Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/78772
Trends With a hat-tip to early devel- opments of UAV technology in Israel, the U.S. UAV business accelerated dra- matically with the military actions in Iraq and Afghanistan in the early- to mid-2000s, and the advent of UAVs for the task of intelligence, surveillance, and reconnaissance (ISR). In early cases, the best, most common use of a UAV was to deliver video ISR data to troops on the ground. Attributes mostly relating to video quality now drive the designs of most small UAV payloads. Video ISR Payload In military applications, the desired product is high-qual- ity video ISR data that can deliver actionable information. What, then, is useful ISR video data? The most common requirement of any ISR video is to provide high-resolution pictures/video of ground targets. Manned surveillance aircraft always delivered high-quality images, but when captured from >5,000 feet, the resolution on the ground was never very high. Manned flight for ISR purposes over dangerous areas is expensive, hazardous, and relatively short in duration due to aircraft and pilot limitations. Small UAVs have been employed primarily in situ- ations where endurance and close tactical sup- port are required. Consider again the value of high-quality ISR. One can fly a cell phone camera on a small UAV 15 feet from a subject and have very high-quality video. But if that close-range, high- quality video modifies the sub- ject's behavior, how valuable is the quality of the ISR? Most UAVs 40 Electronic Military & Defense ■ www.vertmarkets.com/electronics fly overhead undetected and deliver ISR data to deci- sion makers without alter- ing the behav- ior of subjects on the ground. The viewers of ISR data want very high-fidel- ity data, and in most cases, they desire stealth. To complicate matters, consider what is needed to deliver narrow-field-of-view, quality video from a small aircraft. The platform is moving, vibrating, and subject to random and uncontrollable motion of the aircraft. The line of sight for the delivered video needs to point at the object of interest on the ground, hold on that object of interest while the aircraft is flying its course, and be immune to input disturbances that would cause the camera's line of sight to move. So the payload engineer is always combining the basics of imaging requirements with the science of vibration and disturbance rejection. In the small UAV world, we constantly struggle with issues of camera and lens mass/volume/power, the stabilized camera platform, and the requirements of video hold or track from a moving camera platform. Figure 2: Glossary of terms for UAV imaging. AGL = Above ground level. HFOV = Horizontal field of view, the longer dimension of an imager's field of view. Slant range = Distance to target, product of AGL and the sine of the angle from nadir. GSD = Ground sample distance. IFOV = Instantaneous field of view, the angle subtended by one pixel, usually in microradians. The UAV payload designer always returns to the primary issues involved in flying a robotic or remotely piloted small air- craft — mission length and fuel load vs. payload weight. Video quality is a fluid value — how good is the cam- era and how sta- ble is the image. Fundamentally, the small UAV is used to observe small vehicle and human-scale objects on the ground. Much of the time, the design of an ISR payload is driven by the operat- ing altitude, or aircraft above ground level