Ratioing 
Ratioing is a technique whereby the radiance values of one band of 
multispectral data are divided by those of another band. This 
division is best done using a computer on a pixel by pixel basis. 
When more than two bands are available, single ratio images can be 
combined into a ratio color composite (Rowan and others, 1974). 
In addition to dividing the radiance values of one band by those 
of another, the radiance values from the same spectral bands taken 
at different dates can be ratioed, likewise on a pixel by pixel 
basis. Ratioing can be done passively during computer processing 
or interactively with one of the digital interpretation--display 
systems. Ratioing enhances subtle differences between reflectance/ 
absorbtance characteristics of a substance in the various bands. 
One of the more important applications is enhancement of iron rich 
surface material; examples of that and other geologic applications 
are given by Vincent (1973). Olson (1972) reported on the appli- 
cation of ratioing multispectral aircraft data for detection and 
enhancement of diseased vegetation in forest .stands. Ratioing of 
multidate imagery of the same spectral bands has proven to be a 
useful change-detection technique. (Todd and others, 1976). 
References 
Billingsley, F. C., Gillespie, A. R., and Geotz, A.F.H., 1975, 
Computer image processing in Application of ERTS images and 
image processing to regional geologic problems and geologic 
mapping in northern Arizona: Pasadena, CA, Jet Propulsion 
Lab. Tech. Rept. 32-1597, ch III, p. 13-22. 
Colvocoresses, A. P., ed., 1975, Platforms for remote sensing in 
Reeves, R. G. ed.-in-ch., Manual of remote sensing; Falls 
Church, VA, Am. Soc. Photogramm., ch 10, p. 539-588. 
Estes, J. E. and Simonett, D. S., 1975, Fundamentals of imagery 
interpretation in Reeves, R. G., ed. -in-ch., Manual of 
remote sensing: Falls Church, VA, Am. Soc. of Photogramm., 
p. 869-1076. 
Harris, George, Jr. and Graham, L. C., 1976, Landsat-radar synergism: 
in preparation for presentation at the 13th International 
Congress of Photogrammetry, Helsinki, Finland, July 11-23, 
1976. 
Hoffer, R. M., 1972, ADP of multispectral scanner data for land use 
mapping: Purdue Univ. Lab. Applic. Remote Sensing I 
Note 080372, 25 p. (Invited paper 2nd UNESCO/Intl. 
ion Symposium on Geographical Information Systems, Ottawa, 
mara A = 1 Q Q7 \ 
ada, Aug. 1-9, 1972.) 
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