An advanced wide area chemical sensor testbed

ABSTRACT In order to meet current and emerging needs for remote passive standoff detection of chemical agent threats, MIT Lincoln Laboratory has developed a Wide Area Chemical Sensor (WACS) testbed. A design study helped define the initial concept, guided by current standoff sensor mission requirements. Several variants of this initial design have since been proposed to target other applications within the defense community. The design relies on several enabling technologies required for successful implementation. The primary spectral component is a Wedged Interferometric Spectrometer (WIS) capable of imaging in the LWIR with spectral resolutions as narrow as 4 cm -1 . A novel scanning optic will enhance the ability of this sensor to scan over large areas of concern with a compact, rugged design. In this paper, we shall discuss our design, development, and calibration process for this system as well as recent testbed measurements that validate the sensor concept. 1. INTRODUCTION The objective of a standoff LWIR imaging chemical sensor is to determine if and where a chemical release has occurred. The most general requirement of the sensor is to detect the chemical plume with a high probability of detection and low probability of false alarm and be able to do so in time to warn potential victims of an attack. Such a system should also be tailored to the size and weight requirements of its platform. It should be rugged enough to withstand any strain imposed by operational conditions and finally, it should be affordable in terms of the context of its mission. 1.1 Detection parameters The ability of a sensor system to meet the previously stated performance requirements depends on a number of system parameters. These parameters may be divided into two categories: the sensor/ platform parameters, and the scene parameters. The sensor and platform parameters include the noise characteristics of the detector, the spectral resolution of the spectrometer, the detector field of view (FOV), and the area coverage rate (ACR). All of these parameters may be controlled either during the design of the instrument or during the mission. The scene parameters are beyond the users control and include the chemical cloud parameters (temperature, concentration, path length, absorption coefficient), the background scene spectral radiance, the atmosphere, and any other interferents that are present. 1.1.1 Sensor/platform parameters The requirements of the chemical detection system are dependent upon the mission. The two modes of operation addressed in this proceeding are wide area search and cued staring. The system requirements are not only dependent upon the mission and the chemical plume parameters, but are also intimately connected to each other. Detector noise equivalent delta radiance (NEDN) is an important parameter in a chemical detection system. Defined as the signal, in radiance units, required to achieve a SNR of 1, it is a metric of detector sensitivity. *This work was sponsored by the United States Air Force under Air Force contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author and not necessarily endorsed by the United States Government.