Published in Aerospace Testing International.
Ethernet-based networks having become the dominant choice for flight test instrumentation (FTI) applications, requirements for integrating Ethernet-based (IP) cameras with FTI data acquisition (DAQ) equipment, network recorders and telemetry devices have increased. As cameras move to HD formats, transmitting raw video adds complexity and limits the number of video frames that can be transmitted and stored. Synchronizing this data with other flight test parameters 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). Ethernet cameras with integrated compression can address these issues, providing multiple output streams to support recorder and telemetry applications. An Ethernet switch can also manage video streams and synchronize FTI and video data.
The extreme environmental conditions typical of FTI applications require highly ruggedized and reliable HD Ethernet cameras. For new flight test applications, video data needs to be coherently synchronized for telemetry and available for storage. Ideally, data in the telemetry stream will be highly compressed to minimize downlink bandwidth. Recorded data, on the other hand, can be lightly compressed to provide maximum quality for post-flight analysis.
Various image-processing functions are essential for delivering the appropriate image quality during test flights. Rolling shutter cameras can be used in airborne cabin and over-the-shoulder cockpit applications. Global shutters use simultaneous acquisition to capture the entire frame in a single instant of time and can be used where the subject is rotating, or moving with high velocity, to eliminate motion-induced distortion.
Environmental Factors
During flight test, 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. FTI cameras must be designed to meet stringent and harsh environmental requirements in order to withstand extreme vibration, shock, humidity and temperature. For example, an FTI camera may need to operate on a runway at 50°C (122°F), and shortly afterward at -30°C (-22°F). Such thermal differences can change electronic component impedances as a result of temperature or moisture condensation.
Cameras in FTI Applications
Full HD video at 60fps can take up to 3Gbps of bandwidth per channel. Several HD cameras recording uncompressed video can overload the data acquisition system. Also, transmission bit rates affect video quality. Lowering the bit rate will reduce the video quality unless the frame rate is decreased. To maintain video quality, changing the frame rate has a linear effect on the suggested bit rate. Compressing HD video with an industry standard algorithm can reduce bandwidth to a more reasonable amount without significantly affecting image quality.
Read the full article here