When space infrared detection system is detecting weak targets in low Earth orbit, the complex and intense out-of-field stray radiation from Earth, Sun and Moon is several orders of magnitude higher than the target energy, which has a serious impact on detection. Therefore, modeling and analysis of out-of-field stray radiation are needed. In this paper, the observation hemisphere at the entrance of the system is divided into regional grids, and then the stray radiation model in any time and space is established according to the detection geometry, combining the characteristics of the stray radiation from different sources. Taking the long-wave infrared spectrum of a detection system as an example, the energy of stray radiation reaching the focal plane is calculated, and the stray radiation is analyzed in typical space and time state. The out of-field stray radiation accounted for 39.1% of the total radiation, and the out-of-field stray radiation from the incident off axis angle less than 20° accounted for 95.3% of the total radiation. When the observation hemisphere is illuminated by the Sun, the maximum out-of-field stray radiation from the Earth's surface region and the Earth's atmosphere region increases by 16.7% and 10.9%, respectively. The out-of-field stray radiation model established in this study can be used as the support and basis for the design of stray radiation suppression in space infrared detection systems.
High resolution and large FOV represents the developing trends of space optical imaging systems, Considering the characters of infrared optical systems, A low cost and low technical risk method of optical butting concept which offer the promise of butting smaller arrays into long linear detector assemblies is presented in this paper, the design method of optical butting is described, and a hypothetical system is demonstrated as well.
Along with the further application of optical remote sensing, it becomes main trend to realize high spatial resolution, high time resolution, high spectrum resolution and high irradiance sensitivity simultaneously. We present a new satellite-based imaging system that will provide images with these high performances. The structure of the system is compact with small size and light weight. The IR imager, a new generation of high resolution optical remote sensing, is universally acknowledged as the most effective approach to surveil dynamic changes in the environment on the earth. Pushbroom imaging fashion with high efficiency and long-array focal plane detector with passive cooling are adopted to realize area imaging relevant to the flight direction of satellite. The instrument is a dual-optical-path system with long-wave infrared (LWIR) and mid-short-wave infrared (MW-SWIR) bands,which has 4 narrow spectrum bands respectively. An IR dichroic beam-splitter is use to divide wideband incident infrared into LWIR and MW-SWIR. Then two pieces of joint filters, which are integrated in front of detectors and then enveloped by IR Dewars, are used to divide the LWIR and MWIR into 4 spectral bands separately. The focal plane arrays (FPA) are fixed on the optical imaging plane of the lens. The LWIR and MW-SWIR FPA are cooled around 80K or even below. For cooled FPA, optical system must provide a real, accessible exit pupil coupled with a fast f/number refractive component in a Dewar and very close to the FPA. Compared to traditional infrared instruments, high spatial resolution and spectrum resolution can be obtained simultaneously within mass, volume and performance constraints.
Thermal infrared imaging from geostationary satellite can provide all time, real time and video observation, and it can achieve fast pointing and information acquisition of any object on the earth disk. It is more suitable for timely information acquisition of emergent event such as natural disaster. The paper introduces the development and related applications of GEO thermal infrared imaging technologies during the past several decades. It then introduces a concept of all time, real time and video observation from GEO using two thermal infrared staring imagers with different spatial resolution and field of view (FOV). The low spatial resolution and wide FOV thermal infrared staring imager is used to monitor objects within a large area concerned, while the high spatial resolution and narrow FOV thermal infrared staring imager is used to acquire detailed information of the interesting objects within a small area. The main characteristics and technical solutions about the proposed concept are described in the paper.
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