Using a fixed-frequency of oscillation in an FTS system to measure scene inhomogeneity

1. A method for measuring scene inhomogeneity comprising the steps of:

(a) directing radiance of a scene into an interferometer;

(b) oscillating a field of view (FOV) of the interferometer, while directing the radiance of the scene into the interferometer;

(c) obtaining a Fourier transform of signals emerging from the interferometer;

(d) obtaining magnitude values of the Fourier transform as a function of wavelength;

(e) separating the magnitude values into (1) component values occurring within a predetermined wavelength band of the interferometer and (2) a component value occurring outside the predetermined wavelength band;

(f) using the component value occurring outside the predetermined wavelength band to measure scene inhomogeneity; and

(g) providing the measured scene inhomogeneity to a viewer.

2. The method of claim 1 wherein

step (b) includes uniformly changing an angular component of line-of-sight (LOS) perpendicular to the radiance of the scene.

3. The method of claim 1 wherein

step (b) includes uniformly oscillating the FOV of the interferometer according to a sinusoidal function of time.

4. The method of claim 1 wherein

step (b) includes oscillating the FOV of the interferometer at a frequency f 0 and amplitude A.

5. The method of claim 4 wherein

A is approximately between 0.5% and 10% of the FOV radius.

6. The method of claim 4 wherein

f 0 =uσ 0

u is time rate of change of an optical path difference (OPD) imposed on beams traveling through the interferometer, and

σ 0 is a wavenumber.

7. The method of claim 6 wherein the predetermined wavelength band of the interferometer is between σ min and σ max , where σ min and σ max are minimum and maximum wave numbers, respectively, and

step (b) includes oscillating the FOV at a frequency of f 0 =uσ 0 wherein σ 0 is less than σ min or greater than σ max .

8. The method of claim 6 wherein

step (e) includes placing the magnitude value of the component occurring outside the predetermined wavelength band at the wavenumber of σ 0 .

9. The method of claim 1 wherein

step (f) includes judging that the scene is inhomogeneous if the component value occurring outside the predetermined wavelength band is larger than a predetermined threshold value, and

judging that the scene is homogeneous if the component value occurring outside the predetermined wavelength band is smaller than another predetermined value.

10. The method of claim 1 wherein

step (a) includes directing the radiance of the scene from only a single FOV into the interferometer, and

using only the single FOV to measure the scene inhomogeneity.

11. A method for measuring scene inhomogeneity comprising the steps of:

(a) directing radiance of a scene into an interferometer;

(b) oscillating a field of view (FOV) of the interferometer, while directing the radiance of the scene into the interferometer;

(c) obtaining a Fourier transform of signals emerging from the interferometer;

(d) separating the Fourier transform into a real component and an imaginary component;

(e) using the imaginary component obtained in step (d) to measure scene inhomogeneity; and

(f) providing the measured scene inhomogeneity to a viewer.

12. The method of claim 11 wherein

step (b) includes oscillating the FOV of the interferometer according to

n ( t )= A sin(2 πf 0 t )

wherein n is the oscillation component of the FOV in radians,

f 0 is the frequency of oscillation, and

A is the magnitude of the oscillation.

13. The method of claim 12 wherein

f 0 =uσ 0

u is time rate of change of an optical path difference (OPD) imposed on beams traveling through the interferometer, and

σ 0 is a wavenumber.

14. The method of claim 13 wherein the predetermined wavelength band of the interferometer is between σ min and σ max , where σ min and σ max are minimum and maximum wave numbers, respectively, and

step (b) includes oscillating the FOV at a frequency of f 0 =uσ 0 wherein

f

0

≥

u

·

(

σ

m

⁢

⁢

a

⁢

⁢

x

-

σ

m

⁢

⁢

i

⁢

⁢

n

2

)

.

15. The method of claim 11 wherein

step (b) includes oscillating the FOV at a frequency of oscillation and controlling a phase of the frequency of oscillation, and

step (d) includes obtaining the imaginary component of the Fourier transform while controlling the phase of the frequency of oscillation of the FOV.

16. The method of claim 15 wherein

step (e) includes judging that the scene is inhomogeneous if a value of the imaginary component is larger than a predetermined threshold value, and

judging that the scene is homogeneous if the value of the imaginary component is smaller than another predetermined value.

17. The method of claim 11 wherein

step (b) includes oscillating the FOV of the interferometer at a first direction along the scene during a first time interval, and

oscillating the FOV of the interferometer at a second direction along the scene during a second time interval;

step (c) includes obtaining the Fourier transform of signals emerging from the interferometer during the first time interval and, next, during the second time interval; and

step (e) includes measuring the scene inhomogeneity using the imaginary component obtained during the first time interval and, next, during the second time interval.

18. The method of claim 11 wherein

step (b) includes oscillating the FOV of the interferometer in a circular direction with respect to the scene.

19. The method of claim 11 wherein

step (a) includes placing a grid in front of the interferometer and directing the radiance of the scene into the interferometer by way of the grid.

20. A system for measuring scene inhomogeneity comprising

an interferometer including a field of view (FOV) for receiving radiance from a scene and providing output signals based on the received radiance,

an oscillator coupled to the interferometer for oscillating the FOV,

a processor coupled to the interferometer for calculating a Fourier transform of the output signals emerging from the interferometer, and

the processor measuring scene inhomgeneity based on the oscillating FOV.

21. The system of claim 20 wherein

a phase controller is coupled between the interferometer and the oscillator for controlling phase of the oscillating FOV.