HYDRO 2016 Paper 5A3

Global bathymetry from satellite altimeter sensor

Pau Gallés, Maite Muñoz, Bernat Martínez, Eduard Makhoul, María José Escorihuela, Mònica Roca

 

Satellite altimetry derived bathymetry offers global coverage especially in deep waters where other techniques have strong limitations. The principle for estimating bathymetry from satellite altimetry is that topography impacts the earth gravitational field. The sea-mountains add an extra pull of the earth's gravitational field drawing more water around them and swelling of the sea surface to the outside.

The ocean surface can be modelled from satellite altimeter sensors which can be used to derive the geoid by filtering temporary effects on the surface such as tides and wind. Laplace equation helps to define a relationship between the gravity anomalies and the east and north vertical deflection gradients from the filtered surface. The formal gravitational potential definition can be easily related by Fourier transforms with submarine topography undulations therefore the calculation procedure for the global bathymetry from satellite altimeter is completed.

The satellite altimeter method is great for a range of bathymetric wavelengths between (~20 to ~200 km) which is suitable for mid-scale maps. However, undulations out of range are less reliable due to the upward continuation and isostatic compensation physical restrictions. The first phenomena can be explained by Newton's law of universal gravitation, where the gravity is attenuated by the square distance from the source meaning the small protuberances are not detected on water surface. On the other hand large submarine hills with high volumes are reaching the strength of the earth's outer layers. Hence irregularities are buoyant in the mantle leading to compensated gravity anomalies caused by the lack of high-density weight from the mantle replaced by lower-density material from crust. Thus bathymetry from different sources must be integrated in the final model to meet the wavelength range requirements depending on the map scale and the resolution for a specific user case.

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