultraviolet Telescope Confirmation program which was conducted aboard the now defunct Apollo-Soyuz on July 13, 1975.  Nine stars known to be strong emitters of ultraviolet radiation and also known as eruptive visual stars, were monitored around the clock by a team of 18 observers at the observatory.

 

Extragalactic supernovae monitoring has been recorded in Messiers 31, 51, 81, 65 and several of the brighter NGC spiral galaxies.

 

PLANETARY POSITIONAL MEASUREMENTS

 

In addition to normal determinations of planetary longitude(s) via very accurate micrometric transits of features across a planet's Central Meridian (CM) with the large aperture telescope, the classic bifilar micrometer is frequently utilized to measure:

 

1) transitions of planetary features, such as the melting of the polar caps of Mars in correlation with the darkening of the planet's "maria," the motions over time of a Martian dust storm, the changes in the size of Jupiter's GRS, the exact location of a new dark spot on Saturnian rings, and so forth.

 

2) latitude determinations, particularly useful for the constantly growing and subsiding belts and zones of Jupiter.

 

3) cometary dimensions, determining very accurately the coma diameter and its changes as the comet approaches and recedes from the sun, the nucleus diameter if possible, and the length of all tail streamers as well as the position angle of tail extrusion on any given night.

 

4) meteorological determinations and climatic motions on the planet Mars, monitoring the development and motion of blue and white cloud formations on the red planet.

 

5) development and overall size/drift changes over time of Jovian white ovals, dark barges and other dynamic and transient features.

 

PHOTOGRAPHIC/DIGITAL PATROL IMAGES

 

At present, the greatest effort and time at the ASO regarding planetary or patrol studies is in the realm of digital planetary "near real time" imaging for immediate acquisition by astronomers world-wide.  This is unique in that it provides for actual hour-by-hour images to be produced on favorable nights;  as the case of Jupiter for example, each image is accumulated EVERY HOUR, a composite image pulled together by 80 to 110 images rapidly sequenced in only a 3.5 minute period of time.  This short duration is absolutely adhered to and necessary to prevent any image shift or falsification by the planet's very rapid rotation of less than 10 hours.

 

Consider the value and wealth of information gathered just from ONE night's patrol studies of Jupiter:  each hour's composite image represents a fresh face of Jupiter as it has rotated yet another roughly 40 degrees; thus in the course of six sequential hours, over 200 degrees of longitude can be completely recorded in high resolution style, as seen in the following Jupiter sequence from November 12, 2001, showing the sudden appearance of the GRS on the eastern limb along with the dark and large eclipsing shadow of the satellite Ganymede....and following the planet for nearly 200 degrees of rotation - TWO THIRDS of its entire span east-to-west! - until the GRS again rotates from view on the opposite limb.

The effort to attain, process, store and create an accessible database is tremendous.  In any given night, nearly 1,000 raw images are recorded digitally for a sequence of perhaps six (6) final images covering over 200 degrees.  These images are then stored by both date and time AND through the record of their respective System I and System II longitudes for direct comparison and examination to all images within the ASO Archives of the SAME exact face from any given date.  This provides a remarkably valuable reference database for planetary astronomers wishing to see the development of any particular area as indexed by a "standard" telescope using "standardized" methods, procedures and equipment.

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DIGITAL PATROL METHODOLOGY AND EQUIPMENT

 

The Arkansas Sky Observatory has refined its Planetary Patrol Program greatly in recent months, utilizing a dedicated Meade LX 200 0.31m (12-in) f/10 Schmidt-Cassegrain telescope operating at f/46.

This system is unique in that it is totally dedicated to planetary imaging by electronic means.  The telescopes operates afocally, utilizing a 10mm Plossl eyepiece that has been completely checked and verified clear of aberrations and spurious images; this provides a modified f/46 overall imaging scale with the system as projected into an Olympus C-3000 digital camera fitted with a 1/1.8 inch CCD solid state pickup with a gross imaging capacity of 3.340 megs pixels.  All images, for rapid acquisition and transfer, are recorded at TIFF format at 640 x 480 pixels.

