The 3-5μm wave length region has been recognized as an effective mid infrared spectral range for the detection of high
temperature events on Earth surface with remote sensing camera. Most of current mid infrared remote sensors relied on
cooled detectors. Although they have high radiometric sensitivity, they inevitably are large size and weight, high power
consumption, short life-time, and high cost. With the advent of uncooled thermal detectors, the miniaturization of mid
infrared imagers suitable for microsatellite is being investigated widely. Based on uncooled focal plane array, a
conceptual compact midwave infrared sensor has been put forward. It is designed for hot spot detection. First, working
environments and requirements of the sensor for hot spot detection is introduced. Then the characteristic of its main
constituent parts including selected uncooled focal plane array and the designed optical system is presented. Because
uncooled focal plane array has lower radiometric sensitivity than the cooled, we are more concerned about the thermal
resolution of the system. And its performance including sub-pixel hot spot detection capabilities and spatial resolution is
evaluated. It shows that the suggested compact sensor with uncooeld focal plane array can not meet the requirement.
Recent advances of uncooled detector technology especially the development of uncooled micro-bolometer array hold promise for us to develop low-cost and compact MWIR earth observation imager. For comparative lower radiometric performance of uncooled focal plane array, fast speed optical system operating in large spectral bands is compatible. In addition, in order to exhibit advantages over imagers based on cooled detector technology, the optical system should be as compact as possible which means fewer elements, smaller size and light weight. In this article, a high speed optical design meeting these requirement is provided with 100mm focal length, F/1 F number,±2.5°field of view woking in 3-5um wave band. The fast speed MWIR imager has properties mentioned as follows: First, the optical system utilizes a hybrid system including refractive and diffractive elements. Second, the optical system realizes athermalization in simple passive way through distributing power among the refractive elements. It can work under typical temperature scope from -20°C to 60°C for typical space application. Third, Because of high speed aperture, the design makes use of aspheric surface to correct spherical aberration and spherochromatism .Finally, we use Ge and Si material. instead of expensive ZnS material.