A new Concept for a Low-Cost Earth Sensor: Imaging Oxygen Airglow with Arrays of Single Photon Detectors

This paper presents a novel concept for a compact low-cost Earth sensor based on imaging atmospheric oxygen emission at 762 nm using arrays of single photon avalanche diodes (SPADs). In both nighttime and daytime there is continuous emission at 762 nm due to oxygen recombination. The SPADs high sensitivity enables the ES to operate at night and day, over a wide temperature range, with a very compact optical system (e.g. aperture of 10 mm, focal length of 14 mm) and no scanning elements. A modular and low-cost instrument design is described, which uses the same wavelength band, the same detector technology, the same optics, the same power and data interfaces and similar algorithms for LEO and GEO applications. Using the visible band rather than the LWIR band offers several advantages including much lower cost detectors, no need for cooling, a more relaxed thermal design, simpler optics, higher sensitivity and hence low cost. 1. INTRODUCTION Available Earth Sensors (ES) are based on the measurement of Earth's infrared radiation (typically between 14 and 16 μm) to determine the vector to the Earth's centre. Standard designs use bolometers, thermopiles or semiconductor-based detectors, often combined with scanning mirrors to provide excellent accuracies (tens of milli-degrees) over a large field of view. However, these designs are heavy, large, require cooling or temperature stabilization and are power hungry. In addition, the sensor concept for a LEO or GEO Earth Sensor differs significantly, typically requiring two different designs and qualification procedures and therefore increasing the ES cost.