Analysis of spot shape and size on the focal plane of specific infrared non-imaging sensors for the detection of forest fires

ABSTRACT This paper describes some of the work performed in the course of the design and development of a new JR sensorsystem for early detection offorest fires. The proposed device is a non-imaging sensor that would discriminate angularposition by means of a simple JR array, working in the 3 -5 microns wavelength region, placed at the focal plane ofthe optical system. In order to accomplish low cost requirements, a system with a sole JR lens has been designed. Inthis work, a study ofthe spot shape, size and optical JR power on the detector has been performed. From the analysisof the influence of lens-detector distance and incidence angle, we have derived an optimum pixel size and opticalconfiguration. The use of TB-cooled PbSe detectors is proposed, as well as a simplified cell array.KBY WORDS : Infrared sensors, Infrared Arrays, Forest Fire Detection, Bnvironmental Technology, Gas detectors 1. INTRODUCTION Different studies have been published during the past years in the field of forest fire detection based on infrared (IR)sensors'4, most of them devoted to airborne sensor systems"2. As a rule, they are based on an JR focal plane arrayon which the scene is imaged. Sometimes, a scanning device is used in order to expand the system total field of viewas it is usually small (in general, no more than 5 0)Mostof these systems work in the 3-5 m wavelength band, although some work also in the 8 -12 im band.They generally employ JnSb or platinum suicide JR focal plane arrys (FPAs), or HgCdTe linear arrays for the longerwavelengths. These high performance sensors are expensive, and require Stirling or similar cooling systems, with highpower consumption and maintenance. When operated from a fixed observation tower, these equipments need to be