The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission represents NASA’s next investment in satellite ocean color and the study of Earth’s ocean-atmosphere system, enabling new insights into oceanographic and atmospheric responses to Earth's changing climate. PACE objectives include extending systematic cloud, aerosol, ocean biological and biogeochemical data records, making essential ocean color measurements to further understand marine carbon cycles and ecosystem responses to a changing climate, as well as improving knowledge of how aerosols influence ocean ecosystems and, conversely, how ocean ecosystems and photochemical processes affect the atmosphere. PACE objectives also encompass management of fisheries, large freshwater bodies, and water quality and reducing uncertainties in climate and radiative forcing models of the Earth system. PACE observations will also provide information on radiative properties of land surfaces and characterization of the vegetation and soils that dominate their reflectance. The primary PACE instrument – the Ocean Color Instrument (OCI) – is a hyperspectral imaging radiometer that spans the ultraviolet to shortwave infrared, with a ground sample distance of 1-km at nadir. This includes continuous collection of spectra from 340 nm to 890 nm in 5 nm steps. The PACE payload is complemented by two multi-angle polarimeters with spectral ranges that span the visible to near-infrared region. Scheduled for launch in late 2022-to-early 2023, the PACE observatory will enable significant advances in the study of Earth’s biogeochemistry, carbon cycle, clouds, hydrosols, and aerosols in the ocean-atmosphere system. We present a brief overview of the PACE mission, followed by a discussion of the capabilities and design concept of OCI.
The Earth Sensors on GOES-8 exhibit seasonal pointing errors in both the dual and single chord operating modes of the sensors. The errors were largely compensated for by a software patch uploaded to the satellite. The combination of detailed analyses and laboratory test results established that the observed error signatures are the result of stray solar radiation. The nature of the stray radiation paths giving rise to the seasonal errors is such that only the most significant stray path was eliminated in the GOES-9 hardware. The Earth Sensors on GOES-9 show significantly improved pointing performance over GOES-8, validating the origin of the most significant error source in the GOES-8 Earth Sensors. Low level seasonal pointing errors are observed, as expected, in the GOES-9 Earth Sensors. These errors again are effectively compensated for by an additional software patch developed to permit satisfactory single chord Earth Sensor operation. The operating principles of the Earth Sensor are described. On-orbit data of the seasonal anomalies are presented for both the uncompensated and compensated hardware and operating modes.
Following the successful transition of GOES-8 to the on- orbit mode, small disturbances were observed at approximately 14_30 SLT. Further analysis has shown that the disturbance is caused by shadowing of the solar sail by the magnetometer boom. The disturbance is most prominent when the sun is at lower declinations causing the shadow to rise higher along the sail boom. Data for the solar sail snap caused by the magnetometer boom shadow is analyzed, showing the time dependence of the attitude motion in the wheel angular momentum data and earth sensor data. Additional data is presented showing the profile of the shadow as viewed through the imager and sounder cooler radiator patch heater control voltage data. The presentation will demonstrate the following: 1) The attitude variation is caused by the magnetometer boom shadow as it is correlated with the true position of the sun; 2) The magnitude of the spacecraft motion for GOES-8 and GOES-9 is measured and compared over the seasonal duration of the effect; 3) The amount of deflection of the sail boom required to cause the observed attitude motion is estimated; 4) The dependence of the magnitude of the attitude motion is compared with sun angle subtended by the spacecraft north panel at the shadow point on the sail boom; and 5) Use of the onboard computer's reprogrammability function has provided a mechanism of compensating for the disturbance.