Abstract

A technique is described for enhancing fine detail in the production of radiance pictures of targets in which large differences also occur, and where the dynamic range of the picture viewing system is limited. This is achieved by scannig a raster with a mirror-chopper fed detector over the target area, and referencing one sampled area on this target against the next, the radiance intensity from which is reduced by a constant factor. The detector output is then a difference curve related to a derivative trace of the radiance profile, superimposed on the true radiance profile reduced in intensity. The method is compared with a similar technique previously used by Low2, and examples of the use of the present technique both in the laboratory and in observing a feature on the lunar surface are included.

© 1967 Optical Society of America

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References

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  1. J. Rehnberg, J. R. Yoder, G. R. Hunt, Appl. Opt.6, in press (1967).
    [CrossRef] [PubMed]
  2. F. Low, Astrophys. J. 142, 806 (1965).
    [CrossRef]

1965 (1)

F. Low, Astrophys. J. 142, 806 (1965).
[CrossRef]

Hunt, G. R.

J. Rehnberg, J. R. Yoder, G. R. Hunt, Appl. Opt.6, in press (1967).
[CrossRef] [PubMed]

Low, F.

F. Low, Astrophys. J. 142, 806 (1965).
[CrossRef]

Rehnberg, J.

J. Rehnberg, J. R. Yoder, G. R. Hunt, Appl. Opt.6, in press (1967).
[CrossRef] [PubMed]

Yoder, J. R.

J. Rehnberg, J. R. Yoder, G. R. Hunt, Appl. Opt.6, in press (1967).
[CrossRef] [PubMed]

Astrophys. J. (1)

F. Low, Astrophys. J. 142, 806 (1965).
[CrossRef]

Other (1)

J. Rehnberg, J. R. Yoder, G. R. Hunt, Appl. Opt.6, in press (1967).
[CrossRef] [PubMed]

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Figures (6)

Fig. 1
Fig. 1

Optical arrangement in the region of the chopper. In Mode 1 the target radiance is referenced against the emission of a blackbody. In Mode 2 each sampled area on the target is referenced against another sampled area removed Δs from it on the same target.

Fig. 2
Fig. 2

Method of target radiance sampling for three modes of operation. In each case, the total area sampled on the target surface is the same for each position of the chopper. In Mode 1 the total sampled area is referenced against the emission from a blackbody included in the sampling device. For the other two modes, the target area is referenced against other areas on the target, removed Δs (in Mode 2, and (Δs + d) in Mode 3 from the original area. The order of sampling is indicated by the numbers and arrows above the illustrated sampled areas.

Fig. 3
Fig. 3

Detector output as a function of the distance s, along a target surface. (a) True radiance profile, obtained by referencing the target radiance at each point against a constant blackbody source. (b) Difference plot obtained by referencing the radiance of a moving point on the curve in (a) against another spot on that curve removed Δs from it. If this curve is divided by Δs, the resultant curve would be the derivative of the true radiance profile. (c) This curve was produced in the same way as the curve in (b) except that the intensity of the radiance of the reference is reduced by a factor of one-half.

Fig. 4
Fig. 4

(a) Three selected features on a true radiance profile. (b) Difference plot of these features produced in same way as curve in Fig. 3(b). (c) Curve produced in same way as curve in Fig. 3 (c). (d) Curves produced by using alternately sampled spots separated by d, as in the method used by Low.2

Fig. 5
Fig. 5

(a) Raster of radiance profiles across a target composed of a central V section of quartz particles (darker section) in a field of olivine particles. The particle size range of both materials is from 250–500 μ. The picture was produced using an ir camera. (b) Same sample scanned using Mode 2 operation, in which the radiance intensity of every alternate sampled area is reduced by a factor of three-fourths the intensity of the other areas. Corresponding points in the two pictures are marked.

Fig. 6
Fig. 6

(a) Raster of radiance profiles covering the region of the crater Plinius on the Moon. (b) The same lunar feature scanned using Mode 2 operation in the same way as for the picture shown in Fig. 5(a).

Equations (15)

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I = K ( C 2 N T 2 - C 1 N T 1 ) + C ,
N T = f ( s ) ,
I = K [ ρ M 2 N b b - ρ M 1 f ( s ) ] + C
= D - K ρ M 1 f ( s ) ,
N T 2 = f ( s + Δ s )
I = K [ ( ρ M 2 2 ρ M 3 ) f ( s + Δ s ) - ρ M 1 f ( s ) ] + C ,
( ρ M 2 2 ρ M 3 ) f ( s + Δ s ) - ρ M 1 f ( s ) = 0
I = C .
I = K [ ( ρ M 1 ( 1 - k ) f ( s ) + C .
I = K { ρ M 1 [ f ( s + s ) - k f ( s ) ] } + C .
π r 2 + 2 r Δ s .
N T ( total ) = f ( s ) = s - ½ Δ s s + ½ Δ s f ( s ) d s .
N T 1 ( total ) = f ( s ) = N T ( total )
N T 2 ( total ) = f ( s + Δ s ) = s + ½ Δ s s + ³ / Δ s f ( s + Δ s ) d s .
I = K [ f ( s + d + Δ s ) - f ( s ) ] + C .

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