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Rugged High-Speed Cameras Capture Critical Flight Test Video Data

There is increasing demand for high-quality High Definition (HD) video for airborne applications such as Flight Test Instrumentation (FTI). Ideally, such new camera solutions can reduce the weight and difficultly of installing wiring, and enable data to be coherently combined with image data. Ethernet cameras can address these needs with built-in compression and multiple output streams. Additionally, as Ethernet-based networks have become an attractive choice for FTI applications, we see increased requirements for integrating Ethernet-based cameras with FTI data acquisition equipment, network recorders, and telemetry systems as this removes duplication of wiring and devices.

Using an Ethernet camera that supports onboard compression enables video compression to be removed from the FTI Data Acquisition System (DAS), or it can eliminate a dedicated unit. The camera can be connected via an Ethernet switch directly into the system, like any other data acquisition unit. Even better, because there is no need for dedicated hardware compression, SWaP is minimized and installation wiring greatly simplified.

As legacy airborne cameras are rapidly becoming obsolete, designers, systems integrators and end users have sought up-to-date digital video alternatives that offer higher quality images. Older cameras typically use coaxial wiring, which while fairly immune to noise and generally well understood, is heavy and can create installation headaches. In addition, the move to HD also adds complexity and limits the number of video frames that can be transmitted and stored without additional conversion hardware, because of the sheer size of the data they generate.

One approach for meeting the need for higher performance FTI cameras without adding complexity is to use IP cameras that utilize Ethernet wiring, switches and recorders. Ethernet IP cameras offer several key benefits when compared to traditional Composite Video Baseband Signal (CVBS), such as simplified installation, reduced system weight, and high-quality images. Even better, the required infrastructure is often already installed on the aircraft for other data acquisition purposes.

Using Cameras in Test Applications

Video is often used during a test campaign as a virtual “witness” to events (excluding high-speed video which is used for applications such as time magnification and trajectory analysis). It is generally not used as a primary data source for measuring phenomena about the aircraft, but it is a very useful tool nonetheless. When the image data is properly correlated with data from other sensors, busses, etc., one can correlate the physical event with imagery. This is especially useful for environments, like the cockpit, for example, where you can see how the pilots and operators are interacting with instruments and controls for user interface analysis and training (e.g. an organization may be looking at reaction times). Another example is to check that the instruments are displaying the same information as the bus to confirm the data the pilot is getting is accurate.

Many customers now want better quality video than older SD cameras offer. They also want cameras that can cope with being pointed into bright objects (such as the sun). Older cameras tend to use Charge-Coupled Device (CCD) sensors that suffer from pixel bleed and become washed out when encountering bright objects. However, transmitting raw HD video adds complexity and limits the number of video frames that can be transmitted and stored. Synchronizing this video data with other flight test parameters from a Data Acquisition System (DAS) can also pose a challenge. Dedicated compression cards can solve some of these issues, but they have negative implications for size, weight and power (SWaP) – all critical factors for FTI.

The extreme environmental conditions typical of FTI applications require highly reliable cameras ruggedized far beyond the levels supported by most industrial or commercial cameras. Today, a typical FTI system designer uses separate camera and video compression systems, or stand-alone video cameras, with simple recording capability. The video is not usually synchronized to other cameras or DAS data. For flight test applications, camera data for telemetry needs to be coherently synchronized and available for storage. Ideally, the data in the telemetry stream should be highly compressed to minimize downlink bandwidth. Recorded data, on the other hand, should be minimally compressed to provide maximum quality for onboard and post flight analysis.

Camera Functions and Features

Figure 1. Global shutters capture the entire frame at the same time, avoiding the smearing effect rolling shutters can produce.

Various image-processing functions are essential for delivering the appropriate image quality during test flights. Rolling shutter designs, common in consumer cameras, capture an image frame by rapidly scanning vertically or horizontally, but the time difference between different parts of the frame can result in the distortion of moving elements (such as spinning rotor blades) as shown in Figure 1. For flight tests, where the subject being imaged is rotating or moving with high velocity, a ‘global shutter’ is required to eliminate this smearing effect (Figure 1). Global shutters, which use simultaneous acquisition to capture the entire frame in a single instant of time, eliminate motion-induced distortion. Rolling shutters are generally cheaper, however, and can perform better at low light levels, so they can still be useful in some applications.

The more modern CMOS sensors used in many HD cameras today are immune to pixel bleed that CCD sensors suffer from. They can also commonly utilize Wide Dynamic Range (WDR) techniques to enhance the illumination of a scene. WDR techniques identify particularly bright and dark portions of images and control the saturation of pixels in those areas. WDR is important for achieving good image quality and is becoming common in commercial electronics such as cameras and TVs (WDR is often referred to as HDR in these applications).

Environmental Factors and Conditions in FTI

During flight tests, the aircraft must execute maneuvers not often encountered during typical operation. The aircraft and its systems must be pushed to their limits to prove the validity of the design assumptions and to record the safe operational limits. Cameras for FTI must be designed to meet stringent and harsh environmental requirements in order to withstand the extreme vibration, shock, humidity and temperature. For example, an FTI camera may need to operate on a runway at 50°C, and shortly afterwards at -30°C. Such thermal differences can change electronic component impedances as a result of temperature or moisture condensation.

FTI cameras should have rugged optical windows made of sapphire glass, for example, to protect against scratches and breakage. And they should feature ruggedized connectors to maximize the camera's availability. To ensure that environmental requirements are met, the camera should be qualified to DO-160, MIL-STD-461, MIL-STD-464, MIL-STD-810 and MIL-STD-704 at certified laboratories. Manufacturer testing, quality management (ISO 9100, EN/AS 9100), and other manufacturing standards (IPC-A-610E, IPC-A-600, IPC J-STD-011, IPC/WHMAA-A-620) need to be addressed during the design stage.