Technologies For Imaging System In Avionics; ANVIS, FLIR, EFVS
Flying an aircraft in itself can be a tedious and parlous task,yet some circumstances even make the task more demanding than the others.Let’s start with hypothetical scenario, imagine yourself in a cockpit of an aircraft with the view shielded from all sides and you on controls. Picture what it’s like when the blissful light of the day is slowly overshadowed by the dark, and only the star accompany you in your voyage. More to it, what if the mission is tactical ones or the military ones? So is there any form of assistance available to the pilot to behold through the dark? Seems to be obvious question.No, was the answer few decades back but not now.Well, we certainly have heard about the night vision goggles and the thermo graphic camera that senses infrared radiation.During the time of WW2 military operation required the stealthy night travel for the rescuing and for attacking/finding enemies at night. This urged the need for the night visioning system which in turns resulted in the development of Aviators Night Vision Imaging System (ANVIS), Forward Looking Infrared (FLIR) and Enhanced Flight Vision System (EFVS) now.These systems throughtheir development had its application on aircraft which made flight during the night possible.
Aviators Night Vision Imaging System (ANVIS): ANVIS including Night Vision Imaging System (NVIS) and Night Vision Goggles (NVG) are based on image intensification system followed by active illumination in some cases allows aircrews to see under impenetrably dark condition which is impossible through unaided eye. Image intensification system is the system which magnifies the amount of received photons from various natural sources at night that could be starlight or moonlight whereas active illumination combines image intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band. First-generation Night Vision goggles with monocular sensors was remedied to complex dual-sensor systems by improving the shortcomings: ANVIS system was developed. ANVIS has been proven to be useful but it can be overloaded with high levels of outside light since it provides the huge light amplification 10,000 to 80,000. Even small trace of reflecting light in the red to infrared passband of goggles cause blooming and visual distraction for aircrews. So, it works best on rural/ completely unlit areas. This system enhance night VFR(Visual Flight Rules) situation awareness and obstacles avoidance by allowing direct vision of horizon, terrain shadows and other aircraft. Thus it is applicable for night viewing and safe night flying condition not only in military aircraft. Cockpit design must be both daylight and NVG compatible as the NVG have limited tolerance for unwanted stray of light and is used only 10-20% of total flight time.
Forward Looking Infrared (FLIR): FLIR allows a hot object to be clearly visualized against a cooler natural background by imaging technology that senses infrared radiation. Thermal imaging camera detect the wavelength of long wave infrared and medium-wave infrared range which differs from that of the ANVIS which operates in the visible light and near infrared ranges (i.e., 0.4 to 1.0µm).The LWIR (Long-wave infrared) camera operate at 8 to12 µm and can see heat sources which are few miles away but it is not suitable for longer distance because of the absorption, scattering and refraction of the infrared radiation. The MWIR (Medium-wave infrared) camera operates at 3-5µm. This radiation suffers from less water vapor absorption but requires a more expensive sensor and cryogenic cooling. FLIR is beneficial mostly for target accusation, fire control and limited navigation through all hour and through all visibility condition. It also has application in the daylight as it can spot camouflaged vehicles or weapons. On the contrary this radiations can be reflected off of a shiny surfaces and also cannot be seen through glass or pass through the objects. ANVIS and FLIR both have significant but different application.FLIRworks best at night when warm body stand out more clearly against the cooler ambient temperature as well as in daylight but ANVIS allows general vision in very low ambient light. ANVIS has its disadvantages even at the modicum of stray of light.
Enhanced Flight Vision System (EFVS): Since the development of night vision devices for military aircraft, it also became advantageous in commercial aircrafts. Albeit it was not possible for the pilot to lower an aircraft below the required a natural vision limit. The first EVS comprised a MWIR camera, by Kollsman then this EVS was combined to a HUD, was certified for flight with the Gulfstream V aircraft also known as EFVS.EVS are traditionally based on a FLIR camera which gives a thermal image of the world and captures the airport approach lights. However, airports are switching to the more energy efficient LED lighting, which cannot be seen by traditional EVS. The new EVS designs are multispectral which captures both LED lights and the thermal image of previous EVS generation
There are other modern form of the imaging systemi.e., Combined Vision Systemwhich is ,as the word ‘combine’ states, combined form of thermal imaging camera and synthetic imagery for the ocular addition of fleeting inhibition in the approach and landing zone. This system can be regarded as a preliminary step toward future “Verified Synthetic Vision System”. Synthetic vision system is a technology which uses a set of databases stored and presents the visual environment that is external to the aircraft using computer generated imager in a manner analogous to how it would appear to the pilot if forward visibility were not restricted. Thus various technologies have come into existence in the night vision and world of obscured vision(i.e., due to fog,mist,etc.) which has become beneficial to both military and civilian aircraft. These technologies have led visual assistance to pilots to fly milessmoothly and led their application in tactical avionics which is suitable almost in every situation be ita day or night.
Article by; Sunita Pokharel
4th Year Undergraduate Student
Department of Mechanical Engineering