Abstract
Abstract The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array. We present here a generalized expression of sound speed variation in terms of a traveltime residual normalized to the vertical component. With this expression, residual traveltimes to any seafloor transponders will have a same value regardless of their depths and slant angles. This is valid even for the case having horizontal gradient in sound speed structure; the gradient affects only on positioning of a transponder array and not on the estimate of sound speed just beneath the observation point. We monitored temporal variation of this quantity through a GPS/acoustic survey and compared it with in situ expendable bathythermograph (XBT) measurements periodically carried out during the survey. We found that the relative change of the two independent measurements are in good agreement within 5% of the typical amplitude of temporal variation.
Highlights
A combined technique using the Global Positioning System and underwater acoustic ranging (GPS/acoustic) has been put to practical use in seafloor geodesy to provide crucial observations of seafloor deformation where landbased GPS networks are hardly adaptable (Spiess et al, 1998)
The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array
We present here a generalized expression of sound speed variation in terms of a traveltime residual normalized to the vertical component
Summary
A combined technique using the Global Positioning System and underwater acoustic ranging (GPS/acoustic) has been put to practical use in seafloor geodesy to provide crucial observations of seafloor deformation where landbased GPS networks are hardly adaptable (Spiess et al, 1998). The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array.
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