Mar Geophys Res DOI 10.1007/s11001-013-9190-8 Published online: 30 August 2013 Significant improvements in marine gravity from ongoing satellite missions K. M. Marks • W. H. F. Smith • D. T. Sandwell Received: 14 May 2013/ Accepted: 17 August 2013 Abstract Incorporating new altimeter data from CryoSat-2 (30 months), Envisat (18 months), and Jason-1 (7 months) satellites into an updated marine gravity field yields significant reduction in noise and improved resolution. Compared to an older gravity field that did not include the new altimeter data, incoherent power is reduced globally by approximately 2.9 dB at 15 km, 1.6 dB at 20 km, and 1.0 dB at 25 km wavelengths. Coherence analyses between the updated gravity and recent multibeam surveys distributed throughout the world’s oceans shows an average increase of ~0.023 in mean coherence in the 20–160 km waveband, with the biggest increase (>0.08) over fast spreading ridges and smallest (<0.02) over slow spreading ridges and continental shelves. The shortest wavelength at which coherence is above 0.5 decreased globally by ~2 km wavelength, with the biggest decrease (>3.5 km) over fast spreading ridges and smallest (<1.5 km) over slow spreading ridges and continental shelves. In the Clipperton fracture zone area these improvements result in seamounts that are more accurately located, the detection of smaller seamounts, and the expression of north-south trending abyssal hill fabric. As more altimeter data from the ongoing satellite missions are incorporated into future gravity field updates, finer-scale details of the seafloor will continue to emerge. _____________________________________________ K. M. Marks (*) ⋅ W. H. F. Smith NOAA Laboratory for Satellite Altimetry, E/RA 31, 5830 University Research Court, College Park, MD 20740, USA e-mail: karen.marks@noaa.gov D. T. Sandwell Scripps Institution of Oceanography, La Jolla, CA 92093, USA Keywords Satellite gravity ⋅ Multibeam ⋅ Bathymetry ⋅ Coherence ⋅ Noise Introduction The marine gravity field has been effectively mapped using altimeter data from Geosat and ERS-1 satellites (Sandwell and Smith 1997). The close satellite track spacing (~6 to 8 km at the equator) from these missions’ geodetic phases combined with high precision from repeat tracks enabled the derivation of gravity anomalies of unprecedented resolution over the world’s oceans. The marine gravity anomalies were subsequently used to estimate depths in poorly surveyed areas, and combined with ship soundings, the global seafloor was mapped in detail for the first time (Smith and Sandwell 1997). Between 1995 and 2010 there were no new altimeter data collected along densely-spaced tracks. Improvements to the marine gravity field were made by retracking the old ERS-1 (Sandwell and Smith 2005) and Geosat (Sandwell and Smith 2009) geodetic mission data. In the last few years, the CryoSat-2 and Jason-1 missions have collected data in geodetic phases that, when incorporated into the gravity model, serve to augment existing satellite track coverage and therefore increase the data density. Envisat also flew some new tracks for a short time (18 months) before its demise. Data from these altimeters are also more precise than data from Geosat and ERS-1, because the pulse repetition frequency of these satellites is about twice that of Geosat and ERS-1, doubling the data averaging available per second of flight of the spacecraft (Garcia et al. 2013). To assess the resulting gravity field improvements, we compared a gravity field that incorporated these recent satellite data (version 21) to a field that did not (version 18). Both versions were produced by Sandwell and Smith following their published methods (Sandwell