Detecting small seamounts in AltiKa repeat cycle data
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We present a technique of stacking repeat cycles of satellite altimeter sea surface height profiles that lowers the noise and improves the resolution of small seamounts. Our approach differs from other studies because it uses the median (not the mean) of the stacks, which suppresses outliers. Seamounts as small as 720 m tall are easily detected in stacked 40 Hz AltiKa data profiles, and a 500 m tall seamount is perceptible. Noise variance decreases with an increase in the number of cycles stacked, and RMS noise dips below 2 cm when 11 or more cycles are stacked. Coherence analyses between geoid height and bathymetry show that full wavelengths down to about 10 km can be resolved. Comparisons of study areas with and without seamounts find that signal from small seamounts lies in the ~10–28 km waveband. A simple Gaussian band-pass filter based on the seamount waveband passes signals that can be used in seamount detection studies. Such studies may find seamounts <2 km tall that are predicted to be abundant on the ocean floor.
KeywordsSatellite data Geoid height Multibeam Bathymetry Seamounts
The comments of the editor, Dr. Wu-Cheng Chi, and two anonymous reviewers, improved this manuscript. We thank Rob Beaman (James Cook University, Cairns, Australia) for providing multibeam dataset EM122, collected on voyage 2015_v03 of RV Investigator granted by the Marine National Facility, made available under a Creative Commons Attribution 4.0 International license. We also thank Brian Taylor, Andrew Goodliffe, and Fernando Martinez (University of Hawaii, USA) for providing multibeam data covering the Woodlark Basin. We used Google Earth Pro software that is available from Google Inc. (http://www.google.com/work/earthmaps.html). This work also made use of the free software package GNU Octave (http://www.octave.org), and the authors are grateful for the support of the Octave development community. GMT software (Wessel and Smith 1998) was used to make figures. Eric Leuliette provided helpful comments. The views, opinions, and findings contained in this report are those of the authors and should not be construed as an official National Oceanic and Atmospheric Administration or U.S. Government position, policy, or decision.
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