NIGHT VISION/NVS LIMITATIONS AND TECHNIQUES

Question 1

OFF-CENTER VISION

Answer 1

There are no limitations to viewing an object with central vision during daylight. If this same technique is used at night, however, the viewer might not see the object due to the night blind spot that exists under low light illumination. To compensate for this limitation, crewmembers must use the offcenter vision technique.

Question 2

SCANNING

Answer 2

During daylight, objects can be perceived at great distances with good detail. At night, however, range is limited and detail is poor. Objects along the flight path can be more readily identified at night when crewmembers use proper techniques to scan the terrain. Effective scanning requires crewmembers to look from right to left or left to right. They should begin scanning at the greatest distance at which an object can be perceived (top) and move inward toward the aircraft’s position (bottom).

Question 3

SHAPES OR SILHOUETTES

Answer 3

Since visual acuity is reduced at night, objects must be identified by their shapes or silhouettes. Therefore, crewmembers must be familiar with the architectural design of structures in the area covered by the mission.

Question 4

PARALLAX EFFECT

Answer 4

This occurs in a PNVS due to the relative distance between the FLIR sensor and the helmet display unit (HDU). The FLIR sensor is contained within the PNVS turret located on the nose of the aircraft, while the HDU is positioned in front of the aviator’s eye. The PNVS turret is located approximately 10 feet forward and 3 feet below the aviator’s design-eye position. In both crewmember positions, the thermal scene viewed on the HDU is obtained from the physical perspective point of the FLIR sensor. The aviator flying with the PNVS views with the FLIR sensor, not with his or her unaided eye. Attempts to correlate the thermal scene viewed through the HDU with the actual scene viewed using the unaided eye can result in an apparent difference in the location of objects within the scene.

Question 5

NIGHT(SCOTOPIC)VISION

Answer 5

Scotopic vision (figure 8-5, page 8-5) is experienced in low light environments such as partial moonlight and starlight conditions. Cones become ineffective in these conditions, causing poor resolution in detail. Visual acuity decreases to 20/200 or less, and color perception is lost. A central or night blind spot occurs when cone cell sensitivity is lost. Scotopic vision degrades primary color perception to shades of black, gray, and white unless the light source is of adequate intensity to stimulate the cones. Peripheral vision is used primarily while viewing with scotopic vision.

Question 6

VISUAL/NEAR IR SIGHT

Answer 6

During daylight, the greatest source of visible light energy is the sun. The sun continuously emits energy and permits the eye to discern form and color. When the sun sets, most naturally occurring visible light energy is reduced and normal eye function makes the transition to scotopic vision decreasing visual acuity. Scotopic vision requires either naturally occurring night light sources or artificial lights. I2 systems amplify natural and artificial visible and near IR energy.