In order to avoid potential collisions with space debris future spacecraft in geosynchronous (GEO) orbit may be required to detect all objects in their local environment and will be required to have 4pi steradian coverage. Unfortunately the sun can blind and/or damage these sensors if precautions are not built into the sensor. APS is proposing to use an ultra-narrowband filter (0.001 nm), called a Differential Doppler Imager (DDI), to reject the broadband blackbody spectrum of the sun; it uses an atomic emission line from the sun itself as the illumination source for the object. The filter is passively (naturally) locked to the chosen atomic line and only allows that line to pass through the optical system. Rejection of background light can be very high (enables imaging in solar disk) while maintaining high in band filter transmission. APS has: a unique atomic physics computer code that properly models these filters, the ability to model the full optical system performance, and built many of them at a variety of wavelengths. Since the DDI uses the Doppler shift of atomic lines to reject background the device can also measure the line of sight velocity component of the debris.
Benefit: The successful demonstration of imaging in very high dynamic range conditions could have many possible applications in both defense and industry. The proposed instrument enables the GEO satellites to identify, track, and avoid potentially lethal debris. This technology could also be used to build an optical ground moving target indicator instrument for satellite, aircraft, or UAV surveillance missions. A similar sensor might also be used to image high brightness arcs or exhausts in an industrial setting. Another very interesting application is as a passive wind speed monitor for airports or other research applications.
Keywords: High Dynamic Range Imaging, Atomic Line Filter Imager, Persistent Surveillance, Optical Moving Target Indicator, Doppler Sensor
