Updated April 1, 2004 (No kidding :) I removed the .jpg files as they appear to have errors and I coudn't find the correct version of them - use the .bmp instead. I posted on the web the results of my Saturn ringshine estimates. These are images of ringshine on the planet for a wide range of observational geometries. The images also show Saturn's and rings' general appearance and all the shadows. The main message for those planning to observe faint objects on Saturn's darkside background (like our lightning search): Ring-illuminated clouds are often as bright as I/F~0.01 (= few % of the sunlit clouds), i.e., REALLY BRIGHT. P.S. The model can produce virtually any resolutions and geometries, feel free to ask me to run it for you or to provide the IDL code. ******** Ringshine database user's guide *********** LOCATION: http://www.gps.caltech.edu/~ulyana/iss/outs/figs/ color -- .bmp thumbnails where the faint ringshine is color-coded http://www.gps.caltech.edu/~ulyana/iss/outs/sav/ -- accurate IDL-.sav-format ringshine data http://www.gps.caltech.edu/~ulyana/iss/ -- IDL source code - for the reference purposes only - does not work at its present location - all routines are called from the batch file main_scattered_light.pro WHAT IS IN THE DATABASE: The ray-tracing modeled images of Saturn and the rings which account for scattered light from the rings to Saturn's "surface". The images represent different viewing geometries. The brightness is normalized to units of I/F ,i.e., by reflectance of a white Lambertian surface F=(solar flux at Saturn)/pi. ERRORS: About 50% of errors in brightness are expected. They are mostly due to not-yet-measured ring brightness at geometries near face-on, which is extrapolated in the model. WHICH IMAGE FILE TO USE: The filename describes the observational geometry. Search the filenames for the closest match to your geometry. The filenames show the following angles: Incident angle of the sunshine on rings (0 to 27 degrees,each 3 degrees) Emission angle from the rings to the spacecraft (0 to 180 degrees, each 10 degrees) Phase angle (0 to 180 degrees, each 10 degrees) Example: filename: inc84emis40phase100.sav inc84 means that the sun illuminates the rings at 84-deg angle from the local vertical. In this notation edge-on is inc90, face-on is inc0 emis40 means the observer looks at 40-deg angle to the ring plane local vertical. In this notation face-on looking from sunlit side is emis0 edge-on is emis90 face-on from dark ring side is emis180 phase100 means the phase angle (Sun_Saturn-observer) is 100 deg. COLOR BMP images The color .bmp images are meant to give a first-glance impression about the geometry and ringshine magnitude. The COLOR CODING is shown on the scale bar at the right of each image. Scale bar description: The normalized brightness I/F decreases from the value 1 at the top of the scale bar (white) decreasing in brightness down to the value of 0.01 where the scale jumps from black to bright red, then the red brightness decreases down to the value of 0.001 where dark red jumps to the bright blue, then the blue brightness decreases down to the value of 0.0001 where the scale jumps to the bright green and then the green brightness decreases to the black at the bottom of the scale bar. Thus, the shades of grey denote I/F values from 1 to 0.01, ringshine brightness proportional to the greyscale brightness. The shades of red denote I/F values from 0.01 to 0.001, ringshine brightness proportional to the red brightness. The shades of blue denote I/F values from 0.001 to 0.0001, ringshine brightness proportional to the blue brightness. The shades of green denote I/F values from 0.0001 to 0, ringshine brightness proportional to the green brightness. The ringshine images are stored as an IDL array in the (....).sav files. After opening the .sav file (see below ) you will find the variable planet_rings- the modeled image showing Saturn, rings and ringshine in units I/F. HOW TO VIEW THE DATA: This may not work in some IDL's earlier than 5.4 - please let me know how to save IDL 5.3-compatible .sav (extension .dat according to IDL help) file with IDL 5.4. copy the .sav file(s) into '/.../sav/' directory on your computer (right mouse click on the filename, then "save target as"or "save link as") start idl in your '/.../sav/' directory The following sequence of commands should allow you to view the image and to see the values. example: Type each command in idl prompt (i.e., IDL>) restore,'inc84emis40phase100.sav' tvscl, planet_rings ;view the bright crescent and the rings as in .jpg file tv,planet_rings*25500; view the faint ringshine : I/F=0.01 looks white,I/F=0-black ;, brighter sun-illuminated values will be screwed up plot,planet_rings(*,37), /ylog, yrange =[1.e-4,2.] ; view the values at line 37 **********RINGSHINE MODEL************** The model traces the rays reaching each pixel of the image including: *Saturn's reflection of sunlight *Rings' reflection *Rings' transmission *Sun-ring-Saturn-observer reflection summed over a number of ring segments. As of October 29, 2003 each ring segment is 1/10 of the total radial extent of the rings and 10 degrees in aziuth. The following assumptions are taken: Saturn is a spheroid with 10% oblateness. Scattering phase function and albedo of Saturn are represented by the Backstorm law: I/F=A/mu(mu*mu0/(mu+mu0))B where mu and mu0 are cosines of emission and incident angles A and B are coefficients fitted by Dones et al. (1993) for Pioneer observed phase functions. I averaged the coefficients for zones,belts,blue and red filter published in Dones et al. (1993) with equal weights. The high-radial-resolution ring opacity is derived from Voyager observation (H. Throop, L. Dones, private communication). The ring reflection and diffuse transmission is provided as a tabulated output of the Cassini ISS ring brightness model (C. Porco, H. Throop, private communication). The ring brightness model is based on Voyager ring imaging. TESTS. There are couple of dozens ringshine Voyager 1 and 2 on PDS taken in two geometries: Voyager 1 outbound and Voyager 2 outbound. My model results for these 2 geometries agree with these data within 30 %. The direct ring reflection in my images was also agrees with the theoretical equations(Dones et.al 93) at optically-thin limit. Reference: Dones L, Cuzzi J.N.,Showalter M.R., 'Voyager photometry of Saturn's A ring.' Icarus 105,184-215(1993)