ts 
single camera equipped with four lenses (Figure 1). While each of 
these designs have both advantages and disadvantages, the single 
camera system is less costly to maintain and is considerably easier 
to operate. The technical characteristics of a typical four-lens 
multispectral aerial camera are summarized in Table 1. 
Filtration: The selection of filters needed to obtain multispectral 
photography depends, of course, on the type of camera and film em- 
ployed. In normal operation, a four-camera system could use Eastman 
Kodak, Panatomic-X, Type 3400, in three of the cameras and Infrared 
Aerographic, Type 2424, in the fourth camera. In this configuration, 
four Wratten filters* would be required: blue, No. 47; green, No. 56; 
red, No. 25; and infrared, No. 89B. Filters 47, 56, and 25 would be 
used on the cameras containing the Type 3400 emulsion, while the 89B 
filter would be placed on the camera using the Type 2424 film. 
On the four-lens multispectral camera only, one type of film is 
required. In order to obtain sensitivity in the visible and near- 
infrared portions of the spectrum, Infrared Aerographic, Type 2424, 
is normally used. This film is sensitive from 250 to 900 micrometers. 
The filters required with this type of camera system are identical to 
those mentioned above, but in addition to the 47, 56, and 89B filters 
a 103* filter is also required to eliminate near-infrared energy from 
the three visible channels. 
Additive Color Viewer: This viewer is employed to reconstitute the 
broadband black and white film positives into color images. In 
essence, this viewer consists of four projectors, oriented and housed 
in a manner that permits the projected images to be superimposed, in 
registration, upon the viewer screen with a three-time magnification 
(Figure 2). The viewer can be adapted to handle either four 70mm 
film chips or one 9- by 9-inch film positive that contains four sepa- 
rate images (four-lens camera). A color filter wheel containing one 
clear filter and one filter each of the primary colors is placed in 
the optical path of each of the four projectors (2, Figure 3) to 
supply the color for reconstitution of three of the four images. The 
hue or saturation of the color is controlled by a variable resistor 
placed in series with the filament of each projector lamp. Most of 
the viewers on the market today provide for the replacement of the 
viewing screen with a film holder in order that a photograph of the 
image can be obtained on either film or Polaroid positive material. 
Imagery 
Examples of broadband multispectral photography are presented as 
Figures 4 and 5. These photographs, copied from the viewer screen, 
  
*Eastman Kodak filters.