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Kenneth Christian

Publications and source records attributed to Kenneth Christian.

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

A SmallSat Concept to Resolve Diurnal and Vertical Variations of Aerosols, Clouds, and Boundary Layer Height

A SmallSat mission concept is formulated here to carry out Time-varying Optical Measurements of Clouds and Aerosol Transport (TOMCAT) from space while embracing low-cost opportunities enabled by the revolution in Earth science observation technologies. TOMCAT’s “around-the-clock” measurements will provide needed insights and strong synergy with existing Earth observation satellites to 1) statistically resolve diurnal and vertical variation of cirrus cloud properties (key to Earth’s radiation budget), 2) determine the impacts of regional and seasonal planetary boundary layer (PBL) diurnal variation on surface air quality and low-level cloud distributions, and 3) characterize smoke and dust emission processes impacting their long-range transport on the subseasonal to seasonal time scales. Clouds, aerosol particles, and the PBL play critical roles in Earth’s climate system at multiple spatiotemporal scales. Yet their vertical variations as a function of local time are poorly measured from space. Active sensors for profiling the atmosphere typically utilize sun-synchronous low-Earth orbits (LEO) with rather limited temporal and spatial coverage, inhibiting the characterization of spatiotemporal variability. Pairing compact active lidar and passive multiangle remote sensing technologies from an inclined LEO platform enables measurements of the diurnal and vertical variability of aerosols, clouds, and aerosol-mixing-layer (or PBL) height in tropical-to-midlatitude regions where most of the world’s population resides. TOMCAT is conceived to bring potential societal benefits by delivering its data products in near–real time and offering on-demand hazard-monitoring capabilities to profile fire injection of smoke particles, the frontal lofting of dust particles, and the eruptive rise of volcanic plumes.

John E. Yorks↗
NASA NTRS2020

Differences in the Evolution of Pyrocumulonimbus and Volcanic Stratospheric Plumes as Observed by CATS and CALIOP Space-Based Lidars

Recent fire seasons have featured volcanic-sized injections of smoke aerosols into the stratosphere where they persist for many months. Unfortunately, the aging and transport of these aerosols are not well understood. Using space-based lidar, the vertical and spatial propagation of these aerosols can be tracked and inferences can be made as to their size and shape. In this study, space-based CATS and CALIOP lidar were used to track the evolution of the stratospheric aerosol plumes resulting from the 2019–2020 Australian bushfire and 2017 Pacific Northwest pyrocumulonimbus events and were compared to two volcanic events: Calbuco (2015) and Puyehue (2011). The pyrocumulonimbus and volcanic aerosol plumes evolved distinctly, with pyrocumulonimbus plumes rising upwards of 10 km after injection to altitudes of 30 km or more, compared to small to modest altitude increases in the volcanic plumes. We also show that layer-integrated depolarization ratios in these large pyrocumulonimbus plumes have a strong altitude dependence with more irregularly shaped particles in the higher altitude plumes, unlike the volcanic events studied.

Kenneth Christian↗
NASA NTRSDate not supplied

Similarities in the Lidar-Observed Optical Properties in the 2020 Australian Bushfire PyroCb and the 2017 Pacific Northwest PyroCb Stratospheric Plumes

Recent fire seasons have featured volcanic-sized injections of smoke aerosols into the stratosphere where they persist for many months. Unfortunately, the aging and transport of these aerosols are not well understood. Using space-based lidar, the vertical and spatial propagation of these aerosol layers can be tracked and inferences can be made as to the size and shape of the constituent aerosol particles. In this study, space-based CALIOP and CATS lidar were used to track the evolution of the stratospheric aerosol plumes resulting from the 2019 - 2020 Australian bushfire and 2017 Pacific Northwest pyrocumulonimbus events and were compared to two volcanic events: Calbuco (2015) and Puyehue (2011) and two smaller pyrocumulonimbus events: California’s Rim Fire (2013) and Australia’s Black Saturday (2009). The aerosol plumes from the large pyrocumulonimbus events rose many kilometers in the stratosphere in the weeks after injection to upwards of 30km in altitude. The layer-integrated depolarization ratios and color ratios of the 2020 Australian bushfire and 2017 Pacific Northwest pyrocumulonimbus plumes both vary by altitude with the lidar-measured depolarization and color ratios indicating the higher altitude aerosol layers contain smaller and more irregularly shaped aerosol particles. This relationship between altitude and optical properties was not observed in the smaller pyrocumulonimbus or the volcanic event stratospheric plumes.

