{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,17]],"date-time":"2025-12-17T18:16:22Z","timestamp":1765995382818,"version":"build-2065373602"},"reference-count":39,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2024,6,18]],"date-time":"2024-06-18T00:00:00Z","timestamp":1718668800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Italian Space Agency"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The Cassini spacecraft performed several flybys of Saturn\u2019s largest moon, Titan, collecting valuable data. During several passes, altimetric data were acquired. Here, we focus on altimetric measurements collected by Cassini\u2019s radar when flying over the same region at different epochs in order to correlate such measurements (crossovers) and investigate differences in altimetry. In our study, we assess altimetric errors associated with three distinct methods for extracting topography from Cassini\u2019s radar data: the maximum likelihood estimator (MLE), the threshold method, and the first moment technique. Focusing on crossover events, during which Cassini revisited specific areas of Titan\u2019s surface, we conduct a detailed examination of the consistency and accuracy of these three topography extraction methods. The proposed analysis involves closely examining altimetric data collected at different epochs over identical geographical regions, allowing us to investigate potential errors due to the variations in off-nadir angle, relative impact, uncertainties, and systematic errors inherent in the application of these methodologies. Our findings reveal that the correction applied for the off-nadir angle to the threshold and first moment methods significantly reduces the dispersion in the delta difference at the crossover, resulting in a dispersion of the order of 60 m, even lower than what is achieved with the MLE (~70 m). Additionally, an effort is made to assess the potential of Cassini for estimating the tidal signal on Titan. Considering the altimetric errors identified in our study and the relatively low number of crossovers performed by Cassini, our assessment indicates that it is not feasible to accurately measure the tidal signal on Titan using the currently available standard altimetry data from Cassini. Our assessment regarding the accuracy of the Cassini altimeter provides valuable insights for future planetary exploration endeavors. Our study advances the understanding of Titan\u2019s complex landscape and contributes to refining topographical models derived from Cassini\u2019s altimetry observations. These insights not only enhance our knowledge of Saturn\u2019s largest moon but also open prospects for Titan surface and interior exploration using radar systems.<\/jats:p>","DOI":"10.3390\/rs16122209","type":"journal-article","created":{"date-parts":[[2024,6,19]],"date-time":"2024-06-19T04:21:28Z","timestamp":1718770888000},"page":"2209","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Analysis of Cassini Altimetric Crossovers on Titan"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7888-3021","authenticated-orcid":false,"given":"Daniele","family":"Durante","sequence":"first","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"}]},{"given":"Marco","family":"Mastrogiuseppe","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"},{"name":"Department of Human Sciences, Link Campus University, 00165 Rome, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8515-1606","authenticated-orcid":false,"given":"Elisa","family":"Carli","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1053-3225","authenticated-orcid":false,"given":"Valerio","family":"Poggiali","sequence":"additional","affiliation":[{"name":"Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14850, USA"}]},{"given":"Andrea","family":"Di Ruscio","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"},{"name":"Thales Alenia Space, 00131 Rome, Italy"}]},{"given":"Virginia","family":"Notaro","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"},{"name":"Thales Alenia Space, 00131 Rome, Italy"}]},{"given":"Luciano","family":"Iess","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy"}]}],"member":"1968","published-online":{"date-parts":[[2024,6,18]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"970","DOI":"10.1126\/science.1109919","article-title":"Cassini radar views the surface of Titan","volume":"308","author":"Elachi","year":"2005","journal-title":"Science"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"228","DOI":"10.1038\/s41550-019-0917-6","article-title":"A global geomorphologic map of Saturn\u2019s moon Titan","volume":"4","author":"Lopes","year":"2020","journal-title":"Nat. Astron."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"724","DOI":"10.1126\/science.1123257","article-title":"The sand seas of Titan: Cassini RADAR observations of longitudinal dunes","volume":"312","author":"Lorenz","year":"2006","journal-title":"Science"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1016\/j.aeolia.2013.07.001","article-title":"Dunes on Saturn\u2019s moon Titan as revealed by the Cassini Mission","volume":"11","author":"Radebaugh","year":"2013","journal-title":"Aeolian Res."