Reducing ambiguities in synthetic aperture radar images
AssigneeIceye Oy
InventorsOzan Dogan, Vladimir Ignatenko
Life of this patent
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Abstract
A method of operating a synthetic aperture radar “SAR” to acquire SAR echo data for the formation of an image, comprises calculating a nadir ambiguity index for the nadir of the platform; determining a frequency sweep direction sequence for successive pulses of a waveform to be transmitted by the SAR based on the nadir ambiguity index; obtaining a relative phase sequence for the successive pulses of the waveform; and encoding the waveform with the determined frequency sweep direction sequence and the relative phase sequence.
Claims34
A method of operating a synthetic aperture radar “SAR” to acquire SAR echo data for the formation of an image, wherein the SAR is carried on a platform travelling with respect to the surface of Earth and is directed toward the surface of Earth, the method comprising:
- calculating a nadir ambiguity index for the nadir of the platform;
- determining a frequency sweep direction sequence for successive pulses of a waveform to be transmitted by the SAR based on the nadir ambiguity index;
- obtaining a relative phase sequence for the successive pulses of the waveform;
- and
- encoding the waveform with the determined frequency sweep direction sequence and the relative phase sequence.
The method of any preceding claim, wherein the same frequency sweep direction sequence is determined for all instances where the nadir ambiguity index is odd and a plurality of different of frequency sweep direction sequences are determined for different even values of nadir ambiguity index.
The method of any preceding claim, wherein the obtaining a relative phase sequence for the successive pulses of the waveform comprises calculating a range ambiguity index for a point in an ambiguous region other than the nadir, and determining a relative phase sequence for the waveform based on the range ambiguity index.
The method of any preceding claim comprising processing received raw echo SAR data according to an ambiguous image and an unambiguous image, wherein the ambiguous image is an image other than nadir.
The method of 27, further comprising focusing the SAR data using a filter matched to an ambiguous echo signal to obtain a focused ambiguous image, wherein the focusing comprises:
- range compression using a filter matched to the ambiguous echo signal;
- range cell migration correction, wherein a range cell migration term in a range envelope of the ambiguous echo signal is a function of distance to the ambiguous region;
- and
- azimuth compression with respect to a distance to nadir, wherein an azimuthal pulse rate of the ambiguous echo signal is a function of the ambiguity index and the distance to nadir.
A pulsed radio waveform transmitted from a SAR system carried on a platform travelling with respect to the surface of Earth, wherein the waveform is encoded with a frequency sweep direction sequence for successive pulses of the radiation and the frequency sweep direction sequence varies according to the ambiguity at the nadir of the platform.
Dependencies are inferred from the claim text.