converting airspeed (in knots) to feet is 1.7 (kts

×

1.7 =

ft/sec). For example, when the airspeed is 125 knots,

the ground speed, in feet, is 212.5 feet per second (125

×

1.7 = 212.5).

Head winds and tail winds must also be considered.

When head winds are present, you should subtract the

head wind from the airspeed. Tail winds should be

added to the airspeed. For example, when the aircraft

is flying north at 125 knots and the wind is blowing from

the north at 10 mph, then the corrected airspeed is 115

knots (125 - 10= 115). When the air craft is flying south,

then the corrected airspeed is 135 knots (125 + 10 =

135). The corrected airspeed must be used to find the

ground speed, in feet.

For the time interval between exposures, the

following formula should be used:

*T= D*

*S*

Where

T = Time in seconds

D = Ground-gained forward

S = Ground speed in feet per second

NOTE: When the interval between exposures can

be accomplished in full seconds only, the tenths of a

second should be dropped. By doing so, slightly more

than the required 60-percent forward overlap is

provided. This can be advantageous.

**SCALE OF THE FINISHED**

MOSAIC MAP

The scale of the finished mosaic map is determined

by using the following formula:

*F*

*S= *12*A*

Where

S= Scale

F = Lens focal length

A = Altitude

The answer derived by using this formula gives a

representative fraction (RF) in like-units. Notice that

you must convert the altitude to inches, since the lens

focal length is normally in inches. For example, you

used a 10-inch focal-length lens for a mapping mission

flown at 5,000 feet. You can determine the scale of the

finished mosaic as follows:

*S=*

10

12

×

5,000

1

*S= *6,000

The scale of the finished mosaic is 1/6,000 (1:6,000).

To reinforce the mission planning procedures, you

can use the following example:

You are assigned to assist in the mission

calculations required for a recon mapping mission. You

are briefed on the mission and the following

information is provided:

Area to be mapped is 10 nautical miles east and west

by 20 nautical miles north and south.

Forward overlap required is 60 percent.

Side lap required is 40 percent.

Lens focal length is 12 inches.

Negative size is 9

×

9 inches.

True airspeed of aircraft is 140 knots.

The wind is from the north at 15 knots.

The scale of the chart used to plan and fly the

mission is 1/50,000 (1:50,000).

The required scale is 1/12,000 (1: 12,000).

A graphic scale representing 3,000 feet is required

on the printed mosaic map.

1. **Determine the altitude. **The first step in this

problem is to determine the altitude at which the aircraft

must fly to obtain the required scale of 1/12,000. The

IFGA formula used to determine the altitude is as

follows:

*I = G orA=FG*

*F*

*A*

*I*

Since G (ground coverage) is not known, you must

substitute the required scale (1/12,000) for it. At a

required scale of 1/12,000, each unit of I (on the film

plane) records 12,000 units of G. Since A is measured

in feet, you must divide your answer by 12 to get the

units in feet.

*A= *12

×

12,000 = 144,000 =144,000

1

1

Divide by 12 to get altitude units in feet

4-24

Advanced Photography Course