Laser Transmitter System for Ground-to-Space Laser Calibration of Space-borne Radiometric Sensors

On-orbit radiometric sensors provide a wide range of critical data products across many Earth Science disciplines addressing atmospheric, ocean, and land processes and how they change over time. The quality of these data products is directly determined by a sensor’s on-orbit calibration, its accuracy and long-term stability. Instrument changes in orbit result in unwanted impacts on the sensitivity to polarization, out-of-band signal rejection, and relative spectral response. On-board calibration systems are inherently expensive, increase the complexity, power, size, and payload mass, and do not address continuity changes that inevitably occur between mission lifetimes. Ground-to-Space Laser Calibration (GSLC) is a method to address certain types of calibration needs by illuminating on-orbit radiometric sensors from a ground-based laser transmitter station. The approach we are investigating will propagate a specially conditioned flat-top multi-beam phase-scrambled continuous wave laser output designed to mitigate atmospheric and laser coherence effects while conducting desired calibrations by controlling the transmitted laser beam wavelength and polarization state. The ability to calibrate on-orbit sensors from the ground results in a significant benefit, with the potential to impact multiple missions and improve satellite data products. This is especially important for trend analyses of Earth observations, where continuity of data sets and time on orbit needed to reach a scientific conclusion is at a premium. In addition, this approach can potentially reduce the need for complex on-board calibration systems on future missions, resulting in long-term cost savings and risk reduction for satellite operations. For small-size satellite platforms, such as U-class CubeSat systems, the GSLC approach could enable new measurement capabilities in cases where required on-board calibration systems are not possible due to size, power, mass, or cost limitations.