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US 6,549,165 B2Granted
Ocean altimetry interferometric method and device using GNSS signals
AssigneeAgence Spatiale Europeenne
InventorsManuel Martin Neira, Pablo Colmenarejo Matellano, Giulio Ruffini
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Abstract
A method for performing Earth altimetry comprising the steps of: receiving by an upward-looking antenna onboard a platform above the Earth surface, direct signals having at least two different carrier frequencies transmitted by GNSS satellites in view of the upward-looking antenna, receiving by a downward-looking antenna onboard the platform signals reflected by the Earth surface and having the at least two different carrier frequencies, comparing carrier phases of the direct signals and received reflected signals, at the carrier frequencies, and determining from the phase comparisons a surface height.
Claims12
A method for performing Earth altimetry comprising the steps of:
- receiving by an upward-looking antenna onboard a platform above the Earth surface direct signals having at least two different carrier frequencies transmitted by GNSS satellites in view of said upward-looking antenna,
- receiving by a downward-looking antenna onboard said platform signals reflected by the Earth surface and having said at least two different carrier frequencies, and
- comparing carrier phases of said direct signals and said received reflected signals at said carrier frequencies, and determining a surface height from said compared carrier phases.
A method for performing Earth altimetry comprising the steps of:
- receiving by an upward-looking antenna onboard a platform above the Earth surface direct signals having at least two different carrier frequencies transmitted by GNSS satellites in view of said upward-looking antenna;
- receiving by a downward-looking antenna onboard said platform signals reflected by the Earth surface and having said at least two different carrier frequencies;
- comparing carrier phases of said direct signals and said received reflected signals at said carrier frequencies;
- determining a surface height from said compared carrier phases;
- and
- determining for each GNSS in view a point of specular reflection of said direct signals on the Earth surface and determining time observation windows during which the reflected signals should arrive to the downward-looking antenna.
3 more elements
An Earth altimetry device comprising:
- an upward-looking antenna onboard a platform for receiving direct signals having at least two carrier frequencies from GNSS satellites in view,
- a downward-looking antenna onboard said platform for receiving reflected signals at said at least two carrier frequencies, said reflected signals being transmitted by each of said GNSS satellites and reflected by an Earth surface,
- a GNSS receiver connected to said upward-looking antenna for providing direct signals having said at least two carrier frequencies,
- a frequency de-multiplexer connected to said downward-looking antenna for separating said received reflected signals into reflected signals having respectively said at least two carrier frequencies,
- phase comparison means for comparing carrier phases of said direct signals outputted by said GNSS receiver and reflected signals outputted by said frequency de-multiplexer at said at least two carrier frequencies, and means for determining a surface height from said phase comparisons performed by said phase comparison means.
2 more elements
An Earth altimetry device comprising:
- an upward-looking antenna onboard a platform for receiving direct signals having at least two carrier frequencies from GNSS satellites in view;
- a downward-looking antenna onboard said platform for receiving reflected signals at said at least two carrier frequencies, said reflected signals being transmitted by each of said GNSS satellites and reflected by an Earth surface;
- a GNSS receiver connected to said upward-looking antenna for providing direct signals having said at least two carrier frequencies;
- a frequency de-multiplexer connected to said downward-looking antenna for separating said received reflected signals into reflected signals having respectively said at least two carrier frequencies;
- phase comparison means for comparing carrier phases of said direct signals outputted by said GNSS receiver and reflected signals outputted by said frequency de-multiplexer at said at least two carrier frequencies, and means for determining a surface height from said phase comparisons performed by said phase comparison means;
- means for processing said received direct signals, said processing means outputting navigational data and clean replicas of said direct signals for each of said at least two carrier frequencies and GNSS satellites;
- a delay and doppler estimator for determining from said navigational data and for each of said GNSS satellites a point of specular reflection on said surface and time-delays and doppler shifts at which each said received reflected signals should arrive to said downward-looking antenna and for determining a time observation window for each said received reflected signal;
- time-delay blocks for time delaying said clean replicas at all times as a function of each said time observation window;
- numerically controlled oscillators for generating a carrier frequency signal which is shifted by said doppler shifts for each of said at least two carrier frequencies;
- a first set of signal multipliers for modulating said doppler-shifted carriers with the delayed clean replicas;
- and
- a second set of signal multipliers for modulating the modulated signals outputted by said first set of signal multipliers with the separated reflected signals, the modulated signals outputted by said second set of multipliers being applied to said phase comparison means.
9 more elements
A low earth orbit satellite for performing ocean altimetry comprising:
- an upward-looking antenna onboard a platform for receiving direct signals having at least two carrier frequencies from GNSS satellites in view,
- a downward-looking antenna onboard said platform for receiving signals at said at least two carrier frequencies, with said received signals being transmitted by each of said GNSS satellites and reflected by the Earth surface,
- a GNSS receiver connected to said upward-looking antenna for providing direct signals having said at least two carrier frequencies,
- a frequency de-multiplexer connected to said downward-looking antenna for separating said received reflected signals into reflected signals having respectively said at least two carrier frequencies,
- phase comparison means for comparing carrier phases of said direct signals outputted by said GNSS receiver and reflected signals outputted by said frequency de-multiplexer at said at least two carrier frequencies, and means for determining a surface height from phase comparisons performed by said phase comparison means.
2 more elements
An airborne device for performing ocean altimetry comprising:
- an upward-looking antenna onboard a platform for receiving direct signals having at least two carrier frequencies from GNSS satellites in view,
- a downward-looking antenna onboard said platform for receiving signals at said at least two carrier frequencies, with said received signals being transmitted by each of said GNSS satellites and reflected by the Earth surface,
- a GNSS receiver connected to said upward-looking antenna for providing direct signals having said at least two carrier frequencies,
- a frequency de-multiplexer connected to said downward-looking antenna for separating said received reflected signals into reflected signals having respectively said at least two carrier frequencies,
- phase comparison means for comparing carrier phases of said direct signals outputted by said GNSS receiver and reflected signals outputted by said frequency de-multiplexer at said at least two carrier frequencies, and means for determining a surface height from phase comparisons performed by said phase comparison means.
2 more elements
Dependencies are inferred from the claim text.