Interferometric radiometer

• US 20080007451A1
• Filed: 06/15/2007
• Published: 01/10/2008
• Est. Priority Date: 06/16/2006
• Status: Active Grant

• Current Assignee: Agence Spatiale Europeenne
• Original Assignee: Agence Spatiale Europeenne
• Inventors: Emrich, Anders, Christensen, Jacob, Back Andersson, John, Carlstrom, Anders, De Maagt, Peter
• Granted Patent: US 7,460,063 B2
• Time in Patent Office: Days
• US Class Current: 342/351
• CPC Class Codes: G01S 13/955 mounted on satellite
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 21/22 Antenna units of the array energised non-uniformly in amplitude or phase, e.g. tapered array or binomial array
• CPC Class Codes: H01Q 3/02 using mechanical movement of antenna or antenna system as a whole
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A space-borne interferometric radiometer for imaging a radiation emission from a target scene (ED), comprising: a plurality of receiving elements arranged in a two- or three-dimensional array (REA);

• • first signal processing means (SP1) for computing a two-dimensional set of samples of a visibility function by pair-wise cross-correlating signals received by said receiving elements; and
  • second signal processing means (SP2) for reconstructing an image from said samples of said visibility function; characterized in that it further comprises means (ROT) for rotating said two- or three-dimensional array (REA) about a rotation axis (z) which is substantially directed toward said target scene (ED);
  • and in that said second signal processing means (SP2) are adapted for reconstructing said image from a plurality of two-dimensional sets of samples of said visibility function corresponding to different rotational positions of said rotating two- or three-dimensional array (REA) of receiving elements.

Claims

1. An interferometric radiometer for imaging a target scene (ED), comprising:

a plurality of receiving elements (201, 202) for receiving said radiation, said receiving elements (201, 202) being arranged in a two- or three-dimensional array (REA);

first signal processing means (SP1) for computing a two-dimensional set of samples of a visibility function (V) of said radiation emission by pair-wise cross-correlating signals received by said receiving elements (201, 202); and

second signal processing means (SP2) for reconstructing an intensity image (MI) of said radiation emission from said samples of said visibility function (V);

characterized in that it further comprises means (ROT) for rotating said two- or three-dimensional array of receiving elements (REA) about a rotation axis (z) which is substantially directed toward said target scene (ED);

and in that said second signal processing means (SP2) are adapted for reconstructing said intensity image (MI) from a plurality of two-dimensional sets of samples of said visibility function (V), each of said set of samples corresponding to a different rotational position of said rotating two- or three-dimensional array (REA) of receiving elements.

2. A space-borne interferometric radiometer according to claim 1, adapted for imaging a planetary surface (ED).

3. An interferometric radiometer according to claim 1, wherein said array of receiving elements (REA) is substantially bi-dimensional and perpendicular to said rotation axis (z).

4. An interferometric radiometer according to claim 1, wherein the spacings between said receiving elements (201, 202) are not constant, nor are integer multiples of a minimum spacing.

5. An interferometric radiometer according to claim 4, wherein the arrangement of said receiving elements (201, 202) is chosen such as to determine a non-uniform distribution of said samples of said visibility function (V) in a two-dimensional spatial frequency domain, ensuring that the secondary lobes of a synthesized receiving pattern of said interferometric radiometer have a normalized amplitude of −

20 dB or less, and preferably of −

40 dB or less.

6. An interferometric radiometer according to claim 4, wherein the arrangement of said receiving elements (201, 202) is such that the distribution of said samples of said visibility function (V) in a two-dimensional spatial frequency domain approaches an apodization function chosen between a Gaussian function, a cosine, a Hamming window and a Hanning window.

7. An interferometric radiometer according to claim 1, wherein said means (ROT) for rotating said two or three-dimensional array (REA) are adapted for operating at a rotational speed comprised between 0.001 and 100 rpm, preferably between 0.01 and 10 rpm and even more preferably between 0.1 and 1 rpm.

8. An interferometric radiometer according to claim 1, wherein said receiving elements (201, 202) are adapted for receiving electromagnetic radiation in at least a frequency band lying in the 1 GHz-1 THz spectral range.

