Abstract
Satellite instrument change in orbit during a mission lifetime can result in significant error for absolute radiance sensor calibrations. Polarization (POL) response, out-of-band signal rejection (OOB), and relative spectral response (RSR) are important contributors to understanding calibration error, yet no existing systems can conduct all of these diagnostics while a sensor is in space. In this presentation, a system under development is described that enables new diagnostic analyses of radiometers while they are in orbit by propagating a laser beam from the ground. While the system is not expected to provide high accuracy (<7%) absolute radiance calibrations, it is anticipated to provide POL, OOB, and RSR characterization measurements at high precision and repeatability, as these are self-referenced measurements and do not require knowledge of absolute radiance arriving at the sensor. The approach we are investigating will propagate a specially conditioned multi-beam phase-scrambled continuous wave laser transmission designed to mitigate atmospheric and laser coherence effects. To conduct a measurement, the space-borne sensor would need to “point-and-stare” at a pre-determined ground-target location. The ability to evaluate POL, OOB, and RSR changes during a mission enables critically needed insights to the cause of calibration change of current and proposed mission sensors. To achieve the same diagnostic capabilities with on-board hardware would be inherently prohibitive due to expense, increase in complexity, power, size, and payload mass. Understanding calibration change 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 additional 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 Ground-to-Space Laser approach could enable critical diagnostic capability in cases where on-board diagnostic systems are not possible.
Ground-to-Space Transmitter System for Extended Instrument Diagnostics of On-Orbit Operational Radiometric Sensors
Satellite instrument change in orbit during a mission lifetime can result in significant error for absolute radiance sensor calibrations. Polarization (POL) response, out-of-band signal rejection (OOB), and relative spectral response (RSR) are important contributors to understanding calibration error, yet no existing systems can conduct all of these diagnostics while a sensor is in space. In this presentation, a system under development is described that enables new diagnostic analyses of radiometers while they are in orbit by propagating a laser beam from the ground. While the system is not expected to provide high accuracy (<7%) absolute radiance calibrations, it is anticipated to provide POL, OOB, and RSR characterization measurements at high precision and repeatability, as these are self-referenced measurements and do not require knowledge of absolute radiance arriving at the sensor. The approach we are investigating will propagate a specially conditioned multi-beam phase-scrambled continuous wave laser transmission designed to mitigate atmospheric and laser coherence effects. To conduct a measurement, the space-borne sensor would need to “point-and-stare” at a pre-determined ground-target location. The ability to evaluate POL, OOB, and RSR changes during a mission enables critically needed insights to the cause of calibration change of current and proposed mission sensors. To achieve the same diagnostic capabilities with on-board hardware would be inherently prohibitive due to expense, increase in complexity, power, size, and payload mass. Understanding calibration change 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 additional 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 Ground-to-Space Laser approach could enable critical diagnostic capability in cases where on-board diagnostic systems are not possible.