"Zero position of the field of view axis" means the position of the field of view axis parallel to the water surface pointing in the direction right ahead.
"Standard visibility" means the daylight visibility under homogenous atmospheric conditions (i.e. even transmission per length unit) and a contrast threshold value of 0.05.
5 FUNCTIONAL REQUIREMENTS
5.1 REQUIRED FUNCTIONS AND THEIR AVAILABILITY
At night and in restricted visibility, night vision equipment should be capable of locating objects above the water surface within a certain distance from one's own craft, and of displaying the information pictorially in real time. The pictorial display should enable the navigator to unequivocally recognize such objects above the water surface.
5.2 RELIABILITY, ACCURACY, AND DISCRIMINATION
5.2.1 Continuous operation
Night vision equipment on board HSC should be operable continuously while navigating at Sea. After the equipment has been switched on it should be operational after maximally 15 minutes.
5.2.2 Radar-based tracking
Night vision equipment should be capable of automatically adjusting to and of following a point of intersection between electronic bearing line and variable range marker, activated by a single operational control. The point of intersection has to be followed automatically both in azimuth and elevation until this function is deactivated. If night vision equipment is moved by manual control, radar-based tracking should be automatically switched Off.
5.2.3 Fields of view
Night vision equipment should have at least two switchable fields of view with aperture angles in a proportion of minimally 1：3.
The wide field of view should range between 12｡?nd 25｡?orizontally and 6｡?nd 18.9｡?ertically, the narrow field of view between 4｡?nd 8.3｡?orizontally and 2｡?nd 6.3｡?ertically.
5.2.4 Pan and tilt ranges of the fields of view
The axis of the field of view should be capable of being moved at least 175° horizontally to either side and minimally 30°downward and 10°upward, starting from zero position.
5.2.5 Pan and tilt speeds of the fields of view
The minimum horizontal and vertical slewing speed per second should be smaller than 10% of the narrow horizontal field of view, and the maximum horizontal and vertical slewing speed per second should exceed 100% of the wide horizontal field of view.
By activation of a control element, the axis of the field of view should be capable of being returned automatically to the zero position at a minimum angular speed of 40°/s.
