Lucid Dimensions has independently developed methods for distributing sensors on a sphere. This method uses a triangular lattice spacing that exhibits spherical symmetry when projected onto an XY plane. Similar to the 2D histogram of the circular prototype, sensor data over the sphere produces a 3D Gaussian histogram. The sensor data has a maximum where sensors are directly facing the source. Sensors surrounding the maximum will fall off in a predictable manner based on the relative angular position.

A wide range of algorithms can be applied to analyze the incoming sensor data. Using peak deconvolution techniques, overlapping peaks can be analyzed for closely spaced sources. These algorithms include baseline subtraction, smoothing, peak searching, and finding peak maximums.

Figure 3. The spherical sensor response (SSR) with decreasing sensor FOV; a) 30 FOV, b) 20 FOV, and c) 10 FOV.

Figure 3 shows the sensor distribution from three different sources. Assuming all sources are equal, the blue source is the furthest from the sphere, while the red is the closest and green is in between. The three images show the effect of decreasing the sensor FOV in order to separate out peaks. This results in less active sensors per target, allowing more sources to be tracked without having to perform extensive peak deconvolution.

The initial 3D spherical prototype is being designed with a 503 modal sensor distribution. The major problem associated with the system is the large number of lens assemblies, detectors, and associated analog channels. One design being explored is to use fiber optics to bring incoming light into a single bundle that can then be transmitted onto a single CCD or FPA.

A wide range of sensors and optics exist that can be implemented into a SDS. Range, bandwidth, power, and cost become the ultimate driving factors for SDS systems. Low-cost thermopile detectors only offer a short range (~100m) and relatively slow sampling rates (10- 100 Hz). Higher-end Mercury Cadmium Telluride (HgCdTe) offer higher speed and higher detectivity, but at a high cost and with high power requirements for thermo-electrical cooling. For longer range detection associated with missile detection IRST systems, a range of options exists depending on cost and available power.

Heat Signature Determination

There exists a wide range of filters that can be used in combination with single- or multi-element broadband IR detectors. These filters allow for both broadband filtering and narrowband filtering. By implementing particular filters and multi-element detectors, the spherical sensor system can distinguish between different temperature objects. One common example is differentiating between a human IR signature and a ground vehicle IR signature. One of the detector elements can be fitted with a filter in the 3 - 5-um band, while another element will have an 8 - 12-um filter. In this scenario, the human IR signature will not produce a measurable response on the 3 - 5-um band, while the 8 - 12 band will produce a significant response. The vehicle temperature will generally overwhelm the 8 - 12-um sensor, but will also be present in the 3 - 5-um band. This technique can be applied to various spectral bands depending on application. Sensors with 10 channels or more will offer detailed multi-spectral differentiation.

Electrical Subsystem

The electrical subsystem, in combination with the algorithms, represents the heart of the SDS. The biggest hurdle is sampling 500+ sensors simultaneously and processing the data on an FPGA and DSP. Initial design is to obtain the 500 analog channels on the FPGA and then send data to a PC over an Ethernet connection for processing. An ADL945 duo core PC-104 is used for initial processing of the data. The PC-104 processing option enables a configurable system with the ability to add cards for auxiliary system control, but at the cost of higher power consumption. The PC-104 systems are ideal for integration on land- or air-based vehicles. As the algorithms develop, an additional DSP will be implemented for onboard high-speed processing. Basic calculations, such as finding peak maximums, can be accomplished on the DSP at very high speeds. The onboard DSP for data processing allows the SDS to operate at high speeds with low power consumption.

IRST systems classically employ distributed passive electro-optical systems to achieve a large FOR providing improved situational awareness. They are mainly used for detection, classification, and identification of targets within a line of sight. Their advantages over similar active technologies, such as radar, include low power consumption, high-speed scanning, high angular accuracy, high immunity to countermeasures, accurate target discrimination, and passive operation.

Since the 1960s, IRST systems have been used on military jet fighters and in the 1970s on naval ships. Advances in sensing have expanded the application of IRST technologies to a host of platforms for both defense and security operations, including marine vessels, aircraft, ground vehicles, man-portable units, and stationary mounts. IRST systems are now used to detect a multitude of targets, each with their distinct infrared signatures. Target types include small arms fire, missiles, RPGs, vehicles, and, of course, people. Optical ranges and IR band selection depend on the platform and application.

The SDS acts as the primary component of the IRST for immediate detection of threats. Once the SDS determines the angular coordinates and range of targets, the information is communicated to cameras for further identification. The SDS will continuously track targets and provide information to the cameras or other countermeasures, depending on the application.

The SSC’s primary strength lies in its continuous, high-speed, 360° horizontal by 360° vertical field of regard for automated multi-target detection and tracking in 3D. Due to its passive sensing, the unit observes its environment covertly while keeping power consumption and mechanical breakdown to a minimum.

The SSC’s individual sensors are tuned to fit the application by adjusting the optics, sensor type, and filtering. Spherical detector size generally increases for long-range, high-resolution systems. Installing additional SSC units to a platform, such as on large vessels, borders, or fence-lines, improves accuracy and coverage, and provides increased range-finding (triangulation) capabilities.

The SSC core technology offers effective high- and low-cost IRST systems with comprehensive benefits. Utilizing the real-time 3D angular data produced by the SSC, defense and security operations are enhanced for threat detection, reconnaissance, collision avoidance, intrusion detection, and search and rescue.

This article was written by Ryan Riel, Adam Calihman, David Thomson, Nicholas Jentzsch, and Matthew Eames of Lucid Dimensions, Louisville, CO. For more information, click here .