 

The 6-element Zeiss lens operates at f/2.8 at an extended 7.5x zoom set to infinity focus.  All camera operation is totally manual, other than the image output and monitoring system which is discussed following.  The entire system is operated in sync, which incorporates a CCTV monitor and image translator, output via serial cables to a driving IBM Thinkpad computer and integrated heating elements for all elements other than the camera CCD driven by a 30 amp-hour AC to DC converted which is completely filtered and masked to eliminate noise for both the CCTV and the digital output.

Showing the CCTV Imaging Screen (Saturn) to Demonstrate Image Scale (L)

At Right is the Continuous Digital Output readouts  (showing the moon) which aid in monitoring seeing and corrected exposure times

The camera is coupled to the closed-circuit television (CCTV) via serial ST-8 cables; the monitor is used for several vital reasons and has become one of the most integral components of the ASO Planetary Camera:

 

1) it allows real time monitoring of seeing and atmospheric conditions; the exposure compensation (seen in red in the upper right of the CCTV screen) allows for sudden changes in atmospheric transparency which will affect exposure times to be automatically corrected at the telescope during rapid-fire imaging.  For example, exposure times for Jupiter might range from 1/30th second (very brilliant clear air with maximum object magnitude) to as little as 1/15th second (haze, fog or other extraneous conditions that inhibit 100% light transmission to imaging system).

 

2) all focusing is done using the CCTV; more detail can be seen on the CCTV monitor than can be seen with the eye.  The image scale (as can be seen with the Saturn image shown above) is very large; Encke's division on Saturn is routinely seen during monitoring on this screen.  This allows for extremely precise focusing that cannot possibly be done with the eye,and prevents ANY diversion from perfect focus when attaching the imager during post-focus using traditional methods.

 

3) the CCTV allows instant real-time images of major feature transits over the planetary CM, thus allowing immediate output of Longitude via the IBM laptop interface; in addition, the combination of the PC and CCTV allows for immediate acquisition and storage of important image data as it is being accumulated via file on the IBM computer.  This system is ideal to do back-up and rapid confirmation of feature longitudes immediately via a micrometric mylar measuring screen affixed to the 15" monitor.

 

4) the CCTV provides color enrichment NOT visible visually nor recordable either photographically or digitally in white light;  red features are particularly enhanced on the monitor, and features with blue, gray and orange are clearly distinguishable via a color grid for comparison.

 

As mentioned, the IBM computer is used to:

 

1)  accumulate positional data for features crossing the planetary CM via data clicks by the person conducting the imaging sequence;

 

2)  immediate reduction of planetary CM transit to correct Longitude, regardless of planet of System (in the case of Jupiter or Saturn);

 

3) provides continuous readouts of present CM longitude and advanced predicted CM transits of pre-programmed features for imaging planning.

 

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REDUCTION OF PLANETARY PATROL IMAGES

 

As mentioned, the entire concept of the ASO Planetary Patrol, as well as all prior patrol efforts, has been to provide real-time images and/or data on an as-needed basis for astronomers to access and do comparative work.  With the Planetary Patrol, there is NO attempt to produce "pretty pictures," in which some false-entry or over-processed data might produce "Hubble-like" images.  That is note the mission of ASO; the process allows for major feature monitoring and long-period recording of the development of such features with no spurious or induced imagery allowed.  This results in more rapidly accessible images and images which are not artificially colorized, enhanced or changed from the original character of the planet or other celestial object.

 

Our procedure - once the imaging is done - is very simple for processing and Archiving:

 

1)  Images are expected at an interval of about one hour from the previous image on Jupiter, and a period of three hours for Mars; one image per night unless development warrants are targeted for Saturn.  Imaging sequence periods are limited to only 3.5 minutes maximum to minimize rotational shift/blurring of images as the planet rotates.

NOTE:  the images are recorded at three intensity levels:  D = density recordings (1/4th total number) which are slightly overexposed images (1/2 f/stop increase in exposure length) to negate the noise of the CCD and resultant "grain" of low light images;  C = contrast images (1/4th total) which are recorded at slightly underexposed levels (up to one full f/stop) to enhance the color and contrast of very subtle detail and bring out true planetary colors so that false color correction is NOT necessary in the final image; and, V = visual images which are one-half of the total exposed at the proper setting to match the visual image as seen on the CCTV monitor.