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1295","DOI":"10.1109\/JSTARS.2014.2352037","article-title":"Dune Height Estimation on Titan Exploiting Pairs of Synthetic Aperture Radar Images with Different Observation Angles","volume":"8","author":"Callegari","year":"2015","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"114775","DOI":"10.1016\/j.icarus.2021.114775","article-title":"Diverse evolution of mountains and hummocks on Titan as observed by the Cassini RADAR altimeter","volume":"374","author":"Lalich","year":"2022","journal-title":"Icarus"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1146\/annurev-earth-060115-012247","article-title":"The lakes and seas of Titan","volume":"44","author":"Hayes","year":"2016","journal-title":"Annu. Rev. Earth Planet. Sci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"11745","DOI":"10.1002\/2017GL075468","article-title":"Topographic constraints on the evolution and connectivity of Titan\u2019s lacustrine basins","volume":"44","author":"Hayes","year":"2017","journal-title":"Geophys. Res. Lett."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1016\/j.icarus.2015.09.043","article-title":"Constraining the physical properties of Titan\u2019s empty lake basins using nadir and off-nadir Cassini RADAR backscatter","volume":"270","author":"Michaelides","year":"2016","journal-title":"Icarus"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"877","DOI":"10.1007\/s10686-021-09772-2","article-title":"Exploration of Enceladus and Titan: Investigating ocean worlds\u2019 evolution and habitability in the Saturn system","volume":"54","author":"Mitri","year":"2021","journal-title":"Exp. Astron."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1432","DOI":"10.1002\/2013GL058618","article-title":"The bathymetry of a Titan sea","volume":"41","author":"Mastrogiuseppe","year":"2014","journal-title":"Geophys. Res. Lett."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"306","DOI":"10.1038\/s41561-018-0103-y","article-title":"A post-Cassini view of Titan\u2019s methane-based hydrologic cycle","volume":"11","author":"Hayes","year":"2018","journal-title":"Nat. Geosci."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"7887","DOI":"10.1002\/2016GL069679","article-title":"Liquid-filled canyons on Titan","volume":"43","author":"Poggiali","year":"2016","journal-title":"Geophys. Res. Lett."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"214","DOI":"10.1016\/j.icarus.2016.08.003","article-title":"Geomorphologic mapping of titan\u2019s polar terrains: Constraining surface processes and landscape evolution","volume":"282","author":"Birch","year":"2017","journal-title":"Icarus"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"5646","DOI":"10.1109\/TGRS.2016.2563426","article-title":"Radar Sounding Using the Cassini Altimeter: Waveform Modeling and Monte Carlo Approach for Data Inversion of Observations of Titan\u2019s Seas","volume":"54","author":"Mastrogiuseppe","year":"2016","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1016\/j.icarus.2017.09.009","article-title":"Bathymetry and composition of Titan\u2019s Ontario Lacus derived from Monte Carlo-based waveform inversion of Cassini RADAR altimetry data","volume":"300","author":"Mastrogiuseppe","year":"2018","journal-title":"Icarus"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1016\/j.epsl.2018.05.033","article-title":"Cassini radar observation of Punga Mare and environs: Bathymetry and composition","volume":"496","author":"Mastrogiuseppe","year":"2018","journal-title":"Earth Planet. Sci. Lett."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"535","DOI":"10.1038\/s41550-019-0714-2","article-title":"Deep and methane-rich lakes on Titan","volume":"3","author":"Mastrogiuseppe","year":"2019","journal-title":"Nat. Astron."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"e2020JE006558","DOI":"10.1029\/2020JE006558","article-title":"The Bathymetry of Moray Sinus at Titan\u2019s Kraken Mare","volume":"125","author":"Poggiali","year":"2020","journal-title":"J. Geophys. Res. Planets"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"233","DOI":"10.1002\/2015JE004920","article-title":"Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission","volume":"121","author":"Malaska","year":"2016","journal-title":"J. Geophys. Res. Planets"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"457","DOI":"10.1126\/science.1219631","article-title":"The Tides of Titan","volume":"337","author":"Iess","year":"2012","journal-title":"Science"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"123","DOI":"10.1016\/j.icarus.2019.03.003","article-title":"Titan\u2019s gravity field and interior structure after Cassini","volume":"326","author":"Durante","year":"2019","journal-title":"Icarus"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"921","DOI":"10.1126\/science.1168905","article-title":"Size and shape of Saturn\u2019s moon Titan","volume":"324","author":"Zebker","year":"2009","journal-title":"Science"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"11754","DOI":"10.1002\/2017GL075518","article-title":"Titan\u2019s Topography and Shape at the End of the Cassini Mission","volume":"44","author":"Corlies","year":"2017","journal-title":"Geophys. Res. Lett."