Kenneth Christian↗
NASA NTRSDate not supplied

Machine Learning Algorithms for Aerosol and Cloud Detection Using CATS on the ISS

Clouds and aerosols are one of the largest uncertainties in understanding and forecasting the Earth’s changing climate system. The type and height of aerosols are important factors in determining the top-of-atmosphere (TOA) radiation budget, either direct reflection of solar radiation back to space and/or absorption of solar radiation. In addition to their impact on the Earth’s climate system, aerosols near the surface from wildfires, man-made pollution events, and dust storms are hazardous to human health. The phase and height of clouds also play a critical role in determining the role of clouds in the Earth’s climate system. Cirrus clouds in the upper troposphere can induce a significant daytime TOA warming effect, while liquid water clouds near the surface cause a large corresponding cooling effect. Lidar measurements provide accurate vertically resolved information about clouds and aerosols, including complex multi-layer scenes where passive sensors are challenged and at night, when passive sensors are unable to measure cloud and aerosol properties. The Cloud-Aerosol Transport System (CATS) is a lidar instrument that operated for 33 months on the International Space Station (ISS) at the 1064 nm wavelength to measure attenuated total backscatter and depolarization ratio. These fundamental measurements are used to derive “vertical feature mask” cloud and aerosol products, including layer top/base heights, layer geometrical thickness, aerosol type, and cloud phase. While space-based lidar systems like CATS provide cloud and aerosol vertical distributions that improve our understanding of the climate system, averaging of the daytime data from these sensors is required, at the expense of spatial resolution, to improve the daytime signal-to noise (SNR) and thus atmospheric layer detection. This presentation shows results from machine learning (ML) techniques that, when applied to CATS data: 1. improve the 1064 nm SNR 2. enable detection of atmospheric features during daytime with a horizontal resolution of 350 m or 5 km (compared to the 60 km required for standard CATS data products) 3. increase the number of atmospheric layers detected in the CATS data. A Convolutional Neural Network (CNN) trained using CATS standard data products also demonstrated the potential for improved cloud-aerosol discrimination, cloud phase, and aerosol typing compared to the operational CATS algorithms for cloud edges and complex near-surface scenes during daytime. The ML tools described in this paper can facilitate the development of smaller, low-cost lidar systems in the future and enable real-time accessibility of lidar data products from future lidar systems for monitoring and forecasting of hazardous events.

John Yorks↗
NASA NTRSDate not supplied

Characterizing the Seasonal and Diurnal Aerosol Cycles using CATS Space-Based Lidar

The broader effects aerosols have on the earth and climate system is determined by a host of factors including their composition and vertical distribution. Characterizing the vertical distribution of clouds and aerosols is especially important considering it remains one of the greatest uncertainties in climate predictions. Space-based lidar, such as Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud-Aerosol Transport System (CATS), is especially well suited as a remote sensing tool in determining this vertical distribution. CALIOP has been used for over a decade to observe the global and vertical distribution of clouds and aerosols but is limited by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations’ (CALIPSO’s) polar orbit to set equatorial crossing times of ~1:30AM/PM. This limited temporal sampling limits the use of CALIOP in determining the full diurnal variability of clouds and aerosols. On the International Space Station (ISS), with its inclined orbit and variable equatorial crossing times, the CATS lidar provided an opportunity to study the vertical profile of clouds and aerosols at a variety of local times. With this 33-month CATS record, we show that CATS captured the seasonal changes in global aerosol distributions and compares favorably with other instruments and models. Specifically targeting biomass burning regions, we also find CATS could observe the documented diurnal cycle in aerosol altitudes with some caveats. With the next generation of proposed space-based lidars including designs in similar orbits as the ISS and CATS, future studies of the aerosol diurnal and seasonal cycles would also be possible.

Kenneth Christian↗
NASA NTRSDate not supplied

The Roscoe Lidar: Initial Results from the Upward and Downward Looking Airborne Lidar from the ACCLIP and SABRE Campaigns

Backscatter lidars are a staple of airborne remote sensing and are primarily used in determining the altitude, vertical structure, and optical properties of clouds and aerosols. These airborne lidars typically observe in a downward direction which is sufficient for most tropospheric objectives. With more scientific attention being directed to upper tropospheric/lower stratospheric (UTLS) aerosols and recent volcanic and phrocumulonimbus events in the news, developing lidar instruments that can observe the UTLS will be vital in better understanding their composition and optical properties and determining their role in the planet's radiative balance. To meet this need, the downward and upward looking Roscoe lidar was developed and flown on two recent field campaigns: Stratospheric Aerosol processes, Budget, and Radiative Effects (SABRE) and Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) (both 2022). Building on its extensive Cloud Physics Lidar (CPL) heritage, we show that Roscoe can deliver CPL-like products in both the up and down-looking directions providing an unmatched vertical view of the atmosphere from an airborne platform. Future work can leverage Roscoe's updward looking view to quantify the optical properties and extinction of UTLS aerosols.

Kenneth Christian↗
NASA NTRSDate not supplied

NASA GSFC Elastic Backscatter Lidar Efforts Relevant to EarthCARE Calibration/Validation and Synergistic Data Products

At NASA Goddard Space Flight Center (GSFC), several airborne elastic backscatter lidar instruments have been developed to measure vertical profiles of aerosols and cloud in the atmosphere. Here, we present an overview of our airborne capabilities that could be utilized for EarthCare Calibration/Validation through current efforts to leverage joint NASA-ESA field deployments such as the IMPact of Aerosols on Convection in the Tropics (IMPACT). Additionally, GSFC is leading the development of the Atmospheric Lidar Instrument for Clouds and Aerosol Transport (ALICAT) elastic backscatter lidar that is planned to fly in the upcoming NASA Atmosphere Observing System (AOS) Decadal Survey Mission at the end of this decade. We also present an overview of the instrument and potential synergy of data products that could leveraged should the EarthCare and AOS missions overlap.

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