Hybrid receivers that enable switching between direct and coherent detection provide many imaging functions beneficial to scientific and defense applications. A hybrid receiver system is presented wherein a single detector is switched between the Geiger-mode and linear amplification modes of operation. This system benefits from enhanced functionality and lower size, weight, power, cost, and complexity compared with dual receiver implementations. The hybrid receiver sensing modality is reconfigurable on-the-fly between single photon direct detection and amplitude/phase coherent detection. The reconfiguration is achieved by adjusting detector bias (electrically) and by simultaneously enabling or disabling the local oscillator (optically). This work describes these two sensing scenarios, discusses the operation of the receiver system and shows laboratory-scale imaging results for each mode of hybrid receiver operation.
The weaponization and dissemination of biological warfare agents (BWA) constitute a high threat to civilians and
military personnel. An aerosol release, disseminated from a single point, can directly affect large areas and many people
in a short time. Because of this threat real-time standoff detection of BWAs is a key requirement for national and
military security. BWAs are a general class of material that can refer to spores, bacteria, toxins, or viruses. These
bioaerosols have a tremendous size, shape, and chemical diversity that, at present, are not well characterized .
Lockheed Martin Coherent Technologies (LMCT) has developed a standoff lidar sensor with high sensitivity and robust
discrimination capabilities with a size and ruggedness that is appropriate for military use. This technology utilizes multiwavelength
backscatter polarization diversity to discriminate between biological threats and naturally occurring
interferents such as dust, smoke, and pollen. The optical design and hardware selection of the system has been driven by
performance modeling leading to an understanding of measured system sensitivity. Here we briefly discuss the
challenges of standoff bioaerosol discrimination and the approach used by LMCT to overcome these challenges. We
review the radiometric calculations involved in modeling
direct-detection of a distributed aerosol target and methods for
accurately estimating wavelength dependent plume backscatter coefficients. Key model parameters and their validation
are discussed and outlined. Metrics for sensor sensitivity are defined, modeled, and compared directly to data taken at
Dugway Proving Ground, UT in 2008. Sensor sensitivity is modeled to predict performance changes between day and
night operation and in various challenging environmental conditions.