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"461","DOI":"10.1007\/s10236-016-0926-2","article-title":"Numerical study of tides in Ontario Lacus, a hydrocarbon lake on the surface of the Saturnian moon Titan","volume":"66","author":"Vincent","year":"2016","journal-title":"Ocean Dyn."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Mastrogiuseppe, M. (2019). Dual Frequency Orbiter-Radar System for the Observation of Seas and Tides on Titan: Extraterrestrial Oceanography from Satellite. Remote Sens., 11.","DOI":"10.3390\/rs11161898"},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Russell, C.T. (2004). Radar: The Cassini Titan Radar Mapper. The Cassini-Huygens Mission, Springer.","DOI":"10.1007\/1-4020-3874-7"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1777","DOI":"10.1109\/TGRS.2008.2007217","article-title":"Cassini RADAR sequence planning and instrument performance","volume":"47","author":"West","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1567","DOI":"10.1016\/0032-0633(95)00069-0","article-title":"A non-coherent surface backscattering model for radar observation of planetary bodies and its application to Cassini Radar Altimeter","volume":"43","author":"Montefredini","year":"1995","journal-title":"Planet. Space Sci."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"7","DOI":"10.1109\/TGRS.2009.2012718","article-title":"A Waveform Model for Near-Nadir Radar Altimetry Applied to the Cassini Mission to Titan","volume":"47","author":"Alberti","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_31","unstructured":"Bucciarelli, T., Cacopardi, S., Picardi, G., Seu, R., Levrini, G., and Perfetti, R. (1988, January 13\u201316). Tracking Algorithms in Radar Altimetry. Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS\u201988), Edinburgh, UK."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"7262","DOI":"10.1109\/TGRS.2019.2912575","article-title":"High resolution topography of Titan adapting the Delay-Doppler algorithm to the Cassini RADAR Altimeter Data","volume":"57","author":"Poggiali","year":"2019","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"191","DOI":"10.1016\/j.icarus.2013.09.028","article-title":"Titan dune heights retrieval by using Cassini Radar Altimeter","volume":"230","author":"Mastrogiuseppe","year":"2014","journal-title":"Icarus"},{"key":"ref_34","unstructured":"Evans, S., Taber, W., Drain, T., Smith, J., Wu, H., Guevara, M., Sunseri, R., and Evans, J. (2016, January 14\u201317). MONTE: The next generation of mission design and navigation software. Proceedings of the 6th International Conference on Astrodynamics Tools and Techniques, Darmstadt, Germany."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Bellerose, J., Roth, D., and Wagner, S. (June, January 28). The Cassini Mission: Reconstructing Thirteen Years of the Most Complex Gravity-Assist Trajectory Flown to Date. Proceedings of the 2018 SpaceOps Conference, Marseille, France.","DOI":"10.2514\/6.2018-2646"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"A7","DOI":"10.1051\/0004-6361\/202037920","article-title":"Analysis of Cassini radio tracking data for the construction of INPOP19a: A new estimate of the Kuiper belt mass","volume":"640","author":"Fienga","year":"2020","journal-title":"Astron. Astrophys."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"aat2965","DOI":"10.1126\/science.aat2965","article-title":"Measurement and implications of Saturn\u2019s gravity field and ring mass","volume":"364","author":"Iess","year":"2019","journal-title":"Science"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"27","DOI":"10.3847\/PSJ\/ab9f21","article-title":"Possible evidence of p-modes in Cassini measurements of Saturn\u2019s gravity field","volume":"1","author":"Markham","year":"2020","journal-title":"Planet. Sci. J."},{"key":"ref_39","unstructured":"Boone, D., Bellerose, J., and Roth, D. (2017, January 3\u20139). Resolution of Orbit Determination prediction instabilities at Titan during Cassini\u2019s Solstice mission. Proceedings of the 26th International Symposium on Space Flight Dynamics, Matsuyama, Japan."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/16\/12\/2209\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T15:00:35Z","timestamp":1760108435000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/16\/12\/2209"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,6,18]]},"references-count":39,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2024,6]]}},"alternative-id":["rs16122209"],"URL":"https:\/\/doi.org\/10.3390\/rs16122209","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2024,6,18]]}}}