Filters








7 Hits in 0.85 sec

Estimation of the total electron content of the Martian ionosphere using radar sounder surface echoes

Ali Safaeinili, Wlodek Kofman, Jérémie Mouginot, Yonggyu Gim, Alain Herique, Anton B. Ivanov, Jeffrey J. Plaut, Giovanni Picardi
2007 Geophysical Research Letters  
2007), Estimation of the total electron content of the Martian ionosphere using radar sounder surface echoes, Geophys.
doi:10.1029/2007gl032154 fatcat:5osekmq3ufcnfhjumd6hxmxoca

DETERMINING TITAN'S SPIN STATE FROM CASSINI RADAR IMAGES

Bryan W. Stiles, Randolph L. Kirk, Ralph D. Lorenz, Scott Hensley, Ella Lee, Steven J. Ostro, Michael D. Allison, Philip S. Callahan, Yonggyu Gim, Luciano Iess, Paolo Perci del Marmo, Gary Hamilton (+3 others)
2008 Astronomical Journal  
For some 19 areas of Titan's surface, the Cassini RADAR instrument has obtained SAR images during two different flybys. The time interval between flybys varies from several weeks to two years. We have used the apparent misregistration (by 10-30 km) of features between separate flybys to construct a refined model of Titan's spin state, estimating six parameters: North pole right ascension and declination, spin rate, and these quantities' first time derivatives We determine a pole location with
more » ... ght ascension of 39.48 degrees and declination of 83.43 degrees corresponding to a 0.3-degree obliquity. We determine the spin rate to be 22.5781 deg/day or 0.001 degrees per day faster than the synchronous spin rate. Our estimated corrections to the pole and spin rate exceed their corresponding standard errors by factors of 80 and 8, respectively. We also found that the rate of change in the pole right ascension is -30 deg/century, ten times faster than right ascension rate of change for the orbit normal. The spin rate is increasing at a rate of 0.05 deg/day per century. We observed no significant change in pole declination over the period for which we have data. Applying our pole correction reduces the feature misregistration from tens of km to 3 km. Applying the spin rate and derivative corrections further reduces the misregistration to 1.2 km. 1
doi:10.1088/0004-6256/135/5/1669 fatcat:d5vw3krm5jej7dop4w5kljut3a

Cassini RADAR Sequence Planning and Instrument Performance

R.D. West, Y. Anderson, R. Boehmer, L. Borgarelli, P. Callahan, C. Elachi, Yonggyu Gim, G. Hamilton, S. Hensley, M.A. Janssen, W. Johnson, K. Kelleher (+8 others)
2009 IEEE Transactions on Geoscience and Remote Sensing  
Yonggyu Gim received the Ph.D. degree in physics from the University of Maryland, College Park, in 1996.  ... 
doi:10.1109/tgrs.2008.2007217 fatcat:goqcrds5vnd5djwcgpa6mb6r64

Cassini RADAR observations of Enceladus, Tethys, Dione, Rhea, Iapetus, Hyperion, and Phoebe

Steven J. Ostro, Richard D. West, Michael A. Janssen, Ralph D. Lorenz, Howard A. Zebker, Gregory J. Black, Jonathan I. Lunine, Lauren C. Wye, Rosaly M. Lopes, Stephen D. Wall, Charles Elachi, Laci Roth (+7 others)
2006 Icarus (New York, N.Y. 1962)  
Cassini 2.2-cm radar and radiometric observations of seven of Saturn's icy satellites yield properties that apparently are dominated by subsurface volume scattering and are similar to those of the icy Galilean satellites. Average radar albedos decrease in the order Enceladus/Tethys, Hyperion, Rhea, Dione, Iapetus, and Phoebe. This sequence most likely corresponds to increasing contamination of near-surface water ice, which is intrinsically very transparent at radio wavelengths. Plausible
more » ... tes for contaminants include ammonia, silicates, metallic oxides, and polar organics (ranging from nitriles like HCN to complex tholins). There is correlation of our targets' radar and optical albedos, probably due to variations in the concentration of optically dark contaminants in near-surface water ice and the resulting variable attenuation of the high-order multiple scattering responsible for high radar albedos. Our highest radar albedos, for Enceladus and Tethys, probably require that at least the uppermost one to several decimeters of the surface be extremely clean water ice regolith that is structurally complex (i.e., mature) enough for there to be high-order multiple scattering within it. At the other extreme, Phoebe has an asteroidal radar reflectivity that may be due to a combination of single and volume scattering. Iapetus' 2.2-cm radar albedo is dramatically higher on the optically bright trailing side than the optically dark leading side, whereas 13-cm results reported by Black et al. [Black, G.J., Campbell, D.B., Carter, L.M., Ostro, S.J., 2004. Science 304, 553] show hardly any hemispheric asymmetry and give a mean radar reflectivity several times lower than the reflectivity measured at 2.2 cm. These Iapetus results are understandable if ammonia is much less abundant on both sides within the upper one to several decimeters than at greater depths, and if the leading side's optically dark contaminant is present to depths of at least one to several decimeters. As argued by Lanzerotti et al. ], a combination of ion erosion and micrometeoroid gardening may have depleted ammonia from the surfaces of Saturn's icy satellites. Given the hypersensitivity of water ice's absorption length to ammonia concentration, an increase in ammonia with depth could allow efficient 2.2-cm scattering from within the top one to several decimeters while attenuating 13-cm echoes, which would require a six-fold thicker scattering layer. If so, we would expect each of the icy satellites' average radar albedos to be higher at 2.2 cm than at 13 cm, as is the case so far with Rhea [Black, G., Campbell, D., 2004. Bull. Am. Astron. Soc. 36, 1123 as well as Iapetus.
doi:10.1016/j.icarus.2006.02.019 fatcat:aotpacumqzgwbkk5geh46nq3hi

Ground Processing of Cassini RADAR Imagery of Titan

B.W. Stiles, Yonggyu Gim, G. Hamilton, S. Hensley, W.T.K. Johnson, J. Shimada, R.D. West, P. Callahan
2006 IEEE Conference on Radar  
The Cassini RADAR instrument onboard the Cassini Orbiter is currently collecting SAR Imagery of the surface of Saturn's largest moon, Titan. This paper describes the ground processing of Cassini SAR data. We focus upon the unusual features of the data and how these features impact the processing. We exhibit a data dependent mechanism we have implemented for eliminating artifacts due to attitude and ephemeris knowledge error. Finally we describe how we trade-off SAR performance vs. area of
more » ... ge when we design our spacecraft pointing profiles. I.
doi:10.1109/radar.2006.1631767 fatcat:hcydjcl335btxbevnkcevhcpvq

ALTIMETRY BY CASSINI RADAR: PROCESSING AND SIMULATION

Giovanni Alberti
2009
Johnson and Yonggyu Gim.  ... 
doi:10.6092/unina/fedoa/3825 fatcat:lwcoczgbcre5jd73hutu3w22ky

Spin-polarized quasiparticle transport in cuprate superconductors

C.-C. Fu, Z. Huang, N.-C. Yeh
2002 Physical Review B (Condensed Matter)  
Yonggyu Gim, and at Caltech. Sec. 8.1 will cover the procedures of photolithography in general terms.  ... 
doi:10.1103/physrevb.65.224516 fatcat:yufukyonmzacfkajujyneufsva