%0 Journal Article %1 Simonelli2004 %A Simonelli, D. P. %A Buratti, B. J. %D 2004 %J Icarus %K BACKSCATTER; BIDIRECTIONAL COHERENT GALILEAN ICY MOON PHOTOMETRY; REFLECTANCE SATELLITES; SPECTROSCOPY; SURFACE-STRUCTURE; %N 1 %P 149--162 %T Europa's opposition surge in the near-infrared: interpreting disk-integrated observations by Cassini VIMS %V 172 %X Near-infrared observations of Europa's disk-integrated opposition surge by Cassini VIMS, first published in Fig. 4 of Brown et al. (2003, Icarus, 164, 461), have now been modeled with the commonly used Hapke photometric function. The VIMS data set emphasizes observations at 16 solar phase angles from 0.4degrees to 0.6degreesthe first time the < 1degrees phase "heart" of Europa's opposition surge has been observed this well in the near-IR. This data set also provides a unique opportunity to examine how the surge is affected by changes in wavelength and albedo: at VIMS wavelengths of 0.91, 1.73, and 2.25 mum, the geometric albedo of Europa is 0.81, 0.33, and 0.18, respectively. Despite this factor-of-four albedo range, however, the slope of Europa's phase curve at < 1degrees phase is similar at all three wavelengths (to within the error bars) and this common slope is similar to the phase coefficient seen in visible-light observations of Europa. The two components of the opposition surge-involving different models of the physical cause of the surge-are the Shadow Hiding Opposition Effect (SHOE) and the Coherent Backscatter Opposition Effect (CBOE). Because of sparse VIMS phase coverage, it is not possible to constrain all the surge parameters at once in a Hapke function that has both SHOE and CBOE; accordingly, we performed separate Hapke fits for SHOE-only and CBOE-only surges. At 2.25 mum, where VIMS data are somewhat noisy, both types of surges can mimic the slope of the VIMS phase curve at < 1degrees phase. At 0.91 and 1.73 mum, however-where VIMS data are "cleaner"-CBOE does a noticeably poorer job than SHOE of matching the VIMS phase coefficient at < 1degrees phase; in particular, the best CBOE fit insists on having a steeper phase-curve slope than the data. This discrepancy suggests that Europa's near-IR opposition surge cannot be explained by CBOE alone and must have a significant SHOE component, even at wavelengths where Europa is bright. (C) 2004 Elsevier Inc. All rights reserved.

@article{Simonelli2004, abstract = {Near-infrared observations of Europa's disk-integrated opposition surge by Cassini VIMS, first published in Fig. 4 of Brown et al. (2003, Icarus, 164, 461), have now been modeled with the commonly used Hapke photometric function. The VIMS data set emphasizes observations at 16 solar phase angles from 0.4degrees to 0.6degreesthe first time the < 1degrees phase "heart" of Europa's opposition surge has been observed this well in the near-IR. This data set also provides a unique opportunity to examine how the surge is affected by changes in wavelength and albedo: at VIMS wavelengths of 0.91, 1.73, and 2.25 mum, the geometric albedo of Europa is 0.81, 0.33, and 0.18, respectively. Despite this factor-of-four albedo range, however, the slope of Europa's phase curve at < 1degrees phase is similar at all three wavelengths (to within the error bars) and this common slope is similar to the phase coefficient seen in visible-light observations of Europa. The two components of the opposition surge-involving different models of the physical cause of the surge-are the Shadow Hiding Opposition Effect (SHOE) and the Coherent Backscatter Opposition Effect (CBOE). Because of sparse VIMS phase coverage, it is not possible to constrain all the surge parameters at once in a Hapke function that has both SHOE and CBOE; accordingly, we performed separate Hapke fits for SHOE-only and CBOE-only surges. At 2.25 mum, where VIMS data are somewhat noisy, both types of surges can mimic the slope of the VIMS phase curve at < 1degrees phase. At 0.91 and 1.73 mum, however-where VIMS data are "cleaner"-CBOE does a noticeably poorer job than SHOE of matching the VIMS phase coefficient at < 1degrees phase; in particular, the best CBOE fit insists on having a steeper phase-curve slope than the data. This discrepancy suggests that Europa's near-IR opposition surge cannot be explained by CBOE alone and must have a significant SHOE component, even at wavelengths where Europa is bright. (C) 2004 Elsevier Inc. All rights reserved.}, added-at = {2009-11-03T20:21:25.000+0100}, author = {Simonelli, D. P. and Buratti, B. J.}, biburl = {https://www.bibsonomy.org/bibtex/234ae0a83804a2a900936da6596cc3f08/svance}, interhash = {2926fceee218eb5cbf20dd599cf246ad}, intrahash = {34ae0a83804a2a900936da6596cc3f08}, journal = {Icarus}, keywords = {BACKSCATTER; BIDIRECTIONAL COHERENT GALILEAN ICY MOON PHOTOMETRY; REFLECTANCE SATELLITES; SPECTROSCOPY; SURFACE-STRUCTURE;}, number = 1, owner = {svance}, pages = {149--162}, timestamp = {2009-11-03T20:22:14.000+0100}, title = {Europa's opposition surge in the near-infrared: interpreting disk-integrated observations by Cassini VIMS}, volume = 172, year = 2004 }