PACE Validation Science Team

This project establishes the California Cooperative Oceanic Fisheries Investigations (CalCOFI), hosted at Scripps Institution of Oceanography (SIO), as a PACE validation program. Project Objectives are to: 1) collect a broad suite of biogeochemical and biological measurements on CalCOFI cruises for future use in developing, refining, and assessing advanced NASA data products; 2) co-locate in situ hyper- and multi-spectral measurements with the required validation measurement suite from CalCOFI stations; 3) Validate performance of in situ radiometry from the PACE observatory.

SO-PACE will make use of opportunistic instrument deployments on research vessels to produce measurements of hyperspectral Rrs spanning 350 – 750 nm using the pySAS system, a continuous above-water autonomous solar tracking platform to collect water-leaving and sky radiances and downwelling irradiance, from which Rrs is calculated. Complementary measurements of IOPs will be made using underway flow-through systems and using pumps that minimize particle damage. IOP measurements will provide several products including: chlorophyll-a concentrations and spectral absorption of phytoplankton (both derived from particulate absorption), and spectral backscattering coefficients. The slope of particulate attenuation will provide estimates of trends in both bulk particle and phytoplankton size distributions. Concentrations of chlorophyll-a as well as additional phytoplankton accessory pigments will be estimated from both particulate absorption and Rrs spectra. Additionally, discrete water samples will be collected from flow-through systems and prepared for onshore laboratory HPLC analysis of phytoplankton pigments. Continuous measurements of phytoplankton communities will be made using two well-established instruments: an Imaging FlowCytobot (IFCB) and a SeaFlow (a continuous flow cytometer). These two instruments will also be deployed on shipboard flow-through systems, and have a combined range of ~ 0.6-150 microns for quantitative phytoplankton assessment.

The project is focused on data collection for the NASA PACE validation efforts. Specifically, our core targeted observables are phytoplankton carbon biomass (C_phyto), total particulate organic carbon (POC) concentration, net primary production (NPP), and chlorophyll fluorescence quantum yields (φ_f) as well and inherent optical properties and radiometry. 

We will have combined airborne and field sampling at PACE overpass time over two sampling periods October 2024 and May 2025, spanning a wide range of aerosol and ocean states for Monterey Bay, California. Likely potential aerosol conditions include, but not limited to, maritime aerosol, wildfire smoke, long range Asian dust transport, and clear air (Zhao et al., 2013, Lewis et al., 2010, Mardi et al., 2018, Allan et al., 2004, VanCuren 2003). Expected maritime conditions include, but are not limited to, low productivity cold waters, algal blooms, riverine outflow, and turbid waters. The study site has dramatic conditions exacerbated by the changing climate and a recent history of significant fire seasons (Filoncyk et al., 2022), extreme precipitation conditions, namely drought, atmospheric rivers and subsequent changes in riverine outflow, and other climate change impacts such as harmful algal blooms and far-reaching riverine plumes. We achieve PACE validation with hyperspectral (e.g., HyperPro II water optical profiling and 4STAR-B atmospheric transmittance) and aligned contemporary radiometric measurements (C-AIR water-leaving radiance from aircraft and C-OPS water optical profiling). The latter contemporary ocean color detectors have much higher dynamic range than OCI. This unique combination of airborne and surface and profiling instrumentation and water sampling can provide high-accuracy validation of the PACE mission sensors in a globally-representative range of oceanic conditions. The repeated airborne observations can provide the calibration and validation over larger areas and time by collecting measurements over a larger spatial domain during a satellite overpass and different seasons, overcoming the problem of limited spatial coverage presented by using solely ship stations and moored buoy systems.

For validation of advanced PACE aerosol and ocean products, we will use the following combination of airborne instruments: a full suite of state-of-the-art in situ aerosol instrumentation, the state-of-the-art airborne RSP polarimeter with accuracies and spectral ranges that match or exceed those of the PACE instruments in the VIS and SWIR, and the state-of-the-art airborne HSRL lidars that provide highly accurate vertically-resolved aerosol and hydrosol profiles. The in situ measurements furthermore will be combined to produce ambient aerosol products suitable for PACE validation. This combination of airborne in situ, polarimeter, and HSRL lidar data will allow us to validate advanced PACE-retrieved column aerosol properties, ocean products, and provide critically important vertically-resolved aerosol and ocean data to create collocated and curated validation data sets. These combined data sets will allow us to deeply investigate the uncertainties of and characterize any discrepancies in PACE aerosol and ocean products, including in the advanced aerosol optical and microphysical property retrievals from the PACE polarimeters, and the UV and VIS ocean products from the PACE Ocean Color Instrument (OCI).

Measurements of Rrs in the Sargasso Sea, leveraging Hydrostation-S, BATS, and BVAL cruises. Other cruises to be used opportunistically. Planned duration of 2.5 years, encompassing 100+ potential match-ups with PACE.

Rapid response field campaigns (small boats, small crew) to measure radiometry in the Santa Barbara Channel when sea and sky conditions are optimal for matchups. Process and deliver in situ high quality radiometric data for the validation of the reflectance data product of the PACE OCI instrument.

Routine NOAA surveys will be utilized that transect the entire U.S. Northeast Continental Shelf Ecosystem to capture a large volume of validation data across the U.S. Northeast Continental Shelf. Full characterization of AOPs and IOPs via continuous above-water radiometry, profiled radiometry, continuous flow-through IOP observations, and discrete subsamples. Phytoplankton measurements across a broad size range with a flow cytometer and Imaging Flow CytoBot (IFCB), supplemented with discrete HPLC pigment samples. 

