METHOD AND APPARATUS OF BACK LOBE CORRECTION TO ANTENNA TEMPERATURE FOR EARTH-OBSERVING MICROWAVE INSTRUMENTS

• US 20170017534A1
• Filed: 07/16/2015
• Published: 01/19/2017
• Est. Priority Date: 07/16/2015
• Status: Abandoned Application

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration
• Inventors: De Amici, Giovanni
• Application Number:
  US14/800,748
• Publication Number:
  US 20170017534A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 7/4021 of receivers
• CPC Class Codes: G06F 11/00 Error detection; Error correction; Monitoring error detection, correction or monitoring in information storage based on relative movement between record carrier and transducer G11B20/18; monitoring, i.e. supervising the progress of recording or reproducing G11B27/36; in static stores G11C29/00

Abstract

The present invention relates to a method and apparatus which corrects antenna noise temperature in antenna back lobes, for earth-observing microwave instruments on satellites in orbit, to counter signal contamination from celestial bodies. The antenna back lobe signal correction is computer-program-modeled with only a few static and only a few dynamic inputs, and for a given set of parameters (i.e., orbital altitude, pointing characteristics (e.g., nadir or cross-scanning or conical-scanning), frequency selectivity of the receiver/detector) produces a few output files which are then combined by the program to predict the back lobe signal correction which is to be applied.

Claims

1. A method of correcting an antenna noise temperature in an antenna on earth-observing microwave instruments, the method comprising:

providing at least one processor executing program code to implement a correction to the antenna noise temperature in the antenna, said program code including the steps of;

calculating a convolution of a signal from a Galaxy with a full sky map of a pattern of a beam from the antenna;

subtracting a part of said Galaxy which is covered by a Sun;

subtracting a part of said Galaxy which is covered by a Moon; and

subtracting a part of said Galaxy which is covered by an Earth.

2. The method of claim 1, wherein an algorithm which expresses said correction to the antenna noise temperature in the antenna is:

3. The method of claim 2, further comprising:

calculating said contributions of said Galaxy, said Sun, and said Moon, as a function of time.

4. The method of claim 3, further comprising:

pre-calculating a position of said Sun with respect to said beam of said antenna and a gain-weighted signal from said part of said sky covered by said Sun, in one static file.

pre-calculating a position of said Moon with respect to said beam of said antenna and a gain-weighted signal from said part of said sky covered by said Moon, in a second static file;

pre-calculating a gain-weighted signal from said part of said sky which is covered by said Earth, in a third static file; and

determining whether said Sun and/or said Moon are in eclipse behind said Earth.

5. The method of claim 4, further comprising:

obtaining a pointing of said antenna in celestial coordinates;

using said pointing together with contributions from said first static file, second static file, and third static file, to create a two-dimensional array of said convolution of a Galactic contribution which is valid for each day of a year.

6. The method of claim 5, wherein said celestial coordinates of said pointing of said antenna is obtained from a lookup table.

7. The method of claim 6, wherein said position of said Sun and said position of said Moon are celestial coordinates obtained from a lookup table.

8. The method of claim 7, wherein a gain response of said antenna is obtained from a lookup table.

9. The method of claim 7, wherein a position of said Earth in celestial coordinates, and a clock angle of said Earth, are obtained from at least one lookup table.

10. The method of claim 9, wherein a data volume is reduced by a factor about 100, and said correction is modeled with no more than said three static files for contamination in side-and back-lobes of an Earth-pointing antenna.

11. The method of claim 10, wherein each said lookup table is pre-calculated based on said antenna gain response and an orbital altitude which does not require re-calculation of said lookup tables if a timing of an orbit is modified.

12. The method of claim 11, wherein with a nadir-looking instrument, a circularly symmetric antenna gain pattern and a circular low-elliptic orbit of almost-constant altitude, 8 or less static data files are required for said correction during a lifespan of an orbital mission.

13. The method of claim 11, wherein a secular variation of said correction is controlled by said pointing of said beam of said antenna, and calculated at any moment in time from a spacecraft and a microwave instrument ephemeris.

14. The method of claim 11, wherein less than 10 static files are required for said correction during a lifespan of an orbital mission.

15. A system which corrects an antenna noise temperature in an antenna on earth-observing microwave instruments, the system comprising:

at least one processor executing program code to implement a correction to the antenna noise temperature in an antenna, said program code including the steps of;

calculating a convolution of a signal from a Galaxy with a full sky map of a pattern of a beam from the antenna;

subtracting a part of said Galaxy which is covered by a Sun;

subtracting a part of said Galaxy which is covered by a Moon; and

subtracting a part of said Galaxy which is covered by an Earth.

16. A non-transitory computer-accessible medium having a program which contains executable instructions to implement a correction to the antenna noise temperature in an antenna on earth-observing microwave instruments, the program comprising the steps of:

calculating a convolution of a signal from a Galaxy with a full sky map of a pattern of a beam from the antenna;

subtracting a part of said Galaxy which is covered by a Sun;

subtracting a part of said Galaxy which is covered by a Moon; and

subtracting a part of said Galaxy which is covered by an Earth.