The OreSat 0.5 is a novel small satellite developed in collaboration between Portland State University in Portland, Oregon, USA, the University of Maryland, Baltimore County, in Baltimore, MD, USA, and the Mullard Space Science Laboratory at University College London, Surrey, UK. OreSat 0.5 will demonstrate global cirrus cloud detection and mapping from a compact, low-cost platform. In this work, we preview the OreSat 0.5 mission and demonstrate the calibration and science behind its primary payload, the Cirrus Flux Camera (CFC). The CFC is a three-channel shortwave infrared radiometer (870, 1390, 1590 nm bands). Flux ratios between its three bands will be used to differentiate ice versus water and noncloud signals. Along-track and Across-track pointing up to ±45° will allow retrievals of heights and winds of the cirrus cloud tops. We discuss a preliminary pre-launch calibration of CFC and plans to expand upon and maintain this calibration vicariously on-orbit and through proxy sources. OreSat 0.5 launched to space on August 16 2024 and first light data is expected by Q4 2024.
The Hyper-Angular Rainbow Polarimeter-2 (HARP2) was launched on board the Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) mission, in February 2024, for the global measurement of aerosol and cloud properties as well as to provide atmospheric correction over the footprint of the Ocean Color Instrument (OCI). HARP2 is designed to collect data over a wide field of view in the cross-track direction (+/-47deg) allowing for global coverage in about two days, as well as an even wider field of view in the along-track direction (+/-54deg) providing measurements over a wide range of scattering angles. HARP2 samples 10 angles at 440, 550, and 870nm focusing on aerosol and surface retrievals, and up to 60 angles at 670nm for the hyper-angular retrieval of cloud microphysical properties. The HARP2 instrument collects three nearly identical images with linear polarizers aligned at 0°, 45°, and 90° that can be converted to push-broom images of the I, Q, and U Stokes parameters for each angle, and each wavelength. The HARP2 technology was first demonstrated with the HARP CubeSat satellite which collected a limited dataset for 2 years from 2020 to 2022. HARP2 extends these measurements to a full global coverage in two days, seven days a week.
The Hyper-Angular Rainbow Polarimeter (HARP2) is a novel wide-field of view imaging polarimeter instrument on the recently-launched NASA Plankton Aerosol Cloud ocean Ecosystem (PACE) mission. Since launch on February 8 2024, HARP2 has taken over 6 months of global Earth data. In order for this data to meet scientific quality standards, we must ensure that it is as accurate as possible and over long periods of time. We use well-characterized Earth targets, such as Saharan deserts, as well as regular views of the Sun and dark frames to trend our on-orbit calibration. In this work, we discuss the preliminary performance trends derived from these activities and how well they compare with the HARP2 prelaunch calibration.
Dome Concordia (Dome C) in Antarctica is an excellent calibration site for polar-orbiting Earth observation instruments due to its spectral, spatial, and temporal uniformity. These instruments also observe Dome C multiple times a day and at a variety of geometries. The MODIS Characterization Support Team uses regular observations of Dome C by Aqua and Terra MODIS to help validate and improve the calibration of the detector gain and response versus scan angle of the reflective solar bands used to generate NASA’s Level 1B reflectance products. The reflectance trends at Dome C are typically assessed on a yearly basis, due to a six-month sunlit observation period. In this work, we increase the temporal resolution of the trends from yearly to bi-monthly and reduce measurement noise using a reflectance-based snow BRDF model. We show results for Terra and Aqua MODIS BRDF-normalized reflectance using the Collection 7 calibration for bands 1-4, 8-9, and 17. The BRDF model significantly reduces the variations in the bi-monthly reflectance trends with the best results observed near nadir and for the blue bands 3, 8, and 9. The higher temporal sampling allows for better real-time identification of any calibration errors during the sunlit season. In addition, due to its polar location, Dome C is largely insensitive to the recent orbit drift of the Terra and Aqua satellites which has created challenges for MODIS calibration based on other on-board and Earth targets. Combined, these advantages will make Dome C a particularly important calibration reference target during the final years of the Terra and Aqua missions.