Bio-GO-SHIP aims to become an international collaboration to measure, understand, and predict the distribution and biogeochemical role of pelagic plankton communities. The project leverages the global-reaching GO-SHIP platform and its complementary hydrographic measurements. The mission of Bio-GO-SHIP is to quantify the molecular diversity, size spectrum, chemical composition, and abundances of plankton communities across large spatial, vertical, and eventually temporal scales. This will be achieved through systematic, high-quality, and calibrated sampling of ‘omics, plankton imaging, particle chemistry, and optical techniques as operational oceanographic tools. Integration with regular GO-SHIP measurements and their analyses of the physical and chemical environment will allow us to understand (and eventually predict) how plankton communities respond to ocean changes and how biological processes feeds back on carbon, oxygen and nutrient cycles.  

The overarching goal of this project is to establish reliable validation and uncertainty estimates of PACE cloud data products to demonstrate their capabilities to the scientific community and support future scientific investigations. Our plan to validate PACE cloud products centers on using case studies that incorporate a variety of instrument measurements over a range of cloud types and conditions using established approaches and statistical methods. OCI and HARP2 data products will be geolocated and gridded for comparison to airborne in situ and remote sensing measurements. This performance assessment will focus on data collected during the PACE Postlaunch Airborne eXperiment (PACE-PAX), the Arctic Radiation-Cloud-Aerosol-Surface-Interaction Experiment (ARCSIX) and the Earth Care Validation; Tropical Oceans and Organized Convection (EC-TOOC). PACE-PAX instruments that are fundamental to this analysis are the PACE-proxy instruments that include the Airborne Hyper-Angular Rainbow Polarimeter (AirHarp), the Portable Remote Imaging Spectrometer (PRISM) and Push-broom Imager for Cloud and Aerosol Research and Development (PICARD) instruments. Also included in PACE-PAX is the High-Spectral Resolution Lidar (HSRL-2) system that will provide measurements of cloud top height, cloud vertical structure, optical thickness, an in-cloud extinction profile and has sensitivity to cloud phase using a combination of the layer integrated depolarization and integrated attenuated backscatter measurements. The state-of-the-art Research Scanning Polarimeter (RSP) measures intensity and polarization in nine spectral bands across 152 viewing angles, making it capable of retrieving all of the PACE advanced cloud products including, but not limited to: cloud layer detection, optical thickness, the effective radius and variance of the cloud droplet size distribution, liquid water path, cloud phase and the cloud droplet number concentration. A G-band microwave radiometer capable of accurately measuring liquid water path will take part in ARCSIX and be valuable for assessing the performance of the OCI and HARP2 LWP retrievals. An in-situ suite of cloud probes is included in PACE-PAX and ARCSIX and will provide a crucial component to our validation by providing independent and direct measurements of cloud vertical structure, cloud phase, droplet concentration, as well as measurements of cloud size distributions. In-situ measurements will be collocated with complementary remote sensing measurements before being compared with PACE’s advanced products in our multifaceted validation approach. A third objective is to produce and publicly archive L2 cloud data products from airHARP L1C data that are fit-for-purpose and suitable for further scientific analysis.  

Multiple units of in-house built SMART-s (Spectral Measurements for Atmospheric Radiative Transfer-spectrometer, 330–870 nm at ~0.8 nm resolution), as a part of NASA/Pandora network with extended spectral range, will be deployed to support PACE validation over oceanic waters (Eureka Oil Platform, CA; ~8 miles off the coast of Long Beach, CA) and seasonal transported Asian dust, southeastern biomass-burning smoke, and locally generated industrial air pollutants such as trace gases, precursors, and aerosols (Taiwan) sites. Specifically, we propose to accomplish the following two tasks: 1. To evaluate OCI's atmospheric-corrected water-leaving radiance/reflectance: Since the scans of SMART-s are very flexible and programmable, we will initially adopt the AERONET-OC operational criteria (e.g., IOCCG, 2019; Zibordi et al., 2021) for data continuity and consistency checks; then, after accumulating enough lessons learned from SeaPRISM, the advantage of SMART-s spectrometry will help improving the spatial-spectral-temporal sampling efficiency and effectiveness for PACE/OCI intercomparison (validation) and application. These water-leaving radiance/reflectance will be integrated with OCI's spectral response functions to meet their spectral range (i.e., 17 bands in 350–710 nm at 15 nm bandwidth; 665/678 nm at 10 nm bandwidth) and uncertainty requirements. 2. To validate PACE's aerosol and cloud products: We will utilize well-calibrated SMART-s' direct-Sun and sky measurements with SMART-s published methods (Jeong et al., 2018, 2020, and 2022) to retrieve columnar properties of aerosols (e.g., spectral AOD, single-scattering albedo, and Ångström exponent, fine-mode fraction of complex index of refraction) and abundance of trace gases (O3, NO2, H2Ovapor). By leveraging the assets of the upcoming 7-SEAS (Seven SouthEast Asian Studies, 2024–2026, Taiwan in collaborating NASA AERONET/ MPLNET) international field campaigns, SMART-s measurements can be maximized for improving scientific understanding and validating PACE/OCI products.

Validate PACE’s OCI remote sensing reflectance using uncrewed autonomous vessel measuring water-leaving radiance with two methods along with inherence optical properties in the Gulf of Mexico