 

2)  For each hour's image, from 70 to 120 images are taken in rapid-fire sequence at 640 x 480 pixel resolution; this practice allows the CCD to essentially "cancel" turbulence from the worst images and allow selection from only the best images.  All of these images are produced in "jpg" format and must be subsequently converted to bitmaps for stacking and post-stacking editing.

 

3)  Each hour's images will be the net result of digital stacking (via computerized stacking programs) of all images, with only the finest images used for best results.

 

4)  The Raw image from that first stacking sequence (ASO beta1) is saved and added to the batch file for a second series of stackings, using this initial image as the reference and alignment image; it is assigned the "good" rating and an attempt is made to assign as many of the finest raw images now to be stacked again with this image a "good" rating as well.  This double sampling/stacking procedure greatly enhances fine edge resolution, true color and reduces significantly the noise thus requiring considerably less post-stacking processing of all images.  The final image from the second stacking sequence (ASO Beta2) is saved as the image to be post-processed for the Archive file for that hour's imaging.

 

Showing two images of Jupiter, the post-processed image through PhotoPaint and the original Beta2 raw stacked image

5)  The resulting Beta2 image is now resampled to twice and Gaussian blurred and a mild unsharp mask applied, then resampled back down to its original resolution; at this point the Beta2 Bitmap is put into Corel PhotoPaint for bitmap editing; corrections in a) image equalization; b) contrast and brightness; c) color correction; d) unsharp masking and subsequent Gaussian blur are all done in MINIMAL fashion.  It is best to begin with the equalization, followed by contrast and then color correction.  However, it most certainly is a good practice to sometimes repeat any and all of the editing functions to produce what image is consistent with all ASO images and with the color, appearance and contrast of images in seen in "real time."

 

6)  Once the image is deemed acceptable, it is saved as a final bitmap and double-resampled and saved again.  This smoothes the coarse pixel grain and allows for truer and richer colors of planets and darker sky background for comets and deep sky.

 

7)  Each hour's image is recorded in the following sequence using the third image of Jupiter from November 14th as an example (planetary file i.d is used here):

"jupiter1114c2" - represents Jupiter on "11-14" (date) followed by the third image of the sequence "c" which is recorded in actual time on the IBM and manually as a backup for reference to the planet's Central Meridian at the time the image was produced; the designation "2" indicates that two Beta2 images were processed and that the second of them was chosen for the final image to be posted on the ASO archives.

 

NOTE that if the imaging required a period of, say 08:40 to 08:43.5 for a complete series on Jupiter, the time used to extrapolate the CM given in the Archives would be the MEAN of the two, or 08:47.8 U.T.

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Imaging Jupiter through one apparition present the greatest challenge to the on-going ASO Patrol imaging program.  To provide a "complete look" from any given evening or morning might require an uninterrupted 8-hour span of dedicated observing, imaging and processing of images.  With our completely automated and computerized digital system, we sequence for each image in only a 10-minute period which allows for acquisition centering, exposure adjustments, actual recording of up to 100 images and equipment coupling/uncoupling;  following the actual image-taking, the camera/computer is then immediately downloaded into a holding batch for conversion from jpg to bitmap format.....then digitally stacked, followed by all images being check individually to rate as to either "exclude", "poor," "acceptable" and "good."  Once this is done and the new image is created from that assortment, it is saved as a beta1 file and stacking is done again as described above.  The Beta2 image is then converted into a bitmap editing program where processing occurs.

 

The entire sequence has been so carefully refined that it requires EXACTLY 50 minutes from telescope to final processed image for posting; this is a critical time, since after that period it is back to the telescope for the second image of the night.

 

For more information, you many contact us through the Arkansas Sky Observatory or directly via the homepage links.

P. Clay Sherrod

Brian M. Sherrod

Arkansas Sky Observatory

www.arksky.org

Copyright Arkansas Sky Observatory © 2001  [A.S.O.] All rights reserved. Revised: May 30, 2002