The development of science quality miniature payloads for nano satellites has facilitated the implementation of private observatories and even constellations of satellites for all sort of applications. GRASP Earth is currently developing a payload system composed of a multi-angle imaging polarimeter for the measurement of aerosol pollution and a high-resolution spectrometer for the measurement of greenhouse gases like CO2 and CH4, with commercial applications. Based on these measurements the GRASP (Generalized Retrieval of Atmosphere and Surface Properties, https://www.grasp-sas.com/) algorithm can simultaneously retrieve detailed details on the aerosol microphysics including particle size, refractive indices, particle sphericity, and the particle absorption properties, as well as the concentration of the greenhouse gases. These measurements performed from a single platform, and the joint aerosol and gases retrieval by GRASP produces higher accuracy and better sensitivity than each measurement perform independently.
Over the MODIS mission, normalized trends of Earth-view digital numbers (EV-dn) over desert calibration sites (PICS) have shown biases in several Terra MODIS reflective solar bands (RSBs) related to the changes in polarization sensitivity. The MODIS Characterization Support Team (MCST) corrects for these effects at the Level 1B stage in Collection 7 with monthly coefficient updates from NASA Ocean Biology Processing Group (OBPG). However, upcoming orbit changes for both MODIS instruments may require more frequent updates and new algorithms. In this work, we present a vicarious calibration algorithm with the potential to characterize polarization sensitivity using a single MODIS granule, across a range of angles-of-incidence (AOI). Marine stratocumulus cloud targets off the coast of South America, measured in near-real-time by Aqua-MODIS and the polarimeter POLDER-3, are used. These clouds strongly polarize light in optical wavelengths, are spatially uniform over wide areas, and are present year-round. After geo-registering both data to ~50 km superpixels, we find the polarized reflectance fit that best matches the cloud microphysics of the POLDER-3 target at 0.865 μm. We then interpolate the fit to the Aqua-MODIS target geometry. We derive polarization sensitivity coefficients for Aqua-MODIS Band 2 (0.858 μm) at a range of AOI using the POLDER-3 retrieval results for six different matchups in 2005. The results suggest that cloud development in the time between Aqua-MODIS and POLDER-3 measurements (~3 min) and simultaneous nadir overpass (SNO) distance are the main error contributions, combined with relatively low polarization sensitivity for Aqua Band 2. Even so, the derived sensitivity coefficients agree with pre-launch values within uncertainty. Therefore, simultaneous, co-incident radiometer and polarimeter data are optimal, such as from OCI and HARP-2/SPEXone on the upcoming NASA Plankton Aerosol Cloud and ocean Ecosystem (PACE) mission.
The Hyper-Angular Rainbow Polarimeter (HARP) Cubesat started data collection in April 2020 from the ISS orbit and is the first Hyper-Angular imaging polarimeter in space. The HARP payload produces pushbroom images at four wavelengths (440, 550, 670 and 870nm) with up to 60 viewing angles at 670 nm and up to 20 along track angles for the other three wavelengths. HARP swath consists of 94 degs in the cross track direction, allowing for a very wide coverage around the globe, and +/-57 degs in the along track direction, providing wide scattering angle sampling for aerosol and cloud particle retrieval. The HARP satellite is still active on orbit and so far have produce a large collection of scenes providing an unprecedented demonstration of the hyperangular retrieval of cloud and aerosol properties from space. This presentation will discuss the performance of the HARP sensor in space, as well as its first results for aerosol and cloud measurements. HARP is preceded by its airborne version, the AirHARP instrument, which has flown in two NASA aircrafts to demonstrate the capabilities of the HARP payload. The HARP payload is also a precursor to the HARP-2 polarimeter that will fly on the NASA PACE mission to collect global data on aerosol and cloud particles.
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