Figure 2-10 Terrain Elevation After Slewing To Issued Coordinates; Figure 2-11 Slant Range Distance - L3 Communications MX-15i Operation & Maintenance Manual

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Chapter 2 - Video Status Overlays

The accuracy of Terrain Elevation value will affect some of the system's automated functions; like focus clarity,

when operators are utilizing Geo-Focus, or target hold precision in Auto steering mode.

The Terrain Elevation value will be displayed in reverse video when the operator slews the turret to steering

coordinates issued by RCS or a Moving Map source. The reverse video value will report the static command

position, and the value will not update until cleared by a steering mode change. For example, reverting to Manual or

Forward steering.

Target Bearing. Reports the target's angular measure for bearing relative to True North.

Slant Range. Reports the calculated or measured distance of the target's slant range. Slant range is the distance

from the turret to the ground intercept point along the line-of-sight. Display units can be configured by the operator.

Measurement Mode. Reports the system's current measurement mode for calculating target distance. There are

two modes, of which both are passive and managed by the system:

•

LOS mode (passive measurement)

The target's slant range distance and position data (lat and long) are calculated as the line-of-sight ground

intercept point, on the Earth's surface, as defined by the navigational coordinate system of an assumed Earth

model (WGS84). For long range distances, the calculation applies correction factors for the earth's curvature

and atmospheric influences. While accurate, the calculation of target location cannot account for: angular

measurement errors, inaccuracies in GPS position and altitude data, or timing errors introduced by either

extreme turret movement or from latent data updates. For example, viewing a subject at very narrow vertical

angle off the horizon or steering the turret too fast will impact distance calculations.

•

MAP mode (passive measurement)

The target's slant range distance and position data (lat and long) are calculated as the line-of-sight ground

intercept point, on the Earth's surface, as defined by the elevation contour supplied as Digital Terrain Elevation

Data (DTED) from a digital map. Accuracy of this measurement mode will depend upon your map system's

DTED Level. For map data with a DTED Level of 1 or 2, the resolution is between 30 to 100m (98.4 to 328.1 ft).

For map data with DTED Levels 3 through 5, the resolution is much higher (1 to 3m [3.3 to 9.8 ft]), and the

measurement accuracy is comparable to that of a laser range finder. The calculation of target location cannot

account for angular measurement errors and timing errors introduced by either extreme turret movement or

from latent data updates. For example, viewing a subject at very narrow vertical angle off the horizon or steering

the turret too fast will impact distance calculations.

October 2007

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