ED Decision 2023/007/R
DEMONSTRATION OF EQUIVALENT VISUAL ACUITY — SET OF SPECIFICATIONS AND GENERATIONS
(a) When assessing whether different NVG meet the same set of specifications for the purpose of demonstrating equivalent visual acuity, as described in point (a)(2)(ii) of AMC1 SPA.NVIS.110(e), generations may be defined as per US military specifications or using the following criteria:
(1) Generation 0 typically uses an S-1 photocathode with peak response in the blue-green region (with a photosensitivity of 60 micro A /lm), electrostatic inversion, and electron acceleration to achieve gain. Consequently generation 0 tubes are characterised by the presence of geometric distortion and the need for active infrared illumination.
(2) Generation 1 typically uses an S-20 photocathode (with a photosensitivity of 180-200 micro A /lm), electrostatic inversion, and electron acceleration to achieve gain. Because of higher photo-sensitivity, generation 1 was the first truly passive image intensifier. Generation 1 is characterised by the presence of geometric distortion, low performance at low light level and blooming.
(3) Generation 2 typically uses an S-25 photocathode (extended red, with a photosensitivity of 240 micro A /lm or more), and a microchannel to achieve gain. Generation 2 tubes provide satisfactory performance at low light levels and low distortion.
(4) Generation 3 uses gallium-arsenide for the photocathode (photosensitivity of 800+ micro A /lm in the near infrared) and a micro-channel plate for gain. The microchannel is coated with an ion barrier film to increase tube life. Generation 3 has very good to excellent performance at low light level. Recent models have no perceptible distortion.
(b) NVG of ‘generation 3 autogated’ or ‘generation 3+’ as defined by the US military are sometimes called ‘generation 4’ commercially. The differences with generation 3 are limited to the following and are therefore considered not to be significant. Generations 3 to 4 as mentioned above may be considered to be the same generation.
(1) they are autogated, therefore more robust to high illumination and abrupt changes of the illumination level
(2) they are unfilmed, which gives less image noise
(c) A non-civilian set of specifications — other than generations — that ensures sufficient equivalent visual acuity may also be used. For example, OMNI specifications from the US military may be used.
(d) The figure of merit is resolution * signal to noise ratio.
Guidance on defining NVG generations (0-3) by photocathode, gain, and performance, plus treatment of gen 3+ as same generation and use of non-civilian specs like OMNI.
* Summary by Aviation.Bot - Always consult the original document for the most accurate information.
Loading collections...