9. An interferometric radiometer according to claim 8, wherein said receiving elements (201, 202) are adapted for receiving electromagnetic radiation in at least a frequency band lying in the 30 GHz-400 GHz spectral range.

10. An interferometric radiometer according to claim 8, wherein the width of said two- or three-dimensional array (REA) of receiving elements perpendicularly to said rotation axis (z) is sufficient for providing an angular resolution of the reconstructed intensity image of 7 milliradians or less, and preferably of 1 milliradian or less, at least in said frequency band.

11. An interferometric radiometer according to claim 8, wherein the number and the arrangement of said receiving elements (201, 202) are such that, after half a turn of the rotating two- or three-dimensional array (REA), the resulting sampling density of said visibility function (V) is sufficient for providing an unambiguous field of view having a full width of 17°

or more, at least in said frequency band.

12. An interferometric radiometer according to claim 1, wherein said rotation axis (z) passes substantially through the center of inertia of said rotating two- or three-dimensional array of receiving elements (REA).

13. An interferometric radiometer according to claim 1, wherein said receiving elements (201, 202) are aligned along a plurality of linear arms (A1, A2, A3).

14. An interferometric radiometer according to claim 13, wherein said receiving elements (201, 202) are aligned along three linear arms (A1, A2, A3) angularly spaced by 120°

with respect to each other so as to form a Y-shaped array (REA), said rotation axis (z) passing through the center of said array.

15. An interferometric radiometer according to claim 13, wherein the number and the spacing of the receiving elements (201, 202) on said linear arms (A1, A2, A3) are the same.

16. An interferometric radiometer according to claim 1, wherein said first signal processing means (SP1) are adapted for introducing a plurality of relative time delays (τ

) between said received signals to be cross-correlated and for computing delay-dependent visibility functions (V), and said second signal processing means (SP2) are adapted for reconstructing a multi-spectral image (MI) of said radiation emission by Fourier-transforming said delay-dependent visibility functions.

17. An interferometric radiometer according to claim 1, further comprising relative phase calibration means (CM), wherein said calibration means (CM) are adapted for comparing the sets of samples of said visibility function (V) corresponding to different rotational positions of said rotating array of receiving elements (REA) and retrieving relative phase calibration information by said comparison.

18. An interferometric radiometer according to claim 1, further comprising relative amplitude calibration means (CM), wherein said calibration means (CM) are adapted for comparing the sets of samples of said visibility function (V) corresponding to different rotational positions of said rotating array of receiving elements (REA) and retrieving relative amplitude calibration information by said comparison.

19. An interferometric radiometer according to claim 17, wherein said calibration means (CM) are adapted for comparing the sets of samples of said visibility function (V) corresponding to rotational positions of said rotating array of receiving elements (REA) differing by half a turn.

20. An interferometric radiometer according to claim 17, wherein said rotating array of receiving elements (REA) has, at least approximately, a discrete rotational symmetry, and wherein said calibration means (CM) are adapted for comparing the sets of samples of said visibility function (V) corresponding to rotational positions of said rotating array of receiving elements (REA) differing by an angle corresponding to said discrete rotational symmetry.

21. An interferometric radiometer according to claim 1, wherein the receiving elements (201, 202) are adapted for distinguishing between two polarization components the received radiation, and wherein said second signal processing means (SP2) are adapted for reconstructing two intensity images corresponding to different polarization components of said radiation emission.

22. An interferometric radiometer according to claim 21, wherein said second signal processing means (SP2) are adapted for computing the Stokes parameters of the received radiation.

23. A multi-band interferometric radiometer comprising a plurality of individual interferometric radiometers according to claim 1, the two- or three-dimensional arrays of receiving elements of which (REA-53, REA-118, REA-183, REA-380) are mounted on a common rotating structure (STR), each of said individual interferometric radiometers being adapted to operate in a different spectral band.

24. A multi-band interferometric radiometer according to claim 23, comprising a plurality of individual interferometric radiometers wherein said receiving elements (201, 202) are aligned along a plurality of linear arms (A1, A2, A3), and wherein the corresponding linear arms (A1, A2, A3) of said individual interferometric radiometers are parallel to each other.