Responsive, Pre-launch and On-orbit, Electro-Optical Sensor Characterization and Calibration
Frontier Technology, Inc (FTI) received a contract award to provide Kirtland AFB with developing proposed hardware and algorithmic concepts that relate to an overall strategy for rapid and improved calibration of space E-O sensors. R&D, analysis, and empirical verifications will be performed. SBIR topic explores new ideas for achieving a dramatic reduction in timescales for on-orbit sensor calibration & telescope pointing verification, while preserving high calibration fidelity.
Space-based electro-optical (E-O) sensing provides revolutionary capability for a variety of Department of Defense (DoD) missions, yet the timescales traditionally needed for attaining high fidelity image data products remain long. Specifically, on-orbit calibration of E-O systems typically requires significantly more time than the desired ~24 hour goal for Operationally Responsive Space missions. The same remarks also apply to commercial satellite imagery.
These space-based imaging sensors comprise a telescope assembly that focuses radiation onto an array of detectors whose temperature is often carefully regulated. In the infrared region, the focal plane array (FPA) is typically cooled to cryogenic temperatures. Calibration of pixel non-uniformities is often in the form of a two-point non-uniformity correction (NUC), where known (calibrated) photon fluxes at high and low extremes are compared with signal outputs from the individual pixels, thereby establishing a gain and offset calibration for each pixel. Given the sensitivity of dark current to FPA temperature, particularly in the infrared, the NUC typically applies over a narrow range of temperatures and will therefore not be immediately beneficial for the sensor that has recently reached orbit and is still equilibrating in temperature.
This SBIR topic emphasizes R&D on technologies & techniques for accelerated on-orbit calibration. R&D on proposed approaches, e.g., improved radiometric and sensor non-uniformity calibration using novel, on-sensor calibration sources (flood & radiometric), or using the calibration star network or ground-based calibration sites that provide uniform radiance over the FPA, might be coupled with processor subsystems that implement the relevant algorithms. Calibration algorithms and associated novel hardware involving advanced concepts for non-equilibrium calibration might include compensating for FPA temperature instabilities (especially for the infrared) and for the out-gassing of particles in the telescopes near-field (of significant interest due to their reflected solar radiation and their thermal emission in the long wave infra-red), are also of interest. For example, a side car approach that implements NUC in proximity to the FPA, based on temperature readings and calibrated scene input onto the FPA, is one possible approach. Rapid pre-launch characterization & calibration of the E-O sensor also forms an integral part of the overall strategy for achieving a calibrated sensor in orbit, by defining hardware and algorithmic approaches that enable a minimal set of pre- and post-launch calibration activities needed to achieve the desired timeliness.
In addition to radiometric calibration issues, improved methods involving hardware and algorithmic subsystems are sought for a timely initial pointing calibration, including advanced concepts for rapid latitude-longitude determination from initial image products. These initial products might miss the targeted structured scenes (e.g., cities) which facilitate pointing calibration. |
